Summary Safety Review - Methimazole - Assessing the Potential Risk of Inflammation of the Pancreas (Acute Pancreatitis)

Review decision

A Summary Safety Review complements other safety related information to help Canadians make informed decisions about their use of health products. Each summary outlines what was assessed in Health Canada’s review, what was found and what action was taken by Health Canada, if any.


Issued: 2019-09-12

Product

Tapazole (methimazole) and generics

Potential Safety Issue

Inflammation of the pancreas (acute pancreatitis)

Key Messages

  • Methimazole, also known as thiamazole, is a prescription drug authorized for sale in Canada to treat hyperthyroidism, a condition where too much thyroid hormone is produced. It is also used in preparation for radioactive iodine therapy or surgical removal of an overactive thyroid gland, and in cases where the overactive thyroid gland cannot be removed.
  • Health Canada reviewed the potential risk of inflammation of the pancreas (acute pancreatitis) with the use of methimazole after being made aware of international reports.
  • Health Canada's review of available evidence concluded that there is a link between methimazole and the risk of acute pancreatitis.
  • Health Canada is working with the manufacturers to update the Canadian product safety information for all methimazole products to inform healthcare professionals and patients about this risk.

Overview

Acute pancreatitis is an inflammatory disease of the pancreas that is most commonly caused by gallstones and alcohol use, but can also be caused by a drug reaction (drug-induced pancreatitis). It is characterized by a sudden onset of abdominal pain that is often severe.

Health Canada reviewed the potential risk of acute pancreatitis with the use of methimazole when product safety information for methimazole- and carbimazole-containing products was updated in Europe to include the risk of acute pancreatitis. Information on carbimazole was also considered in Health Canada's review, although this product is not marketed in Canada.

Use in Canada

  • Methimazole is a prescription drug authorized for sale in Canada to treat hyperthyroidism, a condition in which too much thyroid hormone is produced. It is also used in preparation for radioactive iodine therapy or surgical removal of the overactive thyroid gland.
  • Methimazole, also called thiamazole, has been marketed in Canada for more than 60 years under the brand name Tapazole, and is available as 5 mg and 10 mg oral tablets. Generic versions have also been authorized for sale in Canada.
  • Use of methimazole oral tablets has remained relatively steady in Canada over the last 5 years at approximately 200,000 prescriptions annually.

Safety Review Findings

  • This safety review is based on 8 robust international published case reports of acute pancreatitis with the use of methimazole (6) or carbimazole (2). Of these 8, 4 reports were found to be linked to the use of methimazole (3) or carbimazole (1), and 4 reports were possibly linked to the use of methimazole or carbimazole.
  • The review also looked at 1 published study that did not observe a relationship between methimazole use and acute pancreatitis. However, there were limitations to this study including small sample size, which makes it difficult to confirm a relationship.
  • At the time of the review, Health Canada received 21 Canadian reportsa of potential acute pancreatitis related to methimazole use. These reports were not assessed further because the cases did not meet the criteria of the review. Specifically, these cases did not report the actual adverse event of interest, or the timing of methimazole use and the development of pancreatitis was unclear, or the reports did not match the diagnosis of drug-induced pancreatitis.

Conclusions and actions

  • Health Canada's review of the available information found that there is a link between methimazole use and the risk of acute pancreatitis.
  • Health Canada is working with the manufacturers to update the Canadian product safety information on methimazole products to inform about this risk.
  • Health Canada will continue to monitor safety information involving methimazole products, as it does for all health products on the Canadian market, to identify and assess potential harms. Health Canada will take appropriate and timely action if and when any new health risks are identified.

Additional information

The analysis that contributed to this safety review included scientific and medical literature, Canadian and international information, and what is known about the use of methimazole, both in Canada and internationally.

For additional information, contact the Marketed Health Products Directorate.

Footnotes

  1. Canadian reports can be accessed through the Canada Vigilance Online Database.

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