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Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
May 1989 - January 1992
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Objective of study:
toxicokinetics
Qualifier:
according to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Version / remarks:
1984
Deviations:
no
GLP compliance:
not specified
Remarks:
The pathology studies were not strictly conducted according to EPA GLP, the experimental techniques, data collection, and analysis methods used were not believed to compromise the integrity of the study. Compliance of GLP is not specified in the study
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source: Du Pont Chemicals, Fibers, and Polymers E.I du Pont de Nemours and Company, Wilmington, Delavare
- Haskell number: 17,834
- Purity: 99.8%
- Physical form: water-white liquid
- Contaminants: water, approximately 0.2%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Stability under test conditions: The test substance was assumed to be stable
Species:
mouse
Strain:
other: Crl:CD-1(ICR)BR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Raleigh, North Carolina
- Age at study initiation: 6-8 weeks old
- Mean body weights three days prior to sacrifice: 29.2-39.5 g
- Housing: in stainless steel, wire-mesh cages
- Diet: Purina Rodent Chow ad libitum
- Water: ad libitum
- Acclimation period: 7 days (the animals were weighed 3 times and observed daily during the quarantine period.)

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 2 °C
- Humidity: 50 ± 20%
- Photoperiod: 12 hours dark/12 hours light
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass exposure chambers (each with a nominal volume of 150 L) with cubical chambers outfitted with square pyramidal top and bottom; a dispersion plate located at the chamber inlet was used to increase turbulence and promote uniform distribution of the test substance.
- Method of holding animals in test chamber: whole-body exposure
- Source and rate of air: conditioned, filtered houseline air only (approximately 50 L/min)
- System of generating vapour: bubbling conditioned, filtered houseline air (approx. 0.3 to 5 L/min) through either gas washing bottles or midget glass impingers containing test substance; vapour generators were placed within heated water baths to facilitate generation of vapour; the vapour was mixed with dilution air or chilled dilution air and swept through glass tubing into the top of the glass exposure chambers.
- Temperature, humidity, pressure in air chamber: 22 ± 2 °C; 50 ± 20 %.
- Air flow rate: approximately 50 L/min
- Air change rate: no data
- Method of particle size determination: no data
- Treatment of exhaust air: through a water-containing scrubber, dry ice cold trap and an MSA activated charcoal/HEPA cartridge filter, prior to discharge into the fume hood

TEST ATMOSPHERE
- Brief description of analytical method used: HP Model 5880 gas chromatograph
- Samples taken from breathing zone: yes
Duration and frequency of treatment / exposure:
6 hours/day, 5 days/week for a total of 10 exposures over a 2-week period and single exposures for 1, 3 and 6 hours
Dose / conc.:
50 ppm
Dose / conc.:
150 ppm
Dose / conc.:
300 ppm
Dose / conc.:
500 ppm
No. of animals per sex per dose:
32 mice per dose per single exposures
32 mice per dose per repeated dose exposures
Control animals:
not specified
Details on study design:
- Dose selection rationale: to assist in dose selection for a chronic inhalation bioassay
- Rationale for animal assignment: after release from quarantine, mice were grouped using a computerized, stratified randomization program so that the mean body weights of each test group were approximately equal.
Details on dosing and sampling:
Whole-body exposures to the test substance were employed for mice for either single or multiple exposures to 50, 150, 300, or 500 ppm of the test substance. In the animals exposed for a single 6-h period, blood samples were taken 1, 2, 4, 6, 8, 12, and 24 h post-exposure. Four mice were sacrificed at each time interval and blood samples were taken by cardiac puncture. Urine samples were collected from rodents used for the 24-h blood samples and were collected at 12 and 24 h. This latter group was housed in metabolism units to collect urine samples. A total of 32 mice were used for each 6-h exposure level.

In addition, 1- and 3-h exposures were conducted in order to estimate the increase in the test substance plasma levels at intermediate time points during a 6-h exposure. Blood samples were taken approximately 0.5 h after termination of exposure. Blood samples were not taken until chamber test substance levels dissipated to safe-handling levels (0.5 h after termination of the 1- and 3-h exposures and 1 h after termination of the 6-h exposures).

For multiple exposures, mice were exposed 6 hours/day, 5 days/week (no exposures were conducted on the weekend following the 5th exposure) for 2 weeks. Blood and urine samples were collected after the final exposure according to the same schedule as presented above for the animals receiving a single 6-h exposure. Each group consisted of 32 mice.
Details on excretion:
Urine samples from mice exposed to 50 and 150 ppm of the test substance did not contain quantifiable amounts of the test substance or NMAC. In mice the quantities of NMAC in urine typically exceeded those of the test substance.
Toxicokinetic parameters:
half-life 1st: 0.3 to 0.5 h
Toxicokinetic parameters:
AUC: increased 9-fold (single exposure) and 4-fold (2-week exposure) between the 300 and 500 ppm exposure levels
Metabolites identified:
yes
Details on metabolites:
DMAC was rapidly metabolized in mice. NMAC was not detected in plasma from mice beyond the 12-h post-exposure timepoint for the 300 and 500 ppm exposures.

Plasma profiles

Plasma concentrations were determined following a single 6-h exposure and following the last of a series of 10 exposures. The test substance and NMAC plasma profiles for mice were not affected by multiple test substance exposures, the plasma profiles of the test substance and NMAC were similar to those from single exposure. Clearance of the test substance and NMAC from plasma was rapid in mice following 300 and 500 ppm of test substance exposures. The test substance was not detected beyond the 8-h time point (post-exposure) and NMAC was not detected beyond the 12-h time point. Plasma profiles were not obtained from mice receiving 50 or 150 ppm exposures. This was due to the time required between termination of exposure and the first blood sample (approximately 1 h). By the third time point (4 h post-exposure) the test substance and NMAC were below the analytical detection limits (0.03 μg/mL).

 

AUC values of DMAC and NMAC

AUC comparisons for mice were difficult to accurately assess due to the time required between exposure termination and the dissipation of the test substance in room air to levels below 10 ppm following the opening of the exposure chambers (approximately 1 h). With estimated test substance plasma half-lives of 0.3 to 0.5 h, the post-exposure of the test substance AUC values were underestimated.

  For mice, the increase in the test substance AUC values was 9-fold (single exposure) and 4-fold (2-week exposure) between the 300 and 500 ppm exposure levels. The AUC values of NMAC in mice increased in proportion to the increase in the test substance exposure levels.

 

Plasma concentrations of DMAC and NMAC

The test substance and NMAC plasma concentrations were determined at the termination of a 1-, 3-, or 6-h exposure to the test substance. The test substance values for mice following all exposures were lower for the 6-h compared to the 3-h exposure. This was probably due to the time between exposure termination and the taking of the post-exposure blood sample (30 min following termination of the 3-h exposure vs. 1-h after the 6-h exposure). In mice, NMAC concentrations were greater than companion test substance concentrations following 1-, 3-, and 6-h exposures to 50 or 150 ppm of the test substance and the 6-h exposure to 300 ppm of the test substance.

 

Plasma half-lives of DMAC and NMAC

In mice, the approximate plasma half-lives ranged from 0.3 to 0.5 h and 0.6 to 1.3 h for the test substance and NMAC, respectively. Plasma half-lives were independent of exposure duration (single vs. repeated exposures). All half-life estimations were based upon plasma concentration data.

 

Urinary excretion of DMAC and NMAC

Urine samples from mice exposed to 50 and 150 ppm of the test substance did not contain quantifiable amounts of the test substance or NMAC. In mice the quantities of NMAC in urine typically exceeded those of the test substance. The magnitude of this difference decreased as exposure concentrations increased and quantities were equal for rats receiving the single 500 ppm exposure.

