Moderate
Established
Descripción
Phenytoin induces CYP3A4-mediated metabolism of dexamethasone, significantly reducing dexamethasone plasma concentrations and risking loss of efficacy (e.g., in cerebral edema or cancer treatment).
Mecanismo
Phenytoin upregulates CYP3A4 and P-glycoprotein, markedly accelerating dexamethasone metabolism; dexamethasone AUC can fall by 50–80% during concurrent phenytoin therapy.
Relevancia clínica
Clinical series in neuro-oncology and transplant patients document loss of dexamethasone efficacy (e.g., return of cerebral edema symptoms) within days of initiating phenytoin.
Manejo clínico
Double the dexamethasone dose when phenytoin is co-administered; monitor clinical response closely; consider levetiracetam as an alternative anticonvulsant to avoid this interaction.