Major
Carbamazepine × Doxycycline
Antiepileptics. Carboxamide derivatives×Tetracyclines
Mechanism
Carbamazepine induces CYP3A4 and accelerates hepatic doxycycline metabolism. Doxycycline half-life shortens from 16 to 7 hours; plasma levels fall.
Symptoms
The patient feels nothing. Risk of subtherapeutic antimicrobial concentrations and treatment failure rises – particularly with pathogens at the susceptibility breakpoint.
Management
Increase doxycycline to 200 mg twice daily during the course (instead of standard 100 mg twice daily). Alternative antibiotics without induction-driven loss: a cephalosporin, amoxicillin, azithromycin. Alternative anticonvulsants without induction: levetiracetam, lamotrigine.
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.