 

Conclusions:
Plasma profiles, plasma test substance/NMAC concentration comparisons following 1-, 3-, and 6-h exposures, and plasma test substance half-life estimations all suggest that mice metabolize inhaled test substance more rapidly than rats. AUC comparisons for mice are difficult to accurately assess due to the time required between exposure termination and the dissipation of the test substance in room air to levels below 10 ppm following the opening of the exposure chambers (approximately 1 h). With estimated test substance plasma half-lives of 0.3 to 0.5 h, the post-exposure of the test substance AUC values were underestimated. The dose-dependent nature of the test substance AUC data and the absence of effects of repeated test substance exposures at 300 and 500 ppm supported a toxicity-driven upper limit of 350 ppm for a chronic inhalation study. The study and the conclusions which are drawn from it fulfill the quality criteria (validity, reliability, repeatability).
Executive summary:

Whole-body inhalation exposures to the test substance were conducted with male mice (Cr1:CD-I®(lCR)BR). Exposure concentrations were 50, 150, 300 and 500 ppm. The exposure routines consisted of single 1-, 3-, or 6-h exposures and ten 6-h exposures (10 exposure days in 2 weeks). Area under the plasma concentration curve (AUC) values were determined for the test substance and its metabolite N-methylacetamide (NMAC), following 6-h exposures (single exposure or last in a series of 10 exposures). The range of exposures was chosen to assess the exposure-dependent nature of the test substance pharmacokinetics in mice. Plasma profiles indicated mice metabolized the test substance rapidly with plasma half-lives from 0.3 to 0.5 h for the test substance. The test substance AUC values from mice were underestimated due to the required time (< 30 min) between termination of exposure and the initial blood sample. NMAC was not detected in plasma from mice beyond the 12-h post-exposure time point for the 300 and 500 ppm exposures. Regardless of exposure level, repeated test substance exposures to mice resulted in plasma profiles of the test substance and NMAC similar to those from a single exposure. The dose-dependent nature of the test substance AUC data and the absence of effects of repeated 300 and 500 ppm of the test substance exposures supported a toxicity-driven upper limit of 350 ppm for a chronic inhalation study. The study and the conclusions which are drawn from it fulfill the quality criteria (validity, reliability, repeatability).

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Objective of study:
toxicokinetics
Qualifier:
according to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Deviations:
no
GLP compliance:
no
Remarks:
Although not strictly conducted according to EPA GLP Regulations, the experimental techniques, data collection, and analytical methods used in this study were considered scientifically appropriate and were not believed to have compromise.
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
- Purity: 99.8 % purity
- Impurities (identity and concentrations): 0.2 % water (approx.)
No details available.
Species:
rat
Strain:
other: Crl:CD®BR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Raleigh, North Carolina
- Age at study initiation: 6-8 weeks old
- Mean body weights three days prior to sacrifice: 256.7 to 347.4 g
- Housing: in stainless steel, wire-mesh cages
- Diet: Purina Rodent Chow ad libitum
- Water: ad libitum
- Acclimation period: 7 days (the animals were weighed 3 times and observed daily during the quarantine period.)

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 2 °C
- Humidity: 50 ± 20 %
- Photoperiod: 12 hours dark/12 hours light
Route of administration:
inhalation: vapour
Vehicle:
unchanged (no vehicle)
Details on exposure:
TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: stainless steel and glass exposure chambers (each with a nominal volume of 150 L) with cubical chambers outfitted with square pyramidal top and bottom; a dispersion plate located at the chamber inlet was used to increase turbulence and promote uniform distribution of the test substance.
- Method of holding animals in test chamber: whole-body exposure
- Source and rate of air: conditioned, filtered houseline air only (approximately 50 L/min)
- System of generating vapour: bubbling conditioned, filtered houseline air (approx. 0.3 to 5 L/min) through either gas washing bottles or midget glass impingers containing test substance; vapor generators were placed within heated water baths to facilitate generation of vapour; the vapour was mixed with dilution air or chilled dilution air and swept through glass tubing into the top of the glass exposure chambers.
- Temperature, humidity, pressure in air chamber: 22 ± 2 °C; 50 ± 20 %
- Air flow rate: approximately 50 L/min
- Air change rate: no data
- Method of particle size determination: no data
- Treatment of exhaust air: through a water-containing scrubber, dry ice cold trap and an MSA activated charcoal/HEPA cartridge filter prior to discharge into the fume hood

TEST ATMOSPHERE
- Brief description of analytical method used: HP Model 5880 gas chromatograph
- Samples taken from breathing zone: yes
Duration and frequency of treatment / exposure:
6 hours/day, 5 days/week for a total of 10 exposures over a 2-week period and single exposures for 1-, 3- and 6-hours
Dose / conc.:
50 ppm
Dose / conc.:
150 ppm
Dose / conc.:
300 ppm
Dose / conc.:
500 ppm
No. of animals per sex per dose:
Repeated dose: 8 rats per concentration
Single exposure: 8 rats per concentration per time point
Control animals:
not specified
Details on study design:
- Dose selection rationale: to assist in dose selection for a chronic inhalation bioassay
- Rationale for animal assignment: after release from quarantine, rats were grouped using a computerized, stratified randomization program so that
the mean body weights of each test group were approximately equal.
Details on dosing and sampling:
Whole-body exposures to the test substance were employed for rats for either single or multiple exposures to 50, 150, 300, or 500 ppm of the test substance. In the animals exposed for a single 6-h period, blood samples were taken 1, 2, 4, 6, 8, 12, and 24 h post-exposure. Serial blood samples from 4 rats in each exposure group were collected from the tail-vein. Urine samples were collected from rats used for the 24-h blood samples and were collected at 12 and 24 h. This latter group was housed in metabolism units to collect urine samples. A total of 8 rats were used for each 6-h exposure level.

In addition, 1- and 3-h exposures were conducted in order to estimate the increase in the test substance plasma levels at intermediate time points during a 6-h exposure. Blood samples were taken approximately 0.5 h after termination of exposure. Blood samples were not taken until room test substance levels dissipated to safe-handling levels (0.5 h after termination of the 1- and 3-h exposures and 1 h after termination of the 6-h exposures).

For multiple exposures, rats were exposed 6 hours/day, 5 days/week (no exposures were conducted on the weekend following the 5th exposure) for 2 weeks. Blood and urine samples were collected after the final exposure according to the same schedule as presented above for the animals receiving a single 6-h exposure. Each group consisted of 8 rats.
Details on excretion:
Urine samples from rats exposed to 50 ppm of the test substance did not contain quantifiable amounts of the test substance nor its metabolite (NMAC). In rats the quantities of NMAC in urine typically exceeded those of the test substance. The magnitude of this difference decreased as exposure concentrations increased and quantities were equal for rats receiving the single 500 ppm exposure.
Toxicokinetic parameters:
half-life 1st: 0.6 to 1.5 h
Toxicokinetic parameters:
AUC: increased approximately 5-fold and 3-fold as exposure concentrations increased from 150 to 300 ppm and 300 to 500 ppm, respectively.
Metabolites identified:
yes
Details on metabolites:
DMAC was rapidly metabolized in rats. NMAC persisted in plasma for at least 24 h after the 150, 300 and 500 ppm exposures to rats.

Plasma profiles

Plasma concentrations were determined following a single 6-h exposure and following the last of a series of 10 exposures. The test substance and NMAC plasma profiles for rats were not affected by multiple test substance exposures. In rats, NMAC persisted through 24 h after the termination of exposure. The test substance was detected in rat plasma 24 h after termination of the 500 ppm exposure. The test substance was not detected beyond the 8-h time point (post-exposure) and NMAC was not detected beyond the 12-h time point. Plasma profiles were not obtained for rats receiving 50 ppm exposures. This was due to the time required between termination of exposure and the first blood sample (approximately 1 h). By the third time point (4 h post-exposure) the test substance and NMAC were below the analytical detection limits (0.03μg/mL).

 

AUC values of DMAC and NMAC

In rats, the AUC for the test substance increased approximately 5-fold between the 150 and 300-ppm exposures and approximately 3-fold between the 300 and 500 ppm exposures. The NMAC AUC values in rats increased in proportion to the increase in the test substance exposure levels. Multiple exposures had no discernible dose response effects on the test substance and NMAC AUC values from rats.

 

Plasma concentrations of DMAC and NMAC

The test substance and NMAC plasma concentrations were determined at the termination of a 1-, 3-, or 6-h exposure to the test substance. The test substance values for rats following the 50 ppm exposure are lower for the 6-h compared to the 3-h exposure. This was probably due to the time between exposure termination and the taking of the post-exposure blood sample (30 min following termination of the 3-h exposure vs. 1-h after the 6-h exposure). For rats, NMAC concentrations were greater than companion test substance concentrations following the 1-, 3-, and 6-h exposures to 50 ppm of the test substance.

 

Plasma half-lives of DMAC and NMAC

Plasma half-life estimations for rats ranged from 0.6 to 1.5 h and 2.2 to 3.0 h for the test substance and NMAC, respectively. Plasma half-lives were independent of exposure duration (single vs. repeated exposures). All half-life estimations were based upon plasma concentration data.

