Cyanamide

Endpoint summary

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

No documentation of individual health status. Limited number of individuals. There is no statement if the study is performed in accordance with internationally accepted ethical standards.

Reason / purpose for cross-reference:

reference to same study

Objective of study:

excretion

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

For principles of method see below.

GLP compliance:

no

Remarks:

however, the study is reported in detail

Radiolabelling:

no

Species:

rat

Strain:

Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

Not indicated

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Duration and frequency of treatment / exposure:

Single dose

Remarks:

Doses / Concentrations:
10 mg/kg bw

No. of animals per sex per dose / concentration:

4 animals

Control animals:

other: Urine samples collected 48 hours before application of cyanamide served as controls.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine
- Time and frequency of sampling: The urine was collected for a period of 48 hours
- Other:
- After treatment the animals were housed in metabolism cages
- All collected samples were analysed for N-acetylcyanamide content.

Details on excretion:

42.8 to 51.5 % of the applied dose was excreted as N-acetylcyanamide in the urine within 48 hours.

Metabolites identified:

yes

Details on metabolites:

N-acetylcyanamide. The animal study which was performed in rats showed that N-acetylcyanamide is the major metabolite of cyanamide in rats (see table below in "Remarks on results")

The findings show that the absorption, metabolism and excretion occur relatively rapid with the majority of the applied dose already excreted as its major metabolite during the first 2 hours after application. Excretion of N-acetylcyanamide in the urine of rats orally treated with 10 mg cyanamide/kg bw:

 

Animal No	N-acetylcyanamide excretion 0 to 48 hours( %)
1	42.8
2	44.9
3	51.5
4	43.2

 

Conclusions:

The study confirmed that N-acetylcyanamide is the main urinary metabolite of cyanamide in rat and its excretion after an oral application is rapid and efficient.

Executive summary:

The aim of the study (Gloxhuber, C., 1989, Doc. No. 512-004) was to elucidate differences in metabolism and excretion of hydrogen cyanamide in rats and humans. The present study record describes a part of this study, the one which was conducted in rats. A group of four animals (male Wistar rats) was treated by gavage with Hydrogen cyanamide (10 mg/kg bw) given as aqueous solution. After treatment the animals were housed in metabolism cages and the urine was collected for a period of 48 hours. Urine samples collected 48 hours before application of cyanamide served as controls. All collected samples were analysed for N-acetylcyanamide content. The results of the animal study showed that N-acetylcyanamide is the major metabolite of cyanamide in rats. 42.8 to 51.5 % of the applied dose was excreted as N-acetylcyanamide in the urine within 48 hours. The findings show that the absorption, metabolism and excretion occur relatively rapid with the majority of the applied dose already excreted as its major metabolite during the first 2 hours after application.

Altogether results of all three parts of the study (rat: gavage, human: oral, dermal) confirmed that N-acetylcyanamide is the main urinary metabolite of cyanamide in rat and man. Both species showed an efficient excretion of orally or dermally administered cyanamide. Cyanamide is absorbed through human skin, however, the dermal absorption is considerably delayed compared to the oral one. The degree of dermal absorption of a 1 % aqueous cyanamide solution for a period of 6 hours exposure was found to be between 0.87 and 3.53 %.

Reference 2

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Objective of study:

absorption

distribution

excretion

metabolism

Qualifier:

according to guideline

Guideline:

EU Method B.36 (Toxicokinetics)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

- Source: SD rats from Harlan Sprague Dawley, Madison, Wisconsin, U.S.A
- All treated animals were housed individually in metabolism cages for the quantitative separation and collection of urine, faeces and expired air.

Route of administration:

other: 3 groups of rats (5 males, 5 females) were administered with the test substance through the oral route. One group (5 males, 5 females) were administered with the test substance intravenously.

Vehicle:

other: For the oral dose solutions: 0.05 M ammonium phosphate was used as an vehicle. For the intravenous dose solutions 0.9 % w/v sodium chloride was used as an vehicle.

Details on exposure:

The oral dose solutions of Hydrogen cyanamide were prepared by dissolving appropriate amounts of non-radiolabelled and radiolabelled substance in appropriate volumes of 0.05 M ammonium phosphate buffer (pH 4.5 to 4.75). Radiolabelled oral dosing solutions were prepared within 2 days of dosing, the non-radiolabelled dosing solutions were prepared within 7 days of dosing. The intravenous dose solutions were prepared by dissolving non-radiolabelled and [14C]-Hydrogen cyanamide in 0.9 % w/v sodium chloride.

Duration and frequency of treatment / exposure:

3 groups administered with a single oral dose/intravenous dose followed by 7 days observation period (168 hours)). One group administered with a single oral (non-labeled) dose per day for 14 days followed by a single oral (radioactive material) dose (see table in " any other information on material and methods")

Remarks:

Doses / Concentrations:
3 groups (low dose groups) were administered (oral/intravenous) with 1 mg/kg bw of the labeled test susbatnce. 1 group (high dose group) was administered (oral) with 20 mg/kg bw of the labeled test substance (see table in " any other information on material and methods")

No. of animals per sex per dose / concentration:

5 animals per dose per sex

Control animals:

no

Positive control reference chemical:

No positive control

Details on study design:

- The experiments were carried out according to a preliminary test that elucidated adequate dose levels and showed if a collection of expired air is necessary (for the preliminary study design, see table in "any other informantion on materials and methods".

Details on dosing and sampling:

Expired air and organic volatiles were trapped in a mixture of 2-ethoxyethanol and ethanolamine (1:1). Activated charcoal, contained within glass tubing, was used to trap expired organic volatiles. The CO2 trapping solution and the charcoal were collected 12 and 24 hours after dose administration and daily thereafter for 7 days postdose. Urine and faeces samples were collected 12 and 24 hours postdose and daily thereafter for 7 days postdose. At the end of the collection period organs and tissues (blood, bone, brain, carcass, fat, heart, kidneys, liver, lungs, muscle, ovaries, spleen, thyroid and uterus) were prepared for analysis of residual radioactivity.
A composite urine sample for each group as prepared by combining proportional aliquots of urine from collection intervals that contained more than 90 % of the urinary radioactivity for each sex/group (with the exception of the group A male urine composite sample, which contained 86.6 %). The collection intervals were 0 to 48 hours postdose for composite urine samples for group A, B and C and 0 to 24 hours postdose for group D. Aliquots of the composite urine samples were fortified with N-acetylcyanamide reference standard for analysis.
Composite faeces samples for male and females in group A were prepared by combining proportional aliquots of faeces collected from 0 to 24 hours postdose.
Kidneys, liver and other organs and tissues did not obtain sufficient amounts of radioactivity to allow the isolation or identification of metabolites
For isolation, characterisation and identification of metabolites, preparative TLC, HPLC and mass spectrometry were used. Co-chromatography with reference standards was also used for the identification of metabolites.

