Professional Monograph
Mode of Action
Methimazole is a thioureylene anti-thyroid drug. Thioureylene blocks the iodination of thyroid hormones
and is concentrated in the thyroid tissue.
Treatment with methimazole is a form of medical management for feline hyperthyroidism and is not
a cure for the disease.
Advantages
Comes in transdermal preparations which are easy to administer to the pinnae of the ear. This is
advantageous because most cats are difficult to pill and may require twice daily dosing for the rest
of their lives. (As some cats are unsuitable candidates for radioiodine or owners may decline radioiodine
treatment).
Efficacious.
Gastrointestinal side effects less common than oral preparations.
Disadvantages
Dearer compared to carbimazole treatment.
Like carbimazole, 10-14 days of treatment are generally required to establish euthyroidism.
Potential side effects
Side effects usually occur within the first 3 months of treatment
Transient gastrointestinal signs such as vomiting, inappetance, anorexia may occur.
Occasional hepatotoxicity and immunological side effects (cytopaenias, serum anti-nuclear antibodies)
have been seen.
Some cats have been reported to self mutilate - scratching their neck and faces. Rare but serious
side effects are bleeding and thrombocytopaenia. Treatment with methimazole should be discontinued
in these cats.
Drug interactions
Should not be used with phenorbarbitone as it will reduce its clinical efficacy
CLIENT COUNSELLING INFORMATION
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