 

Urinary excretion of DMAC and NMAC

Urine samples from rats exposed to 50 ppm of the test substance did not contain quantifiable amounts of the test substance or NMAC. In rats, the quantities of NMAC in urine typically exceeded those of the test substance. The magnitude of this difference decreased as exposure concentrations increased and quantities were equal for rats receiving the single 500 ppm exposure.

Conclusions:
Conclusion
Plasma profiles, plasma test substance/NMAC concentration comparisons following 1-, 3-, and 6-h exposures, and plasma test substance half-life estimations all suggest that mice metabolize inhaled test substance more rapidly than rats.
Rats exhibited approximate 5- and 3-fold increases in AUC values for the test substance as exposure levels increased from 150 to 300 ppm and 300 to 500 ppm (2- and 1.7-fold increases in exposure levels). The disproportionate increases in AUC values are suggestive of saturation of the test substance metabolism. In addition, plasma NMAC levels were similar following 3- and 6-h exposure to the test substance at 300 and 500 ppm suggesting saturation of metabolism. 
The dose-dependent nature of the test substance AUC data and the absence of effects of repeated test substance exposures at 300 and 500 ppm supported a toxicity-driven upper limit of 350 ppm for a chronic inhalation study. The study and the conclusions which are drawn from it fulfill the quality criteria (validity, reliability, repeatability).
Executive summary:

Whole-body inhalation exposures to the test substance were conducted with male rats (Crl:CD®BR). Exposure concentrations were 50, 150, 300 and 500 ppm. The exposure routines consisted of single 1-, 3-, or 6-h exposures and ten 6-h exposures (10 exposure days in 2 weeks). Area under the plasma concentration curve (AUC) values were determined for the test substance and its metabolite N-methylacetamide (NMAC), following 6-h exposures (single exposure or last in a series of 10 exposures). The range of exposures was chosen to assess the exposure-dependent nature of the test substance pharmacokinetics in rats. The test substance plasma half-life in rats ranged from 0.6 to 1.5 h. The AUC values for the test substance in rats increased approximately 5-fold and 3-fold as exposure concentrations increased from 150 to 300 ppm and 300 to 500 ppm, respectively. NMAC persisted in plasma for at least 24 h after the 150, 300 and 500 ppm exposures to rats. Regardless of exposure level, repeated test substance exposures to rats resulted in plasma profiles of the test substance and NMAC similar to those from a single exposure. The dose-dependent nature of the test substance AUC data and the absence of effects of repeated 300 and 500 ppm of the test substance exposures supported a toxicity-driven upper limit of 350 ppm for a chronic inhalation study. The study and the conclusions which are drawn from it fulfill the quality criteria (validity, reliability, repeatability).

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
(partly limited documentation, e.g. no details about the test substance or analytical results on exposure concentration)
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
Dose and exposure time dependent toxicokinetics in male mice after inhalation exposure to N,N-dimethylacetamide (DMAC)
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
- Purity: > 99 %
No further details available.
Radiolabelling:
no
Species:
mouse
Strain:
other: Crl :CD-1(ICR)BR
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc ., Raleigh, NC
- Age at study initiation: 6-8 weeks old
- Weight at study initiation: no data
- Acclimatisation period: 1 week
- Housing: no data
- Individual metabolism cages: not clearly stated, presumably no individual cages
- Certified diet and water ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature: 20-24 °C
- Humidity: 30-70 %
- Photoperiod: 12 hours dark/12 hours light
Route of administration:
inhalation: vapour
Vehicle:
other: air
Details on exposure:
Vaporization of the test substance in bottles by bubbling air through the bottles at specific temperatures of the liquid test substance (28-32 °C); concentration varied by different temperatures and air flowrates (0.3 to 5 L/ min); filtered houseline air was added to dilute and sweep the vapour through glass transfer tubes into the chamber inlet (total airflow approx. 50 L/min).
Whole body exposure.
DMAC concentrations in the chamber were analyzed by gas chromatography (GC) during exposure; impinger samples collected and analyzed at 20-, 30-, and 60-min intervals for exposures of 1, 3, and 6 h duration, respectively; chamber temperature was approximately 23 °C and relative humidity approximately 50 %.
Data on analytical results were not given.
Duration and frequency of treatment / exposure:
a) single 1-h exposure
b) single 3-h exposure
c) single 6-h exposure
d) multiple exposure, 6 h per day for 5 days/week for 2 weeks
Dose / conc.:
50 ppm
Remarks:
ca. 0.18 mg/l
Dose / conc.:
150 ppm
Remarks:
ca. 0.54 mg/l
Dose / conc.:
300 ppm
Remarks:
ca. 1.08 mg/l
Dose / conc.:
500 ppm
Remarks:
ca. 1.80 mg/l
No. of animals per sex per dose:
4 mice per measurement of plasma level
32 mice for urine sampling
Control animals:
no
Positive control:
no
Details on study design:
Blood sampling in a+b) 0.5 h after termination of exposure
Blood sampling in c) 1, 2, 4, 6, 8, 12, and 24 h post-exposure
Blood sampling in d) 1, 2, 4, 6, 8, 12, and 24 h after the last exposure
Urine sampling 0-24 h after exposure
Details on dosing and sampling:
DMAC and N-methylacetamide (NMAC) in plasma and urine were analysed by GC methods.
Plasma half-lives for DMAC and NMAC concentrations were estimated by linear regression analysis of the log of the plasma concentration vs. sample time over the decay portion of the plasma concentration curve; areas under the plasma concentration-time curves (AUC) were determined by the trapezoidal method; the plasma half-life was used to extrapolate to a plasma concentration of zero.

The analytical detection limit was 0.03 μg/mL.
Statistics:
Means ± standard deviation were calculated.
Details on distribution in tissues:
The DMAC and NMAC plasma profiles for mice were not affected by multiple DMAC exposures. Clearance of DMAC and NMAC from plasma was more rapid in mice than in rats. Plasma profiles were not obtained from mice receiving 50 or 150 ppm exposures, due to the time required between termination of exposure and the first blood sample (approximately 1 h); by the third timepoint (4 h post-exposure) DMAC and NMAC were below the analytical detection limits. For mice, the increase in DMAC AUC values was 9-fold (single exposure) and 4-fold (2-week exposure) between the 300 and 500 ppm exposure levels. Multiple exposures had no discernible dose response.
In mice, NMAC concentrations were greater than companion DMAC concentrations following 1-, 3-, and 6-h exposures to 50 and 150 ppm DMAC and the 6-h exposure to 300 ppm DMAC.
Details on excretion:
In mice, the approximate plasma half-lives ranged from 0.3 to 0 .5 h and 0.6 to 1.3 h for DMAC and NMAC, respectively. Plasma half-lives were independent of exposure duration (single vs. repeated exposures).
In urine samples from mice the quantities of NMAC in urine typically exceeded those of DMAC. The magnitude of this difference decreased as exposure concentrations increased.
Metabolites identified:
yes
Details on metabolites:
According to the authors, N-methylacetamide (NMAC) was the major metabolite in mice. N-hydoxymethyl-N-methylacetamide (DMAC-OH) was presumed to be an intermediate in the conversion of DMAC to NMAC.
Conclusions:
The disproportionate increases in AUC values and data on urinary excretion profile (quantities of NMAC in urine typically exceeded those of DMAC; the magnitude of this difference decreased as exposure concentrations increased) suggested saturation of DMAC metabolism at ≥300 ppm. DMAC was rapidly metabolized, plasma half-life in mice ranged from 0.3 to 0.5 h; saturation of DMAC metabolism at high exposure concentrations has been shown; multiple DMAC exposures did not enhance DMAC metabolism.
Executive summary:

The dose and exposure time dependent toxicokinetics in male Crl :CD-1(ICR)BR mice was studied after single or multiple inhalation exposures to 50 -500 ppm N,N-dimethylacetamide (DMAC).

According to the authors, N-methylacetamide (NMAC) was the major metabolite in mice. N-hydoxymethyl-N-methylacetamide (DMAC-OH) was presumed to be an intermediate in the conversion of DMAC to NMAC.

DMAC and N-methylacetamide (NMAC) in plasma and urine were analysed by GC methods and plasma half-lives for DMAC and NMAC concentrations were estimated.

