Thyrozol Mechanism of Action

Pharmacology: Pharmacodynamics: Thiamazole inhibits dose-dependently the incorporation of iodine into tyrosine and thereby the neo-synthesis of thyroid hormones. This property permits symptomatic therapy of hyperthyroidism regardless of its cause. Whether thiamazole furthermore affects the 'natural course' taken by the immunologically induced type of hyperthyroidism (Graves' disease), i.e. whether it suppresses the underlying immunopathogenitic process, can presently not be decided with certainty. The release of previously synthesised thyroid hormones from the thyroid is not affected. This explains why the length of the latency period until normalisation of the serum concentrations of thyroxine and triiodothyronine, and thus to clinical improvement, differs in individual cases. Hyperthyroidism due to the release of hormones after destruction of thyroid cells, e.g. after radioiodine therapy or in thyroiditis, is also not affected.
Pharmacokinetics: Thiamazole is absorbed rapidly and completely. After administration, maximum serum levels are reached within 0.4 to 1.2 hours.
Protein binding is negligibly low. Thiamazole accumulates in the thyroid where it is metabolised only slowly. In spite of fluctuating serum levels, the accumulation of thiamazole in the thyroid gland still leads to a concentration plateau. This results in a duration of action of nearly 24 hours for the single dose. According to present knowledge, the kinetics of thiamazole is independent of thyroid function. The elimination half-life is about 3 to 6 hours and is prolonged in hepatic insufficiency. Thiamazole undergoes renal and biliary elimination; excretion with the faeces is slight, suggesting enterohepatic circulation. 70% of the substance are excreted by the kidneys within 24 hours. Only a small amount is excreted in unchanged form. At present, no experience is available on the pharmacological activity of the metabolites.