Valganciclovir is an L-valyl ester (prodrug) of ganciclovir, which is rapidly converted to ganciclovir by intestinal and hepatic esterases after oral administration. Ganciclovir is a synthetic analogue of 2’-deoxyguanosine that inhibits the replication of herpes viruses. Human viruses sensitive to ganciclovir include cytomegalovirus (CMV), herpes simplex viruses type 1 and type 2 (Herpes simplex), human herpesvirus types 6, 7 and 8 (HHV-6, HHV-7, HHV-8), Epstein-Barr virus, varicella zoster virus and hepatitis B virus. The clinical antiviral effect of the drug was demonstrated by a decrease in CMV excretion from patients from baseline 46% (32/69) to 7% (4/55) after 4 weeks of treatment with valganciclovir.