In view of the considerable debate concerning the possible failure of contraception in women taking broad spectrum antibiotics, we have examined a group of 12 women aged 22-32 in a controlled study. Each woman had been on long-term therapy with oral contraceptive steroids (OCS) containing ethynylestradiol (EE2) and levonorgestrel (Ng) for at least 6 months and all were in good general health. Blood samples were taken about 11.0 hours after dosing with their OCS on days 5, 6, 7 and 8 of their contraceptive cycle, for measurement of EE2, Ng, FSH and LH by radioimmunoassay. In addition blood samples were taken on days 19, 20 and 21 of the contraceptive cycle for assay of progesterone concentrations in plasma. The study was repeated in the next cycle of use of their OCS during which they took temafloxacin, a broad spectrum quinolone antibiotic in a dose of 600 mg twice daily for 7 days starting on day 1 of the cycle. All women completed the study satisfactorily as judged by diary cards, tablet counts and plasma temafloxacin concentrations. In the early part of the study some nausea and headaches were seen due to taking temafloxacin on an empty stomach but these effects were not seen when the antibiotic was later given with food. There was no evidence of any interaction between temafloxacin and the OCS. The plasma concentration of EE2 was 61.4 +/- 21.1 pg/ml in the control cycle and 68.5 +/- 26.6 pg/ml in the temafloxacin cycle.(ABSTRACT TRUNCATED AT 250 WORDS) :In view of the considerable debate concerning the possible failure of contraception in women taking broad spectrum antibiotics, the authors examined a group of 12 women ages 22-32 in a controlled study. Each had been on longterm therapy with oral contraceptives (OCs) containing ethinyl estradiol (EE) and levonorgestrel (Ng) for at least 6 months and all were in good general health. Blood samples were taken about 11.0 hours after dosing with OCs on days 5, 6, 7, and 8 of their contraceptive cycle, for measurement of EE2, Ng, FSH, and LH by radioimmunoassay. In addition, blood samples were taken on days 19, 20, and 21 of their contraceptive cycle for assay of progesterone concentrations in plasma. The study was repeated in the next cycle of OC use during which the patients took temafloxacin, a broad spectrum quinoline antibiotic in a dose of 600 mg twice daily for 7 days, beginning on day 1 of the cycle. All women completed the study satisfactorily as judged by diary cards, tablet counts, and plasma temafloxacin concentrations. In the early part of the study, some nausea and headaches were experienced; this was due to the taking of the drug on an empty stomach. When the antibiotic was administered with food, this problem was no longer a concern. There was no evidence of any interaction between temafloxacin and OCs. The plasma concentration of EE2 was 61.4 +or- 21.2 pg/ml in the control cycle and 68.5 +or- 26.6 pg/ml in the temafloxacin cycle. The plasma progesterone concentration was 0.53 +or- 0.1 ng/ml in the control cycle and 0.6 +or- 0.24 ng/ml in the temafloxacin cycle (p0.01). No woman demonstrated any significant rise in plasma FSH or LH concentrations during temafloxacin therapy. The authors conclude that there is no evidence for a systematic interaction between temafloxacin and OCs and that there is no need for use of alternative contraceptive methods in women taking OCs who are also being treated with temafloxacin.