Thymidine

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

According to REACH Annex IX, column 1, section 8.7 experimental testing for reproductive toxicity was waived. The available toxicity data indicates no adverse effects on reproductive organs or tissues.

Link to relevant study records

Reference

Endpoint:

toxicity to reproduction

Data waiving:

other justification

Justification for data waiving:

other:

Reproductive effects observed:

not specified

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Short description of key information:
According to REACH Annex IX, column 1, section 8.7 experimental testing for reproductive toxicity was waived. The available toxicity data indicates no adverse effects on reproductive organs or tissues.

Effects on developmental toxicity

Description of key information

A combined rat fertility and embryo-fetal development study (combined segments I and II) was carried out according to ICH Harmonised Tripartite Guideline: Detection of Toxicity to Reproduction for Medicinal Products & Toxicity to Male Fertility S5(R2). There were no test article-related changes in male or female fertility following the administration of the test item. No fetal abnormalities were observed.

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: See read-across justification attached.

Qualifier:

according to guideline

Guideline:

other: ICH Harmonised Tripartite Guideline: Detection of Toxicity to Reproduction for Medicinal Products & Toxicity to Male Fertility S5(R2)

Deviations:

no

Principles of method if other than guideline:

Combined rat fertility and embryo-fetal development study (combined segments I and II).

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:CD(SD)IGS BR

Route of administration:

oral: gavage

Vehicle:

CMC (carboxymethyl cellulose)

Remarks:

0.5 % (wt/vol)

Details on exposure:

- Dosing of males, 28 days prior to cohabitation through the day before completion of cohabitation
- Dosing of females, 15 days prior to cohabitation through gestation day 17

Analytical verification of doses or concentrations:

not specified

Details on mating procedure:

Males and females were cohabitated (1:1) for a maximal period of 21 days. Females not mated within the first 14 days of cohabitation were assigned an alternate male rat from the same dose group that had mated and remained in cohabitation for a maximum of seven additional days. Likewise, males not mated within the first 14 days of cohabitation were assigned an alternate female rat and remained in cohabitation for a maximum of three additional days.

Duration of treatment / exposure:

Male rats (25 animals/group) were orally administered the test item at doses of 0, 100, 500, or 1,000 mg/kg/day, starting 28 days prior to cohabitation and continuing through the day before the completion of cohabitation. Female rats (25 animals/group) were dosed starting 15 days prior to cohabitation and continuing through gestation day 17. Male rats were sacrificed at the completion of cohabitation, whereas females were sacrificed on gestation day 21.

Frequency of treatment:

Daily treatment.

Duration of test:

Male treatment was started 28 days prior to cohabitation. Treatment of females was started 15 days prior to cohabitation. Treatment was completed on gestation day 21.

Remarks:

Doses / Concentrations:
0, 100, 500 and 1000 mg/kg bw/day
Basis:

No. of animals per sex per dose:

25/sex/group

Control animals:

yes, concurrent vehicle

Details on study design:

Male fertility toxicity was evaluated based on mating and impregnating rate; sperm count, mobility, and morphology; and microscopic examinations of testes and epididymides.

Ovaries and uterine content:

Female fertility was evaluated based on estrous cycling, mating and pregnancy rate, number of corpora lutea, number and distribution of implantation sites, early resorption, and microscopic examination of ovaries.

Fetal examinations:

Fetotoxicity and teratologic potential were evaluated based on mid and late resorptions; the numbers of live and dead fetuses; external sex; body weight; and gross external alterations and microscopic internal alterations, such as major malformations, minor external visceral and skeletal anomalies, and common skeletal variants.

Details on maternal toxic effects:

Maternal toxic effects:no effects

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: other:

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Abnormalities:

not specified

Developmental effects observed:

not specified

In the combined segment I and II study in rats, there were no test article-related changes in male or female fertility following the administration of the test item. However, the pregnancy rate was 76 % in rats dosed at 500 mg/kg/day and 72 % in rats dosed at 1000 mg/kg/day; these rates were slightly lower than that of the control group (92 %) but still remained within the historical control range of the testing facility.

Conclusions:

In the combined segment I and II study in rats, there were no test article-related changes in male or female fertility following the administration of the test item. No fetal abnormalities were observed.

Executive summary:

A combined rat fertility and embryo-fetal development study (combined segments I and II) was carried out according to ICH Harmonised Tripartite Guideline: Detection of Toxicity to Reproduction for Medicinal Products & Toxicity to Male Fertility S5(R2). Male fertility toxicity was evaluated based on mating and impregnating rate; sperm count, mobility, and morphology; and microscopic examinations of testes and epididymides. Female fertility was evaluated based on estrous cycling, mating and pregnancy rate, number of corpora lutea, number and distribution of implantation sites, early resorption, and microscopic examination of ovaries. Fetotoxicity and teratologic potential were evaluated based on mid and late resorptions; the numbers of live and dead fetuses; external sex; body weight; and gross external alterations and microscopic internal alterations, such as major malformations, minor external visceral and skeletal anomalies, and common skeletal variants.

There were no test article-related changes in male or female fertility following the administration of the test item. However, the pregnancy rate was 76% in rats dosed at 500 mg/kg/day and 72% in rats dosed at 1,000 mg/kg/day; these rates were slightly lower than that of the control group (92%) but still remained within the historical control range of the testing facility.

In conclusion in this combined segment I and II study in rats, there were no test article-related changes in male or female fertility following the administration of the test item. No fetal abnormalities were observed.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

Good quality data base.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the data available the substance is not classified and labeled according to Regulation 1272/2008/EEC (CLP) and Directive 67/548/EEC (DSD).