Number of concomitant drugs with thrombocytopenic adverse effects and the extent inflammatory response resolution are risk factors for thrombocytopenia in patients treated with linezolid for more than 14 days.

Prolonged treatment with linezolid (LZD) is known to cause thrombocytopenia. However, some patients do not develop thrombocytopenia despite long-term administration of LZD. To determine the risk factors for LZD-associated thrombocytopenia in patients undergoing long-term LZD therapy, we conducted a retrospective cohort study among 212 patients receiving LZD treatment between December 2011 and June 2014 at a tertiary referral university hospital in Nagoya, Japan. Of the 217 patients who received LZD, 37 were treated with LZD for more than 14 days and were enrolled in the study. We compared data on demographic characteristics, underlying disease, microbiology, concomitant drugs, and laboratory tests between the thrombocytopenia group and the non-thrombocytopenia group. Thrombocytopenia was defined as having a platelet count < 100 × 10/μL or a ≥ 50% reduction in platelet count compared to baseline. Among the 37 patients who received LZD for more than 14 days, 17 (45.9%) developed thrombocytopenia. Multivariate logistic regression revealed that both the number of concomitant drugs with thrombocytopenic adverse effects (DTADE) (OR = 1.690; 95% CI = 1.037-2.754; = 0.035) and a small decrease in the level of C-reactive protein (CRP) 14 days post-administration (OR = 0.965; 95% CI = 0.939-0.993; = 0.013) were associated with thrombocytopenia during long-term LZD therapy. Therefore, the number of concomitant DTADE and a small decrease in CRP on the 14th day of treatment were key factors for the appearance of LZD-associated thrombocytopenia in patients with long-term LZD therapy. Our findings may be useful for preventing thrombocytopenia in patients treated with LZD for longer than 14 days.