Drug Interaction Report

MONITOR: Theoretically, coadministration of adefovir dipivoxil with other drugs that are eliminated by active tubular secretion may result in increased plasma concentrations of adefovir and/or the coadministered drug(s). The mechanism is competitive inhibition of renal excretion. Drugs that are thought to undergo active tubular secretion include metformin, cimetidine, ranitidine, procainamide, flecainide, quinidine, triamterene, midodrine, cidofovir, acyclovir, valacyclovir, tenofovir, ganciclovir, and valganciclovir.

MANAGEMENT: Patients receiving adefovir dipivoxil in combination with other drugs that undergo active tubular secretion should be monitored for excessive pharmacologic effects of one or both drugs, and the dosages of the drugs adjusted if necessary.

Ethanol may increase the acetylation of procainamide. Subtherapeutic plasma levels of procainamide may result in some patients. Because the acetylated metabolite of procainamide also possesses antiarrhythmic properties, the clinical effects are unclear.