Plasma levels of norethisterone (NET), ethinyl estradiol (EE), Ampicillin or Metronidazole were estimated in 16 women, who were taking low-dose oral combination contraceptive pills (containing norethisterone acetate 1 mg and ethinyl estradiol 30 microgram) and in whom concurrently, either Ampicillin (6 women) or Metronidazole therapy (10 women) was given. Neither Ampicillin nor Metronidazole therapy altered the 'peak' or 24-hour plasma levels and area under the curve, for NET and EE. Furthermore, oral contraceptive treatment did not alter the 'peak' levels of Ampicillin or Metronidazole. Progesterone (P) levels were in the anovulatory range in all Ampicillin treated cycles. However, in Metronidazole treated group, two out of 10 women showed a P rise of more than 4 ng/ml. The study was expanded to include another group of 15 women treated with Metronidazole, where only one women showed a P rise of more than 4 ng/ml. The occurrence of 'escape ovulation' as suggested by P rise of more than 4 ng/ml in three out of 25 Metronidazole treated women is either a chance incidence due to a different pharmacological response in them, or most probably due to the default in the regular intake of pills in these women. This is supported by the observation that one out of three women showing a P rise (greater than 4 ng/ml( during concurrent Metronidazole therapy, also showed ovulatory P values in oral contraceptive-only treated cycles. Furthermore, in the control group also, one out of 10 women had ovulatory P levels (greater than 4 ng/ml) in oral contraceptive-only treated cycles.
PIP: Plasma levels of (NET) norethisterone, (EE) ethinyl estradiol, Ampicillin, or Metronidazole were estimated in 16 women who were taking low-dose (OC) oral contraceptives (containing norethisterone acetate, 1 mg, and ethinyl estradiol, 30 mcg) and in whom concurrently, either Ampicillin (6 women) or Metronidazole therapy (10 women) was given. Neither drug altered the peak or 24-hour plasma levels and area under the curve for NET and EE. Furthermore, OC treatment did not alter the peak levels of either Ampicillin or Metronidazole. (P) Progresterone levels were in the anovulatory range in all Ampicillin-treated cycles. However, in Metronidazole-treated group, 2 of 10 women showed a P rise of more than 4 ng/ml. The study was expanded to include another group of 15 women treated with Metronidazole and only 1 woman showed a P rise of more than 4 ng/ml. The occurrence of 'escape ovulation' as suggested by a P rise of more than 4 ng/ml in 3 of 25 Metronidazole-treated women is either a chance incidence due to a different pharmacological response in them, or most probably due to the default in the regular intake of pills in these women. This is supported by the observation that 1 out of 3 women showing a P rise ( 4 ng/ml) during concurrent Metronidazole therapy also showed ovulatory P values in OC-only treated cycles. Furthermore, in the control group, 1 out of 10 women had ovulatory P levels ( 4 ng/ml) in OC-only treated cycles.