Macrocytosis as an indicator of medication (zidovudine) adherence in patients with HIV infection.

This retrospective chart review was conducted in an outpatient human immunodeficiency virus (HIV) clinic to determine if macrocytosis can be used as a clinical indicator of zidovudine adherence in HIV-infected outpatients. This study included 71 HIV-positive patients who were taking zidovudine and 93 HIV-positive controls who were not taking zidovudine, for 8 weeks or longer. One control and 16 subjects were excluded secondary to insufficient laboratory data or preexistence of other macrocytosis-inducing etiologies. The incidence of macrocytosis (mean corpuscular volume [MCV] >/= 100 fL) was significantly different among subjects and controls: 78% versus 32.6% (p < 0.001), respectively. Adherence (determined by documentation from a physician/pharmacist) was assessed among subjects for whom zidovudine was prescribed, comparing those with and without macrocytosis. Adherence was observed in 77% and 18% of the macrocytosis-positive and macrocytosis-negative subjects, respectively (p < 0.001). Macrocytosis was also observed in patients receiving stavudine (another thymidine analogue, in the class of nucleoside reverse transcriptase inhibitors). Twenty-seven of the 41 patients for whom stavudine was prescribed developed macrocytosis (65.8%). These results indicate that macrocytosis may be useful in assessing adherence to zidovudine-containing antiretroviral regimens and may also have a role in assessing stavudine adherence.