A person's genetic make-up may determine how well they respond to some anti-HIV drugs, a study suggests.
Abacavir has been available since 1998
Doctors in Australia studied 248 HIV patients who were taking the anti-retroviral drug Abacavir.
They found that 17 of the 18 people who were hypersensitive to the drug had similar variations in two key genes.
Writing in the Proceedings of National Academy of Sciences, they said genetic tests may identify those patients who are unlikely to do well on the drug.
Abacavir has been used in combination with other drugs to treat people with HIV since 1998.
Like all anti-retrovirals, it is a powerful drug. Studies have shown that some patients can become hypersensitive to it. They can suffer fever, rashes, upset stomachs or lethargy.
At the moment, there is little way of knowing which patients are likely to suffer these side-effects.
Dr Jacques Miller and colleagues at The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia, carried out DNA tests on all those involved in the study.
They found that most of those who were hypersensitive to Abacavir had variations in the genes HLA-B*5701 and Hsp70-Hom, which are near each other on chromosome 6.
This genetic combination was present in only one of the 230 patients who tolerated the drug well.
The researchers said their findings have an impact on HIV treatment.
"These findings have significant implications...in terms of the clinical management of Abacavir exposed HIV-infected patients," they said.
They said genetic testing could identify those patients most at risk of suffering side-effects and reduce the incidence of hypersensitivity to less than 1%.
GlaxoSmithKline, which manufactures Abacavir, said it was aware that genes could play a role in determining who benefits from the drug.
A spokeswoman said the company had carried out initial research in a small group of patients to identify possible genetic markers. She said further studies are planned.
"This exciting area of new research will hopefully produce results that will help healthcare professionals in the successful management of their patients with HIV infection," she said.