Minor
Ethinylestradiol × Metronidazole
Estrogens. Natural and semisynthetic estrogens, plain×Imidazole derivatives (antiprotozoal / antibacterial)
Mechanism
Metronidazole does not induce CYP3A4 and does not affect hepatic ethinylestradiol metabolism. The historical theory of reduced COC efficacy is rejected by meta-analyses.
Symptoms
The combination usually causes no specific symptoms. Each drug's individual side effects remain.
Management
Additional contraception during short metronidazole courses is not needed. Exclude alcohol throughout the course and for 48 hours after due to a disulfiram-like reaction.
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.