Generic name: acyclovir (injection) [ a-SYE-klo-veer ]
Brand name:  Zovirax
Dosage forms: intravenous powder for injection (1000 mg); intravenous solution (25 mg/mL; 50 mg/mL)
Drug class:  Purine nucleosides

What is acyclovir?

Acyclovir  is an antiviral drug. It slows the growth and spread of the herpes virus in the body.  Acyclovir  will not cure herpes, but it can lessen the symptoms of the infection.

Acyclovir  injection is used to treat severe infections caused by herpes viruses, including severe forms of genital herpes,  shingles , herpes  encephalitis  (swelling of the brain), and herpes infections in people with other diseases that weaken the immune system.

Acyclovir may also be used for other purposes not listed in this medication guide.


Follow all directions on your medicine label and package. Tell each of your healthcare providers about all your medical conditions,  allergies , and all medicines you use.

Before taking this medicine

You should not use this medication if you are allergic to acyclovir or  valacyclovir  ( Valtrex ).

Tell your doctor if you have ever had:

  • kidney disease (or if you are on dialysis);
  • liver disease ;
  • breathing problems; or
  • an electrolyte imbalance (such as high or low levels of calcium, sodium, or potassium in your blood).

Tell your doctor if you are pregnant. Herpes can be passed to your baby during childbirth if you have a genital lesion when your baby is born. If you have genital herpes, it is very important to prevent herpes lesions during pregnancy. Use your medicine as directed to best control your infection.

It may not be safe to breastfeed while using acyclovir. Ask your doctor about any risk.

How should I use acyclovir injection?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Treatment with acyclovir should be started as soon as possible after the first appearance of symptoms (such as tingling, burning, blisters).

Acyclovir is given as an infusion into a vein, usually once every 8 hours. A healthcare provider will give your first dose and may teach you how to properly use the medication by yourself.

This medicine must be given slowly, and the infusion can take at least 1 hour to complete.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you don’t understand all instructions.

Acyclovir must be mixed with a liquid (diluent) before using it. When using injections by yourself, be sure you understand how to properly mix and store the medicine. Prepare an injection only when you are ready to give it. Mixed medicine must be used within 24 hours.

Drink plenty of liquids while you are using acyclovir to keep your kidneys working properly.

You may need to use acyclovir injection for up to 21 days. Use this medicine for the full prescribed length of time, even if your symptoms quickly improve. Skipping doses may increase the risk of your virus becoming resistant to medication.

Lesions caused by herpes viruses should be kept as clean and dry as possible. Wearing loose clothing may help to prevent irritation of the lesions.

Store acyclovir injection at room temperature away from moisture and heat.

Use a needle and syringe only once and then place them in a puncture-proof “sharps” container. Follow state or local laws about how to dispose of this container. Keep it out of the reach of children and pets.

Detailed Acyclovir dosage information

What happens if I miss a dose?

Use the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not use two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include  agitation , seizure, decreased energy, or coma.

What should I avoid while using acyclovir injection?

Herpes infections are contagious and you can infect other people, even while you are being treated with acyclovir. Avoid letting infected areas come into contact with other people. Avoid touching an infected area and then touching your eyes. Wash your hands frequently to prevent passing the infection to others.

Using acyclovir will not prevent you from passing genital herpes to your sexual partner. Avoid sexual intercourse while you have active lesions or the first symptoms of an outbreak. Genital herpes may still be contagious through “viral shedding” from your skin, even if you have no symptoms.

Acyclovir injection side effects

Get emergency medical help if you have signs of an allergic reaction:  hives ; difficulty breathing; swelling of your face, lips, tongue, or throat.

Acyclovir may cause serious side effects. Call your doctor at once if you have:

  • confusion, agitation, hallucinations, feeling less alert than usual;
  • tremors, seizure;
  • blood in your urine;
  • kidney problems–little or no urination, swelling in your feet or ankles, feeling tired or short of breath; or
  • low blood cell counts–fever, chills, tiredness, mouth sores, skin sores, easy bruising, unusual bleeding, pale skin,  cold hands  and feet, feeling light-headed or short of breath.

Common side effects of acyclovir may include:

  • swelling or bruising around the IV needle;
  • nausea ,  vomiting , loss of appetite;
  • rash, itching, hives; or
  • low blood cell counts.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Acyclovir side effects  (more detail)

What other drugs will affect acyclovir injection?

Acyclovir can harm your kidneys, especially if you also use certain medicines for infections, cancer,  osteoporosis , organ transplant rejection, bowel disorders,  high blood pressure , or pain or arthritis (including  Advil ,  Motrin , and  Aleve ).

Tell your doctor about all your other medicines, especially:

  • probenecid .

This list is not complete. Other drugs may affect acyclovir, including prescription and over-the-counter medicines,  vitamins , and  herbal products . Not all possible drug interactions are listed here.

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