High exposure compared with standard exposure to metoclopramide associated with a higher risk of parkinsonism: a nationwide population-based cohort study

Aims: We conducted a cohort study utilizing a nationwide health insurance database to assess the European Medicines Agency's restrictions on using metoclopramide and its association with the risk of parkinsonism. Methods: New oral metoclopramide users aged ≥20 years, and age- and gender-matched non-users were recruited between 2001 and 2011. Users were divided into high-exposure (dose >30 mg day^–1 and/or duration >5 days) and standard-exposure (dose ≤30 mg day^–1 and duration ≤5 days) groups. The adjusted hazard ratio (aHR) with 95% confidence interval (CI) estimated the risk of parkinsonism. Results: During a 1-year period, 122 of 218 931 (0.06%) users of metoclopramide vs. 56 of 218 931 (0.03%) non-users developed parkinsonism (P < 0.001). Among the 122 cases of parkinsonism in users, 64 (0.04%) were from 168 566 standard-exposure users and 58 (0.12%) from 50 365 high-exposure users. Compared with non-users, the risk of parkinsonism was higher in users (aHR 2.16; 95% CI 1.54, 3.02), including standard-exposure (aHR 1.73; 95% CI 1.11, 2.70), and high-exposure (aHR 3.15; 95% CI 1.78, 5.57) users. High-exposure users had a higher risk of parkinsonism than standard-exposure users (aHR 1.83; 95% CI 1.28, 2.63). Within the high-exposure group, 45 233 of 50 365 (89.81%) users and 55 of 58 (94.83%) parkinsonism were from long-duration exposure; 5 132 of 50 365 (10.19%) users and 3 of 58 (5.17%) parkinsonism were from high-dose exposure and long-duration + high-dose exposure. Conclusions: The risk of parkinsonism in metoclopramide users, although extremely low (0.06%), is 2.16-fold greater than in non-users. High-exposure users have a 1.83-fold higher risk than standard-exposure users. As users in high-exposure group had a higher risk of parkinsonism than in standard-exposure group, and the majority of users and parkinsonism in high-exposure group were from long-duration exposure; thus, physician are advised to avoid prescribing metoclopramide for >5 days, even if the daily dose is ≤30 mg.