Abacavir hypersensitivity: quick facts and what to do

Abacavir hypersensitivity is a potentially serious reaction to the HIV drug abacavir. It usually starts within the first 6 weeks of treatment and can affect several body systems at once. Knowing the signs and acting fast can prevent a life-threatening problem.

How to recognize abacavir hypersensitivity

Symptoms often come on together, not one by one. Look for fever plus at least one of these: rash, nausea or vomiting, diarrhea, abdominal pain, sore throat, cough, shortness of breath, or joint aches. People can feel very tired or just "off." The rash can be mild or widespread. If multiple symptoms appear within weeks of starting abacavir, treat it as an emergency until a clinician says otherwise.

Most cases happen in the first 2 to 6 weeks. That timing matters: if symptoms begin after months on abacavir, other causes are more likely, but don't ignore them. Also know that a previous mild reaction can get much worse with continued abacavir use.

Testing, prevention, and what to do if it happens

Before starting abacavir, doctors should test for HLA-B*5701. This simple blood test finds a genetic marker strongly linked to hypersensitivity. If the test is positive, abacavir should be avoided. If it's negative, the risk is much lower but not zero. You still need to watch for symptoms.

If you suspect hypersensitivity, stop abacavir immediately and seek medical care. Do not restart abacavir later—even if symptoms improve—unless a specialist rules it out. Re-challenge can cause a faster, more severe reaction. Tell every healthcare provider and note it in your medical records and medication lists.

If HLA-B*5701 testing wasn’t done before treatment, get tested now and share the result with your provider. If the test is positive, switch to a different HIV regimen that doesn’t contain abacavir. Common alternatives include tenofovir-based options, but your clinician will pick the best substitute based on your history and resistance testing.

Report suspected reactions to your clinic or national adverse event system. Ask your provider about wearing a medical alert or carrying a note that you cannot take abacavir. That helps in emergencies where you can’t speak for yourself.

Short, practical takeaways: get HLA-B*5701 tested before starting abacavir, watch for multi-system symptoms in the first weeks, stop abacavir at the first sign of hypersensitivity, and never restart without specialist advice. Talk to your HIV care team if you have questions—this is a manageable risk when you know how to handle it.