The HLA-B*5701 test to predict who will have a hypersensitivity reaction (HSR) to abacavir (found in Ziagen, Epzicom and Trizivir) works equally well in black and white patients with HIV, according to a study published in the April 1 issue of Clinical Infectious Diseases. The results, reported by Michael Saag, MD, of the University of Alabama at Birmingham and his colleagues, refute concerns that the test may not predict the potentially life-threatening allergy to the nucleoside reverse transcriptase inhibitor as accurately in black patients as it does in whites.
Roughly five percent of people who take abacavir are likely to have an HSR, an allergic reaction to the drug that can cause fever, malaise, upset stomach, rash and difficulty breathing. This can be serious and generally requires that drugs containing abacavir be stopped immediately and never taken again.
Though the exact mechanism by which abacavir causes an HSR remains unknown, it has been observed that people with a genetic mutation known as HLA-B*5701 are more likely to have an HSR. Previous studies, however, have found that black patients were less likely than white patients to have both symptoms of an HSR and the genetic mutation, suggesting that testing would be less sensitive in this population.
Dr. Saag’s group enrolled 199 people living with HIV, 130 who identified as white and 69 who identified as black, into the Study of Hypersentivity to Abacavir and Pharmacogenetic Evaluation (SHAPE). SHAPE compared people who had a suspected HSR to abacavir, based on physical symptoms, with people who taken abacavir and had no symptoms. All patients were tested for the HLA-B*5701 mutation and wore skin patches with diluted amounts of abacavir to clinically confirm an HSR.
The study results indicate that one hundred percent of both black and white patients whose skin reacted to the abacavir patches carried the HLA-B*5701 mutation, meaning that if a person does not carry the gene, it is very unlikely for them to have an HSR. Some of the people who do carry the gene, however, don’t have HSR symptoms and others do not react to the skin patch. This was equally true for both black and white patients. This means that some people who carry the HLA-B*5701 mutation could possibly take abacavir safely. But, as there is no additional test to determine who these people are, the general recommendation is that anyone with the mutation should not take abacavir.
Though the SHAPE study results in black patients stand in contrast to earlier studies, the authors assert that the skin patch testing offers the most rigorous method for confirming an HSR and add the results are strong enough to allow physicians to be confident that the HLA-B*5701 test will accurately predict abacavir HSRs in both black and white patients.
