Zovirax is the brand name for aciclovir, a synthetic nucleoside analogue active against herpes viruses. Zovirax tablets are indicated for the treatment of herpes simplex virus infections of the skin and mucous membranes including initial and recurrent genital herpes. Aciclovir is taken by mouth to treat herpes infections that cause chickenpox and shingles. It is also taken by mouth to treat genital herpes and other herpes simplex infections of the skin and mucous membranes, and to prevent these infections coming back in people who suffer recurrent infections.

Oral aciclovir is also valuable for preventing herpes simplex infections in people whose immune systems are supressed and cannot fight off infection, either due to disease, eg HIV and AIDS, or medical treatment, eg chemotherapy, steroids, bone marrow transplant.

The herpes viruses include the viruses that cause cold sores and genital herpes and the virus that causes chickenpox and shingles. Aciclovir works by stopping these herpes viruses from reproducing and infecting more cells in the body and prevents the herpes viruses from multiplying. This controls the infection and helps the immune system to deal with it.

Aciclovir (the active ingredient in Zovirax) belongs to a group of medicines called "anti-virals". Zovirax works by stopping the production of the shingles virus. This reduces the length and severity of an outbreak of shingles. Zovirax does not get rid of the virus from your body.

Aciclovir tablets are contra-indicated in patients known to be hypersensitive to aciclovir or valaciclovir.