Pharmacotherapeutic group: antithyroid preparations: sulphur-containing imidazole derivatives.
ATCvet code: QH03BB02
Pharmacodynamic properties
Thiamazole acts by blocking the biosynthesis of thyroid hormone in vivo. The primary action is to inhibit binding of iodide to the enzyme thyroid peroxidase, thereby preventing the catalysed iodination of thyroglobulin and T3 and T4 synthesis.
Pharmacokinetic particulars
Following oral dosing with the product in healthy cats, at a dose rate of 5 mg, thiamazole is rapidly and completely absorbed. Elimination of the drug from cat plasma is rapid with a half-life of 4.35 hours. The time of peak plasma levels occur 1.14 hours after dosing. Cmax is 1.13 µg/ml.
In rats thiamazole has been shown to be poorly bound to plasma protein (5%); 40% was bound to red blood cells. The metabolism of thiamazole in cats has not been investigated, however, in rats thiamazole is rapidly metabolised in the thyroid gland. About 64% of the administered dose being eliminated in the urine and only 7.8% excreted in faeces. This is in contrast with man where the liver is important for the metabolic degradation of the compound. The drug residence time in the thyroid gland is assumed to be longer than in the plasma.