Entecavir is an antiviral medicine that is used to treat chronic hepatitis B virus (HBV) in adults and children who are at least 2 years old and weigh at least 22 pounds (10 kilograms).

Entecavir is not a cure for hepatitis. It is not known whether entecavir will prevent cirrhosis or liver cancer.

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

You should not take entecavir if you have HIV (human immunodeficiency virus) that is not being treated.

You may develop 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.

Hepatitis B may become active or get worse after you stop using entecavir. You may need frequent liver function tests for several months.

Entecavir comes as a tablet and solution (liquid) to take by mouth. It is usually taken once a day on an empty stomach, at least 2 hours after a meal and at least 2 hours before the next meal. Take entecavir at around the same time every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take entecavir exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

To use the entecavir oral solution, follow these steps:

1. Hold the spoon that came with your medication upright and slowly fill it with entecavir solution up to the mark that matches your dose.
2. Hold the spoon with the volume marks facing you and check to see that the top of the liquid is level with the mark that matches your dose.
3. Swallow the medication right from the measuring spoon. Do not mix the medication with water or any other liquid.
4. Rinse the spoon with water after each use, and allow it to air dry.
5. Put the spoon in a safe place where it will not get lost because you will need to use it every time you take your medication. If you do lose the dosing spoon, call your doctor or pharmacist.

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

Take entecavir on an empty stomach, at least 2 hours before or 2 hours after eating.

Measure liquid medicine carefully, using the dosing syringe with your medicine (not a kitchen spoon). Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you do not understand these instructions.

Entecavir doses are based on weight (especially in children and teenagers). Your dose needs may change if you gain or lose weight.

Use entecavir regularly to get the most benefit and to keep your condition from getting worse. Call your doctor if your hepatitis symptoms do not improve, or if they get worse.

Do not change your dose or dosing schedule without your doctor's advice. Every person with HBV should remain under the care of a doctor.

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

Keep the bottle of oral liquid in its original carton. Throw away any unused entecavir oral liquid after the expiration date on the label has passed.

Hepatitis B may become active or get worse in the months after you stop using entecavir. You may need frequent liver function tests while using entecavir and for several months after your last dose.

You should not take entecavir if you are allergic to it, or if you also have HIV (human immunodeficiency virus) that is not being treated.

You may need to be tested for HIV before you start taking entecavir. Taking medicine to treat chronic hepatitis B can cause HIV infection to become resistant to certain HIV and AIDS medications.

Tell your doctor if you have ever had:

• HIV or AIDS (or if you have been exposed to HIV);

• kidney disease;

• liver problems other than HBV;

• a liver transplant; or

• if you also take lamivudine (Epivir, Epzicom, Trizivir) or telbivudine (Tyzeka).

Tell your doctor about all medicines you have used to treat hepatitis B in the past. Entecavir may not be the right medication if you have used certain other medicines for HBV.

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

Tell your doctor if you are pregnant or breastfeeding.

If you are pregnant, your name may be listed on a pregnancy registry to track the effects of entecavir on the baby.

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.

Keep this medication in the container it came in, tightly closed, and out of reach of children and pets. Store it at room temperature and away from excess heat, light, and moisture (not in the bathroom medicine cabinet or near the kitchen sink).

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Unless your doctor tells you otherwise, continue your normal diet.

Using entecavir 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 HBV 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: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Some people using entecavir develop lactic acidosis, which can be fatal. Get emergency medical help if you have even mild symptoms such as:

• unusual muscle pain;

• feeling cold;

• trouble breathing;

• feeling dizzy, light-headed, tired, or very weak;

• stomach pain, vomiting; or

• fast or irregular heartbeats.

Entecavir may also cause severe liver symptoms. Call your doctor at once if you have: swelling around your midsection, nausea, stomach pain, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common side effects of entecavir may include:

• nausea;

• dizziness, tired feeling; or

• headache.

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 may affect entecavir, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.