Flunarizine and the risk of parkinsonism in a newly diagnosed type 2 diabetic population in Taiwan: A nested case-control study.

Previous studies demonstrated that both diabetes and flunarizine use can increase the risk of parkinsonism. The aim of the current study was to investigate the risk of developing parkinsonism after flunarizine treatment, in a cohort of patients newly diagnosed with type 2 diabetes. We conducted a nested case-control study of a type 2 diabetic cohort from the Taiwan Longitudinal Health Insurance Database 2005 (LHID 2005). Each incident case of parkinsonism, during the period from 2001 to 2013, was randomly matched with 3-10 controls, according to age, sex, calendar year of cohort entry, and the duration of follow-up. Conditional logistic regression was used to estimate the odds ratio (OR) of parkinsonism associated with flunarizine use. The cohort consisted of 44,644 patients with newly diagnosed type 2 diabetes from 2001 to 2013, of whom 464 patients had a parkinsonism event during the follow-up period. The adjusted OR of parkinsonism with relation to flunarizine use was 2.75 (95% confidence interval: 2.26-3.36). There were also duration- and dose-response effects. Compared to those who had not used it, the OR for developing parkinsonism was 1.77 for patients who used flunarizine for less than 1 month. When the exposure period expanded over 3 months, the OR increased to 7.03. Our findings suggested that flunarizine use is a potential risk factor for parkinsonism in patients with newly diagnosed type 2 diabetes, especially when the drug is persistently used for over 3 months.