An investigation of the interaction between isoniazid and the contraceptive steroid norethindrone in vivo.

Isonicotinic acid hydrazide (isoniazid) was shown to react readily with 17 alpha-ethinyl-17 beta-hydroxyestr-4-en-3-one (norethindrone) to form the isonicotinyl hydrazone of the steroid under conditions likely to exist in the stomach. The hydrazone was detected in guinea-pig, but not rat, plasma following its oral administration. Rat liver tissue metabolized the compound more rapidly than guinea-pig liver in vitro which probably accounts for the failure to detect the hydrazone in rat plasma.