Drug Interactions between adefovir and famotidine / ibuprofen

MONITOR CLOSELY: Coadministration of adefovir dipivoxil with other nephrotoxic agents may increase the risk and severity of renal impairment due to additive effects on the kidney. Additionally, renal impairment secondary to the use of these agents may reduce the clearance of adefovir, which is primarily eliminated by renal excretion. The use of adefovir dipivoxil has been associated with dose-related nephrotoxicity characterized by a delayed onset of gradual increases in serum creatinine and decreases in serum phosphorus. Generally, the risk is low in patients with adequate renal function receiving 10 mg/day but increases with increasing dosage and in patients with underlying renal impairment.

MANAGEMENT: Caution is advised if adefovir dipivoxil must be used in patients who have recently received or are receiving treatment with other potentially nephrotoxic agents (e.g., aminoglycosides; polypeptide, glycopeptide, and polymyxin antibiotics; amphotericin B; cidofovir; tenofovir; foscarnet; cisplatin; deferasirox; gallium nitrate; lithium; mesalamine; certain immunosuppressants; intravenous bisphosphonates; intravenous pentamidine; high intravenous dosages of methotrexate; high dosages and/or chronic use of nonsteroidal anti-inflammatory agents). Renal function should be evaluated prior to and during therapy with adefovir dipivoxil. Patients with renal insufficiency at baseline or during treatment may require dosage adjustment in accordance with the manufacturer's product labeling.

H2 antagonists may alter the pharmacokinetic disposition of some nonsteroidal anti-inflammatory drugs (NSAIDs), resulting in increased or decreased plasma concentrations. Data have been varied, even for the same NSAID. The mechanism may involve inhibition of metabolism, changes in gastric pH resulting in altered absorption, and/or reduced urinary elimination of the affected NSAIDs. Statistically significant changes have been small and of limited clinical significance when interactions have been observed.