Metabolic fate of the new angiotensin-converting enzyme inhibitor imidapril in animals. 4th communication: placental transfer and secretion into milk in rats.

Imidapril hydrochloride ((-)-(4S)-3-[(2S)-2-[[(1S)-1-ethoxycarbonyl-3- phenylproply]amino]propionyl]-1-methyl-2-oxoimidazolidine-4-car box ylic acid hydrochloride, imidapril, TA-6366, CAS 89396-94-1) labeled with 14C was administered orally or intravenously to pregnant rats on the 13th or 19th day of pregnancy, and lactating rats on the 7th or 13th day after delivery at a dose of 1 or 5 mg/kg. The placental transfer and the secretion into milk were studied using whole-body autoradiographic methods and/or quantitative determination of total radioactivity after autopsy. Irrespective of the stages of pregnancy, the placental transfer of imidapril was low in the rats after oral administration. The transfer of total radioactivity per fetus on the 13th and 19th day of pregnancy was below 0.001 and 0.07%, respectively, of the dose to their dams during the observation periods. This indicates that the substance-associated radioactivity penetrates the placental barrier to a low extent. After oral administration of [N-methyl-14C]-imidapril to lactating rats on the 7th day after delivery, the concentration of radioactivity in the milk attained a peak at 4 h after administration (0.05 microgram equivalents of imidapril/g), which was about 1/3 of Cmax in the blood. The transfer of imidapril and/or its radioactive metabolites to each suckling via milk after oral dosing was only below 0.03% of the dose to the dams on the 13th day after delivery during the observation periods. The present autoradiographic findings confirmed the above results of tissue distribution studies.