IntroductionLinezolid (LZD) is one of the antibiotics used to treat methicillin-resistantStaphylococcus aureus. In Japan, the dose of LZD is not generally adjusted by renal function or therapeutic drug monitoring and is readily available for critically ill patients. The adverse effects of LZD include pancytopenia, especially thrombocytopenia. We investigated the effect of LZD on platelet counts in critically ill patients with thrombocytopenia during admission to the intensive care unit (ICU).MethodsFifty-five critically ill patients with existing thrombocytopenia (platelet count < 100 ×103/μL) who received LZD for five days or more during the period from January 2011 to October 2018 were included. Changes in platelet count and frequency of platelet concentrate (PC) transfusion were evaluated retrospectively.ResultsMean (± standard error) platelet count prior to initiation of LZD was 47 ± 4 ×103/uL, which increased significantly to 86 ± 13 ×103/uL on day 15 (p<0.01). Median [interquartile range] duration of LZD therapy was 9 [8–12] days. Thirty-two patients (58.2%) required PC transfusion in the 15-day study period. The daily rate of PC transfusion decreased from 30.2% on days 1–5 to 18.2% on days 11–15. Similar tendencies were observed in patients with non-hematological and hematological disease.ConclusionThrombocytopenia in critically ill patients in the ICU did not worsen after initiation of LZD therapy, and may be considered for the treatment of MRSA in this setting.