Details on absorption:

After a single oral dose of 1 mg/kg bw at 168 hours organs (blood, bone, brain, fat, heart, kidneys, liver, lungs, muscle, ovaries, spleen, thyroid and uterus) accounted for 4.36 % for males and 3.3 % for females, carcass contained 2.31 % for males and 1.37 % for females of the radioactivity.

After a single oral dose of 20 mg/kg bw at 168 hours organs (blood, bone, brain, fat, heart, kidneys, liver, lungs, muscle, ovaries, spleen, thyroid and uterus) contained little radioactivity (0.85 % for males and 0.45 % for females); carcass accounted for 2.26 % (males) and 2.4 % (females).

After a single intravenous dose of 1 mg/kg at 168 hours organs (blood, bone, brain, fat, heart, kidneys, liver, lungs, muscle, ovaries, spleen, thyroid and uterus) contained little radioactivity (1.89 % males and 1.23 % females); carcass accounted for 4.31 % (males) and 3.24 % (females).

After 14 days of 1 mg/kg bw (non-radiolabelled, followed by a single oral dose of 1 mg/kg bw) at 168 hours tissues contained a total of 1.53 % for males and 1.0 % for females, residual carcass accounted for 4.0 % in males and 2.9 % in females.

Details on distribution in tissues:

The amounts of radioactivity in blood collected 168 hours post-dose ranged from 0.46 % to 0.92 % in males and 0.26 % to 0.61 % in females. All tissues (blood, bone, brain, fat, heart, kidneys, liver, lungs, muscle, ovaries, spleen, thyroid and uterus) collected 168 hours after postdose contained 0.03 % or less of the radioactivity, except liver and kidney. Livers from males contained 0.33 % to 1.18 %, from females 0.14 % to 0.60 %. Kidneys form males from all groups contained 0.03 % to 0.09 % of the 14C dose and from females 0.2 % to 0.07 %.
The concentration of radioactivity in tissues at 168 hours post-dose was consistently highest in the blood, followed by the liver and kidneys, regardless of route of administration or dose level. The concentration of radioactivity was 40 % less in the livers of animals given 14 consecutive days 1 mg/kg bw Hydrogen cyanamide before a single [14C] Hydrogen cyanamide dose when compared with animals given only a single 1 mg/kg oral dose. This data is in agreement with the data regarding 14CO2 formation of these groups and suggests that metabolism of Hydrogen cyanamide is altered after repeated dosings.

Details on excretion:

Radioactivity was rapidly excreted, regardless of the route of administration. A total of approximately 67 % to 92 % was excreted by all routes in the first 24 hours postdose. The main route of excretion was via the urine. The faeces and CO2 accounted for 26 % and 19 % for the intravenous dose and less than 15 % for oral dose.
The amounts of radioactivity eliminated in the urine, faeces and CO2 were influenced by the route of administration, dose level and sex of the animal. The fecal excretion of radioactivity was 3 to 4 times higher after an intravenous dose compared with a similar oral dose. This suggests that biliary excretion may be an important mechanism after intravenous administration. The elimination of radioactivity as 14CO2 was reduced by approximately 30 % in animals repeatedly dosed with Hydrogen cyanamide when compared with animals given a single oral dose, indicating that metabolism of the compound was somewhat different after single or by repeated dosing. The percent of the administered dose eliminated in the CO2 was much lower for animals given the high dose compared with those animals given the low dose. The opposite result was observed for the percent of dose in the urine. This data suggest, that the metabolic route resulting in the metabolism of Hydrogen cyanamide to CO2 has a limited capacity. For animals administered the low dose, the excretion of radioactivity as CO2 was approximately twice as high in males when compared with females. Conversely, the amount of radioactivity eliminated in the urine tended to be greater in females than in males in the low dose group.
The amounts of radioactivity eliminated in the urine, faeces and CO2 were influenced by the route of administration, dose level and sex of the animal. The fecal excretion of radioactivity was 3 to 4 times higher after an intravenous dose compared with a similar oral dose. This suggests that biliary excretion may be an important mechanism after intravenous administration. The elimination of radioactivity as 14CO2 was reduced by approximately 30 % in animals repeatedly dosed with Hydrogen cyanamide when compared with animals given a single oral dose, indicating that metabolism of the compound was somewhat different after single or by repeated dosing. The percent of the administered dose eliminated in the CO2 was much lower for animals given the high dose compared with those animals given the low dose. The opposite result was observed for the percent of dose in the urine. This data suggest, that the metabolic route resulting in the metabolism of Hydrogen cyanamide to CO2 has a limited capacity. For animals administered the low dose, the excretion of radioactivity as CO2 was approximately twice as high in males when compared with females. Conversely, the amount of radioactivity eliminated in the urine tended to be greater in females than in males in the low dose group.

The amounts of radioactivity eliminated in the urine, faeces and CO2 were influenced by the route of administration, dose level and sex of the animal. The fecal excretion of radioactivity was 3 to 4 times higher after an intravenous dose compared with a similar oral dose. This suggests that biliary excretion may be an important mechanism after intravenous administration. The elimination of radioactivity as 14CO2 was reduced by approximately 30 % in animals repeatedly dosed with Hydrogen cyanamide when compared with animals given a single oral dose, indicating that metabolism of the compound was somewhat different after single or by repeated dosing. The percent of the administered dose eliminated in the CO2 was much lower for animals given the high dose compared with those animals given the low dose. The opposite result was observed for the percent of dose in the urine. This data suggest, that the metabolic route resulting in the metabolism of Hydrogen cyanamide to CO2 has a limited capacity. For animals administered the low dose, the excretion of radioactivity as CO2 was approximately twice as high in males when compared with females. Conversely, the amount of radioactivity eliminated in the urine tended to be greater in females than in males in the low dose group.

Key result

Toxicokinetic parameters:

other: 67-92% total excretion by all routes (i.e. oral and i.v.) during the first 24 h post dose.

Metabolites identified:

yes

Details on metabolites:

Metabolites determined were N-acetylcyanamide as the major biotranformation product both in urine and faeces. Other metaboiltes were formed at levels of less than 10% of the dose given and were not further characterized.

