Facial excoriations from thiamazole in cats: what to do
11-year-old cat with hyperthyroidism that started oral thiamazole 4 weeks ago. He now has intense pruritus of the head and neck with self-inflicted excoriations. He had no previous skin problems.
What is most appropriate?
chevron_right Show answer and explanation
A. Switch to carbimazole, which does not cause this reaction
Carbimazole is a prodrug converted into thiamazole: it shares its adverse effects and the reaction would recur.
B. Continue thiamazole and control the itch with glucocorticoids
This reaction responds poorly to corticosteroids and antihistamines while the drug is continued, and lesions can be severe.
C. Stop thiamazole and switch to another option: radioiodine, thyroidectomy or iodine-restricted diet
Correct. Facial excoriations are an immune-mediated adverse reaction, typical of the first months, that requires stopping the drug. Lesions resolve after withdrawal, and hyperthyroidism is controlled by another route.
D. Switch to transdermal thiamazole, which avoids skin effects
The transdermal route reduces gastrointestinal effects, but not immune-type reactions such as excoriations or blood dyscrasias.
lightbulb Key takeaway
Facial excoriations, hepatopathy and blood dyscrasias caused by thiamazole require withdrawal and are not avoided with carbimazole or the transdermal route. Have a definitive alternative or the diet ready.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.