Toxicity of ethylenethiourea in pregnant cats

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Abstract
Ethylenethiourea (ETU) was administered orally in single daily doses of 0, 5, 10, 30, 60 or 120 mg/kg to time‐mated cats. Daily dosing was started on day 16 of gestation in all test groups and was discontinued on the appearance of toxicity signs (between days 27–34 of gestation) in the 120 mg/kg group and on day 35 of gestation in the remaining test groups. Signs of toxicity, observed at all dose levels except in the 5 mg/kg and control, were delayed in onset and characterized by progressive loss in body weight, ataxia, tremors and hind‐limb paralysis. A number of cats died or were killed in a moribund condition in the 30, 60 and 120 mg/kg dose groups. Eleven of the thirty‐five fetuses obtained from six cats killed in a moribund state (4 from the 30 mg/kg and 1 each from the 60‐ and 120 mg/kg groups) were malformed, with coloboma occurring in four fetuses, cleft palate in two, spina bifida in one and umbilical hernia in four fetuses. Incidences of abortion and non‐pregnancy, both unrelated to the treatment, were found in all groups including the control. All surviving cats were necropsied on day 46 of gestation and fetuses were collected for teratologic evaluation. No clear evidence was found for teratogenicity of ETU in live fetuses.