Table 1: Excretion balance (in  % of administered radioactivity) after single oral dose of 1 mg/kg bw at 168 hours:

	Urine	Faces	Expired CO2	Total excreted*	Residual carcass and tissues	Recovery
Males	79.00 %	4.15 %	10.00 %	93.15 %	7.66 %	99.90 %
Females	86.20 %	4.07 %	5.77 %	96.04 %	3.68 %	101.00 %

* includes cage wash

 

Table 2: Excretion balance (in  % of administered radioactivity) after single oral dose of 20 mg/kg bw at 168 hours

	Urine	Faces	Expired CO2	Total excreted*	Residual carcass and tissues	Recovery
Males	95.30 %	2.76 %	2.31 %	100.37 %	3.11 %	103.00 %
Females	97.70 %	3.26 %	1.45 %	102.41 %	2.85 %	105.00 %

* includes cage wash

 

Table 3: Excretion balance (in  % of administered radioactivity) after single intravenous dose of 1 mg/kg at 168 hours:

	Urine	Faces	Expired CO2	Total excreted*	Residual carcass and tissues	Recovery
Males	82.6 %	4.14 %	7.08 %	93.82 %	5.53 %	99.3 %
Females	90.7 %	2.86 %	3.78 %	97.34 %	3.9 %	101 %

*includes cage wash

 

 

Metabolism

The major metabolic reaction of [14C] Hydrogen cyanamide was acetylation of the nitrogen. The major metabolite observed in urine and faeces was N-acetylcyanamide. N-acetylcyanamide accounts for 58 % to 74 % of the radioactivity in the composite urine samples analysed and for over 80 % of the radioactivity in the composite faeces sample analysed (group A). The other radioactive areas observed in the TLC profile accounted for less than 10 % of the administered dose and therefore were not characterised (with the exception of another metabolite, described as UM-1). The radioactive area UM- 1 accounted for 9.7 % and 11.9 % of the administered dose for group A males and females, respectively. Subsequent attempts to isolate this compound by preparative TLC were unsuccessful due to the unstable nature of the compound.

 

Conclusions:

Cyanamide is rapidly absorbed and excreted after oral and i.v. administration indicating no potential for bioaccumulation. According to the amounts excreted with the urine, cyanamide can be regarded to be nearly quantitatively bioavailable both after single low, single high and repeated low dose administration via the oral route.

Executive summary:

A study that examined absorption, distribution, metabolism, and excretion in Harlan Sprague Dawley rats was conducted with the test substance (labelled and non-radiolabeled) Hydrogen cyanamide. The test substance was applied to 5 male and 5 female rats per group orally and intravenously in two different doses in a single and repeated dose as described in the following: An oral high dose (20 mg/kg bw) group, an oral low dose (1 mg/kg bw) group, an intravenous dose (1 mg/kg bw) group and a group which was administered orally with the test substance 1 mg/kg bw (unlabelled material) for 14 days followed by single oral dose of 1 mg/kg bw (radioactive material).

Results showed that [14C]-Hydrogen cyanamide was rapidly excreted, regardless of the route of administration. A total of approximately 67 % to 92 % was excreted by all routes in the first 24 hours postdose. The main route of elimination for [14C]-Hydrogen cyanamide was in the urine for all animals. The percent excreted in the urine after oral administration ranged from approximately 79.0 % to 97.7 % at 168 hours postdose. Differences among groups and sexes were noted in the amount of radioactivity eliminated in CO2, in the faeces or remaining as residues in the liver. Radioactivity of [14C]-Hydrogen cyanamide was apparently completely absorbed after oral administration. Biliary excretion of radioactivity was not an important mechanism for the high dose, however it may be important for an intravenous dose. Repeated doses of Hydrogen cyanamide resulted in a decrease in the amount of radioactivity as CO2 and in the concentration of radioactivity remaining in the liver at 168 hours postdose. This suggests that the disposition of radioactivity was influenced by repeated administration of cyanamide. The metabolism of cyanamide after oral and intravenous dosing can be described as follows: Starting with the unchanged parent compound, the major metabolic reaction was acetylation of the nitrogen, forming N-acetylcyanamide. N-acetylcyanamide is the major metabolite in both urine and faeces. Other radioactive metabolites were present in the urine and faeces but they represented less than 10 % of the administered dose in each case.

It can be concluded that results indicated that cyanamide has no potential for bioaccumulation as it is rapidly absorbed and excreted after oral and i.v. administration. According to the amounts excreted with the urine, cyanamide can be regarded to be nearly quantitatively bioavailable both after single low, single high and repeated low dose administration via the oral route.

Reference 3

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

very well documented publication

Objective of study:

toxicokinetics

Qualifier:

no guideline required

Principles of method if other than guideline:

For principles of method see below.

GLP compliance:

no

Remarks:

The study is a publication

Radiolabelling:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

- Source: Charles River France

Route of administration:

other: 1 group by an intravenous injection, 2 groups by gavavge.

Vehicle:

water

Details on exposure:

- The Cyanamide solution was prepared from COLME (6 % cyanamide solution) by dilution with distilled water to a concentration of 1.74 % parts per volume.

Duration and frequency of treatment / exposure:

Single dose (gavage or i.v)

Remarks:

Doses / Concentrations:
35 mg/kg bw

No. of animals per sex per dose / concentration:

5 male rats per group

Control animals:

no

Positive control reference chemical:

No positive control

Details on study design:

One group of fasted animals received 35 mg/kg bw cyanamide by intravenous injection, a second and third group of fasted and unfasted, respectively animals received 35 mg/kg bw of an aqueous cyanamide solution by gavage.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: plasma
- Time and frequency of sampling: 0, 120 minutes post adminisration period

Key result

Toxicokinetic parameters:

half-life 1st: 1 hour after i.v administration of 35 mg/kg bw of the test substance.

Key result

Toxicokinetic parameters:

Tmax: = Total plasma clearance (Clp) of 0.02 L/kg/min after i.v administration of 35 mg/kg bw of the test substance

Key result

Toxicokinetic parameters:

other: The volume distribution in the central compartment (Vc) is 0.52 L/kg after i.v. administration of 35 mg/kg bw of the test substance.

Key result

Toxicokinetic parameters:

AUC: 1870.2 µg/mL/min obtained from the group which was applied with the test substance by i.v

Key result

Toxicokinetic parameters:

AUC: 1686.8 µg/mL/min obtained from the group of the fasted rats after oral administration (gavage).

Key result

Toxicokinetic parameters:

AUC: 1545.9 µg/mL/min obtained from the group of the unfasted rats after oral administration (gavage).

Key result

Toxicokinetic parameters:

other: Bioavailability of 93.3% obtained from the group of the fasted rats after oral administration (gavage).

