Influence of rifampicin treatment on the metabolic fate of [4-14C] mestranol in women.

[4-14C] Mestranol was administered to 2 rifampicin treated and to 3 untreated hysterectomised women with normal liver functions. The urinary excretions of mestranol, ethynylestradiol, 2-hydroxy-ethynylestradiol and of the total radioactivity were measured within the following 5 days. After this period the total urinary excretion of radioactivity amounted to approx. 43% (38%-50%) of the administered dose and no difference was found for the rifampicin treated and untreated women. Moreover, in the urines of both of these groups the same amounts of radioactive mestranol (1.1%-6.3% of the urinary radioactivity) and 2-hydroxy-ethynylestradiol (0.9%-3.9% of the urinary radioactivity) were measured. In contrast, the urinary excretion of ethynyl-estradiol was definitely lower in the rifampicin treated women (3.5% and 4.9% of the urinary radioactivity) as compared to the control group (15%-23%).