Endocrine Abstracts

Purpose: Methimazole (MMI) is a widely used antithyroid agent for first-line treatment of hyperthyroidism. A warning has been recently issued by the European Medicine Agency (EMA) regarding a potential increased risk of acute pancreatitis (AP) in MMI users, based on evidences from published case reports and post-marketing surveillance. The aim of this study was to investigate the association between MMI treatment and the diagnosis of AP in drug users.

Materials and methods: Retrospective analysis of administrative databases: inhabitants registry, hospital discharge records (HDRs) and the drug claims registry of the Piedmont Region, Italy. In the study period 2013–2018, MMI users were identified using the drug claims registry (ATC H03BB02) and cases of AP through HDRs (ICD-9-CM 577.0). General population (non-users) was used as comparative group. To investigate the association between MMI treatment and AP risk, we identified hospitalizations for AP occurring in each trimester comprised in the first 18 months following the first prescription of MMI. Poisson regression was used to estimate the age- and sex-adjusted Rate Ratios (adjRRs), and the relative 95% confidence intervals (CI), comparing rates of AP between MMI users and non-users. The absolute risk of AP in MMI users was also calculated.

Results: A total of 23,087 users of MMI were identified. Among these, 13 hospitalizations for AP were recorded within the first trimester of treatment, for a total of 61 hospitalizations occurring within the first 18 months. The crude RR for AP in the first trimester of treatment was 270 per 100,000 person-year [95% CI 170–428] in MMI users and 60 per 100,000 person-year [95% CI 59–61] in the general population. Values of adjRRs according to trimesters of observation were 3.40 [95% IC 2.12–5.48] for the first, 2.40 [95% IC 1.36–4.23] for the second, 2.80 [95% IC 1.66–4.73] for the third, 1.20 [95% IC 0.54–2.68] for the forth, 1.60 [95% IC 0.80–3.21] for the fifth and 0.80 [95% IC 0.30–2.14] for the sixth trimester. The absolute risk for AP in MMI users was less than 0.39%, considering both sex and different ages.

Conclusions: AP should be considered as a rare-uncommon adverse drug reaction in MMI-users; further studies are warranted to identify subgroups at higher risk.