The DMAC and NMAC plasma profiles for mice were not affected by multiple DMAC exposures. Clearance of DMAC and NMAC from plasma was more rapid in mice than in rats. Plasma profiles were not obtained from mice receiving 50 or 150 ppm exposures, due to the time required between termination of exposure and the first blood sample (approximately 1 h); by the third timepoint (4 h post-exposure) DMAC and NMAC were below the analytical detection limits.  The increase in DMAC AUC values was 9-fold (single exposure) and 4-fold (2-week exposure) between the 300 and 500 ppm exposure levels.  Multiple exposures had no discernible dose response. NMAC concentrations were greater than companion DMAC concentrations following 1-, 3-, and 6-h exposures to 50 and 150 ppm DMAC and the 6-h exposure to 300 ppm DMAC. The approximate plasma half-lives ranged from 0.3 to 0 .5 h and 0.6 to 1.3 h for DMAC and NMAC, respectively. Plasma half-lives were independent of exposure duration (single vs. repeated exposures). In urine samples from mice the quantities of NMAC in urine typically exceeded those of DMAC. The magnitude of this difference decreased as exposure concentrations increased.

Conclusion: The disproportionate increases in AUC values and data on urinary excretion profile (quantities of NMAC in urine typically exceeded those of DMAC; the magnitude of this difference decreased as exposure concentrations increased) suggested saturation of DMAC metabolism at ≥300 ppm. DMAC was rapidly metabolized, plasma half-life in mice ranged from 0.3 to 0.5 h; saturation of DMAC metabolism at high exposure concentrations has been shown; multiple DMAC exposures did not enhance DMAC metabolism.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
(no details about test substance; restricted to one metabolite in urine) but was invalid concerning dermal absorption rate
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
Excretion of N-methylacetamide (NMAC) via urine measured in rabbits after dermal exposure to DMAC
GLP compliance:
not specified
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
No details available.
Species:
rabbit
Strain:
New Zealand White
Sex:
male
Details on test animals and environmental conditions:
no data available
Route of administration:
dermal
Vehicle:
unchanged (no vehicle)
Details on exposure:
The test substance was applied directly to the shaved skin; an occlusive dressing was used.
The exposure period was 4 h. Following removal of the wrapping, the application site skin was washed.
Duration and frequency of treatment / exposure:
once
Dose / conc.:
0.23 other: ml
Remarks:
per rabbit (no body weight data)
No. of animals per sex per dose:
5 rabbits
Control animals:
yes, concurrent no treatment
Positive control:
no
Details on dosing and sampling:
Urine was collected 0-8 h after initiation of exposure and at 8-24 h. Analysis was restricted to NMAC.
Details on absorption:
Dermal absorption was not quantifiable, but rapid absorption via the skin was presumed since high amounts of NMAC were found in 0-8-h urine and clearly lower levels in 8-24-h urine.
Details on excretion:
NMAC was excreted mainly 0-8 h after initiation of exposure; the NMAC concentration in urine of the 5 rabbits varied between 113-462 µg/mL, the concentration in 8-24-h urine varied between 10 and 40 µg/mL (n = 4). In two untreated control rabbits urinary NMAC concentration was <1 and up to 11 µg/mL (4 measurements).
Metabolites identified:
yes
Details on metabolites:
NMAC
Conclusions:
The study data indicate a rapid absorption of the test substance via the skin (dermal absorption was not quantified).
Executive summary:

The excretion of N-methylacetamide (NMAC) via urine was measured in 5 male New Zealand White rabbits after dermal exposure to DMAC.

0.23 mL of the unchanged test material per rabbit (no body weight data) were applied directly (no vehicle) to the shaved skin; an occlusive dressing was used. The exposure period was 4 h. Following removal of the wrapping, the application site skin was washed. Urine was collected 0-8 h after initiation of exposure and at 8-24 h. Analysis was restricted to NMAC.

Dermal absorption was not quantifiable, but rapid absorption via the skin was presumed since high amounts of NMAC were found in 0-8-h urine and clearly lower levels in 8-24-h urine.

NMAC was excreted mainly 0-8 h after initiation of exposure; the NMAC concentration in urine of the 5 rabbits varied between 113-462 µg/mL, the concentration in 8-24-h urine varied between 10 and 40 µg/mL (n = 4). In two untreated control rabbits urinary NMAC concentration was <1 and up to 11 µg/mL (4 measurements).

Conclusion: The study data indicate a rapid absorption of the test substance via the skin (dermal absorption was not quantified).  

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
(pilot study, one dose level; data of 3 rats evaluated; tabulated results not available)
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
Toxicokinetic parameters measured in rats after inhalation exposure to the test substance at 5 ppm for 12 h.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
- Chemical purity: 99.8 %
- Radiochemical purity: >98 %
- Activity: 10.15 mCi/mmole
- Lot No.: 800916
- Source: Pathfinder Laboratories, Inc ., St . Louis
No further details available.
Radiolabelling:
yes
Remarks:
N,N-Dimethylacetamide-carbonyl-14C
Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River
- Acclimatisation period: 1 week
- Housing: held singly in metabolism cages
- Diet and water: certified diet and water ad libitum (except during inhalation exposure period)

no further data vailable
Route of administration:
inhalation: vapour
Vehicle:
other: filtered room air
Details on exposure:
Animals were whole body exposed (dermal absorption was also assessed); test substance vapour was generated in a diffusion tube at 70-80 °C, diluted with air and the DMAC concentration was measured when the animal was present in the inhalation chamber; exposure in modified glass Roth metabolism chamber.
The DMAC exposure concentration was determined throughout the exposure period by collection of measured volumes of air into impingers; DMAC concentration was measured by GC methods and liquid scintillation counting.
Duration and frequency of treatment / exposure:
Single inhalation exposure for 12 h
Dose / conc.:
5 ppm
Remarks:
steady state reached after 4 h
No. of animals per sex per dose:
3 male rats
Control animals:
no
Positive control:
no
Details on study design:
Immediately after exposure, the rats were placed into glass Roth metabolism units equipped for the separate collection of urine, feces and expired air.
Details on dosing and sampling:
Urine and feces were collected at 12, 24, 36, 48 and 60 h after the termination of exposure; gas chromatographic quantitation of DMAC, N-methylacetamide (NMAC) and acetamide (AC).
Blood was sampled at termination of exposure and 12, 24, 36 and 48 h post exposure.
Cage washes were conducted at the end of the exposure period.
Expired air volatiles were trapped and samples collected 12, 24, 36 and 60 hours after termination of exposure.
At termination (60 h), radioactivity was determined in the liver, lung, kidney, fat tissue, muscle, blood and residual carcass.
Statistics:
Means value ± standard deviation were calculated.
Details on absorption:
All data related to recovered radioactivity; determination of applied radioactivity was not possible (no data about absorption available).
Details on distribution in tissues:
Significant levels of radioactivity were present in all tissues examined (no further details). Fat and muscle appeared to be the major sites of accumulation of radiolabel with relatively high tissue/blood ratios at 60 hours after the termination of exposure.
Half-life of radioactivity in plasma was 22.4 ± 0.6 h.
Details on excretion:
There was significant elimination of radioactive material via the expired air (CO2 presumed; no further details).
56.3 ± 12.0 % of recovered radioactivity was excreted during the 60-h post exposure period via urine and feces.
Excretion via urine was the main elimination route for radioactivity.
The half-life for elimination of radioactivity from the body was 39.1 ± 9.6 h.
22.4 ± 6.6 % of the recovered radioactivity were detected in carcass and organs at termination.
Metabolites identified:
yes
Details on metabolites:
DMAC, NMAC and acetamide (AC) represented 14.8 ± 6.2, 25.8 ± 7.5 and 46.5 ± 17.0 %, respectively, of total in urine plus cage wash.

- There was rapid absorption via inhalation (and presumably via the dermal route).

- There was even distribution of radioactivity in all organs, with preference in fat and muscle; radioactivity derived from DMAC showed some persistence in the body (half-life: 39 h).

- Demethylation was identified as the major route of metabolism resulting in NMAC and AC formation.

- Urine was the major route of elimination but there was excretion of radioactivity also via feces and expired air (CO2; presumably further metabolism of AC).

Conclusions:
Whole body inhalation exposure of rats resulted in rapid absorption, distribution, metabolism, and excretion mainly via urine; demethylation of the parent substance resulted in N-methylacetamide and acetamide formation
Executive summary:

Toxicokinetic parameters were measured in 3 Sprague-Dawley rats after single inhalation exposure to the vapour of the radiolabelled test substance at 5 ppm for 12 h.

