Aciclovir is an antiviral drug that inhibits DNA synthesis in cells infected by herpes viruses, although it does not eradicated of them. Its only effective if started at the onset of infection; its uses include systemic treatment of varicella-simplex infections of the skin and mucous membranes ( including genital herpes); it is also used topically in the eye. It is especially valuable for the treatment of herpes infections in thoses with immunodeficiency and may be required for prevention of recurrence and prophylaxix-indeed, it mat be life saving.