Major
Carbamazepine × Ethinylestradiol
Antiepileptics. Carboxamide derivatives×Estrogens. Natural and semisynthetic estrogens, plain
Mechanism
Carbamazepine induces CYP3A4 and accelerates ethinylestradiol metabolism. Combined oral contraceptive efficacy drops; pregnancies during regular use have been reported.
Symptoms
Breakthrough bleeding, missed periods, unplanned pregnancy. The patient feels no symptoms at the moment of dosing.
Management
Switch hormonal contraception to non-hormonal methods (copper IUD or barrier methods) for the duration of carbamazepine therapy. Alternatives: depot progesterone or a levonorgestrel IUD.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Sources
- WHO: Medical eligibility criteria for contraceptive use (2015)– World Health Organization. Medical eligibility criteria for contraceptive use, 5th edition, 2015 (updated 2019).