Key result

Toxicokinetic parameters:

other: Bioavailability of 85.9% obtained from the group of the unfasted rats after oral administration (gavage).

Metabolites identified:

no

Intravenous kinetics:

The half-life (t_½) of cyanamide in the anaesthetised rat is about 1 hour, its plasma clearance (Cl_p) is 0.02 (L/kg)/min and its volume of distribution in the central compartment (V_c) is 0.52 L/kg. From the physiological properties of cyanamide and the volume of distribution in the central compartment it appears that cyanamide is distributed throughout the whole body-water.

 

Oral kinetics:

Cyanamide is rapidly absorbed in fasted rats. The relative bioavailability of cyanamide in fasted rats indicate that practically all the administered dose is absorbed. Cyanamide is also rapidly absorbed in non-fasted rats. The bioavailability in non-fasted rats is also high, corresponding to approximately 86 %.

 

Pharmacokinetic parameters of cyanamide after i.v. administration:

	Total plasma clearance (L/kg)/min Tmax(hours)	Terminal t½[min]	AUC (µg/mL)/min]
Male Sprague Dawley rats	0.02	56.6	1870.2

 

Pharmacokinetic parameters of cyanamide after oral administration:

	Bioavailability ( %)	AUC (µg/mL)/min
Male Sprague Dawley rats (fasted)	93.3	1686.8
Male Sprague Dawley rats (unfasted)	85.9	1545.9

 

Conclusions:

The absorption of cyanamide is almost complete after oral administration of 35 mg/kg bw of cyanamide solution to unfasted and fasted rats, the relative bioavailabilities being 86 and 93 %, respectively. The half-life (t1/2) of cyanamide is very short with approximately 1 hour (56 min).

Executive summary:

The study was conducted in order to elucidate blood pharmacokinetic of cyanamide after intravenous and oral administration to male Sprague Dawley rats. Cyanamide solution was prepared from COLME (6 % cyanamide solution) by dilution with distilled water to a concentration of 1.74 % parts per volume. The rats were assigned at three groups of five animals each. One group of fasted animals received 35 mg/kg bw cyanamide by intravenous injection, a second and third group of fasted and unfasted, respectively animals received 35 mg/kg bw of an aqueous cyanamide solution by gavage. Blood was sampled from the right cannulated carotid artery after i.v. administration of 35 mg/kg bw in rats. After i.v administration of 35 mg/kg bw the half-life (t½) of cyanamide in the anaesthetised rat was about 1 hour, its plasma clearance (Clp) was 0.02 (L/kg)/min and its volume of distribution in the central compartment (Vc) was 0.52 L/kg. From the physiological properties of cyanamide and the volume of distribution in the central compartment it appears that cyanamide is distributed throughout the whole body-water. Oral administration results showed that cyanamide is rapidly absorbed in fasted rats. The relative bioavailability of cyanamide in fasted rats (93.3%) indicated that practically all the administered dose is absorbed. Cyanamide is also rapidly absorbed in non-fasted rats. The bioavailability in non-fasted rats is also high, corresponding to approximately 86 %. The half-life (t1/2) of cyanamide is very short with approximately 1 hour (56 min).

Reference 4

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1989

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: No documentation of individual health status. Limited number of individuals. There is no statement if the study is performed in accordance with internationally accepted ethical standards.

Reason / purpose for cross-reference:

reference to same study

Objective of study:

excretion

metabolism

Qualifier:

no guideline followed

Principles of method if other than guideline:

For principles of method see below.

GLP compliance:

no

Remarks:

however, the study is reported in detail

Radiolabelling:

no

Species:

other: Human

Sex:

male

Details on test animals or test system and environmental conditions:

Not indicated

Route of administration:

oral: unspecified

Vehicle:

water

Duration and frequency of treatment / exposure:

Single dose

Remarks:

Doses / Concentrations:
20 mg of cyanamide (aqueous solution)

No. of animals per sex per dose / concentration:

6 male volunteers

Control animals:

other: Urine samples collected before the cyanamide application served as controls.

Details on dosing and sampling:

PHARMACOKINETIC STUDY (Absorption, distribution, excretion)
- Tissues and body fluids sampled: urine, blood
- Time and frequency of sampling: After the intake of cyanamide urine samples were collected over a period of 48 hours in 12 hours aliquots.

- Other:
- Samples were analysed for N-acetylcyanamide as well as for thiocyanate.
- Blood samples of the volunteers were collected prior to the intake of cyanamide as well as 2 and 4 hours after dosing. Blood was analysed for cyanide content.

Details on excretion:

The results of the human urinary excretion of N-acetylcyanamide were analogous to those observed in the animal studies. It was found that a considerable part of the oral applied dose (28.2 to 57.8 %) was excreted as N-acetylcyanamide in the urine. Therefore, N-acetylcyanamide is also to be regarded as the major cyanamide metabolite in the man. The absorption, metabolism and excretion are rapid, the main part of the total administered test substance is already excreted in the urine within the first 12 hours after cyanamide application. The concentrations of thiocyanate in the urine showed no significant differences before and up to 48 hours after the cyanamide application. The concentrations of thiocyanate in the urine showed no significant differences before and up to 48 hours after the cyanamide application.

Metabolites identified:

yes

Details on metabolites:

N-acetylcyanamide and thiocyanate (for results see above in "Results: Excretion and in the table below in "Remarks on results")

Excretion of N-acetylcyanamide in the urine of volunteers after oral intake of 20 mg cyanamide:

 

Volunteer No	N-acetylcyanamide excretion 0 to 48 hours( %)
1	37.1
2	47.5
3	57.8
4	37.8
5	28.2
6	31.3

 

- The cyanide concentrations in the blood before as well as 2 and 4 hours after oral cyanamide application did not reveal indications that the cyanide content of the blood is affected by cyanamide intake. Thedetermined values did not show significant differences from the controls.

Conclusions:

This part of the study (human, oral) also confirmed that N-acetylcyanamide is the main urinary metabolite of cyanamide (in human and in rat). The excretion of cyanamide in human (as well as in the rat) was found to be efficient and rapid.

