What is abacavir?

Abacavir is a medication used to treat HIV. It is marketed under the brand name Ziagen, but generic versions are also available. It is taken in combination with other antiretroviral drugs.

The usual adult dose of abacavir is 600mg per day. You could take two 300mg tablets once a day, or one 300mg tablet twice a day.

Abacavir is also available in combination tablets. Several companies make a pill which contains abacavir and another drug, lamivudine, in one pill. It is also available in a combination pill with lamivudine and dolutegravir, marketed as Triumeq.

How does abacavir work?

Abacavir is from a class of drugs known as nucleoside reverse transcriptase inhibitors (NRTIs). Your doctor will prescribe abacavir as part of your HIV treatment, along with antiretrovirals from another class of drugs. It is important to take all the drugs as prescribed, every day. Each drug class works against HIV in a different way.

The aim of HIV treatment is to reduce the level of HIV in your body (viral load). Ideally, your viral load should become so low that it is undetectable – usually less than 50 copies of virus per ml of blood. Taking HIV treatment and having an undetectable viral load protects your immune system and stops HIV being passed on to someone else during sex.

How do I take abacavir?

You can take abacavir with or without food.

You can take the tablets with some water, or if you have difficulty swallowing them, you can crush them and take them with food or water. It’s very important to take the whole dose, so if you do crush a tablet, make sure you take all of it.

HIV treatment works best if you take it every day. When would be a good time for you to plan to take your treatment? Think about your daily routine and when you will find it easiest to take your treatment.

If you forget to take a dose of abacavir, take it as soon as you remember. If it has been more than 12 hours since your dose was due, then don’t take a double dose, just skip the dose you’ve forgotten and carry on.

If you regularly forget to take your treatment, or you aren’t taking it for another reason, it’s important to talk to your doctor about this.

Allergic reaction

Abacavir can cause a serious hypersensitivity (allergic) reaction in some people. This is associated with the presence of a particular gene. Before starting treatment with abacavir (or any treatment that contains abacavir) you should have a test to see if you have this gene (HLA-B*5701). If the test is positive you must not take abacavir. If the test is negative, it is highly unlikely that an allergic reaction will occur, but contact your HIV clinic immediately (or A&E if out of hours) if you begin to feel unwell after starting the drug.

In the box with the drug there is an ‘alert card’, which you should carry with you for the first six weeks of taking abacavir. The particular side effects you should look out for during this time are:

  • a skin rash

or if you get one or more symptoms from at least two of the following groups:

  • fever
  • shortness of breath, sore throat or cough
  • nausea or vomiting, or diarrhoea or abdominal pain
  • severe tiredness or achiness or generally feeling ill.

You should never retry abacavir, if you have had an allergic reaction to it previously.

What are the other possible side effects of abacavir?

All drugs have possible side effects. It’s a good idea to talk to your doctor about possible side effects before you start taking a drug. If you experience something that might be a side effect, talk to your doctor about what can be done. A full list of side effects, including less common side effects, should be included in the leaflet that comes in the packaging with abacavir. As well as the information on side effects below, it’s important to understand the potential for a hypersensitivity reaction (see previous section). If you have any questions about this, talk to your doctor or pharmacist.

We generally divide side effects into two types:

Common – a side effect that occurs in at least one in a hundred people (more than 1%) who take this drug.

Rare – a side effect that occurs in fewer than one in a hundred people (less than 1%) who take this drug.

The most common side effects of abacavir are hypersensitivity (allergic) reaction (see previous section), feeling sick, headache, being sick, diarrhoea, loss of appetite, tiredness, lack of energy, fever (high temperature).

Does abacavir interact with other drugs?

You should always tell your doctor and pharmacist about any other drugs or medication you are taking. That includes anything prescribed by another doctor, medicines you have bought from a high-street chemist, herbal and alternative treatments, and recreational or party drugs (‘chems’).


antiretroviral (ARV)

A substance that acts against retroviruses such as HIV. There are several classes of antiretrovirals, which are defined by what step of viral replication they target: nucleoside reverse transcriptase inhibitors; non-nucleoside reverse transcriptase inhibitors; protease inhibitors; entry inhibitors; integrase (strand transfer) inhibitors.

viral load

Measurement of the amount of virus in a blood sample, reported as number of HIV RNA copies per milliliter of blood plasma. Viral load is an important indicator of HIV progression and of how well treatment is working. 


undetectable viral load

A level of viral load that is too low to be picked up by the particular viral load test being used or below an agreed threshold (such as 50 copies/ml or 200 copies/ml). An undetectable viral load is the first goal of antiretroviral therapy.


Any perceptible, subjective change in the body or its functions that signals the presence of a disease or condition, as reported by the patient.



An allergic reaction.

Some medicines or drugs are not safe if taken together – the interaction could cause increased, dangerous levels, or it could stop one or both of the drugs from working. Other drug interactions are less dangerous but still need to be taken seriously. If levels of one drug are affected, you may need to change the dose you take. This must only be done on the advice of your HIV doctor.

A list of drugs, known to have interactions with abacavir, should be included in the leaflet that comes in the packaging with abacavir. Tell your doctor if you are taking any of these drugs, and other drugs that are not on the list.

If you are taking phenytoin (used to treat epilepsy), your doctor may need to monitor you while you are taking abacavir. If you are taking methadone (used as a heroin substitute), it’s important your doctor is aware of this, as your dose may need to be changed.

Can I take abacavir in pregnancy?

If you are considering having a baby, or think you might be pregnant, talk to your doctor as soon as possible about which combination of anti-HIV medications would be right for you. It is important to take antiretroviral treatment during pregnancy to prevent passing HIV from mother to baby.

Abacavir’s manufacturer does not recommend using the drug during pregnancy. 

However, many women have taken abacavir while pregnant without any problems. The British HIV Association (BHIVA) recommends that women who are already taking anti-HIV medications and become pregnant can usually continue to take the same medication throughout their pregnancy. In addition, BHIVA lists abacavir (in combination with other medications) as an option that may be recommended for women who start HIV treatment in pregnancy, depending on their individual circumstances.

Can children take abacavir?

Abacavir can be taken by children weighing 14kg or more. Tablets will be split for children weighing 14-20kg. A liquid formulation of Ziagen is also available for children and people who have swallowing difficulties.

Talking to your doctor

If you have any concerns about your treatment or other aspects of your health, it’s important to talk to your doctor about them.

For example, if you have a symptom or side effect or if you are having problems taking your treatment every day, it’s important that your doctor knows about this. If you are taking any other medication or recreational drugs, or if you have another medical condition, this is also important for your doctor to know about.

Building a relationship with a doctor may take time. You may feel very comfortable talking to your doctor, but some people find it more difficult, particularly when talking about sex, mental health, or symptoms they find embarrassing. It’s also easy to forget things you wanted to talk about.

Preparing for an appointment can be very helpful. Take some time to think about what you are going to say. You might find it helpful to talk to someone else first, or to make some notes and bring them to your appointment. 

For detailed information on this drug, visit the abacavir page in the A-Z of antiretroviral medications.

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