Interactions between mysoline(primidone) and Rescriptor (delavirdine)
primidone and delavirdine (Major Drug-Drug)
GENERALLY AVOID: Coadministration with drugs that are inducers of CYP450 3A4 may decrease the plasma concentrations of delavirdine, which is primarily metabolized by the isoenzyme. In seven HIV-infected patients, rifampin (600 mg once daily for 15 days) decreased the peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and trough plasma concentration (Cmin) of delavirdine (400 mg three times a day for 30 days) by 90%, 97% and 100%, respectively, compared to administration of delavirdine alone. Rifabutin (300 mg once daily for 15 days) decreased those same values by 72%, 82% and 94%, respectively. Population pharmacokinetic data available for eight patients suggest that coadministration with phenytoin, phenobarbital, or carbamazepine also results in a substantial reduction in trough plasma delavirdine levels.
MANAGEMENT: Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiretroviral drug levels, delavirdine labeling recommends that the drug not be used with carbamazepine, phenobarbital, phenytoin, rifampin, or rifabutin. It may be advisable to also avoid coadministration with primidone and fosphenytoin (if used for more than 2 or 3 days), since these drugs are metabolized in vivo to phenobarbital and phenytoin, respectively.
