Zovirax Dispersible (Acyclovir)

(℞) Prescription Required

Zovirax (Acyclovir) Dosage and Side Effects

ZOVIRAX is a prescription medication used to treat viral infections from the varicella virus that causes chicken pox and shingles, as well as infections from the virus that causes genital herpes. The drug works by preventing viruses from dividing and multiplying.

Proper Use of this medication

Medication should not be shared with others. The prescribed dosage should not be exceeded.

Suspension (liquid) bottle should be shaken before use.

Usual dose for shingles:

For the treatment of shingles (herpes zoster), the usual dose of ZOVIRAX is 800 mg every 4 hours, 5 times daily for 7 to 10 days. ZOVIRAXmust be taken as early as possible within 72 hours of the onset of lesions.

Usual dose for chickenpox:

For the treatment of chickenpox (varicella), the usual dose of ZOVIRAX is 20 mg/kg (not to exceed 800 mg) 4 times daily for 5 days. ZOVIRAXmust be taken as early as possible within 24 hours of the appearance of rash.

Usual dose for genital herpes:

For the treatment of an initial episode of genital herpes, the usual dose of ZOVIRAX is 200 mg every 4 hours, 5 times daily (maximum 1 g daily) for 10 days. ZOVIRAX must be taken as early as possible following onset of signs and symptoms.

For the suppression of genital herpes, the usual dose of ZOVIRAX is 200 mg 3 to 5 times daily or 400 mg twice daily. You should follow dosing instructions carefully. The objective is to keep enough of the drug in the body at all times to prevent the herpes virus from multiplying. Your doctor will try to prescribe the minimum dose required to do this in your case and may therefore increase or decrease your dose during the first few weeks. Follow your doctor's instruction carefully to ensure that you get the best possible response to treatment.

For the treatment of recurrent episodes of genital herpes, the usual dose of ZOVIRAX is 200 mg every 4 hours 5 times daily for 5 days. ZOVIRAX must be taken at the earliest sign or symptom (prodrome) of recurrence.


In case of drug overdose, contact a health care practitioner, hospital emergency department or regional Poison Control Centre immediately, even if there are no symptoms.

Missed dose:

If you forget to take a dose, take it as soon as you remember. Then continue with the next dose at the proper time interval. Do not double doses.

Side Effects

As with any widely prescribed medication, adverse events in association with the use of ZOVIRAX are reported from time to time.

Common side effects may affect up to 1 in 10 people:

  • Headache

  • Nausea, diarrhea, upset stomach, vomiting

  • Feeling unwell

  • Weakness, lack of energy

  • Skin tingling, itching

Other side effects include: dizziness; high temperature (fever); itchy, bumpy rash; skin reaction after exposure to light (photosensitivity); hair loss; unusual bruising or bleeding; shortness of breath; effects on blood and urine tests; swelling of the face, lips, mouth, tongue or throat; increases in the enzymes that work in the liver; feeling agitated or confused; feeling shaky, unsteady and a lack of co-ordination; difficulty speaking or hoarseness; seeing or hearing things that are not really there; feeling drowsy or sleepy; inability to think or judge clearly or concentrate; disturbances of behaviour, speech and eye movements; unconsciousness; yellowing of the skin and whites of the eyes, inflammation of the liver; and changes to blood test results (reduced numbers of red blood cells, white blood cells, or blood platelets).

This is not a complete list of side effects. For any unexpected effects while taking ZOVIRAX, contact your doctor or pharmacist.

Warnings and Precautions

Before using ZOVIRAX, tell your doctor if:

  • You have kidney problems or if you are 65 years of age or older. Your doctor may give you a lower dose of ZOVIRAX and/or ask you to stay hydrated.

  • You are severely immunocompromised (e.g. suffering a severe disease or have recently undergone an organ transplant, and are taking immunosuppressant drugs for either of these conditions).

  • You are pregnant, planning to become pregnant, breastfeeding or planning to breastfeed.

The safety and effectiveness in children less than 2 years of age are not known.

You must make sure you drink plenty of liquids such as water while you are being given ZOVIRAX.

Feeling drowsy or sleepy may impair your ability to concentrate and react. Make sure you are not affected before you drive or operate machinery.

When using ZOVIRAX for suppression of genital herpes, your doctor may periodically stop your drug therapy in order to reassess your need for continuous treatment. The effect of long-term use in humans has not been fully assessed. Prudence is therefore suggested when choosing continuous, long term therapy with ZOVIRAX. Suppression of recurrent genital herpes is therefore, only recommended in those who are severely affected. Some patients experience increased severity of the first episode of genital herpes after stopping treatment.

Genital herpes is passed from one person to another through direct intimate contact. To reduce the risk of transmission, wash your hands immediately if you touch your skin sores, and do not touch other parts of your body until you have done so. Especially avoid intimate contact with others when the disease is visible. Herpes virus particles may also be released when you do not have blisters or sores. For this reason, it is safest to believe that you can spread the infection to your partner even when sores are not present.

Although decreased sperm counts were observed in animals treated with high doses, these effects did not occur in humans.

Interactions with this medication

Some drugs may affect the way ZOVIRAX works, and ZOVIRAX may affect other drugs you are taking.

It's very important to let your doctor know about all drugs you are taking, including any over-the-counter herbs or supplements.

Drugs that may interact with ZOVIRAX include:

  • Several medications used to treat bacterial or fungal infections, including amphotericin B (Fungizone) and several antibiotics such as amikacin (Amikin), gentamicin (Garamycin), kanamycin (Kantrex) and tobramycin (Tobi, Nebcin)
  • Over-the-counter pain relievers (Advil, Motrin, Aleve)
  • Medications used to treat HIV/AIDS, such as zidovudine (Retrovir, AZT)
  • Other Acyclovir Interactions

You do not need to change your diet or your activities while on ZOVIRAX .

However, drink plenty of fluids when taking this medication.

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The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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