Valtrex Drug Interactions

No clinically significant interactions have been identified.
Aciclovir is eliminated primarily unchanged in the urine via active renal tubular secretion. Any drugs administered concurrently that compete with this mechanism may increase aciclovir plasma concentrations following VALTREX administration.
Following 1 g VALTREX, cimetidine and probenecid increase the AUC of aciclovir by this mechanism and reduce aciclovir renal clearance. However, no dosage adjustment is necessary at this dose because of the wide therapeutic index of aciclovir.
In patients receiving higher doses of VALTREX (4 g or more/day), caution is required during concurrent administration with drugs which compete with aciclovir for elimination, because of the potential for increased plasma levels of one or both drugs or their metabolites. Increases in plasma AUCs of aciclovir and of the inactive metabolite of mycophenolate mofetil, an immunosuppressant agent used in transplant patients, have been shown when oral aciclovir and mycophenolate mofetil are co-administered.
Care is also required (with monitoring for changes in renal function) if administering higher doses of VALTREX (4 g or more/day) with drugs which affect other aspects of renal physiology (e.g cyclosporin, tacrolimus).