Aciclovir (Xyclovirax) 400mg Antiviral Tablets 30's are used to treat infections caused by the herpes simplex virus (such as cold sores and genital herpes) and the varicella-zoster virus (shingles and chickenpox). Each tablet contains 400mg of aciclovir, which works by inhibiting viral replication, helping to reduce the severity and duration of outbreaks. The pack contains 30 tablets, typically taken as directed by a healthcare provider to manage and control viral infections effectively.