Antithyroid drug-induced leukopenia and G-CSF administration: a long-term cohort study.

Although antithyroid drug (ATD)-induced agranulocytosis is a significant concern, its risks associated with long-term use and re-administration are not fully elucidated. Therefore, we performed this study to determine the incidence of ATD-induced leukopenia and G-CSF administration using administrative claims database. Retrospective cohort study. This study was performed using the DeSC Japanese administrative claims database. A total of 12,491 patients with newly diagnosed Graves' disease (GD) who received methimazole or propylthiouracil between April 2014, and February 2021 among 3.44 million patients in the database were included in the study. We measured the six-year incidence of leukopenia and granulocyte colony-stimulating factor (G-CSF) administration. The incidence of leukopenia and G-CSF administration was 1.34% (168 patients) and 0.30% (38 patients), respectively. Leukopenia had a dose-dependent and biphasic incidence. The incidence of leukopenia and G-CSF administration was 37.2 (0.7%) and 8.0 (0.2%) per 1000 person-years during the first 72 days of ATD initiation, whereas it was 3.1 and 0.7 per 1000 person-years during the subsequent 6 years, respectively. The incidence of both outcomes was comparable between first administration and re-administration of ATD. The incidence of ATD-induced leukopenia and G-CSF administration was high in the first 72 days, with a reduced risk for at least 6 years thereafter. The incidence was similar between first administration and re-administration. ATD, a standard therapy, is often administered for a long period; therefore, our findings can guide the treatment of GD.