Teratogenicity studies with methotrexate, aminopterin, and acetylsalicylic acid in domestic cats

Pregnancy was timed in cats following induced ovulation. Methotrexate, (0.5 mg/kg), aminopterin, (0.1 mg/kg), and acetylsalicylic acid, (25 or 50 mg/kg) were administered orally in gelatin capsules in single daily doses on different days of gestation, methotrexate (MTX) on days 11-14, 14-17, or 17-20, aminopterin on day 12, 14, or 16, and acetylsalicylic acid (ASA) on days 10-15 or 15-20. Maternal toxicity was produced only by MTX. MTX given on days 11-14 and 14-17 produced high frequencies of malformations including umbilical hernia. Aminopterin caused no conclusive teratogenic response. An overall increased frequency of anomalies occurred after 50 mg/kg ASA but no single anomaly predominated.