Drug Interactions between didanosine and valganciclovir

MONITOR: The coadministration of didanosine and ganciclovir may result in significantly elevated plasma concentrations of didanosine, while the pharmacokinetics of ganciclovir are minimally affected. In a study consisting of 11 subjects with HIV infection, ganciclovir (1 gram orally every 8 hours) increased the peak plasma concentration and area under the concentration-time curve of didanosine (200 mg orally every 12 hours) by an average of 58% and 71%, respectively. Other studies have reported similar or even greater alterations with both intravenous and oral ganciclovir. The mechanism is unknown but may involve competitive inhibition of didanosine renal tubular secretion or increased bioavailability of didanosine by ganciclovir. Caution is advised if didanosine must be used concomitantly with ganciclovir or its prodrug, valganciclovir.

MANAGEMENT: Close monitoring for toxicities associated with didanosine such as pancreatitis, lactic acidosis, and peripheral neuropathy is recommended during concurrent therapy. Patients should be advised to promptly notify their physician if they experience possible symptoms of toxicity (e.g., abdominal pain, nausea, vomiting, diarrhea, weakness, dizziness, lightheadedness, irregular heartbeat, or numbness, pain, or tingling in the hands and feet).