Objectives: The aim of the study was to evaluate the effect of lamivudine on the erythrocyte mean corpuscular volume. Methods: We conducted a retrospective evaluation of the mean corpuscular volume in patients prescribed lamivudine, and a comparison group of patients not taking lamivudine or other NRTIs known to affect the MCV, using electronic patient records from a single UK centre. Results: A total of 456 patients whilst on lamivudine were compared to 483 patients not having taken lamivudine. The mean MCV in the lamivudine group was 94.1 (83-100fl)., which was statistically significantly higher than that in patients not taking lamivudine, 91.6 fl, including those taking emtricitabine (p-value < 0.0001). Of patients prescribed lamivudine, 49 (10%) developed a clinically significant macrocytosis, with an odds ratio for macrocytosis of 3.3 compared to patients not taking lamivudine. The effect of lamivudine on MCV was independent of patient age, sex, ethnicity, weight, dose of lamivudine or duration of therapy with lamivudine. A similar, but lesser, effect was seen with emtricitabine. Conclusions: This study suggests that lamivudine causes an increase in the mean corpuscular volume of erythrocytes, and that this is sufficient to cause a clinical macrocytosis in 10% of patients. This is of clinical relevance for practitioners managing patients prescribed lamivudine, in guiding the need for investigating macrocytosis.
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