Antacid does not reduce the bioavailability of oral contraceptive steroids in women.

ABSTRACT

PIP: The serum levels of both the estrogen and progestin in 2 different oral contraceptives were analyzed by radioimmunoassay (RIA) for 24 hours after taking a single contraceptive pill with or without an antacid. 6 Indian women not taking any other medication took a 30 mcg ethinyl estradiol (EE) and 1 mg norethisterone (NET) pill, and 6 others took a 30 mcg EE with 150 mcg levonorgestrel (LNg) pill at 9 AM. 4 wks later they took the same steroid pill after chewing a tablet of antacid containing magnesium trisilicate .5 g and aluminum hydroxide .25g (Gelusil, Warner). Serum RIA levels and areas under the curves were identical, when each group served as its own control, except that EE levels were significantly higher in the NET combination. The reasons for this discrepancy, whether due to pill excipients, radioimmunoassay cross reactions or biological factors such as sex hormone binding globulin activities, were unexplained. Apparently, self-dosing with this antacid will not affect bioavailability of oral contraceptive steroids.