Zovirax (Acyclovir): Uses, Dosing, and Safety Tips

Zovirax (acyclovir) is an antiviral medicine used mainly for herpes viruses. You probably know it for cold sores and genital herpes, but it also helps chickenpox and shingles in certain cases. It comes as a topical cream, oral pills or suspension, and in hospital settings as an IV infusion.

Dosage depends on the infection, age, and kidney function. For cold sores, topical cream applied at first tingle can shorten duration. For oral treatment adults commonly use 200–800 mg at intervals—your doctor will set the exact dose. If you have kidney problems, doses need lowering and doctors often check blood levels and hydration.

Acyclovir works best when started early. For shingles and severe infections, treatment within 48–72 hours gives the most benefit. It won’t cure herpes permanently, but it reduces symptoms, speed of healing, and virus spread.

Common side effects are nausea, headache, and mild stomach upset. Topical use can cause local burning or irritation. Rarely, high doses or IV use can affect the kidneys or cause confusion—this is more likely if you’re dehydrated or already have renal disease.

Drink enough water when taking Zovirax by mouth. Avoid using it while dehydrated. If you’re diabetic, watch blood sugar when sick—fever, reduced eating, or dehydration can impact glucose control. Tell your doctor about all medicines you take; some drugs change how your kidneys handle acyclovir.

Some drugs—like probenecid and certain chemotherapy agents—can raise acyclovir levels. Combining other antivirals is sometimes appropriate but should be managed by a specialist. Pregnant or breastfeeding? Your provider will weigh risks and benefits; oral acyclovir is often used when the benefit outweighs potential risk.

Zovirax is a prescription medicine in most places. Only buy from trusted pharmacies that require a prescription. Watch product form and concentration—cream strengths and tablet doses differ. If buying online, check pharmacy licensure, customer reviews, and secure payment. Never share prescription medicine or use someone else’s leftover pills.

If you have frequent outbreaks, ask your doctor about suppressive therapy to cut outbreak frequency and reduce transmission. For one-off cold sores, a short course at the first sign can help. Questions about dosing, kidney checks, or interactions? Talk to your pharmacist or healthcare provider.

Store Zovirax at room temperature away from moisture and heat. Cream should be kept in its original tube and not used past the expiry date.

Children and older adults need special dosing. Kids' liquid doses are weight based (mg/kg). Elderly often need lower doses because kidneys decline with age; doctors may test kidney function.

To reduce spreading the virus, avoid kissing or sex while sores are active. Condoms help but don’t protect areas not covered. Wash your hands after touching a sore.

Apply cream with clean fingers or cotton swab and wash hands. For pills, finish the full course even if you feel better.

Acyclovir is available as a generic and usually costs less than brand name. Ask your pharmacist about cheaper options.

Seek urgent care for rash, swelling, trouble breathing, very low urine output, severe dizziness, or confusion. Carry a medicine and allergy list to each visit.