Cyanamide

Basic toxicokinetics

Administrative data

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

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1993

Report date:

1993

Materials and methods

Objective of study:

absorption

distribution

excretion

metabolism

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

EU Method B.36 (Toxicokinetics)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPP 85-1 (Metabolism and Pharmacokinetics)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Cyanamide

EC Number:

206-992-3

EC Name:

Cyanamide

Cas Number:

420-04-2

Molecular formula:

CH2N2

IUPAC Name:

cyanamide

Test material form:

solid

Details on test material:

Substance radiolabled

Radiolabelling:

yes

Test animals

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.

Administration / exposure

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")

Doses / concentrations

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.

Results and discussion

Toxicokinetic / pharmacokinetic studies

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.

Toxicokinetic parameters

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.

Metabolite characterisation studies

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.

Any other information on results incl. tables

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.

 

Applicant's summary and conclusion

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.