Executive summary:

The aim of the study (Gloxhuber, C., 1989, Doc. No. 512-004) was to elucidate differences in metabolism and excretion of hydrogen cyanamide in rats and humans. The present study record described a part of this study, the one which was conducted in human administered with cyanamide by the oral route (20 mg). Regarding the urinary excretion of N-acetylcyanamide the results from this human study are analogous to those observed in the animal study. In the presented human study it was found that a considerable part of the oral applied dose (28.2 to 57.8 %) was excreted as N-acetylcyanamide in the urine. Therefore, N-acetylcyanamide is also to be regarded as the major cyanamide metabolite human. The absorption, metabolism and excretion are rapid, the main part of the total administered test substance is already excreted in the urine within the first 12 hours after cyanamide application. The concentrations of thiocyanate in the urine showed no significant differences before and up to 48 hours after the cyanamide application. The concentrations of thiocyanate in the urine showed no significant differences before and up to 48 hours after the cyanamide application. The cyanamide concentrations in the blood before as well as 2 and 4 hours after oral cyanamide application did not reveal indications that the cyanide content of the blood is affected by cyanamide intake. The determined values did not show significant differences from the controls.

Altogether results of all three parts of the study (rat: gavage, human: oral, dermal) confirmed that N-acetylcyanamide is the main urinary metabolite of cyanamide in rat and man. Both species showed an efficient excretion of orally or dermally administered cyanamide. Cyanamide is absorbed through human skin, however, the dermal absorption is considerably delayed compared to the oral one. The degree of dermal absorption of a 1 % aqueous cyanamide solution for a period of 6 hours exposure was found to be between 0.87 and 3.53 %.

Reference 5

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

no guideline followed

Principles of method if other than guideline:

For priciples of method see below.

GLP compliance:

no

Radiolabelling:

no

Species:

other: human

Sex:

male

Details on test animals or test system and environmental conditions:

-The same group of 6 volunteers from the study with oral intake of cyanamide participated in this subsequent dermal absorption study

Type of coverage:

occlusive

Vehicle:

water

Duration of exposure:

6 hours

Doses:

The same dose that was applied in the oral study, 20 mg (10 mg cyanamide were applied to each forearm). The dosage was applied to the skin by a gauze patch that was charged with 1 mL of a 1 % aqueous cyanamide solution.

No. of animals per group:

6 human volunteers

Control animals:

yes

Remarks:

Urine samples collected before the Cyanamide application served as controls.

Details on study design:

- Cyanamide was applied on the skin by fixing a gauze patch under a watertight rubber foil on the inner side of each of the two forearms (2 patches per person). Each gauze was charged with 1 mL of a 1 % aqueous cyanamide solution for a period of 6 hours.
- The urine samples were collected over a period of 48 hours in 12 hours aliquots beginning immediately after the dermal application of cyanamide. Urine samples collected before the cyanamide application served as controls. Another urine sample was collected six days after cyanamide application
- After removal of the patches the contaminated skin areas were rinsed with water and wiped dry.

Signs and symptoms of toxicity:

not examined

Dermal irritation:

not examined

Absorption in different matrices:

Under the experimental conditions of the study the absorbed dose of cyanamide after dermal application was estimated to be between 0.87 and 3.53 % (see table below in "Remarks on results")

Conversion factor human vs. animal skin:

Not needed, the presented skin absorption study was performed in human

Absorbed quantity of Cyanamide after dermal administration of 20 mg cyanamide for six hours (human volunteers):

Volunteer No	Cyanamide absorption 0 to 48 hours ( %)
1	2.04
2	3.20
3	0.87
4	1.14
5	2.06
6	3.53

 

 

- The N-acetylcyanamide concentration in the urine of the test persons, except volunteer No 1 and 3 before and 6 days after the dermal application of the test material were below the limit of quantification. N-acetylcyanamide values of these two volunteers were very close to the above limit of quantification. It may be concluded that the values are caused by methodical variations at the limit of quantification. However, the urinary excretion of N-acetylcyanamide was completed for the most part after 24 hours.

- Dermal absorption figure was calculated by taking into account the excretion of N-acetylcyanamide of each human volunteer after oral administration of 20 mg cyanamide/person. As it is known that cyanamide is quantitative absorbed after oral administration the dermal absorbed dose can be determined.

Conclusions:

The results of the dermal absorption study in human confirmed that N-acetylcyanamide is the main urinary metabolite of cyanamide. Cyanamide is absorbed through human skin and its excretion is efficient. The degree of dermal absorption of a 1 % aqueous cyanamide solution for a period of 6 hours exposure was found to be between 0.87 and 3.53 %.

Executive summary:

The aim of the study (Gloxhuber, C., 1989, Doc. No. 512-004) was to elucidate differences in metabolism and excretion of hydrogen cyanamide in rats and humans. The present study record describes a part of this study, the one which was conducted in human and examined the dermal absorption of cyanamide.

The same group of 6 volunteers from the study with oral intake of cyanamide participated in a subsequent dermal absorption study. The inner sides of the forearms were chosen as application site. 10 mg cyanamide were applied to each forearm (20 mg per person). A gauze patch was charged with 1 % aqueous cyanamide solution and applied to the skin by an occlusive dressing for 6 hours. The urine samples were collected over a period of 48 hours in 12 hours aliquots beginning immediately after the dermal application of cyanamide. Urine samples collected before the cyanamide application served as controls. Another urine sample was collected six days after cyanamide application. After removal of the patches the contaminated skin areas were rinsed with water and wiped dry. The used patches were analysed for residual cyanamide to demonstrate that cyanamide was not decomposed during the application period.

The study results confirmed the results of the other two parts of the study (rat and human; oral), showing that N-acetylcyanamide is the main urinary metabolite of cyanamid. The excretion of cyanamide is efficient in human after dermally administered cyanamide as by orally administered cyanamide in rats and human, however, the dermal absorption is considerably delayed compared to the oral one. The degree of dermal absorption of a 1 % aqueous cyanamide solution for a period of 6 hours exposure was found to be between 0.87 and 3.53 %.

Reference 6

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.7600 (Dermal Penetration)

Deviations:

yes

Remarks:

There was no sampling after dermal application in order to observe serial non-detects in excreta.

GLP compliance:

yes

Radiolabelling:

yes

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male

Details on test animals or test system and environmental conditions:

The rats were obtained from Charles River Laboratories (Massachusetts U.S.A)

Type of coverage:

other: Non-occlusive

Vehicle:

water

Duration of exposure:

Up to 24 hours

Doses:

0.1, 1 and 10 mg of Hydrogen cyanamide for a rat in a volume of 100 µL.

