Acyclovir (Intravenous, Oral)

The medication cannot cure these conditions, but it is useful in helping to control, manage and reduce the symptoms that these diseases cause. You may find that your doctor recommends that you use Acyclovir in conjunction with other drugs to treat your condition.


Acyclovir (US brand name Zovirax) is an oral and intravenous antiviral medication that is used to treat the symptoms of shingles, chickenpox, genital herpes virus, herpes virus affecting the skin, brain, and mucous membranes of the mouth and lips. The medication is also used to treat widespread herpes virus in newborn babies and to prevent the recurrence of genital herpes infections.

Acyclovir cannot cure herpes, but it is effective in relieving the discomfort, pain, and itching caused by the condition, and it can also help any sores that are present to heal more quickly. The medication is effective in decreasing the severity and length of herpes outbreaks. In patients with a compromised immune system, Acyclovir can reduce the risk of the virus becoming more widespread and causing serious infections.

Conditions treated

  • chickenpox
  • shingles
  • genital herpes virus
  • herpes simplex virus infections of the skin, brain, and mucous membranes
  • herpes virus in newborns

Type of medicine

  • Antiviral


Although this medication will ultimately be of benefit to you, you may experience a few minor side-effects when you first start taking it. If you have ever suffered from allergic reactions to any medication or if you are allergic to foods, preservatives, animals or dyes, always tell your doctor before you begin taking Acyclovir.

The majority of people who are prescribed this medication do not suffer any side-effects. However, the most common side-effects that are experienced by patients who are taking Zovirax include nausea, diarrhea, vomiting, and headaches. Understandably, this can lead to a loss of appetite and weight loss.

In patients who receive their medication intravenously, reddening and bruising may occur around the injection site, although this should resolve within a few days.

If you are affected by any of the minor side-effects outlined above, always consult your pharmacist or doctor who may be able to suggest ways of managing any problems you may be experiencing. Once your body becomes acclimatized to the medication, you will probably find that any side-effects resolve by themselves without the need for further medical intervention.

There are some more serious side effects that occur less commonly. Some patients experience feelings of lethargy or drowsiness for no obvious reason. You may find that you become agitated or confused, which is out of the ordinary for you, and you could begin to suffer from hallucinations, such as when you see or hear things that are not there. If your friends or relatives notice that you are exhibiting odd or unusual behaviors, this could be a side-effect of your medication.

Acyclovir can sometimes cause side or back pain and problems urinating. This should be treated as a major cause for concern, as these symptoms could be indicative of kidney problems. Zovirax is also inclined to cause dehydration, which can lead to feelings of excessive thirst. It is important that you combat this side-effect by drinking plenty of water throughout the day.

Some patients taking Acyclovir find that they begin to have problems with slurring their speech. This often occurs in conjunction with coordination problems, trembling, and unsteady movement.

In more extreme and rare cases patients may experience side-effects that are much more serious, affecting the blood cells and kidneys. You are more vulnerable to these problems if you have an existing condition where your immune system has been weakened or compromised, for example HIV, kidney transplant, or bone marrow transplant.

If any of the following dangerous side-effects occur, you should contact your doctor or medical professional as a matter of urgency:

  • extreme fatigue
  • irregular, very slow or very rapid heart rate
  • unusually easy bleeding or bruising
  • fever
  • yellowing of the eyes or skin (jaundice)
  • itching or a rash affecting the face, throat or tongue
  • extreme dizziness or fainting
  • breathing difficulties
  • problems swallowing
  • black, tarry stools
  • blood present in the urine or stools
  • hives
  • red pinpoint spots on the skin
  • blistering or peeling of the skin
  • blurred or double vision

Any or all of these symptoms could indicate a serious allergic reaction to the medication and you should contact your doctor immediately.

This list of recognized side-effects experienced by patients taking Acyclovir is not exhaustive. If you begin to feel unwell or if you notice anything unusual about your behavior or how you feel, always ask your doctor for advice.


