Dosage in Adults: Treatment of herpes simplex infections: 200 mg Zovirax should be taken five times daily at approximately four hourly intervals omitting the night time dose. Treatment should continue for 5 days, but in severe initial infections this may have to be extended. In severely immunocompromised patients (e.g. after marrow transplant) or in patients with impaired absorption from the gut the dose can be doubled to 400 mg Zovirax or alternatively intravenous dosing could be considered. Dosing should begin as early as possible after the start of an infection; for recurrent episodes this should preferably be during the prodromal period or when lesions first appear. Suppression of herpes simplex infections in immunocompetent patients: 200 mg Zovirax should be taken four times daily at approximately six-hourly intervals. Many patients may be conveniently managed on a regimen of 400 mg Zovirax twice daily at approximately twelve-hourly intervals. Dosage titration down to 200 mg Zovirax taken thrice daily at approximately eight-hourly intervals or even twice daily at approximately twelve-hourly intervals, may prove effective. Some patients may experience break-through infection on total daily doses of 800 mg Zovirax.