No. of animals per group:

24 animals per group

Control animals:

yes

Details on study design:

- The dosing solutions were prepared by mixing appropriate amounts of [14C] Hydrogen cyanamide stock solution in deionized water (adjusted to pH 4.5 with phosphoric acid). Three dosing solutions were prepared to deliver 0.1, 1 and 10 mg of Hydrogen cyanamide in a volume of 100 µL on an area of 12.5 cm2.
- Approximately 24 hours before dosing, the back and shoulders of each rat were shaved and the shaved area was washed with acetone. At 0 hour, the test material solution was applied evenly to the test site. The application site was then covered with a non-occlusive cover to prevent disturbance of the application site and mechanical loss of the test material.
- A single cumulative faeces sample was collected from each rat from the time of dosing to the time of sacrifice. After all urine and faeces samples had been collected, each cage was rinsed and the cage wash was collected. Four rats from each group were sacrificed at each of the six times (0.5; 1; 2; 4; 10 and 24 hours) after application of the test substance. Blood was collected via cardiac puncture. The skin at the application site (with cover in place) and carcass were collected for analysis. All samples were assayed by liquid scintillation counting (LSC).
- A single cumulative urine sample was collected from each rat from the time of dosing to the time of sacrifice. Any residual urine present at sacrifice was collected and added to the appropriate urine sample.

Signs and symptoms of toxicity:

not specified

Dermal irritation:

not specified

Absorption in different matrices:

Blood:
For the animals in the lowest dose group (0.1 mg dose) mean blood radioactivity concentrations ranged from non-detectable at 2 and 4 hours to 0.002 µg equivalents/g at 24 hours. Higher concentrations were observed for the animals in the mid (1 mg dose) and the high (10 mg dose) dose with mean values for each group generally increasing with time of exposure up to 10 hours. For the mid dose group the mean blood radioactivity concentration ranged from 0.006 µg equivalents/g at 0.5 hours to 0.37 µg equivalents at 10 hours. For the high dose group the mean concentrations ranged from 0.029 µg equivalents/g at 0.5 hours to 1.04 µg equivalents/g at 10 hours.

Urine and faeces:
The amount of radioactivity found in urine ranged between n.d. and 0.22 % during the period from 0.5 to 4 h when considering all dose levels. After 10 h exposure the recoveries of radioactivity in urine were 0.7, 1.45 and 4.38 % for the low, mid and high dose, respectively. In faeces of the low dose animals, no radioactivity was found up to and including 10 h exposure. The recoveries after 24 application were 0.05, 0.02, < 0.01 and 0.07 % for the individual test animals. In faeces of the mid dose animals, no radioactivity was found up to and including 4 h exposure. The recovery after 10 h application was 0.07 %. After 24 h application, < 0.01, 0.04, 0.06 and 0.08 % of radioactivity was recovered in the faeces of individual test animals. In faeces of the high dose animals, no radioactivity was found up to and including 4 h exposure. The recoveries after 10 h application was < 0.01, < 0.01 and 0.23 %. After 24 h application, 0.28, 0.12, 0.19 and 0.22 % of radioactivity was recovered in the individual animals.

Carcass:
Radioactivity was detectable in the carcass of animals from all three dose levels with highest amounts of mean radioactivity at 10 and 24 hours. The result are also consistent with the blood data.

The result indicate some systemic absorption of the test material at all dose levels. The amounts of absorbed dose increased with exposure time and reached maximum values at 24 hours.

Amount of dose remaining in or on the skin after washing:
The amount of radioactivity found in the skin of all test groups after wash is constant between 0.5 h and 10 h. The amount in the skin ranged between 4.4 and 8.7 % for the low and mid dose in the time period 0.5 to 10 h. The variation over time observed for the high dose animals was larger. However, the mean recovery over time (0.5 – 10 h) is comparable to the low and mid dose.

Amount of unabsorbed dose:
For all three dose groups the amount of radioactivity recovered was inversely related to the amount of absorbed dose and skin radioactivity observed at the later time points. At 0.5 hours the mean radioactivity recovered in the skin rinses as approximately 97 % for the low and mid dose group and approximately 90 % for the high dose group. The values decreased to 69 %, 68 % and 53 % for the low, mid and high dose group respectively at 24 hours.

The average material balance indicate that there was no appreciable loss of radioactivity due to formation of volatile products either on the skin or from absorbed dose. The mean material balance was between 93.34 % and 98.61 %.

Key result

Dose:

0.1 mg/rat

Parameter:

percentage

Absorption:

1.2 %

Remarks on result:

other: After 10 hours exposure

Remarks:

The total means systemically absorbed dose including the amount located in the skin is 8.23%.

Key result

Dose:

1 mg/rat

Parameter:

percentage

Absorption:

2.6 %

Remarks on result:

other: After 10 hours

Remarks:

The total means systemically absorbed dose including the amount located in the skin is 9.45%.

Key result

Dose:

10 mg/rat

Parameter:

percentage

Absorption:

7.5 %

Remarks on result:

other: After 10 hours exposure

Remarks:

The total means systemically absorbed dose including the amount located in the skin is 14.34%.

Conversion factor human vs. animal skin:

Conversion factor C (rat ->human) is not indicated in the study report.
Based on the following calculation C can be received as follows:
C (rat, in vito ->human, in vitro) = % absorbance in an in-vitro rat study / % absorbance in-vitro human
Based on the resulting C the % absorbance in-vivo human can be calculated by:
% absorbance in-vivo human = % absorbance in an in-vivo rat study (present study) / C

Mean percent dose in urine, faeces and carcass at specified time postdose:

Sacrifice time (hours)	Mean percent dose in urine			Mean percent dose in faeces			Mean percent dose in carcass
	0.1*	1.0*	10.0*	0.1*	1.0*	10.0*	0.1*	1.0*	10.0*
0.5^a)	nd**	nd**	< 0.01	nd**	nd**	nd**	0.07	0.16	0.12
1^a)	0.02	nd**	nd**	nd**	nd**	nd**	0.17	0.29	0.65
2^a)	0.05	< 0.01	nd**	nd**	nd**	-	0.08	0.65	0.91
4^a)	0.17	nd**	0.22	-	-	nd**	0.10	0.53	1.63
10	0.7	1.45	4.38	nd**	0.02	0.06	0.5	1.07	2.35
24	0.93	1.69	7.65	0.04	0.05	0.2	0.65	0.89	2.05

*mg/animal in a volume of 100 µL on an area of 12.5 cm² **not detectable

 

Amount of [¹⁴C] Hydrogen cyanamide systemically absorbed as indicated by the total radioactivity found in carcass, excreta, cage wash and cage wipe:

Sacrifice time (hours)	Total radioactivity found in carcass, excreta, cage wash and cage wipe
	0.1 (mg/animal)	1.0 (mg/animal)	10.0 (mg/animal)
0.5	0.07 %	0.16 %	0.12 %
1	0.19 %	0.29 %	0.66 %
2	0.13 %	0.69 %	0.91 %
4	0.27 %	0.53 %	1.85 %
10	1.2 %	2.64 %	7.53 %
24	1.79 %	2.84 %	11.1 %

