Abacavir is an NRTI used as part of combination HIV treatment. It is distinctive because a simple genetic test is carried out before it is prescribed. This guide explains what abacavir is, how it works, why that safety test matters, and the points a treating doctor keeps under review.
The testing requirement is one of the clearest examples of personalised prescribing in HIV care, and it exists to prevent a specific reaction in a small group of people.
| Important note This article is general information about medicines used in HIV care. It does not include dosing instructions and is not a substitute for medical advice. All HIV medicines are prescription-only and are selected, started, and changed by a qualified doctor. |
Quick Summary / Key Takeaways
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Abacavir is an NRTI used as part of HIV combination treatment. It is well established and appears in several fixed-dose combinations, including those widely used in practice. What makes abacavir distinctive within the NRTI class is the safety test carried out before starting. This guide explains what abacavir is, why the genetic test matters, what side effects can occur, and the safety points a treating doctor keeps in mind.
Abacavir, abbreviated to ABC, is a nucleoside reverse transcriptase inhibitor. Like other NRTIs, it blocks the reverse transcriptase enzyme HIV needs to copy its genetic material inside human cells. Without that step, the virus cannot replicate. The NRTI class as a whole forms the backbone of most HIV regimens, as described in the HIV medicine name list.
Abacavir carries a well-documented risk of a serious hypersensitivity reaction in people who carry a specific genetic variant called HLA-B*57:01. This reaction can be severe if the medicine is started in someone who carries the variant. For this reason, a genetic test is carried out before treatment begins:
| Hypersensitivity warning If abacavir is started and a person develops symptoms such as fever, rash, nausea, or breathing difficulty, they should contact their doctor immediately. Abacavir must not be restarted in someone who has had a hypersensitivity reaction. |
Abacavir is used in combination, not on its own. It is most commonly paired with lamivudine, often in a fixed-dose combination tablet. This pairing forms the NRTI backbone of a regimen, to which an anchor medicine such as an integrase inhibitor is added. More on how regimens are built appears in first-line ART regimens explained.
Apart from the hypersensitivity reaction in carriers of the gene variant, abacavir is generally well tolerated in people who have tested negative. Early effects that may occur include:
| Feature | Abacavir (ABC) | Tenofovir (TDF/TAF) |
|---|---|---|
| Class | NRTI | NRTI |
| Genetic test needed | Yes, HLA-B*57:01 | No |
| Kidney considerations | Not the primary concern | Kidney function monitored routinely |
| Common pairing | Lamivudine | Lamivudine or emtricitabine |
| Place in regimens | NRTI backbone option | NRTI backbone, most common globally |
| Myth | Fact |
|---|---|
| Everyone reacts badly to abacavir. | Only people who carry the HLA-B*57:01 variant are at risk. Most people do not carry it. |
| The genetic test is optional. | It is carried out routinely before abacavir is prescribed. |
| Mild early effects mean a hypersensitivity reaction is starting. | Mild early effects differ from a full hypersensitivity reaction; a doctor advises on the difference. |
| Abacavir can be restarted after a hypersensitivity reaction. | It must never be restarted in someone who has had a confirmed reaction. |
| It is taken alone. | It is used in combination as part of a full regimen. |
| When to Consult a Doctor Medical advice is appropriate before starting abacavir, if any early symptoms such as fever, rash, or breathing difficulty appear in the first weeks of treatment, and where other medicines are being taken. A consultation is available through an HIV doctor consultation. |
Abacavir is an effective NRTI backbone option in HIV treatment, used in combination with other medicines. What sets it apart is the genetic test carried out beforehand: people who test positive for HLA-B*57:01 do not receive it, while those who test negative can use it safely. As with all ART, it is prescribed and monitored by a treating doctor.
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Abacavir (ABC) is an NRTI used as part of HIV combination treatment. It blocks the reverse transcriptase enzyme HIV needs to copy its genetic material, preventing the virus from replicating inside human cells.
A small number of people carry a genetic variant called HLA-B*57:01 that causes a serious hypersensitivity reaction to abacavir. The test identifies who carries this variant so the medicine is only given to those who do not.
They are not given abacavir. An alternative NRTI backbone option is chosen instead.
In people who have tested negative for the gene variant, abacavir is generally well tolerated. Early effects may include nausea, headache, tiredness, and sleep disturbance.
Signs can include fever, rash, nausea, vomiting, diarrhoea, stomach pain, or breathing difficulty, appearing in the first weeks of treatment. Anyone noticing these should contact their doctor immediately.
No. It must never be restarted in someone who has had a confirmed hypersensitivity reaction, as the reaction can be more severe on rechallenge.
It is used in combination, most commonly paired with lamivudine in a fixed-dose tablet, to which an anchor medicine such as an integrase inhibitor is added.
Both are NRTIs and work in the same broad way, but abacavir requires the HLA-B*57:01 test beforehand, while tenofovir does not. Tenofovir is the more widely used backbone globally, while abacavir is an option for those for whom tenofovir is less suitable.
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