There was no significant interaction of Valtrex with other drugs have been identified.
Cimetidine and Probenecid something can increase the level Valtrex in blood by slowing its output with the urine, however, there is no need to change the dose.
After organ transplants sometimes prescribed mycophenolate mofetil (the drug to suppress the immune response to the transplant). The use of Valtrex increased levels of both drugs derived substances in plasma. Valtrex high doses in combination with drugs that affect renal function (e.g., cyclosporine, tacrolimus), needs careful medical supervision.