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.

H2 antagonists may reduce the clearance of nicotine. Cimetidine, 600 mg given twice a day for two days, reduced clearance of an intravenous nicotine dose by 30%. Ranitidine, 300 mg given twice a day for two days, reduced clearance by 10%. The clinical significance of this interaction is not known. Patients should be monitored for increased nicotine effects when using the patches or gum for smoking cessation and dosage adjustments should be made as appropriate.