Incidence of abacavir hypersensitivity reactions in EuroSIDA

Background: The aim of the study was to investigate the incidence of abacavir-related hypersensitivity reaction (HSR) and associated deaths in EuroSIDA HIV-1-infected patients. Methods: Poisson regression models were developed to compare incidence of abacavir discontinuation according to the line of therapy within which abacavir was received, geographical regions, calendar time and drug formulation (abacavir/lamivudine combination tablet versus abacavir as a single drug or abacavir/zidovudine/lamivudine combination). Results: Of 3,278 patients that started abacavir, 2,101 (64.1%) discontinued. Of these, 167 (5.1%) discontinued abacavir within 3 months due to HSR with an incidence of 22.1 (95% confidence interval [Cl] 18.7-25.4) per 100 person-years of follow-up. After adjustment for gender, prior AIDS, hepatitis C serostatus, baseline CD4(+) T-cell count, region and calendar time, HSR incidence was significantly higher in those starting abacavir in a first-line regimen compared with second-line (incidence rate ratio [IRR] 2.04 [95% Cl 1.24-3.38]; P=0.005). There was no significant difference between regions. HSR incidence from 2005 onwards was significantly lower compared with 1999-2000 (IRR 0.54 [95% Cl 0.32-0.92]; P=0.024). There was a lower observed incidence in patients starting abacavir/lamivudine compared with other formulations (IRR 0.33 [95% Cl 0.13-0.88]; P=0.027), however, available data were limited. Conclusions: Incidence of abacavir-related HSR is higher in patients starting abacavir in first-line therapy, which could indicate increased over-diagnosis. HSR incidence has decreased in recent years, which might reflect the wider availability of genetic screening and improved awareness of symptoms. There were no reported deaths due to abacavir HSR.