Animals were whole body exposed (dermal absorption was also assessed); test substance vapour was generated in a diffusion tube at 70-80 °C, diluted with air and the DMAC concentration was measured when the animal was present in the inhalation chamber. The DMAC exposure concentration was determined throughout the exposure period by collection of measured volumes of air into impingers; DMAC concentration was measured by GC methods and liquid scintillation counting.

Urine and feces were collected at 12, 24, 36, 48 and 60 h after the termination of exposure; gas chromatographic quantitation of DMAC, N-methylacetamide (NMAC) and acetamide (AC). Blood was sampled at termination of exposure and 12, 24, 36 and 48 h post exposure. Cage washes were conducted at the end of the exposure period. Expired air volatiles were trapped and samples collected 12, 24, 36 and 60 hours after termination of exposure. At termination (60 h), radioactivity was determined in the liver, lung, kidney, fat tissue, muscle, blood and residual carcass.

DMAC, NMAC and acetamide (AC) represented 14.8 ± 6.2, 25.8 ± 7.5 and 46.5 ± 17.0 %, respectively, of total in urine plus cage wash. Significant levels of radioactivity were present in all tissues examined (no further details). Fat and muscle appeared to be the major sites of accumulation of radioactivity with relatively high tissue/blood ratios at 60 hours after the termination of exposure. Half-life of radioactivity in plasma was 22.4 ± 0.6 h.

There was significant elimination of radioactive material via the expired air (CO2 presumed; no further details). 56.3 ± 12.0 % of recovered radioactivity was excreted during the 60-h post exposure period via urine and feces. Excretion via urine was the main elimination route for radioactivity. The half-life for elimination of radioactivity from the body was 39.1 ± 9.6 h. 22.4 ± 6.6 % of the recovered radioactivity were detected in carcass and organs at termination.

Conclusion: Whole body inhalation exposure of rats resulted in rapid absorption, distribution, metabolism, and excretion mainly via urine; demethylation of the parent substance resulted in N-methylacetamide and acetamide formation

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
(restricted to plasma levels and amounts in urine and feces measured 0-24 h after gavage of unlabelled test substance; elimination via exhaled air not measured)
Objective of study:
toxicokinetics
Qualifier:
no guideline followed
Principles of method if other than guideline:
Bioavailability and distribution of dimethylacetamide (DMAC) after single oral application by gavage to the pregnant rat.
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
Purity: 99.8 %
Batch no: 83 S 7329
Date of receipt: 6 April 1999
Based on the nature of the chemical (solvent) a degradation in the vehicle did not occur.
No further details available.
Radiolabelling:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Crl:CD(SD)BR strain obtained from Charles River Wiga GmbH, 97633 Sulzfeld, Germany
- Age at study initiation: 8-12 weeks old at the time of mating
- Weight at study initiation: ≥ 200 g at the time of mating
- Fasting period before study: no data
- Housing: housed individually
- Individual metabolism cages: yes
- Certified diet and tap water ad libitum (analysed for contaminations)
- Acclimation period: at least 7 days after arrival


ENVIRONMENTAL CONDITIONS
- Temperature: 19-25 °C
- Humidity: 30-70 %
- Air changes: 10 air changes per hour
- Photoperiod: 12 hours dark/12 hours light
Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
Application volume 5 mL/kg bw
Duration and frequency of treatment / exposure:
Once
Dose / conc.:
500 other: mg/kg bw
Remarks:
concentration 100 mg/ml
Dose / conc.:
1 000 other: mg/kg bw
Remarks:
concentration 200 mg/ml
No. of animals per sex per dose:
16 rats (see also details of study design)
Control animals:
no
Positive control:
no
Details on study design:
All rats were gavaged on Day 15 post-coitum (GD 15). Results related to pregnant animals.
Group 1a: 500 mg/kg bw (n = 6); blood sampling at 1, 4 and 12 h after dosing; urine and feces collected in metabolism cages for 12 h after dosing; necropsy at 12 h after gavage.
Group 1b: 500 mg/kg bw (n = 6), blood sampling at 0.5, 2, 8 and 24 h after dosing; urine and feces collected in metabolism cages for 24 h after dosing; necropsy at 24 h after gavage.
Group 2a: 1000 mg/kg bw (n = 8); blood sampling at 1, 4 and 12 h after dosing; urine and feces collected in metabolism cages for 12 h after dosing; necropsy at 12 h after gavage.
Group 2b: 1000 mg/kg bw (n = 5), blood sampling at 0.5, 2, 8 and 24 h after dosing; urine and feces collected in metabolism cages for 24 h after dosing; necropsy at 24 h after gavage.

Blood samples were collected, centrifuged and plasma stored at -20 ± 2°C until analysis.
At necropsy, amniotic fluid was collected from each pregnant female. Urine, feces and amniotic fluid were stored deep frozen at -20 ± 2 °C until analysis .
The body weight of each female was recorded on Days 0, 6, 9, 12 and 15 post-coitum.
Clinical signs were recorded.
Details on dosing and sampling:
See Details on study design.
The analytical measurements of DMAC and N-methylacetamide (NMAC) were performed by GC methods.
Statistics:
Mean values ± standard deviations were calculated.
Details on absorption:
No data available
Details on distribution in tissues:
Plasma levels of DMAC increased to plateau phase 1-2 h after application (lasting for ca. 12 h, lower plasma levels after 24 h); even after 0.5 h ca. 70 % of max. level was reached suggesting rapid absorption after oral gavage administration.
NMAC levels in plasma reached max. values 24 h after 500 or 1000 mg/kg bw (no later readings). NMAC plasma levels were clearly lower than DMAC levels suggesting rapid excretion of the metabolite via urine.

DMAC and NMAC concentrations in amniotic fluid and plasma were very similar at 12 and 24 h after gavage of 500 or 1000 mg/kg bw DMAC suggesting equal distribution.
Details on excretion:
Amount of DMAC and NMAC excreted is dose dependent.
DMAC excretion via urine occurred mainly 0-12 h after application at the low dose level since the increase in total amounts excreted 12-24 after gavage was low. At 1000 mg/kg bw, the excretion rate of DMAC via urine was constant (0-12 h versus 12-24 h). However, excretion of the metabolite NMAC increased 12-24 h after application at both dose levels. The amount of NMAC excreted via urine was clearly higher than that of the parent substance DMAC.
Excretion via the feces was a minor route of elimination compared with excretion via urine. Evaluation was hampered by interindividual variability but data on the high dose level suggested increased excretion of DMAC and NMAC via feces 12-24 h after gavage compared to the excretion 0-12 h after application.
Metabolites identified:
yes
Details on metabolites:
N-methylacetamide (NMAC) was measured in plasma, urine, and feces. No further data about metabolites.

Toxicokinetic data in pregnant Sprague-Dawley rats after a single gavage at gestation day 15

Parameter

500 mg/kg bw
(urine 0-12 h)

500 mg/kg bw
(urine 0-24 h)

1000 mg/kg bw (urine 0-12 h)

1000 mg/kg bw (urine 0-24 h)

DMAC in amniotic fluid at termination (µg/mL)

511 ± 75

163 ± 27

1152 ± 119

562 ± 71

DMAC in plasma at termination (µg/mL)

529 ± 26

194 ± 34

1107 ± 156

581 ± 74

NMAC in amniotic fluid at termination (µg/mL)

55 ± 6

76 ± 12

80 ± 19

102 ± 28

NMAC in plasma at termination (µg/mL)

55 ± 7

89 ± 18

45 ± 19

104 ± 24

DMAC in urine (µg/mL)

1197 ± 244

1354 ± 486

2252 ± 361

2563 ± 1169

Total µg DMAC in urine

5744 ± 3271

7836 ± 3713

9373 ± 3039

18952 ± 6295

NMAC in urine (µg/mL)

1375 ± 793

3422 ± 1055

1939 ± 683

4002 ± 960

Total µg NMAC in urine

6182 ± 3193

20900 ± 11695

7654 ± 2731

32570 ± 16940

DMAC in feces (in µg)

683 ± 520

813 ± 586

358 ± 284

2937 ± 1183

NMAC in feces (in µg)

292 ± 353

200 ± 136

14 ± 18

465 ± 575

Means ± SD

Plasma levels (in µg/mL) of DMAC and NMAC in rats after gavage of 500 or 1000 mg/kg bw

Time after gavage

(h)

DMAC after

500 mg/kg bw

NMAC after

500 mg/kg bw

DMAC after

1000 mg/kg bw

NMAC after 1000 mg/kg bw

Group 1a

1

655 ± 141

18 ± 4

975 ± 167

40 ± 23

4

749 ± 349

34 ± 10

1078 ± 157

49 ± 27

12

529 ± 26

55 ± 7

1107 ± 156

45 ± 19

Group 1b

0.5

550 ± 99

10

856 ± 90

14 ± 3

2

639 ± 112

15 ± 3

914 ± 111

20 ± 3

8

657 ± 143

54 ± 11

1084 ± 89

55 ± 11

24

194 ± 34

89 ± 18

581 ± 74

104 ± 24

Means ± SD

Conclusions:
Data on plasma levels indicated rapid absorption after single gavage in pregnant rats; there was equal distribution between maternal and fetal bloodstream; excretion occurred via urine, mainly after metabolism to N-methylacetamide.
Executive summary:

The bioavailability and distribution of dimethylacetamide (DMAC) after single oral application by gavage to the pregnant rat was studied.

