Abstract: OBJECTIVE To explore the effects of various factors including the combined use of P-glycoprotein(P-gp) inhibitors on the concentration of linezolid exceeding the standard, so as to reduce the adverse reactions caused by the high concentration of linezolid. METHODS A retrospective analysis of patients treated with linezolid and concentration detected in the First Affiliated Hospital of Zhejiang University School of Medicine from January 2018 to December 2019 was conducted, to study the association of linezolid concentration exceeding the standard with adverse effects of thrombocytopenia and to perform a risk factor analysis for linezolid concentration exceeding the standard. RESULTS A total of 35 patients had thrombocytopenia in 102 cases treated with linezolid. The occurrence of this adverse reaction was positively correlated with the highest valley concentration of linezolid(Kendall’s tau-b=0.418, P<0.001). Binary logistic regression analysis found that creatinine clearance, number of doses used and combined with P-gp inhibitors were risk factors for linezolid concentrations exceeding the standard(>8 mg·L^-1), and OR of combination with P-gp inhibitors was 4.132(95%CI 1.250-13.657, P=0.020). The correlation between combined P-gp inhibitors and thrombocytopenia was not statistically significant. CONCLUSION The linezolid concentration exceeding the standard is related to thrombocytopenia, combination of P-gp inhibitors is an important risk factor for linezolid concentration exceeding the standard. In order to reduce the occurrence of adverse reactions, attention should be paid to the combined use of linezolid.