RESUMO
A healthy woman aged 21 years who used the oral contraceptive Trigynon became pregnant while being treated with Minocin (minocycline; 100 mg per day) for acne conglobata. While the risk of use of antibiotics such as this one reducing the efficacy of oral contraceptives is small, patients should nevertheless be informed that the risk exists.
PIP: A 21-year old woman using an oral contraceptive, the combination preparation Trigynon containing levonorgestrel (LNG) and ethinyl estradiol (EE), since June 1987 had experienced pain in the groin. In September 1988 she had a single occurrence of bleeding, a sign of lessened effectiveness of the OC. She was treated with 50 mg of minocycline/day as of April 1989, and for inguinal acne conglobata with locally applied clindamycine (10 mg/ml of clindamycine hydrochloride lotion). She switched to another OC, and the next month timely, normal menstruation ensued. A few days later the dose of minocycline was raised to 100 mg/day. Subsequently she had a regular breakthrough bleeding followed by a missed cycle and a positive pregnancy test. There have been several recent reports about the interaction between antibiotics and OCs (breakthrough bleeding and contraceptive failure). Rifampicin and griseofulvin are known to reduce the activity of OCs via induction of liver enzymes. Between 1968-84 there was a total of 62 failures of OCs (15 using OCs with 50 mcg of EE) reported in the UK. The suspected cause was the combined use with antibiotics (70% penicillin and tetracycline). In the Netherlands 6 cases of possible interactions were reported during 1980-86: 2 cases caused by nitrofurantoin and/or trimethoprim, and 1 case by sulfamethoxazol with trimethoprim. The interference of minocycline with the intestinal flora can occur as 34% of it is excreted in feces, and its antibacterial spectrum corresponds to that of tetracycline hydrochloride (reduction of beta-glucuronidase in the feces). The failure of Trigynon cannot be irrefutable ascribed to minocycline as unintended pregnancy also occurs while using OCs without antibiotics. Clindamycine could have also influenced the intestinal flora percutaneously.