Zovirax cannot be bought over the counter and is only available on prescription from your doctor. The medication may be dispensed in tablet form, in capsule form, as a powder for mixing into a solution, in pre-mixed suspension form, or as an intravenous injection.

The dose of this medication will vary between patients and depend on the condition being treated. Always follow your doctor's instructions or the directions on the dispensed product packaging. The dosage outlined below is the average recognized dose for use with this medication. However, you should not change the dose that you have been prescribed, unless you are advised to do so by your doctor.

Do not attempt to guess at the amount of medication you should be taking; always ask your doctor or pharmacist for clarification if you cannot remember the prescribed dose or frequency.

The following are the recognized usual doses of Acyclovir for the various conditions that it is used to treat.

For the treatment of genital herpes

  • adults and children over 12 years: 200mg, five times daily for a period of ten days
  • children up to 12 years: use and dosage as directed by your doctor

For the prevention of genital herpes infections

  • adults and children over 12 years: 200 to 400mg, two to five times daily for a period of five days or up to 12 months, depending on the frequency of the outbreaks
  • children up to 12 years: use and dosage as directed by your doctor

For the treatment of chickenpox

  • adults and children who weigh more than 88 pounds: 800mg, four times daily for a period of five days
  • children two years and older who weigh 88 pounds or less: use and dosage as directed by your doctor
  • children up to two years of age: dosage and use as directed by your doctor

For the treatment of shingles

  • adults and children over 12 years: 800mg, five times daily for a period of seven to ten days
  • children up to 12 years: use and dosage as directed by your doctor

For the treatment of widespread herpes in newborns

The dose of Acyclovir that is used for the treatment of widespread herpes virus in infants and newborns is usually based on body weight and as such must be determined by the treating physician. The usual dose is 4.5mg per pound of the patient's body weight. The medication should be injected into a vein and should be dispensed gradually over a minimum of a one-hour period. This dose should be repeated every eight hours for a period of ten days.

If you miss a dose of your medication, you should try to take it as soon as possible. However, if it is almost time for your next dose, you should omit the one that you have missed and resume your regular dosing schedule. Do not take double doses.

When using Acyclovir to treat the symptoms of shingles or herpes infection, for example burning, pain or blistering, you should begin using the medication as soon as possible after the symptoms appear. If you have chickenpox, you should begin taking Acyclovir as soon as possible following the first signs of a rash, generally within one day. If you or a relative begins to develop symptoms, it is important that you seek medical attention immediately so that the appropriate drug therapy can be commenced as soon as possible.

It is important to note that Acyclovir can cause dehydration, so it is important to take your medication with a full glass of water. Be sure to drink plenty of water throughout the day to keep your kidneys functioning properly. You can take the oral forms of this medication with meals or on an empty stomach if you prefer.

It is important to continue taking the complete course of Acyclovir as prescribed for you by your doctor in order to gain the full benefit of the drug. This is essential, even if your symptoms start to resolve after a few days. Do not miss out any of your doses. However, you should not use the medication for longer than your doctor has directed. If your symptoms have not subsided or if you think your condition is actually becoming worse, you should seek medical advice immediately.

When measuring out your medicine, it is very important that you do so accurately. For this reason you should always use a proper measuring spoon or other device that can be obtained from your doctor or pharmacist. A standard household teaspoon may not hold the correct amount of liquid and may therefore not be accurate when it comes to measuring out your medicine.

Do not take more than the prescribed dose of Acyclovir. If you think that you or someone in your household has overdosed accidentally or intentionally on this medication, you must seek medical advice immediately, or call 911.

During your course of treatment, try to keep the areas that are affected by shingles, herpes or chickenpox as clean and dry as possible. You can prevent rubbing and irritation of sores and blisters by wearing lightweight, loose-fitting clothing that is made from natural fibers, such as cotton. Try not to allow children to become too hot, especially in bed at night as this can aggravate the itching caused by chickenpox scabs. Use cotton sheets and keep bedrooms well-ventilated.

