Retrospective Assessment of Possible Hypersensitivity Reactions to Abacavir

Abstract

Objective:

To document the frequency of abacavir hypersensitivity reactions in HIV-positive patients followed in a Veterans Affairs outpatient clinic.

Methods:

Abacavir's manufacturer lists the incidence of hypersensitivity as 5%. We conducted a retrospective review of all patients in our clinic who received abacavir from January 1999 to December 1999 to document the rate of discontinuation of the drug due to possible hypersensitivity reactions. The duration of abacavir therapy, concomitant antiretrovirals, most recent CD4+ count, most recent viral load, number of antiretroviral regimens previously tried, and the number and types of new antiretrovirals started concomitant with abacavir were collected.

Results:

Of 24 patients analyzed, nine (38%) discontinued abacavir, with six (25%) having a potential hypersensitivity reaction. Four reactions were classified as probable and two as possible according to the Naranjo scale. Only one patient was hospitalized for the reaction. Patients who discontinued abacavir due to a hypersensitivity reaction had similar CD4+ counts, viral loads, and had received a similar number of antiretroviral regimens compared with patients who continued the drug. However, 67% of patients who discontinued abacavir due to a hypersensitivity reaction had at least one previously documented adverse event that led to the discontinuation of another antiretroviral, compared with 7% of the patients who continued the drug (p = 0.02).

Conclusions:

The frequency of possible hypersensitivity reactions to abacavir in patients seen in our HIV clinic is higher than the manufacturer's reported rate of 5%. These patients may be more prone to adverse reactions based on previous medication history and adverse events.