Patients at risk of suffering a potentially fatal reaction to a leading HIV drug could be identified by testing their genetic makeup, scientists suggest.

Approximately 5% of those given the antiretroviral drug abacavir suffer "hypersensitivity syndrome", which can kill in extreme cases.

A team of researchers from the Royal Perth Hospital, Australia, looked at the genes of 200 HIV patients given the drug.

In particular they looked at a set of genes known to have some role in immune response.

Of the 200, 18 developed hypersensitivity, and 167 were confirmed as being tolerant to the drug.

Patients with a certain genetic set-up were more than 100 times more likely to be hypersensitive to abacavir.

This arrangement of genes was found in 14 of the 18 who were hypersensitive, but only four of the 167 who were tolerant.

Safety check

This means that, in theory, doctors might be able to test in advance for patients who could react badly to the drug - and place them on another kind of anti-HIV medication.

Lead researcher Dr Simon Mallal, writing in the Lancet medical journal, said: "The findings have important clinical implications.

"In our population, withholding abacavir in patients with this haplotype would be expected to reduce the prevalence of this potentially life-threatening event from 9% to 2.5% without inappropriately denying the drug to any patients."

Vigilant doctors

However, he warned that four of the 18 who fell ill had none of the genetic signs found in the other patient, and that doctors would have to remain vigilant for HIV patients suffering unexpected reactions to their medication.

Another antiretroviral expert, Professor Amalio Telenti from the University Hospital, Lausanne, Switzerland, predicted that this particular test, costing $500 per patient, would mean that it would cost between $10,000 and $50,000 for every case of hypersensitivity prevented.

However, he said that there were a host of genetic markers which could reveal which drugs were most likely to succeed, and if these were tested at the same time, it could have a positive effect on patients.