Incidence and risk estimate of drug-induced agranulocytosis in Hong Kong Chinese. A population-based case-control study

Purpose Drug-induced agranulocytosis is a rare but life-threatening adverse drug reaction. Its epidemiology in Chinese is largely unknown. This study aimed to estimate the incidence, mortality, and risk of the drugs associated with agranulocytosis in Hong Kong Chinese. Methods A population-based case-control study was conducted using the Clinical Data Analysis and Reporting System, a database managed by the Hong Kong Hospital Authority. Patients with drug-induced agranulocytosis from 1 January 2004 to 31 December 2013 were identified. World Health Organization causality assessment was used to evaluate the possible drug aetiology of each case. Odd ratios (ORs) of the drug exposure were calculated using exact conditional logistic regression. Results A total of 155 cases of drug-induced agranulocytosis were identified. Mean age was 51.4 years, and 95 cases were female. Incidence rate was estimated to be 2.2 cases per million person-years, and the all-cause mortality of patients with drug-induced agranulocytosis was 3.9%. Among the cases, the most common associated drug groups were antithyroid drugs (41.9%), antimicrobials (20%), anticonvulsants (10.3%), and antipsychotics (6.5%). Carbimazole had the highest risk of agranulocytosis (adjusted OR 416.7, 95% confidence interval (CI) 51.5-3372.9) with an incidence of 9.2 (95% CI 6.9-12.1) per 10 000 users and 3.6 (95% CI 2.7-4.8) per 10 000 user-years. Other drugs with significant risk included cephalosporins, clozapine, penicillins, phenytoin, and propyl thiouracil. Conclusions The incidence and mortality in Hong Kong Chinese were relatively low compared to Caucasians. Antithyroid drugs were the most common implicated drug class, and carbimazole had the highest risk of agranulocytosis. Copyright (C) 2017 John Wiley & Sons, Ltd.