Acyclovir

About Acyclovir

Acyclovir is a nucleoside analog that stops herpes simplex and varicella-zoster viruses from copying their DNA; it is not a cure for genital herpes, and there are no data on whether it prevents passing it to others. By mouth, it is labeled for acute shingles (800 mg five times a day for 7 to 10 days), first-episode genital herpes (200 mg five times a day for 10 days), recurrent genital herpes (200 mg five times a day for 5 days from the first sign, or 400 mg twice a day as suppression for up to 12 months, then reassessed) and chickenpox (800 mg four times a day for 5 days for adults and children over 40 kg; 20 mg/kg four times a day from age 2). Treatment starts as early as possible; the label has no data on shingles treatment started more than 72 hours after the rash, or on chickenpox treatment started more than 24 hours after symptoms. Oral forms are not established for children under 2. Cold sores are not among the labeled uses of oral acyclovir.

There is no boxed warning. Anyone who has had a clinically significant hypersensitivity reaction, such as anaphylaxis or a severe skin reaction, to acyclovir, valacyclovir or an ingredient must not take it. Since November 2025 the oral labels also warn of severe skin reactions, such as DRESS and Stevens-Johnson syndrome: a painful rash involving mucous membranes, or a spreading severe rash, means stopping it at once. Kidney failure, in some cases fatal, has been reported, so doses are lowered for reduced kidney function, fluids are kept up and extra care is taken with other drugs that can harm the kidneys. Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome, blood disorders that have been fatal, have occurred in people with weakened immune systems. Confusion, hallucinations, agitation, seizures and other nervous system effects have been reported and may be marked in older adults and in people with kidney impairment. Nausea, vomiting and diarrhea are among the side effects reported.

Zovirax 5 percent cream treats recurrent cold sores in people 12 and older with normal immune function: it is applied five times a day for 4 days, starting as early as possible after the first signs, and is not used in the eyes, inside the mouth or nose, or on the genitals. Zovirax 5 percent ointment is labeled for initial genital herpes and limited, non-life-threatening herpes simplex skin and mucous membrane infections in people with weakened immunity; it is applied every 3 hours, six times a day, for 7 days, and is not for preventing recurrences. The oral label says to use it in pregnancy only if the potential benefit justifies the risk, and with caution while breastfeeding.

Taking Acyclovir

How to take it

By mouth with or without food, as prescribed, starting as soon as possible after symptoms begin and until the prescription is finished. Shake the suspension well, and keep up your fluids. Apply the cream only where a cold sore has formed or is starting, and the ointment with a finger cot or rubber glove; keep both out of the eyes.

If you miss a dose

By mouth: take the missed dose as soon as you remember and space the rest of that day’s doses evenly, unless the next dose is almost due; do not take a double dose. Cream or ointment: apply it when you remember unless the next application is almost due, and do not apply extra.

Storage

Capsules, tablets and suspension at room temperature, protected from light and moisture, out of reach of children; cream and ointment no warmer than 77 degrees F, the ointment in a dry place.

Interactions to know about

Extra care is needed with other medicines that can harm the kidneys. Tell the prescriber about kidney disease, a weakened immune system, or possible dehydration from a recent illness or activity.

This summarizes the official prescribing information. Your prescriber’s and pharmacist’s instructions, and the leaflet that comes with your medicine, take priority.

Why the cash price for Acyclovir differs from pharmacy to pharmacy

Generic capsules, tablets and suspension each come from several makers, so quotes differ by each pharmacy’s fee and markup and by whether acyclovir is on its flat-price generic list. Courses run from two to five doses a day for 5 days to a year, so each prescription is quoted as written.

A pharmacist substitutes only a generic rated equivalent to the cream or ointment written, never one for the other, and a prescription that names Zovirax and blocks substitution is filled with the brand.

Ways to pay less for Acyclovir without insurance

• Check that the prescription allows a generic, especially for the cream or ointment, where Zovirax is still sold.
• For 800 mg doses, ask whether the prescription can be written as 800 mg tablets, which the label says match four 200 mg capsules.
• For suppressive therapy, ask the prescriber whether a ninety-day supply suits you once the dose is settled.
• Ask whether acyclovir is on the pharmacy’s flat-price generic list, and compare more than one pharmacy.
• Upload the prescription to Script Unlock so licensed pharmacies can quote their cash price. You pay the pharmacy directly.

Questions to ask your pharmacist about Acyclovir

1. 1.How much should I drink while I take it?
2. 2.Is my dose adjusted for my kidney function?
3. 3.Where should I apply my cream or ointment, and where should I avoid it?
4. 4.Which side effects, such as confusion or passing less urine, mean I should call?

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