AdultHerpes zoster 1,000 mg tds for 7 days. Immunocompetent & immunocompromised patient CrCl at least 50 mL/min1 g tds, 30-49 mL/min1 g bd,10-29 mL/min1 g once daily,<10 mL/min500 mg once daily. Herpes simplex infections 500 mg bd for 3-5 days (for recurrent episodes) or 10 days (for initial episodes). Immunocompetent patient CrCl at least 30 mL/min 500 mg bd, <30 mL/min 500 mg once daily. Suppression of herpes simplex infection recurrence in immunocompetent patient 500 mg once daily. CrCl at least 30 mL/min 500 mg once daily, <30 mL/min 250 mg once daily. Immunocompromised patient 500 mg bd. CrCl at least 30 mL/min 500 mg bd, <30 mL/min 500 mg once daily. Reduction of transmission of genital herpes 500 mg once daily.