1 Thirteen women taking long term oral contraceptive steroids were studied while taking ampicillin (500 mg three times daily) and compared to a control cycle while not taking ampicillin. 2 There were no significant changes in the plasma concentrations of ethinyloestradiol, levonorgestrel, follicle stimulating hormone or progesterone, although lower concentrations of ethinyloestradiol were noted in two women. 3 We conclude that most patients taking oral contraceptive steroids do not need to take alternative contraceptive precautions while taking ampicillin.
PIP: The authors report on a study of women taking oral contraceptives (OCs) to examine the effect of coadministration of the antibiotic ampicillin and to study the mechanism of interaction seen. 7 women between the ages of 19-27 were studied; all were on long-term OC therapy (5 with Eugynon 30, 1 with Ovranette, and 1 with Minovlar). 500 mg 3 times daily for 8 days was prescribed when 4 patients presented with cystitis and 3 patients with acute bronchitis. 6 volunteers between ages 21-24 who had been on long-term OC therapy for at least 3 months (5 with Eugynon 30 and 1 with Ovran) were studied. An identical dose regimen was provided for this group as well. Blood samples were centrifuged for 10 minutes at 2000 rev/minute. Plasma concentrations of ethinyl estradiol (EE), progesterone, FSH, and Ng were measured. Ampicillin concentrations in plasma were measured by a standard microbiological cup plate assay. No subjects displayed any side effects nor was there any evidence of disturbance in cycle control. Among the patients, the mean EE concentration was 46.4 +or- 15.2 pg/ml during ampicillin therapy and 60.2 +or- 4.8 pg/ml after ampicillin, a difference which is not statistically significant. Plasma levonorgestrel concentration was 2.0 +or- 0.3 ng/ml during ampicillin treatment and 2.05 +or- 0.4 ng/ml after (P0.05). FSH concentration during ampicillin was 2.1 +or- 0.3 mIU/ml and 2.05 +or- 0.5 mIU/ml (P0.05) after. Plasma progesterone concentrations did not exceed 200 pg/ml. Ampicillin concentration was not detectable in 4 of the patients. Among the volunteers, the mean plasma EE concentration was 31.4 +or- 5.0 pg/ml before ampicillin while it was 28.2 +or- 2.8 pg/ml during ampicillin therapy. Mean plasma levonorgestrel was 2.13 +or- 0.63 ng/ml before ampicillin and 2.00 +or- 0.59 ng/ml during ampicillin treatment. FSH concentration before ampicillin treatment was 1.12 +or- 0.23 mIU/ml while during ampicillin treatment, the figure was 0.93 +or- 0.27 mIU/ml. In this study, ampicillin had no significant effect on plasma concentrations of EE and levonorgestrel in women taking OCs. 2 recent studies have shown that ampicillin does not significantly interfere with OC therapy. It did not lower plasma OC concentrations and based on this, women taking OCs do not require alternative contraceptive precautions when taking ampicillin.