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Toxicological information

Basic toxicokinetics

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Administrative data

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

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1992
Report Date:
1992

Materials and methods

Objective of study:
toxicokinetics
Test guideline
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

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
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

Test animals

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

Administration / exposure

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
Doses / concentrationsopen allclose all
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.

Results and discussion

Toxicokinetic / pharmacokinetic studies

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 parametersopen allclose all
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

Metabolite characterisation studies

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.

Any other information on results incl. tables

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.

 

Applicant's summary and conclusion

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).