HSV infection 200 mg every 4 hr for 5 days, extend treatment if necessary. Suppression of recurrent genital HSV & prophylaxis of HSV infection in immunocompetent adults 200 mg every 6 hr. Prophylaxis of HSV infection in immunocompromised adults 200 mg every 6 hr, may be increased to 400 mg. Treatment of HZV & varicella zoster Adult800 mg every 4 hr for 7 days. Treatment of varicella zoster Adolescent 12-18 yr 800 mg qds for 5 days.