The safety of Comazole in human pregnancy has not been established. At doses greatly in excess of the recommended human therapeutic dose, trimethoprim has been reported to be teratogenic in rats with effects typical of a folate antagonist and preventable by administration of dietary folate. No significant drug-related malformations have been demonstrated in rabbits, but at doses approximately 10 times in excess of human therapeutic dose, an increase in foetal death was noted. Despite the excretion of trimethoprim and sulphamethoxazole into breast milk, the administration of comazole to lactating women represents a negligible risk to the suckling infants.
Comazole should not be given during pregnancy especially in late pregnancy because of risk of kernicterus. It also should be used with caution in nursing mothers because it can pass the placenta and is excreted in breast milk and may cause kernicterus.