Acyclovir (Zovirax, Cyclovir, Herpex, Acivir, Acivirax, Zovir, Acycloguanosine, ACV), is an FDA-approved prescription medication belonging to a class of antiviral agents called synthetic nucleoside analogues. It works to stop the spread of the herpes virus within your body but it doesn’t prevent the spread of the virus to other, uninfected people, nor is it a cure for herpes. Acyclovir comes in several different preparations including topical cream and ointment, tablets, capsules, and liquid.

The topical cream and ointment are used to treat cold sore outbreaks caused by the herpes simplex virus and eczema caused by the herpes zoster virus. Either the cream or the ointment may be applied directly to the affected area several times a day for several days continuously. Acyclovir may also be prescribed orally to treat shingles which is also caused by the herpes zoster virus.

If you’re taking acyclovir, follow the instructions carefully and complete the course of medication in exactly the amount and frequency prescribed by your doctor. Serious side effects associated with acyclovir include swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs; hoarseness; difficulty breathing or swallowing; rash; hives; and itching. If you experience any of these, call your physician immediately.