Level 2: Mid-level evidence
Screening for the presence of the HLA-B*5701 allele before starting abacavir may prevent a hypersensitivity reaction, based on a trial of 1,956 patients aged 18-77 years with HIV infection and no previous exposure to abacavir (N Engl J Med. 2008;358:568-579). Participants were randomized to screening (abacavir prescription given only if negative) vs. abacavir prescription without screening. Among 980 patients in the screening group, 55 (5.6%) had positive HLA-B*5701 screening and were not given abacavir; 27 of 803 (3.4%) who took abacavir had a clinically diagnosed hypersensitivity reaction, but none had a positive reaction to abacavir on epicutaneous skin-prick test. Among 976 patients in the control group, 847 who were evaluated for clinically diagnosed hypersensitivity reaction had retrospective HLA-B*5701 screening: HLA-B*5701 screening was positive in 30 of 66 patients (45.5%) who had a clinically diagnosed hypersensitivity reaction and in all 23 (100%) who had an immunologically confirmed hypersensitivity reaction (skin-prick testing done if clinically diagnosed hypersensitivity reaction). HLA-B*5701 screening had a 47.9% positive predictive value (PPV) and 100% negative predictive value (NPV) for an immunologically confirmed hypersensitivity reaction, and a 61% PPV and 95.5% NPV for a clinically diagnosed hypersensitivity reaction.
Comparing screening vs. no screening in 1,650 patients (84.4%) evaluated, 3.4% vs. 7.8% had a clinically diagnosed hypersensitivity reaction (P<.001, NNT 23) and 0% vs. 2.7% had an immunologically confirmed hypersensitivity reaction (P<.001, NNT 37). Intention-to-treat analyses with range of 0-100% dropouts being counted as having hypersensitivity reactions were consistent and statistically significant.
Abacavir comes in preparations alone (Ziagen) and in combination with other HIV medications (Trizivir, Kivexa/Epzicom).