Hyperphalangeal bones induced in rat pups by maternal treatment with nifedipine.

Hyperphalangeal bones were found in postnatal rat pups of mothers treated with nifedipine during pregnancy. The anomaly occurred only at the region between the middle and distal phalanges of the 3rd and 4th fingers and toes. The critical periods of the anomaly were days 13 and 14 of pregnancy for the fingers, and days 14 and 15 of pregnancy for the toes. The incidences were dose-related, being more than 90% in both fingers and toes at a single dose of 150 mg/kg, and even more marked at the 4th digits than at the 3rd digits. Neither right/left difference nor sex difference was manifested in the incidence of the anomaly.