16 rats were gavaged on Day 15 post-coitum (GD 15) with 500 or 1000 mg/kg bw.

Clinical signs were recorded. Blood, urine and feces were collected in intervals up to 24 h after application. Necropsy was performed.

There were no deaths, no significant clinical signs, no effects on body weight gain (presumably compared to untreated historical controls) and no abnormalities at necropsy. Determination of pregnancy status revealed 12 pregnant females in group 1 (500 mg/kg bw) and 13 pregnant females in group 2 (1000 mg/kg bw) .

Plasma levels of DMAC increased to plateau phase 1-2 h after application (lasting for ca. 12 h, lower plasma levels after 24 h); even after 0.5 h ca. 70 % of max. level was reached suggesting rapid absorption after oral gavage administration. NMAC levels in plasma reached max. values 24 h after 500 or 1000 mg/kg bw (no later readings). NMAC plasma levels were clearly lower than DMAC levels suggesting rapid excretion of the metabolite via urine. DMAC and NMAC concentrations in amniotic fluid and plasma were very similar at 12 and 24 h after gavage of 500 or 1000 mg/kg bw DMAC suggesting equal distribution.

The amount of DMAC and NMAC excreted was dose dependent. DMAC excretion via urine occurred mainly 0-12 h after application at the low dose level since the increase in total amounts excreted 12-24 after gavage was low. At 1000 mg/kg bw, the excretion rate of DMAC via urine was constant (0-12 h versus 12-24 h). However, excretion of the metabolite NMAC increased 12-24 h after application at both dose levels. The amount of NMAC excreted via urine was clearly higher than that of the parent substance DMAC.

Excretion via the feces was a minor route of elimination compared with excretion via urine. Evaluation was hampered by interindividual variability but data on the high dose level suggested increased excretion of DMAC and NMAC via feces 12-24 h after gavage compared to the excretion 0-12 h after application.

Conclusion: Data on plasma levels indicated rapid absorption after single gavage in pregnant rats; there was equal distribution between maternal and fetal bloodstream; excretion occurred via urine, mainly after metabolism to N-methylacetamide.

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
(only 2 rats per dose; no data about sex; radioactivity in excreta related to recovered and not to applied radioactivity [quantitative data on absorption not available])
Objective of study:
toxicokinetics
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 417 (Toxicokinetics)
Deviations:
no
GLP compliance:
no
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
Source: Amersham
Specific activity: 11.5 mCi/mole
Purity: >90 %
No further details available.
Radiolabelling:
yes
Remarks:
14C-labelled DMAC
Species:
rat
Strain:
other: Charles-River CD
Sex:
not specified
Details on test animals and environmental conditions:
TEST ANIMALS
- Initial body weight: 289-328 g
- Certified diet and water ad libitum

No further data available.
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on exposure:
33 mg or 92 mg of 14C-labelled DMAC given by gavage to rats; dilution of radiolabelled DMAC with unlabelled substance.
Duration and frequency of treatment / exposure:
Once
Dose / conc.:
33 other: mg per rat
Dose / conc.:
92 other: mg per rat
No. of animals per sex per dose:
2 rats per dose (no data about sex)
Control animals:
no
Positive control:
no
Details on dosing and sampling:
Rats were held in metabolism cages for 72 h after gavage.
Excretion products were collected for 72 h (urine, feces, exhaled air).
Exhaled air: trapping solutions were changed every 6 or 12 h; urine and feces were collected with each change of trapping solution.
At termination (72 h) radioactivity was determined in blood, organs, carcass and in cage wash samples.
Statistics:
no data
Details on absorption:
Data were related to recovered radioactivity (and not related to applied radioactivity).
No statement on oral absorption was possible.
Details on distribution in tissues:
At termination, 72 h after the oral gavage exposure, only trace levels of radioactivity were found in tissues indicating no storage in the body.
Distribution was uniform but organs involved in metabolism like liver, kidney, intestine showed the highest concentrations.
Details on excretion:
Within 24 hours, 80-87 % of the recovered radioactivity was excreted via urine. Urine contained 93 % of the radioactivity, feces only 5 %, and tissues examined at 72 hours contained 2 %; exhaled radioactivity was <1 % suggesting that very small amounts were hydrolyzed and eliminated as radiolabelled carbon dioxide.
Metabolites identified:
yes
Details on metabolites:
Nine radioactive components were found, but not all were identified. Concerning urine, 60 to 70 % of recovered radioactivity was identified as N-methylacetamide, 7 to 10 % as N-hydroxymethylacetamide, and 7 to 10 % as acetamide. DMAC was also found in the urine (14% of recovered radioactivity after the low dose).
Authors suggested that non-identified metabolites (ca. 9 % of recovered radioactivity) were N-methyl-N-hydroxymethylacetamide, acetic acid and acetylated biological material. A very small amount (< 1 %) was hydrolyzed and eliminated as radiolabelled carbon dioxide.
Conclusions:
After oral application 14C-DMAC was rapidly absorbed in rats and radioactivity was mainly excreted via urine. The main metabolite was N-methylacetamide, formed by demethylation. There was no bioaccumulation potential based on study results.
Executive summary:

Single doses 33 mg or 92 mg of 14C-labelled DMAC were given to 2 rats by gavage. Rats were held in metabolism cages for 72 h after gavage. Excretion products were collected for 72 h (urine, feces, exhaled air). At termination (72 h) radioactivity was determined in blood, organs, carcass and in cage wash samples.Metabolites in urine were analysed by TLC and GC and confirmed by MS techniques. Radioactivity was measured by scintillation counting.

Data were related to recovered radioactivity (and not related to applied radioactivity). No statement on oral absorption was possible.

At termination, 72 h after the oral gavage exposure, only trace levels of radioactivity were found in tissues indicating no storage in the body. Distribution was uniform but organs involved in metabolism like liver, kidney, intestine showed the highest concentrations. Nine radioactive components were found, but not all were identified. Concerning urine, 60 to 70 % of recovered radioactivity was identified as N-methylacetamide, 7 to 10 % as N-hydroxymethylacetamide, and 7 to 10 % as acetamide. DMAC was also found in the urine (14% of recovered radioactivity after the low dose).

Authors suggested that non-identified metabolites (ca. 9 % of recovered radioactivity) were N-methyl-N-hydroxymethylacetamide, acetic acid and acetylated biological material. A very small amount (< 1 %) was hydrolyzed and eliminated as radiolabelled carbon dioxide.

Conclusion: After oral application 14C-DMAC was rapidly absorbed in rats and radioactivity was mainly excreted via urine. The main metabolite was N-methylacetamide, formed by demethylation. There was no bioaccumulation potential based on study results.

