HLA-B*57:01 and abacavir: preventing a serious HIV-medicine reaction

Many pharmacogenetic stories involve enzymes that speed up or slow down a medicine. The abacavir story is different. HLA genes belong to the immune system. MedlinePlus Genetics explains that the HLA-B gene produces a protein that displays small pieces of other proteins on the surface of cells so that immune cells can recognise invaders.

For people with the HLA-B*57:01 version, abacavir appears to alter what is displayed in a way that provokes an unwanted immune response. The reaction is therefore not about too much drug in the blood but about the way the immune system sees the drug, which is why simply lowering the dose is not a safe workaround.

MedlinePlus Genetics describes the adverse reaction in HIV patients taking abacavir as involving fever, rash and gastrointestinal symptoms. These features can look like a viral illness, which is part of why a test before the first dose is so valuable: it removes the guesswork.

Any new fever, rash, vomiting or breathlessness after starting an HIV medicine should be reported to the HIV clinic promptly, and sudden breathing difficulty, facial swelling or collapse needs 999. Do not simply stop an antiretroviral medicine on your own without speaking to the clinic, unless you are advised to in an emergency, since gaps in HIV treatment carry their own risks.

The FDA states that abacavir should not be used in patients positive for HLA-B*57:01. In practice the test is done once, before abacavir is prescribed, because the gene variant is inherited and does not change over a lifetime. A negative result means the strongest predictor of this reaction is absent, and a positive result means abacavir is avoided and other antiretrovirals are chosen instead.

The NHS describes HIV treatment as daily tablets from specialist clinics, with the goal of an undetectable viral load, typically reached after around six months. The NHS pages retrieved do not describe the abacavir test itself, so ask your HIV team how it is handled locally and whether your result is documented in your records.

• The test is done before treatment, not after a reaction begins.

• The result stays valid for life because it reflects inherited DNA.

• A positive result is recorded as an allergy-type warning in your health record.

A positive HLA-B*57:01 result does not affect your health in daily life. It only means one medicine should be avoided. Many other effective antiretroviral options exist, and the specialist team can choose between them.

It is sensible to mention the result to any new prescriber or pharmacist, and to keep it in a personal note. Because the gene is inherited, blood relatives may share it, but there is no need for relatives to be tested unless they are going to be prescribed abacavir.

The NHS describes HIV care as delivered through specialist clinics, with monitoring of viral load, adjustment of treatment where needed and counselling and peer support. Charities such as the Terrence Higgins Trust are named as sources of help. Getting tests and medicines right at the start is part of that clinic-led approach.

People who are newly diagnosed can find the wider picture in the HIV condition guide on this site.

HLA-B*57:01 is the best-known pairing, but not the only one. MedlinePlus Genetics also describes HLA-B*15:02 with carbamazepine, linked to Stevens-Johnson syndrome and toxic epidermal necrolysis, and HLA-B*58:01 with allopurinol. A separate guide covers the carbamazepine link.

The pattern is consistent: for immune-mediated reactions, the test is used to avoid a medicine rather than to adjust a dose.