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 will not cure herpes, but it can lessen the symptoms of the infection.

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

Use only as directed. Tell your doctor if you use other medicines or have other medical conditions or allergies.

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.

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 could make your virus 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.

Do not reuse a needle or syringe. Place them in a puncture-proof "sharps" container and dispose of it following state or local laws. Keep out of the reach of children and pets.

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.

Ask a doctor if it is safe to breastfeed while using acyclovir.

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.

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.

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.

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--swelling, urinating less, 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 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.