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
GLP and guideline study
Qualifier:
according to
Guideline:
other: Guideline on Detection of Toxicity to Reproduction for Medicinal Products; Federal Register/Vol. 59, No. 183
GLP compliance:
yes
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
- Batch No.: 83S7329
- Density: 0.94 g/cm³ (20 °C)
- Purity: 99.8 %
- Expiration date of the batch: April 2001
- Storage condition of test material: room temperature
No further details available.
Radiolabelling:
no
Species:
monkey
Strain:
Macaca fascicularis
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: BEST ENGINEERING COMPANY LIMITED, Rm. 1209,12/F, Block A, New Trade Plaza, 6 On Ping Street, Shatin, N.T., Hong Kong
- Age at study initiation: at least 3 years old
- Weight at study initiation: 3.6-4.0 kg
- Fasting period before study: no
- Housing: single
- Diet: Twice daily (morning and afternoon of working hours) each monkey was offered about 50 g of Ssniff P 10 pellets (Ssniff Spezialdiäten GmbH, 59494 Soest, Germany). In addition, the animals received fresh fruit approximately twice weekly and one slice of bread once weekly.
- Water: ad libitum
- Acclimation period: 6 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 19-25 °C
- Humidity: 30-70 %
- Air changes: 10 changes per hour
- Photoperiod: 12 hours dark / 12 hours light

Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
PREPARATION OF DOSING SOLUTIONS: Solutions of the test substance in the vehicle (distilled water) were prepared once.
Duration and frequency of treatment / exposure:
The test substance was administered once on Day 100 post-coitum to the first animal and on Day 105 post-coitum to the second animal 24 hours prior to Caesarean section.
Dose / conc.:
500 mg/kg bw/day
No. of animals per sex per dose:
2 monkeys
Control animals:
no
Details on study design:
Mating
Female animals were placed with untreated fertile male animals 1 or 2 days before the theoretical middle of the menstrual cycle, or on the basis of the consistency of the cervical mucus. The duration of mating was ≤ 18 hours. The day on which mating was terminated was considered Day 0 of gestation (or post-coitum), GD 0.
Details on dosing and sampling:
TOXICOKINETICS
On gestational day 100 (GD 100, first animal) and on GD 105 (second animal), blood samples (about 3 mL) were collected from the brachial or femoral vein 0.5, 1, 2, 4, 8, 12 and 24 hours after dosing. Fetal blood (about 2 mL from the umbilical vein) and amniotic fluid (10 and 4 mL, respectively) were collected at Caesarean section. Blood samples were centrifuged and serum and amniotic fluid were stored deep frozen at -20 ± 2°C until analysis. Urine and feces samples were collected in trays inserted under each cage 12 h and 24 h after dosing. Urine and feces samples were stored deep frozen at -20 ± 2°C until analysis .

ANALYTICAL METHOD
The method entailed the extraction of DMAC and NMAC from serum, urine and feces with ethanol containing N,N-diethylacetamide as internal standard, centrifugation and injection of supernatant liquid onto GC-NPD.
Statistics:
none
Details on absorption:
At 24 hours, the levels of DMAC and NMAC were comparable in maternal and fetal serum and amniotic fluid. For serum, the mean DMAC concentration found over the 24-hour sampling period after dosing ranged from 310.5 µg/mL at 0.5 hours increasing to a peak level of 729 μg/mL at 4 hours and then decreasing to 303.5 μg/mL at 24 hours. The mean NMAC concentration found in serum over the 24 hour sampling period after dosing ranged from <10 to 15 μg/mL at 0.5 hours increasing to a peak level of 185 μg/mL at 24 hours.
Details on excretion:
For feces and urine, the level of DMAC increased at 0-12 hours and decreased at 12-24 hours and the level of NMAC decreased at 0-12 hours and increased at 12-24 hours.

The mean DMAC concentration found in feces was 328 μg/g at 0-12 hours and 183 μg/g at 12-24 hours. The mean NMAC concentration found in feces was 59 μg/g at 0-12 hours and 139 μg/g at 12-24 hours.

The mean DMAC concentration found in urine was 988.5 μg/g at 0-12 hours and 619 μg/g at 12-24 hours. The mean NMAC concentration found in urine was 2016.5 μg/g at 0-12 hours and 3511 μg/g at 12-24 hours.
Metabolites identified:
yes
Details on metabolites:
N-Methylacetamide (NMAC), as the major metabolite of DMAC.

Morbidity and mortality

No deaths were observed in this study.

Clinical observations

No treatment related clinical signs were observed during the course of the study.

Body weights

The body weight was not affected by treatment.

Fetal data and external findings

Placental and fetal weights did not reveal any effect of treatment. The fetuses did not show any external abnormalities.

Conclusions:
There was no treatment effect of the test substance on pregnant monkeys and their fetuses following a single oral gavage administration of DMAC at 500 mg/kg bw.
NMAC was identified as the main metabolite. Urine was the main route of excretion.
Executive summary:

In the course of a reproduction study the toxicokinetics of DMAc in 2 monkeys was studied after a single oral administration of 500 mg/kg bw via gavage.

The test substance was administered once on Day 100 post-coitum to the first animal and on Day 105 post-coitum to the second animal 24 hours prior to Caesarean section. On gestational day 100 (GD 100, first animal) and on GD 105 (second animal), blood samples (about 3 mL) were collected from the brachial or femoral vein 0.5, 1, 2, 4, 8, 12 and 24 hours after dosing. Fetal blood (about 2 mL from the umbilical vein) and amniotic fluid (10 and 4 mL, respectively) were collected at Caesarean section. Urine and feces samples were collected in trays inserted under each cage 12 h and 24 h after dosing.

At 24 hours, the levels of DMAC and NMAC were comparable in maternal and fetal serum and amniotic fluid. For serum, the mean DMAC concentration found over the 24-hour sampling period after dosing ranged from 310.5 µg/mL at 0.5 hours increasing to a peak level of 729 µg/mL at 4 hours and then decreasing to 303.5 µg/mL at 24 hours. The mean NMAC concentration found in serum over the 24 hour sampling period after dosing ranged from <10 to 15 µg/mL at 0.5 hours increasing to a peak level of 185 µg/mL at 24 hours.

For feces and urine, the level of DMAC increased at 0-12 hours and decreased at 12-24 hours and the level of NMAC decreased at 0-12 hours and increased at 12-24 hours. The mean DMAC concentration found in feces was 328 µg/g at 0-12 hours and 183 µg/g at 12-24 hours. The mean NMAC concentration found in feces was 59 µg/g at 0-12 hours and 139 µg/g at 12-24 hours.

The mean DMAC concentration found in urine was 988.5 µg/g at 0-12 hours and 619 µg/g at 12-24 hours. The mean NMAC concentration found in urine was 2016.5 µg/g at 0-12 hours and 3511 µg/g at 12-24 hours.

Conclusion: There was no treatment effect of the test substance on pregnant monkeys and their fetuses following a single oral gavage administration of DMAC at 500 mg/kg bw. NMAC was identified as the main metabolite. Urine was the main route of excretion.

Endpoint:
basic toxicokinetics
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
other: This study has to be carefully evaluated as it was performed at Industrial Bio-test Labs which is known to have conducted scientific fraud. Therefore, the reliability is not assignable.
Remarks:
Only a summary of the report is available but data are sufficient for evaluation; restrictions: no detailed tabulated documentation of results; no data about strain; no details about test substance or test animals; data on cage washes not given; no data given on oral absorption rate but estimation possible.
Objective of study:
absorption
toxicokinetics
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 417 (Toxicokinetics)
GLP compliance:
no
Specific details on test material used for the study:
- Name of test material: dimethylacetamide (DMAC)
Specific activity: 1.33 mCi/mM
Source: Monsanto Company
No further details available.
Radiolabelling:
yes
Remarks:
14C-DMAC (no further details)
Species:
rat
Strain:
not specified
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Weight at study initiation: 195-237 g

