A comparative evaluation of adverse platelet outcomes among Veterans Affairs patients receiving linezolid or vancomycin

The primary objectives were to compare the incidences of severe thrombocytopenia, critical thrombocytopenia and a relative decline in platelets from baseline (epsilon 50 decline) between patients receiving linezolid and those receiving vancomycin. The secondary objective was to assess the relationship between vancomycin trough concentration and adverse platelet outcomes. A matched cohort study was performed at the Upstate New York Veterans Affairs Healthcare Network from January 2005 until February 2008. Eligibility criteria were: (i) receipt of linezolid or vancomycin therapy for epsilon 48 h; (ii) initiation of therapy as an inpatient; and (iii) baseline platelets available for evaluation. Patients who received linezolid were matched 1:1 to patients who received vancomycin. Cumulative incidences and times to event for (i) platelet count 50000 cells/mm(3), (ii) platelet count 20000 cells/mm(3) and (iii) epsilon 50 decline in platelets from baseline were evaluated. Multivariate analyses were performed. The study included 502 patients (251 matched pairs). The occurrences of platelet counts 50000 cells/mm(3) and 20000 cells/mm(3) did not differ significantly between linezolid and vancomycin patients. A epsilon 50 decline in platelets from baseline was observed in 78 (31.1) patients receiving vancomycin and 43 (17.1) patients receiving linezolid (risk ratio 0.55; 95 CI 0.400.77). A clear exposureresponse relationship was observed between vancomycin trough concentration and epsilon 50 decline in platelets from baseline. The incidence of thrombocytopenia was low and did not differ significantly among vancomycin and linezolid patients.