Background:  Recently zidovudine (AZT) therapy has been recognized as a risk factor for the development of lipoatrophy in HIV-infected patients. Tenofovir (TDF) and abacavir (ABC) are alternative nucleosides without this concern and available in convenient fixed-dose combination formulations. Historically the use of ABC has been less attractive because of its association with a hypersensitivity reaction. HLA-B*5701 is strongly associated with ABC hypersensitivity; by genotyping individuals before starting or changing therapy the incidence of this adverse event may be considerably reduced.

Methods:  A prospective study of B*5701 testing in patients starting or switching HAART. ABC was avoided in those testing positive for this allele and the safety of ABC use in those testing negative was assessed. Hypersensitivity reaction rates in the latter subjects were compared with the rate in those starting ABC prior to B*5701 testing. Rates were compared using Fisher’s exact test and 95% confidence intervals were calculated using Hanley’s rule of 3 approximation.

Results:  Of 114 patients tested, 16 (14%) were positive. Gender and ethnicity were as follows:  males = 93 (82%), females = 21 (18%); black = 23 (20%), white = 87 (76%), other ethnicity = 4 (4%). The carriage rate was 14 of 87 = 16% in whites and 2 of 23 = 9% in blacks. Of the total, 40 patients were naïve or re-starting therapy and 73 were considering switching (68 of the latter were on a thymidine analogue); 38 patients subsequently started ABC with an hypersensitivity reaction rate of 0 (95%CI 0 to 13%) compared with 14 of 320 = 4% hypersensitivity reaction rate prior to B*5701 testing. This comparison failed to reach significance at this point but as more B*5701 negative patients start ABC the confidence interval is expected to narrow considerably.

Conclusions:  This is one of the first studies to report on B*5701 carriage rate in a U.K.-based clinical cohort. The carriage rate is higher than reported in other studies. Incorporating this strategy into routine clinical practice is likely to lead to significant enhancements in patient safety.