Summary Safety Review - Methimazole - Assessing the Potential Risk of Inflammation of the Blood Vessels (Vasculitis)
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.
Tapazole (methimazole) and generics
Potential Safety Issue
Inflammation of the blood vessels (vasculitis)
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 by the thyroid gland.
- treat and prepare the overactive thyroid gland for surgical removal or for radioactive iodine treatment.
- treat the overactive thyroid gland that cannot be removed.
- Methimazole has been marketed in Canada since 1951 under the brand name Tapazole and is currently available as 5 mg and 10 mg oral tablets. A generic version of Tapazole is also available for sale in Canada.
- The average use of methimazole oral tablets in Canada over the last 5 years was approximately 200,000 prescriptions annually.
Safety Review Findings
- Health Canada reviewed 13 international case reports of vasculitis in patients receiving methimazole. Of the 13 case reports, 11 reports showed a possible link to methimazole use, one report showed a slightly stronger link and one report was unlikely linked to methimazole use.
- Health Canada also assessed 22 articles from the published scientific literature. Many of them suggested that there was a potential risk of vasculitis with methimazole use but the frequency of the risk was considered very rare (less than one person suffered from vasculitis out of 10,000 taking methimazole).
Conclusions and actions
- Health Canada's review concluded that there is a link between the risk of vasculitis and use of methimazole.
- Health Canada is working with the manufacturers to update the Canadian 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.
The analysis that contributed to this safety review included scientific and medical literature, Canadian and international adverse reaction reports and what is known about the use of this drug both in Canada and internationally.
For additional information, contact the Marketed Health Products Directorate.