Synthetic nucleoside which is analogue of guanine, structurally very closed related to acyclovir.Indicated for the treatment and prevention of Cytomegalovirus (CMV) in immunocompromised patients. At latest update no published data on excretion into breast milk were found. It is used in newborns and premature who are affected with CMV infection.Its low oral bioavailability hinders the passage from ingested milk towards the infant’s plasma, except in preterm babies and immediate neonatal period, which may show an increased intestinal permeability.