Thursday, July 24, 2008
The New York Times reports that the FDA is urging doctors to use a genetic test to screen patients before prescribing the drug abacavir, which is widely used for HIV infections and AIDS. Andrew Pollack writes,
Seeking to prevent life-threatening side effects, the Food and Drug Administration is urging doctors to use a genetic test to screen patients before prescribing a drug widely used for H.I.V. infection and AIDS.
In an advisory it is expected to issue Thursday, the agency says that patients with a particular variation in an immune system gene should not be given the drug abacavir because they are at a far higher risk of a severe allergic reaction to the drug.
Abacavir, developed by GlaxoSmithKline, is sold under the name Ziagen. It is also a component of two combination pills — Trizivir and Epzicom.
The recommendation for the test is part of a movement toward so-called personalized medicine, in which genetic or other tests are used to determine which drugs are best for a patient and which should be avoided.
The labels of several other drugs, like the blood thinner warfarin and the cancer drug irinotecan, also recommend tests aimed at avoiding side effects or helping to adjust the dose.
F.D.A. officials said they believed that the genetic test, which is already available from some laboratories, would be quickly adopted for screening patients before prescribing abacavir. In part that is because the test recommendation will be included in a black box warning, the strongest kind, on the drug’s label.
A small percentage of abacavir users suffer so-called hypersensitivity reactions, either when they start the drug or when they resume using it after some interval. Symptoms can include fever, rash, nausea and breathing difficulties.
The association between the variant in the immune system gene and risk of the reactions was first reported several years ago. But F.D.A. officials said a randomized clinical trial had since definitively proved the value of the genetic prescreening.
The study, published in The New England Journal of Medicine in February, found that prescreening reduced the incidence of suspected hypersensitivity reactions to 3.4 percent, from 7.8 percent. Based on that data it was estimated that 61 percent of people with the genetic variant — called HLA-B*5701 — would suffer a hypersensitivity reaction, in contrast to only 4 percent without the variant, according to new information on the drug’s label.
Drug companies often are reluctant to back tests that exclude patients from getting their drug. But GlaxoSmithKline sponsored and helped conduct the study published in February.
Because only about 5 percent of people have the genetic variant, excluding them from using abacavir does not shrink the market much. But it may reassure doctors that they can safely prescribe the drug for a vast majority of patients who do not have the variant.
The label for abacavir is also being changed to mention a study that found a correlation between taking the drug and elevated incidence of heart attacks. But the label also mentions that Glaxo then did its own review, pooling the results of numerous clinical trials, and found no elevated risk of heart attack.
The new label says that “in totality” the data are “inconclusive” on whether there is an elevated risk of heart attack, but that doctors should be cautious nonetheless.