 

Amount of [¹⁴C]-Hydrogen cyanamide in skin:

Sacrifice time (hours)	Mean percent dose in skin at specified times postdose
	0.1 (mg/animal)	1.0 (mg/animal)	10.0 (mg/animal)
0.5	6.57 %	4.41 %	7.47 %
1	6.80 %	4.03 %	11.7 %
2	7.48 %	8.67 %	9.46 %
4	6.48 %	5.99 %	5.33 %
10	7.03 %	6.81 %	6.81 %
24	17.0 %	13.5 %	11.1 %

 

Total amount of [¹⁴C]-Hydrogen cyanamide absorbed as calculated by including the amount located in the rat skin:

Dose levels	% absorbed of dose applied after 10 h exposure
	systemically	total*
10 mg/rat	7.53	14.34
1 mg/rat	2.64	9.45
0.1 mg/rat	1.20	8.23

* total means systemically absorbed dose including the amount located in the skin

Conclusions:

Hydrogen cyanamide is absorbed through rat skin (Total amount of systemically absorbed dose at 10 h:1.2% (low dose) to 7.53% (high dose). At 10 h: 1.2% (low dose) to 11.1% (high dose)).

Executive summary:

The study was performed using male Crl:CD(SD)BR rats. Each dose group consisted of 24 animals. The dosing solutions were prepared by mixing appropriate amounts of [14C] hydrogen cyanamide stock solution in deionized water (adjusted to pH 4.5 with phosphoric acid). Three dosing solutions were prepared to deliver 0.1, 1 and 10 mg of hydrogen cyanamide in a volume of 100 µl on an area of 12.5 cm2. A single cumulative faeces sample was collected from each rat from the time of dosing to the time of sacrifice. After all urine and faeces samples had been collected, each cage was rinsed and the cage wash was collected. Four rats from each group were sacrificed at each of the six times (0.5; 1; 2; 4; 10 and 24 hours) after application of the test substance. Blood was collected via cardiac puncture. The skin at the application site (with cover in place) and carcass were collected for analysis. All samples were assayed by liquid scintillation counting (LSC). At 0 hour, the test material solution was applied evenly to the test site. The application site was then covered with a non-occlusive cover to prevent disturbance of the application site and mechanical loss of the test material. The control animals were treated in the same way as the treated animal, but dosed with the vehicle.

The amount of systemically absorbed [14C] hydrogen cyanamide increased with the dose level and with time of exposure. Maximum blood concentration of radioactivity were observed at 24 hours for the low and mid dose and at 10 hours for the high dose. Urinary excretion of radioactivity increased with time and amount of the test material applied. The amount of radioactivity associated with the washed skin was relatively constant (average 5 % to 10 % of the applied dose). The majority of the applied dose was recovered in the skin wash. The amount of radioactivity in the skin wash generally decreased with time through 24 hours and did not appear to be related to the applied dose. The total amount of systemically absorbed dose averaged 1.2 %, 2.64 % and 7.53 % of the dose at 10 hours and 1.79 %, 2.84 % and 11.1 % of the dose at 24 hours for low, mid and high dose, respectively.

Reference 7

Endpoint:

dermal absorption in vivo

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1991

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Human volunteer study with hydrogen cyanamide.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Human volunteer dermal absorption study.

GLP compliance:

no

Radiolabelling:

no

Species:

human

Strain:

other: not applicable

Sex:

male

Details on test animals or test system and environmental conditions:

Six male volunteers:
- Age: 33-60 years (mean 49.7 years)
- Body weight: 71-100 kg (mean 80.8 kg)

Type of coverage:

occlusive

Vehicle:

water

Duration of exposure:

6 h

Doses:

mean dose of 0.25 mg/kg bw

No. of animals per group:

6 male volunteers

Details on study design:

A group of six male volunteers participated in the study. 10 mg cyanamide was applied to each forearm, producing a mean dose of 0.25 mg/kg. The cyanamide was applied on the skin of the participants by fixing a gauze patch (4x4 cm) under a watertight rubber foil on the inner side of each of the two forearms (two patches per person). Each gauze was charged with 1 mL of a 1% aqueous cyanamide solution. From pre-tests it was known that this concentration is not irritating to human skin. the period of application was 6 h. Urine samples were collected before the cyanamide application served as controls. After dermal application urine samples were collected over a period of 48 h in 12h intervals. All samples were analysed for acetylcyanamide. After removal of the patches the contaminated skin areas were rinsed with water and wiped dry. The used patches were stored at -18 °C up to the end of the study and then analysed for residual cyanamide. This was to demonstrate that cyanamide was not decomposed during the application period.

Signs and symptoms of toxicity:

no effects

Dermal irritation:

no effects

Absorption in different matrices:

Except for one volunteer, the acetylcyanamide concentrations in the urine of all other test persons before the dermal application of the test material were below the limit of quantification (< 10 µg/L). The acetylcyanamide value of 13 µg/L found in the urine of this volunteer was very close to the above limit of quantification. The reason for this finding is unclear. A causal relation, however, to the controlled dermal application of cyanamide can be excluded. The urinary excretion of acetylcyanamide was completed for the most part after 24 h. Under the applied experimental conditions a mean 2.3 mg cyanamide was available for dermal absoprtion. A mean portion of 7.7 % of this quantity was excreted as acetylcyanamide in the urine of the participants.

Key result

Time point:

6 h

Dose:

0.25 mg/kg bw

Parameter:

percentage

Absorption:

7.7 %

Conclusions:

In a dermal absoprtion human volunteer study, cyanamide was applied over a 6 -hour period topically to the skin of human volunteers and of the dosage applied, 7.7% were found as acetylcyanamide in the urine 48 hours after application.

Executive summary:

In a dermal absorption study with six male volunteers, 10 mg cyanamide was applied to each forearm, producing a mean dose of 0.25 mg/kg. The cyanamide was applied on the skin of the participants by fixing a gauze patch (4x4 cm) under a watertight rubber foil on the inner side of each of the two forearms (two patches per person). Each gauze was charged with 1 mL of a 1% aqueous cyanamide solution. From pre-tests it was known that this concentration is not irritating to human skin. the period of application was 6 h. Urine samples collected before the cyanamide application served as controls. After dermal application urine samples were collected over a period of 48 h in 12h intervals. All samples were analyzed for acetylcyanamide.

