HLA-B*57:01 Screening for Abacavir Hypersensitivity

Abacavir is a drug used to treat HIV infection, similar to zidovudine (AZT) and lamivudine (3TC). Abacavir is available as a single drug (Ziagen) or in single-pill combinations with lamivudine (Kivexa) or zidovudine and lamivudine (Trizivir).

What is abacavir hypersensitivity?

Most patients can safely take abacavir; however, a small number of patients experience a severe side effect known as abacavir hypersensitivity. The most common symptoms are skin rash, fever, nausea, vomiting and diarrhea. About 5% of patients who take abacavir experience abacavir hypersensitivity. This reaction can sometimes be very serious and in some cases can cause death.

Who is at risk for abacavir hypersensitivity?

Scientists have discovered that people who have a specific gene called HLA-B*57:01 are much more likely to have this reaction than patients who do not. Therefore, patients with the HLA-B*57:01 gene should not take abacavir. Approximately 5-8% of Europeans, 1-2% of Asians, and 2% of Africans have this gene.

How does screening work?

A test called HLA-B*57:01 Screening can be ordered before the start of therapy containing abacavir. The test requires drawing a single tube of blood which will be sent to the BC Centre for Excellence in HIV/AIDS laboratory for analysis. The laboratory extracts genetic material from the patient’s blood and uses sequencing technology to identify whether the patient has the HLA-B*57:01 gene.

In contrast to other HIV laboratory tests such as viral load and CD4 count which can change over time, a person’s HLA-B*57:01 result does not change. This test needs to be done only once.

What do the test results mean?

A positive test result means that a patient has the HLA-B*57:01 gene and therefore is at higher risk of a hypersensitivity reaction. Usually this patient should not take abacavir. A negative test result means that a patient does not have the HLA-B*57:01 gene.

Having a negative test result does not guarantee that abacavir hypersensitivity will not develop. It only means that the patient is at low risk. Patients should let their doctors know immediately if they develop a rash, fever or have any of the above symptoms when taking abacavir.