Possible interactions between antibiotics and oral contraceptives.

The incidence and manifestation of drug interaction decreasing ther action of contraceptive tablets have been examined in 79 women receiving antibiotic therapy concurrently with the use of oral contraceptives. The antagonistic interaction of antibiotics manifested itself in intermenstrual spotting, rarely in break-through bleeding, but it did not completely inhibit the contraceptive action (pregnancy). Drug interaction occurred individually and, in the majority of cases, it showed reciprocal relation to the hormone content of the used oral contraceptive. Though the exact mechanism of interaction is not known, it has to be considered in the course of therapy since both drug types are widely used.