Epivir is an antiviral medicine that prevents human immunodeficiency virus (HIV) or hepatitis B virus from multiplying in your body.

Epivir is for treating HIV in adults and children at least 3 months old. HIV is the virus that can cause acquired immunodeficiency syndrome (AIDS). Lamivudine is not a cure for HIV or AIDS.

Epivir-HBV is for treating hepatitis B in adults and children at least 2 years old. It should not be used in people who are infected with both hepatitis B and HIV.

You should not take Epivir-HBV (for treating hepatitis B) if you also take other medicine that contains lamivudine or emtricitabine. This includes Atripla, Combivir, Complera, Emtriva, Epzicom, Stribild, Trizivir, and Truvada.

Epivir may cause a serious condition called lactic acidosis, a dangerous build-up of lactic acid in your blood. Call your doctor or get emergency medical help if you have unusual muscle pain, trouble breathing, stomach pain, dizziness, feeling cold, or feeling very weak or tired.

Epivir can also cause severe or life-threatening effects on your liver or pancreas. Call your doctor at once if you have: severe pain in your upper stomach spreading to your back, nausea, loss of appetite, dark urine, clay-colored stools, or jaundice (yellowing of the skin or eyes).

If you've ever had hepatitis B, it may become active or get worse after you stop using Epivir. You may need frequent liver function tests for several months.

The hepatitis B virus may become resistant to treatment while you are taking Epivir-HBV. Resistant hepatitis B can lead to worsening liver disease or death. Tell your doctor if you have new hepatitis symptoms.

Take Epivir exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed. You should not take Epivir (for treating HIV) together with Epivir-HBV (for treating hepatitis B).

You may take this medicine with or without food.

Lamivudine doses are based on weight in children. Your child's dose needs may change if the child gains or loses weight. Children who weigh more than 30 pounds (14 kilograms) should use the tablet form if possible. The liquid form may not be as effective.

You may need to break a tablet in half when giving this medicine to a child for HIV. Call your doctor if the child has any trouble swallowing the tablet.

Measure liquid medicine carefully. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

The Epivir brand contains a higher dose of lamivudine than Epivir-HBV brand. Epivir is for treating HIV and Epivir-HBV is for treating hepatitis B. Each time you get a refill of this medication, be sure you have received the correct brand to treat your condition.

You will need frequent medical tests, including frequent HIV testing. If you become infected with HIV while you are taking lamivudine to treat hepatitis B, the HIV could become resistant to antiviral medicines if not treated right away.

The hepatitis B virus can mutate while you are taking Epivir-HBV and may become resistant to treatment. Resistant hepatitis B can lead to worsening liver disease or death. Tell your doctor if you have new or worsening hepatitis symptoms.

Use all HIV medications as directed and read all medication guides you receive. Do not change your dose or dosing schedule without your doctor's advice. Every person with HIV should remain under the care of a doctor.

Store at room temperature away from moisture and heat. Keep the bottle tightly closed when not in use.

If you've ever had hepatitis B, this virus may become active or get worse in the months after you stop using Epivir. You may need frequent liver function tests while using this medicine and for several months after your last dose.

You should not take Epivir if you are allergic to lamivudine.

You should not take Epivir-HBV (for treating hepatitis B) if you also take other medicine that contains lamivudine or emtricitabine, which includes Atripla, Biktarvy, Cimduo, Combivir, Complera, Descovy, Emtriva, Epzicom, Genvoya, Odefsey, Stribild, Symfi, Triumeq, Trizivir, and Truvada.

Tell your doctor if you have ever had:

• liver disease (especially hepatitis B or C, or a liver transplant);

• pancreatitis;

• kidney disease; or

• diabetes (liquid lamivudine contains 3 to 4 grams of sucrose per dose).

You may develop lactic acidosis, a dangerous build-up of lactic acid in your blood. This may be more likely if you have other medical conditions, if you've taken HIV medication for a long time, or if you are a woman. Ask your doctor about your risk.

Tell your doctor if you are pregnant, and use your medications properly to control your infection. HIV can be passed to your baby if the virus is not controlled during pregnancy. Your name may be listed on a registry to track any effects of antiviral medicine on the baby.

You should not breast-feed while you are using lamivudine to treat hepatitis B. Women with HIV or AIDS should not breast feed a baby. Even if your baby is born without HIV, the virus may be passed to the baby in your breast milk.

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

Get your prescription refilled before you run out of medicine completely.

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

Avoid taking other medications that contain an ingredient called sorbitol, often used as a sweetener in liquid medicines. Ask your pharmacist if you are not sure a medicine contains this ingredient.

Using lamivudine will not prevent your disease from spreading. Do not have unprotected sex or share razors or toothbrushes. Talk with your doctor about safe ways to prevent HIV transmission during sex. Sharing drug or medicine needles is never safe, even for a healthy person.

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

Mild symptoms of lactic acidosis may worsen over time, and this condition can be fatal. Get emergency medical help if you have: unusual muscle pain, trouble breathing, stomach pain, vomiting, irregular heart rate, dizziness, feeling cold, or feeling very weak or tired.

Call your doctor at once if you have:

• pancreas problems - severe pain in your upper stomach spreading to your back, nausea and vomiting, fast heart rate; or

• liver problems - swelling around your midsection, right-sided upper stomach pain, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Lamivudine affects your immune system, which may cause certain side effects (even weeks or months after you've taken this medicine). Tell your doctor if you have:

• signs of a new infection - fever, night sweats, swollen glands, cold sores, cough, wheezing, diarrhea, weight loss;

• trouble speaking or swallowing, problems with balance or eye movement, weakness or prickly feeling; or

• swelling in your neck or throat (enlarged thyroid), menstrual changes, impotence.

Common Epivir side effects may include:

• nausea, diarrhea;

• headache;

• fever, tiredness, general ill feeling;

• ear infection - ear pain or full feeling, trouble hearing, drainage from the ear, fussiness in a child; or

• nose or throat infection - stuffy nose, sneezing, sore throat, cough.

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.

Other drugs can interact with lamivudine, and some drugs should not be used at the same time. Tell your doctor about all your current medicines and any medicine you start or stop using. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here.