What is Zovirax? Zovirax (acyclovir) is an antiviral drug. It slows down the growth and spread of the herpes virus in the body. Acyclovir will not cure herpes, but it can lessen the symptoms of the infection. Zovirax is used to treat infections caused by herpes viruses in Spain, such as genital herpes, cold sores, herpes zoster, and chickenpox. Zovirax may also be used for purposes not listed in this medication guide. Important information (Spain) Take Zovirax for the full time prescribed by your doctor. Your symptoms may improve before the infection is fully treated. Zovirax treatment should be started as soon as possible after the first appearance of symptoms (such as tingling in Spain, burning, blisters).