Major drug interactions

Some medications should not be used together, but in other cases, different drugs can be used in tandem, even if an interaction may occur. In these circumstances, your doctor may decide to change the dose or to take other precautions. If you are prescribed Acyclovir, always tell your doctor if you are already taking any of the following medicines:

  • Foscarnet
  • Mycophenolate Mofetil
  • Fosphenytoin
  • Phenytoin
  • Mycophenolic Acid
  • Valproic Acid

Some medicines should not be used when consuming food or certain types of food, when smoking or when using alcohol. If you use tobacco or alcohol, discuss this with your doctor before you begin using the medication.


In addition to discussing any allergies and other drugs that you are taking, you should also mention to your doctor any existing health conditions that you have.

Taking Acyclovir may cause drowsiness, dizziness, and confusion in elderly patients because they can be more sensitive to the effects of Acyclovir on the central nervous system than younger people. If you begin to experience any of these side effects, you should refrain from driving and ask your doctor for advice.

There is currently no evidence to suggest that taking Acyclovir can harm unborn babies. However, you should tell your doctor if you are pregnant or if you are breastfeeding. Acyclovir can pass from mother to baby in the breast milk, so seek your doctor's advice regarding alternative feeding arrangements for your infant.

If you suffer from genital herpes and you are pregnant, you should note that herpes virus can be passed to your baby if you have genital lesions when the baby is born. For this reason, it is extremely important that you take steps to prevent yourself from developing genital herpes lesions during your pregnancy. Seek the advice of your doctor and take your medication as directed for the duration of your pregnancy.

The following medical conditions can affect the use of this medicine and should be mentioned to your doctor if you suffer from any of them:

  • kidney disease
  • dehydration
  • nervous system problems

If you are being treated for genital herpes, it is extremely important to remember that Acyclovir will not prevent you from transmitting herpes to other people. Genital herpes virus can be spread readily through any form of sexual contact and activity, even if you are not exhibiting any symptoms.

The infection is much more likely to be spread if there are any sores or blisters present. It is therefore advisable to avoid any form of sexual activity if either you or your partner are displaying any symptoms of genital herpes. Wait until any sores have healed completely and the scabs have dropped off, before resuming sexual activity. Always use a latex condom during sexual contact to help prevent the spread of the herpes virus. It is worth noting that spermicide creams or jellies, or diaphragms will not prevent infection. If you know that you or your partner carry the genital herpes virus, it is best to avoid oral sex.


Always keep your medication in a sealed, airtight container and at room temperature. Do not freeze the medication, expose it to direct sunlight or to sources of extreme heat. Keep the medication away from children and pets. In the event that a pet consumes Acyclovir, always seek veterinary advice immediately.

Do not keep any leftover medication and do not use any drugs that have become out-of-date. Do not flush unwanted medication down the toilet or throw it out with your trash, as this could present a danger to small children. Always ask your doctor or pharmacist for advice on the safe disposal of unwanted or unused medication.


Acyclovir is a highly effective antiviral drug that is used in the treatment of chickenpox, shingles, and herpes virus. Although Acyclovir cannot cure the herpes virus, it is extremely effective at controlling it and managing its symptoms.

The medication can cause dehydration so patients with a history of kidney or liver problems should mention this to their doctor. It is also important that you drink plenty of water during the course of your treatment with Acyclovir. In addition, there are a number of drugs and medical conditions that can interact adversely with Acyclovir. For this reason you must be sure to mention any medical conditions that you have and the drugs that you are taking to treat them, including non-prescription herbal products.

Acyclovir can greatly ease the symptoms of ongoing conditions such as genital herpes virus, but it is important that patients work closely with their medical practitioner in order to manage this condition and prevent it from spreading to others.

Last Reviewed:
December 10, 2017
Last Updated:
April 04, 2018