J Rheum Dis 2019; 26(3): 186-190  
Tocilizumab-induced Thrombocytopenia in Patients with Rheumatoid Arthritis
Jung Sun Lee1, Ji Seon Oh2, Seokchan Hong1, Chang-Keun Lee1, Bin Yoo1, Yong-Gil Kim1
1Division of Rheumatology, Department of Internal Medicine, and 2Department of Biomedical Informatics, University of Ulsan College of Medicine, Asan Medical Center, Seoul, Korea
Correspondence to: Yong-Gil Kim http://orcid.org/0000-0002-8029-7355
Division of Rheumatology, Department of Biomedical Informatics, University of Ulsan College of Medicine, Asan Medical Center, 88 Olympic-ro 43-gil, Songpa-gu, Seoul 05505, Korea. E-mail:bestmd2000@amc.seoul.kr
Received: February 18, 2018; Revised: April 5, 2019; Accepted: April 25, 2019; Published online: July 1, 2019.
© Korean College of Rheumatology. All rights reserved.

This is a open Access article, which permits unrestricted non-commerical use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Objective. Interlukin-6 (IL-6) increases platelet count during inflammation and may act in a manner similar to thrombopoietin. Tocilizumab is a monoclonal antibody of the IL-6 receptor and widely used in the treatment of rheumatoid arthritis (RA). Here, we evaluated the incidence of tocilizumab-induced thrombocytopenia and clinical factors associated with the development of thrombocytopenia. Methods. Patients with RA, who were treated with tocilizumab and had exposed to other biologics previously in a tertiary hospital between January 2014 and December 2017, were retrospectively evaluated. We compared occurrence of thrombocytopenia between tocilizumab and previous biologics. Furthermore, the factors associated with thrombocytopenia were analyzed using logistic regression analysis. Results. In total, 114 patients with RA were treated with tocilizumab for mean 90.5 weeks (interquartile range, 30.9∼174.9). Thrombocytopenia was reported in 14 patients (12.3%) and it was higher rate compared with previous biologics. Most cases were grade 1 thrombocytopenia. Multivariate analysis showed that patient age (odds ratio [OR], 2.170; 95% confidence interval [CI], 1.118∼4.211; p=0.022) and platelet count prior to treatment with tocilizumab (OR, 0.972; 95% CI, 0.954∼0.990; p=0.002) were significantly associated with the development of thrombocytopenia. Conclusion. Old age is risk factor for developing tocilizumab-induced thrombocytopenia and higher platelet count prior to treatment is associated with lowering risk of development of thrombocytopenia. However, thrombocytopenia was tolerable.
Keywords: Rheumatoid arthritis, Interleukin-6, antibodies, Thrombocytopenia


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