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Entecavir for hepatitis B


Entecavir is an antiviral medicine. You have been prescribed it for chronic hepatitis B infection.

It is important to take entecavir regularly every day, preferably at the same time each day.

Common side-effects are feeling sick (nausea), feeling dizzy, diarrhoea, and headache.

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About entecavir

Type of medicine

An antiviral medicine

Used for

Chronic hepatitis B infection

Also called


Available as

Tablets and oral liquid medicine

Hepatitis means inflammation of the liver. Some viruses can cause hepatitis. Hepatitis B is a virus which is carried in your bloodstream to your liver, where it can cause inflammation and damage. Following infection with hepatitis B, a few people develop a persistent infection called chronic hepatitis B.

People with chronic hepatitis B usually need treatment to stop or to reduce the activity of the virus. This limits damage to the liver, which is a complication of the infection. One of the types of treatment currently given is an antiviral medicine. Antiviral medicines like entecavir work by stopping the hepatitis B virus from multiplying (replicating); this reduces the amount of the virus in your body.

A doctor who is a liver specialist will usually start the treatment for you. Treatment for chronic hepatitis B usually continues for several years, but can be lifelong.

Before taking entecavir

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking entecavir it is important that your doctor knows:

  • If you are pregnant, trying for a baby, or breastfeeding.

  • If you have a problem with the way your kidneys work.

  • If you know you are also infected with human immunodeficiency virus (HIV).

  • If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

  • If you have ever had an allergic reaction to a medicine.

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How to take entecavir

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside your pack. It will give you more information about entecavir, and it will also provide you with a full list of the side-effects which you could experience from taking it.

  • Take entecavir exactly as your doctor tells you to. If you have been given tablets to take, the usual dose is one tablet daily. Your dose will be printed on the label of the pack to remind you about what the doctor said. There are two strengths of tablet available (0.5 mg and 1 mg), so each time you collect a fresh supply, check to make sure you have been given the same strength of tablet as before. If you (or your child) have been prescribed the oral liquid medicine, your doctor will tell you how much should be taken, and how to measure out the dose using the measuring spoon provided in the pack.

  • Try to take your doses at the same time of day each day, as this will help you to remember to take entecavir regularly.

  • Carefully follow any directions you are given with regard to taking entecavir with or without food. Some people must take entecavir when their stomach is empty, which means taking it two hours before eating any food, or waiting until two hours after eating. This is because less entecavir is absorbed when taken with food, which means the medicine will be less effective.

  • If you forget to take a dose at your usual time, take it as soon as you remember. However, if you do not remember until the following day, leave out the missed dose. Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Keep your regular appointments with your doctor so that your progress can be monitored. You are likely to need regular blood tests to check how well the medicine is working for you, and also to see how well your liver is working.

  • It is important that you continue to take entecavir regularly. Treatment for hepatitis B can be long-term. Continue to take it until you are advised otherwise, even if you feel well.

  • Treatment with entecavir does not stop you from passing the infection on to others through sexual contact, sharing needles to inject drugs, or from mother to baby. A vaccine is available which protects against hepatitis B and can be offered to your sexual and household contacts who are at risk of being infected. Do not have sex with anyone (especially any sex without using a condom) until they have been fully immunised and have had their blood checked to see that the immunisation has worked.

  • Most people with chronic hepatitis B will be advised to eat a normal healthy balanced diet. However, it is likely you will be advised not to drink alcohol. Alcohol will increase the risk and speed of you developing liver damage.

  • Medicines similar to entecavir have been associated with a serious side-effect in a few people. This is known as lactic acidosis. It is a problem where there is too much lactic acid in the blood. The symptoms associated with it are listed in the next section 'Can entecavir cause problems?'. Although this has occurred in only a very few people, you must let your doctor know straightaway if you develop the symptoms listed below.

  • You must avoid getting pregnant while you are taking entecavir. Make sure you have discussed with your doctor which types of contraception are suitable for you.

  • If you buy any medicines or remedies 'over the counter', check with a pharmacist that they are suitable to take with entecavir and your other medicines.

  • If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

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Can entecavir cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the more common ones associated with entecavir. The best place to find a full list of the side-effects which can be associated with your medicine, is from the manufacturer's printed information leaflet supplied with the medicine. Alternatively, you can find an example of a manufacturer's information leaflet in the reference section below. Speak with your doctor or pharmacist if you develop any side-effects. This is because some of the common side-effects of entecavir are similar to the symptoms of lactic acidosis - a much less common but more serious problem.

Common entecavir side-effects (these affect fewer than 1 in 10 people)

What can I do if I experience this?

Feeling sick (nausea) or being sick (vomiting), indigestion

Stick to simple meals - avoid fatty or spicy food. If it continues, speak with your doctor


Drink plenty of water to replace lost fluids

Feeling dizzy, tired, or weak

Do not drive and do not use tools or machines while affected. If this continues, speak with your doctor


Drink plenty of water and ask a pharmacist to recommend a suitable painkiller. If the headaches continue, let your doctor know

Problems sleeping

If troublesome, speak with your doctor

Changes to some blood tests (more likely in children taking entecavir)

Your doctor will check for these

Your doctor will discuss with you the possibility of this medicine causing a problem called lactic acidosis. Let your doctor know straightaway if you develop the following symptoms:

  • Feeling sick (nausea) or being sick (vomiting), tummy pain, loss of appetite, loss of weight, feeling weak or dizzy, and fast or gasping breathing.

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

How to store entecavir

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article History

The information on this page is written and peer reviewed by qualified clinicians.

  • Next review due: 22 Oct 2025
  • 23 Oct 2022 | Latest version

    Last updated by

    Michael Stewart, MRPharmS

    Peer reviewed by

    Sid Dajani
  • 29 May 2013 | Originally published

    Authored by:

    Helen Allen
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