The effect of cotrimoxazole on oral contraceptive steroids in women

• Published in: Contraception (Stoneham) Vol. 28; no. 1; pp. 53 - 59
• Main Authors: Grimmer, S.F.M., Allen, W.L., Back, D.J., Breckenridge, A.M., Orme, M., Tjia, J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.1983
• Subjects: Adult; Anti-Bacterial Agents - pharmacology; Anti-Infective Agents, Urinary - pharmacology; Contraceptives, Oral - pharmacology; Contraceptives, Oral, Combined - blood; Contraceptives, Oral, Hormonal - pharmacology; Drug Combinations - pharmacology; Drug Interactions; Ethinyl Estradiol - metabolism; Ethinyl Estradiol - pharmacology; Ethinyl Estradiol-Norgestrel Combination; Female; Humans; Levonorgestrel; Norgestrel - blood; Norgestrel - pharmacology; Sulfamethoxazole - pharmacology; Trimethoprim - pharmacology; Trimethoprim, Sulfamethoxazole Drug Combination; Use-effectiveness; Ethinyl Estradiol > analysis; Levonorgestrel; Contraceptive Agents, Estrogen > analysis; Gonadotropins; Biology; Contraception; Hormones; Family Planning; Endocrine System; Contraceptive Effectiveness; Gonadotropins, Pituitary; Contraceptive Methods; Contraceptive Agents > analysis; Physiology; Follicle Stimulating Hormone > analysis; Oral Contraceptives; Progesterone; Contraceptive Agents, Female
• ISSN: 0010-7824; 1879-0518
• DOI: 10.1016/S0010-7824(83)80005-5

Nine women taking long-term oral contraceptive steroids (Trinordiol) were studied during a cycle while taking cotrimoxazole (1 gm twice daily) and the results were compared to the previous control cycle. During the cotrimoxazole cycle, there was a significant increase in the plasma concentration of ethynylestradiol (EE). In plasma samples taken on 4 successive days 10–12 hours after dosing, the plasma EE concentration rose from 29.3 ± 5.0 pg/ml to 38.2 ± 5.8 pg/ml (mean ± S.E. P ≤ 0.02). In samples taken 24 hours after dosing, the increase was from 18.9 ± 2.5 pg/ml to 27.8 ± 4.0 pg/ml (P ≤ 0.05). Plasma F.S.H. values in these latter samples, decreased from 4.8 ± 0.6 mIu/ml to 3.4 ± 0.5 mIu/ml (P ≤ 0.01). No significant changes were noted in the plasma concentrations of levonorgestrel or progesterone. The rise in plasma concentration of EE during cotrimoxazole therapy is attributed to an inhibition of the metabolism of EE by cotrimoxazole as has been shown with other drugs. Short courses of cotrimoxazole are unlikely to cause any adverse effects on contraceptive control when given to women taking long-term oral contraceptive steroids.