| Abstract: | Previous studies from this laboratory reported that 3H-labeled metabolites with half-lives of more than 24 hours may remain in the plasmaa of women receiving an intravenous injection of 3H norethindrone or 3H mestranol. To confirm the presence of these metabolites, blood samples were collected for five days after injection of 3H norethindrone or 3H mestranol; 3H representing metabolites of norethindrone disappeared with half-life values of 42 to 84 hours (mean 67 hours), while 3H representing metabolites of mestranol declined with an average half-life of 45 hours (range 37 to 65 hours). When the 3H-labeled drugs were administered orally, metabolites of similar half-life were formed. Because these compounds exist for several days after a single administration and since oral contraceptive drugs are normally taken daily, the possiblity of the accumulation of 3H in the plasm of women receiving several consecutive doses of 3H norethindrone was investigated. The results of this study show a stepwise accumulation of the 3H metabolites when 3H norethindrone was administered in six daily oral doses. However, the 3H levels declined from the peak on the sixth and last day of the treatment at a rate equivalent to those previously measured after intravenous or oral administration. |
