STUDIES WITH 4-14-C-MESTRANOL IN LACTATING WOMEN

Abstract

ABSTRACT 14C-Mestranol (5 μc) was administered orally in a Lyndiol®**-tablet (= 5 mg lynestrenol*** + 150 μg mestranol) to four women using Lyndiol® during the lactation period shortly after delivery. The concentration of radioactivity in the plasma and the excretion of radioactivity in the urine and milk were studied. The clearance rate of radioactivity from the blood was very low. A halflife in the order of 40–60 h was found for labelled »mestranol and its metabolites«. In three cases 31–36% of the radioactivity was excreted into the urine within 5 days after oral administration of the labelled material; in the fourth patient this value was about 52 %. During a collection period of 4 days after the oral administration of the 14C-mestranol-containing tablet, 0.0002–0.013 per cent of the administered dose was excreted into the milk. These very low values were partly due to the low amounts of milk that could be collected. It was calculated that with the regular oral administration of one Lyndiol®-tablet daily, with 150 μg mestranol per tablet, about 0.03–0.06 μg (0.02–0.04 % of the administered dose) of mestranol or its metabolites might be excreted per 100 ml milk. The significance of these amounts, in view of the transfer to infants during breast-feeding, is discussed.