Methimazole Treatment and Risk of Acute Pancreatitis: A Population-based Cohort Study

Area of Science:

• Pharmacovigilance
• Clinical Epidemiology
• Drug Safety

Background:

• A European Medicine Agency (EMA) warning highlighted a potential increased risk of acute pancreatitis (AP) in patients using methimazole (MMI).
• Methimazole is a common antithyroid medication used to treat hyperthyroidism.
• Understanding the specific risks associated with MMI is crucial for patient safety and clinical decision-making.

Purpose of the Study:

• To investigate the association between methimazole (MMI) use and the diagnosis of acute pancreatitis (AP).
• To evaluate the temporal relationship between MMI treatment initiation and AP risk.
• To quantify the absolute risk of AP in MMI users.

Main Methods:

• Retrospective analysis of administrative health databases from 2013-2018.
• Inclusion of data from inhabitants registry, hospital discharge records (ICD-9-CM 577.0), and drug claims registry (ATC H03BB02).
• Poisson regression used to calculate age- and sex-adjusted rate ratios (RR) and 95% confidence intervals (CI) for AP in MMI users versus non-users, with stratification by treatment trimester.

Main Results:

• A total of 23,087 new MMI users were identified, with 61 hospitalizations for AP.
• An increased risk of AP was observed during the first three trimesters of MMI therapy (RR 3.40, 2.40, and 2.80, respectively).
• The risk of AP diminished after the initial period, and the absolute risk remained below 0.4% in all subgroups.

Conclusions:

• The study findings support the EMA warning regarding an elevated AP risk associated with MMI.
• The increased risk appears confined to the initial months of methimazole treatment.
• The absolute probability of developing AP remains low, under 1%, even with MMI use.