No further details available.
Route of administration:
oral: gavage
Vehicle:
water
Details on exposure:
Dose volumes ranged from 0.39-0.71 mL/rat (14C-DMAC diluted with cold DMAC); each rat received approximately 7 µCi of 14C-activity.
Duration and frequency of treatment / exposure:
a) single application of DMAC
b) daily gavage with cold DMAC for 2 weeks and then 14C-DMAC once
Dose / conc.:
1 other: mg/kg bw
Remarks:
a) single application of DMAC
Dose / conc.:
3 other: mg/kg bw
Remarks:
a) single application of DMAC
Dose / conc.:
10 other: mg/kg bw
Remarks:
a) single application of DMAC
Dose / conc.:
30 other: mg/kg bw
Remarks:
a) single application of DMAC
Dose / conc.:
3 mg/kg bw/day
Remarks:
b) daily gavage with cold DMAC for 2 weeks and then 14C-DMAC once
Dose / conc.:
30 mg/kg bw/day
Remarks:
b) daily gavage with cold DMAC for 2 weeks and then 14C-DMAC once
No. of animals per sex per dose:
3 rats
Control animals:
no
Positive control:
no
Details on dosing and sampling:
Rats were placed in metabolism cages. All excreta (urine, feces, expired air) were collected (no details were given but presumably excreta were collected for 96 h [see sacrifice 96 h after gavage]; see also results); rats were sacrificed 96 h after gavage with 14C-DMAC.
Statistics:
no data
Details on absorption:
The authors stated in the summary that 80-100 % of the applied radioactivity was recovered. Measured radioactivity in excreta and tissues was related to total recovered radioactivity. Absorption rate was not given by the authors, but assuming that radioactivity in feces was absorbed radioactivity after gavage which was excreted via the bile (compared with inhalation experiments in Section 7.1.1; however, only 2-8 % of recovered radioactivity was excreted via feces) the absorption rate was >= 80 % of applied radioactivity.
Details on distribution in tissues:
At termination (sacrifice 96 h after gavage) only small amounts of radioactivity were measured in tissues; the highest percentage was recorded at the low dose: 1.1 % of recovered radioactivity. The distribution in selected tissues was similar in all test groups; liver, skin, muscle and fat tissues contained the highest concentrations of radiocarbon.
Details on excretion:
Most radioactivity was excreted during the first 24 h after application. The main route of excretion was urine.
84-92 % of recovered radioactivity was excreted via urine, 75 to 87 % during the first 24 h after application.
5.5-7.0 % of the recovered radioactivity was detected in expired air, mainly as radiolabelled carbon dioxide (1-3 % 14C-labeled materials other than radiolabelled carbon dioxide).
2-8 % of recovered radioactivity was excreted via feces (most radioactivity excreted 0-24 h after gavage)
1.1 % of recovered radioactivity was detected in tissues (sacrifice after 96 h) at a dose of 1 mg/kg bw, significantly lower amounts were found at 30 mg/kg bw.
Non-preexposed rats (a) tended to excrete higher percentages of radioactivity in urine and feces during the first 12 h; however, the preexposed rats (b) reached and/or exceeded these levels at 24 h post-dosing and thereafter.
Metabolites identified:
not measured
Conclusions:
Rapid and nearly complete absorption of DMAC was noted in rats after oral test substance application via gavage; there was rapid metabolism and excretion, mainly via urine (only ≤ 1 % of radioactivity was retrieved in tissues after 96 h).
There were no clinical signs. Rats appeared normal at sacrifice.

Description of key information

N,N-Dimethylacetamide (DMAC) is readily absorbed following oral, dermal and inhalation exposure. Oral and inhalation absorption is assumed to be quantitative and twice as high as dermal absorption. Metabolism occurs via N-demethylation to N-methylacetamide (NMAC) and acetamide (AC). There is no bioaccumulation potential. Urinary excretion predominates.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
100
Absorption rate - dermal (%):
50
Absorption rate - inhalation (%):
100

Additional information

Discussion of exisiting TK-data 

The toxicokinetic properties of DMAC were studied in rodents (rats and mice), primates and humans.

DMAC is readily absorbed into the mammalian system following oral, dermal and inhalation exposure. Oral absorption after a single gavage treatment with radiolabelled DMAC was quantified in rats (Monsanto, 1974; Kennedy, 1986). In both studies the oral absorption was above 80 % indicating nearly quantitative absorption. The percentage of dermal and inhalation absorption was not explicitly determined in animals or humans. The molecular weight below 100, the log Pow of -0.77 and the vapour pressure of 2 hPa are in favor of a higher potential of inhalative than dermal absorption. A skin permeability constant of 10.7 ± 1.9 mg/cm²/h was determined in vitro using human skin (Ursin et al., 1995) and observations indicative for rapid dermal absorption were seen in rabbits after occlusive dermal exposure to DMAC (Finlay et al., 2001) as well as in humans after dermal exposure to DMAC vapour (e.g. Nomiyama et al., 2000; Maxfield et al., 1975, chapter 7.10) or liquid (Maxfield et al., 1975, chapter 7.10). High inhalation absorption was indicated in many studies in rodents (e.g. Hundley et al., 1994; Monsanto, 1982) and humans (e.g. Maxfield, 1975; Nomiyama et al., 2000, and Dupont, 1987, chapter 7.10).

In twelve male volunteers who were exposed to a vapour exclusively via the skin or via inhalation route (6.1 ± 1.3 ppm, exposure duration 4 h) the individual dermal absorption rates defined as dermal absorption over dermal plus respiratory absorption fluctuated widely between 12.9 % and 73.3 %, the mean value was 40 % (Nomiyama et al., 2000, chapter 7.10.3). Two male volunteers were exposed to a vapour at a concentration of 10 ppm for 6 h and DMAC was absorbed a) via inhalation and dermal route in an exposure chamber (most part of the body naked) or b) only via the dermal route (breathing of normal air outside the chamber via mask; Maxfield et al., 1975, chapter 7.10.3). The highest urine concentration of N-methylacetamide (NMAC, 45-100 ppm) was found in a). In b) the values were in the range of 6 to 23 ppm. The difference in the amount of NMAC excreted following exposure with and without the mask in a) and b) indicated that more DMAC was absorbed through the lungs (70 %) than through the skin (30 %) during an exposure to the vapour. The results show that dermal absorption contributes significantly to the overall amount of systemically available DMAC following vapour exposure.  

The metabolism of DMAC is similar in rodents, monkeys and humans and independent from the route of exposure.The metabolic pathway in vivo is N-demethylation leading to NMAC, via N-hydroxymethyl-methylacetamide, as the main metabolite and also to acetamide (AC). The parent substance and its metabolites are mainly excreted via urine.

Interspecies differences in toxicokinetics which are not related to differences in basal metabolic rate were not observed between mouse and rat (Hundley et al., 1994) and pregnant rat and pregnant monkey (BASF, 2001 and 2000). Plasma half-life ranged from 0.6 to 1.5 h for DMAC and 2.2 to 3.0 for NMAC in rats, and from 0.3 to 0.5 h for DMAC and 0.6 to 1.3 h for NMAC in mice after single and repeated inhalation exposure (Hundley et al., 1994). Saturation of metabolism seemed to occur at concentrations ≥150 ppm in rats and ≥300 ppm in mice. In both species the plasma profiles, plasma AUC values and plasma half-lives were not affected by multiple exposures to DMAC. The plasma profiles were similar to those from a single exposure. Pregnant rats (n = 12) were gavaged once with 500 mg/kg bw at gestation day 15 (GD15; BASF, 2001). Similarly, two pregnant monkeys (Macaca fascicularis) were gavaged once with 500 mg/kg bw on GD 100 or GD 105 (BASF, 2000). The maximum DMAC concentration was reached 1-2 hours and 2-8 hours after gavage in rats and monkeys, respectively. In both species, high concentrations of DMAC were already found 0.5 hours after treatment (70 % and 40 % of Cmax in rats and monkey, respectively). In both species, DMAC excretion was the highest during the first 12 hours after gavage; NMAC concentrations increased in the second half of the post-treatment period (12-24 hours) and were the highest at termination (24 hours after treatment). Maternal and fetal DMAC and NMAC levels were comparable 24 hours after gavage (very similar DMAC and NMAC concentrations were noted in amniotic fluid and maternal plasma in rats, and in maternal and fetal serum in monkeys).

Conclusions for DNEL setting  

On the basis of the toxicokinetics data together with the physico-chemical properties it is concluded that oral and inhalation absorption occur rapidly and nearly quantitatively. Even though dermal absorption is rapid as well and contributes significantly to the total internal dose after inhalation exposure to DMAC vapour, it is reasonable to assume that under non-occlusive conditions dermal absorption is lower than oral or inhalation absorption due to the relatively high volatility of DMAC. For DNEL calculation purposes it is therefore assumed that dermal absorption is 50 % and thus, 2 fold lower than oral and inhalation absorption. This value is still conservative compared to the default dermal absorption value of 25 % which has been agreed for small organic molecules in the plant protection area (EFSA, 2012). The kinetic data provide no indications for susceptibility differences between species which are not related to differences in basal metabolic rate.

Reference

EFSA (2012). Scientific opinion: Guidance od Dermal Absorption. EFSA Journal 2012; 10(4): 2665 [30 pp].