The urinary excretion of acetylcyanamide was completed for the most part after 24 h. Under the applied experimental conditions a mean 2.3 mg cyanamide was available for dermal absoprtion. A mean portion of 7.7 % of this quantity was excreted as acetylcyanamide in the urine of the participants.

Description of key information

Short description of key information on bioaccumulation potential result:
4 studies (three in rat and one in human) were available for evaluation. Results of all studies revealed that cyanamide is almost completely absorbed after oral administration with a very short half life of approximately 1 hour in rats and bioavailability of 86-93%. N-acetylcyanamide was detected as the major urinary metabolite in rat and in human.

Short description of key information on absorption rate:
Three in vivo dermal absorption studies were evaluated with the test substance cyanamide, one in rats and two in human volunteers. Results of the studies showed that cyanamide is absorbed through human and rat skin to the same order of magnitude. For the 1% aqueous dilution of cyanamide the dermal adsorption in rats was approximately 2% compared to 0.87% to 3.53% or 7.7 % in humans. The extrapolated dermal absorption of 2.5 % cyanamid by rat skin was 3 %. A dermal absorption of 31.5 % was deduced for the concentrated cyanamide (Cyanamid L500).

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Four available studies regarding the toxicokinetic, metabolism, distribution and excretion of cyanamide / hydrogen cyanamide were evaluated. Results of all four studies supported and completed one another.

 

The results from the metabolism study in rats (Sprague Dawley rat) with [14C]-cyanamide (Struble, 1993, Doc.No 512-001) demonstrated, that the compound is completely absorbed after oral administration and was rapidly excreted. The percent excreted in the urine ranged from approximately 79.0 to 97.7% of the applied dose at 168 hours (faeces 2.76-4.15% and expired CO2 1.45-10%). Regardless of the route of administration a total of approximately 67% to 92% was excreted by all routes in the first 24 hours postdose. The major metabolic reaction was found to be acetylation of the nitrogen, forming N-acetylcyanamide. N-acetylcyanamide was the major metabolite in both urine and faeces. Other radioactive metabolities were present in the urine and faeces but they represented less than 10% of the administered dose in each case.

 

Similar results were obtained from the studies of Gloxhuber (1989, Doc. No. 512-004) in rat (Wistar) and human. The studies confirmed that a considerable part of the oral applied dose (28.2 to 57.8%) was excreted as N-acetylcyanamide. It was therefore found to be the main urinary metabolite of cyanamide in rat and human. The concentrations of thiocyanate in the urine showed no significant differences before and up to 48 hours after oral cyanamide application. The cyanide concentrations in the blood before as well as 2 and 4 hours after oral cyanamide applicataion did not reveal indications that the cyanide content of the blood is affected by cyanamide intake.

 

The metabolism study in rats with [14C]-cyanamide (Struble, 1993, Doc.No 512-001) also showd that, all tissues (blood, bone, brain, fat, heart, kidneys, liver, lungs, muscle, ovaries,spleen, thyroid, and uterus) collected 168 hours after postdose contained 0.03% or less of the radioactivity, except liver and kidney containing 0.14 to 1.18% and 0.02 to 0.09% respectively, indicating no tendency for accumulation of cyanamide.

 

The study of Obach (1986, Doc. No.592-019) which examined the bioavailabilty of cyanamide in fasted and unfasted rats (Sprague Dawley), showed like in the [14C]-cyanamide (Struble, 1993, Doc.No 512-001) study that the absorption of cyanamide is almost complete after oral administration . In addition the study showed a very short half-life of approximately 1 hour (i.v. of 35 mg/kg bw) and bioavailability of 86-93% in unfasted and fasted rats respectively.

 

Discussion on absorption rate:

Three in vivo studies were evaluated for dermal absorption of cyanamide. In the study of LeVan (1989, Doc. No. 511-001) 24 Charles River male rats were administered with [14C]-hydrogen cyanamide in three dosing solutions: 0.1, 1 and 10 mg of hydrogen cyanamide in a volume of 100 µL on an area of 12.5 cm² (in a non-occlusive dressing). Results showed that the amount of systemically absorbed [14C] hydrogen cyanamide increased with the dose level and with time of exposure. The total amount of systemically absorbed dose ranged from 0.27 (low dose) to 1.85% (high dose) of the applied cyanamide dose after 4 hour exposure and from 1.2 % (low dose) to 7.53% (high dose) of the applied cyanamide dose after 10 hour exposure and from 1.79 (low dose) to 11.1% (high dose) after a maximum application exposure of 24 hours.

 

The in vivo rat study of LeVan showed comparable results to those found in the human volunteer study for the same applied cyanamide concentration (1%). The human volunteers study of Gloxhuber (1989, Doc. No. 512-004) examined 6 human volunteers who were administered with 20 mg cyanamide (1% aqueous cyanamide solution) applied to the skin with a gauze in an occlusive dressing for a period of 6 hours.

 

In another dermal absorption study (Mertschenk, 1991, Doc No. 592 -005) with six male volunteers, 10 mg of a 1 % aqueous cyanamide solution was applied to each forearm for 6 h, producing a mean dose of 0.25 mg/kg bw. After dermal application urine samples were collected over a period of 48 h in 12h intervals. All samples were analyzed for acetylcyanamide. The urinary excretion of acetylcyanamide was completed for the most part after 24 h. Under the applied experimental conditions a mean 2.3 mg cyanamide was available for dermal absoprtion. A mean portion of 7.7 % of this quantity was excreted as acetylcyanamide in the urine of the participants.

 

These results show that dermal absorption potential of cyanamide in humans and rats is comparable.

 

As the human volunteers study of Gloxhuber examined the dermal as well as the oral route (gavage), it is concluded that after dermal exposure the metabolism of cyanamide is considerably delayed compared to oral exposure.

 

Based on the present results a linear regression analysis was performed to extrapolate the dermal absorption rate for the cynamide concentrate (Cyanamid L500, 50 %). Comparable absorption rates for human and rat skin were indicated by the studies of Gloxhuber, Mertschenk and LeVan, therefore, extrapolation based on the results obtained from testing in rats were considered applicable. The following table summarises the extrapolation results:

 

Cyanamide concentration (%)	Dermal absorption
	"systemic" measured rat in vivo (%)	"systemic" extrapolated (%)
0.1	1.2	1.6
1.0	2.6	2.1
2.5	-	3.0
10	7.5	7.5
50	-	31.5

 

The extrapolated dermal absorption of 2.5 % cyanamid by rat skin was 3 % and thus similar to the human in vivo absorption of 3.5 %. Consequentially a dermal absorption of 31.5 % was deduced for the concentrated cyanamide (Cyanamid L500).