Indications: herpes simplex and varicella–zoster.

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: By mouth, herpes simplex, treatment, 200 mg (400 mg in the immunocompromised or if absorption impaired) 5 times daily, usually for 5 days (longer if new lesions appear during treatment or if healing incomplete; increase dose to 800 mg 5 times daily for genital herpes in the immunocompromised); CHILD under 2 years, half adult dose, over 2 years, adult dose

Herpes simplex, prevention of recurrence, 200 mg 4 times daily or 400 mg twice daily possibly reduced to 200 mg 2 or 3 times daily and interrupted every 6–12 months Herpes simplex, prophylaxis in the immunocompromised, 200–400 mg 4 times daily; CHILD under 2 years, half adult dose, over 2 years, adult dose Varicella and herpes zoster, treatment, 800 mg 5 times daily for 7 days; CHILD, varicella, 20 mg/kg (max. 800 mg) 4 times daily for 5 days or under 2 years 200 mg 4 times daily, 2–5 years 400 mg 4 times daily, over 6 years 800 mg 4 times daily.

Attenuation of chickenpox (if varicella–zoster immunoglobulin not indicated), ADULT and CHILD 40 mg/kg daily in 4 divided doses for 7 days starting 1 week after exposure.

By intravenous infusion, treatment of herpes simplex in the immunocompromised, severe initial genital herpes, and varicella–zoster, 5 mg/kg every 8 hours usually for 5 days, doubled to 10 mg/kg every 8 hours in varicella– zoster in the immunocompromised and in simplex encephalitis (usually given for at least 10 days in encephalitis, possibly for 14–21 days); prophylaxis of herpes simplex in the immunocompromised, 5 mg/kg every 8 hours on the basis of ideal body weight.

NEONATE and INFANT up to 3 months, with disseminated herpes simplex, 20 mg/kg every 8 hours for 14 days (21 days if CNS involvement); varicella–zoster 10–20 mg/kg every 8 hours for at least 7 days; CHILD 3 months–12 years, herpes simplex or varicella–zoster, 250 mg/m2 every 8 hours usually for 5 days, doubled to 500 mg/m2.

every 8 hours for varicella–zoster in the immunocompromised and in simplex encephalitis (usually given for at least 10 days in encephalitis, possibly for 14–21 days)