It is prodrug for Aciclovir.

Indications: treatment of herpes zoster; treatment of initial and suppression of recurrent herpes simplex infections of skin and mucous membranes including initial and recurrent genital herpes; reduction of transmission of genital herpes; prevention of cytomegalovirus disease following renal transplantation.

Cautions: maintain adequate hydration (especially with infusion or high doses); monitor neutrophil count at least twice weekly in neonates; renal impairment; pregnancy, breast-feeding.

Side Effects: nausea, vomiting, abdominal pain, diarrhoea, headache, fatigue, rash, urticaria, pruritus, photosensitivity; very rarely hepatitis, jaundice, dyspnea, neurological reactions (including dizziness, confusion, hallucinations, convulsions and drowsiness), acute renal failure, anaemia, thrombocytopenia and leucopenia; on intravenous infusion, severe local inflammation (sometimes leading to ulceration), and very rarely agitation, tremors, psychosis and fever.

Dose: Herpes zoster, 1 g 3 times daily for 7 days Herpes simplex, first episode, 500 mg twice daily for 5 days (longer if new lesions appear during treatment or if healing incomplete); recurrent infection, 500 mg twice daily for 5 days.

Herpes simplex, suppression, 500 mg daily in 1–2 divided doses (in immunocompromised, 500 mg twice daily) Reduction of transmission of genital herpes, 500 mg once daily to be taken by the infected partner.

Prevention of cytomegalovirus disease following renal transplantation (preferably starting within 72 hours of transplantation), 2 g 4 times daily usually for 90 days CHILD not recommended.