A 28-year-old man with HIV infection (CD4 count 80 cells/μL) presents with painful vesicles on the genitals and perianal region for 5 days. The lesions are small, grouped on an erythematous base, and have begun to ulcerate. He reports a history of similar lesions 6 months ago. Direct fluorescent antibody (DFA) testing confirms HSV-2. He is currently on antiretroviral therapy but not on antiviral prophylaxis. What is the most appropriate initial management?