Products
Thiamazole is approved in the form of film-coated tablets and as [solution for injection>injections] (Thiamazol Henning, Germany). In many countries, it is commercially available only as a veterinary drug for cats. This article refers to human use. Thiamazole is also known as methimazole.
Structure and properties
Thiamazole (C4H6N2S, Mr = 114.2 g/mol) is a sulfur-containing imidazole and thiourea derivative. It exists as a white to pale yellow-brown crystalline powder that is readily soluble in water. It has a typical odor and slightly bitter taste. Thiamazole is the active metabolite of carbimazole (Néo-Mercazole).
Effects
Thiamazole (ATC H03BB02) has thyrostatic properties. The effects are due to inhibition of the synthesis of thyroid hormones by inhibiting their iodination. Thiamazole acts directly on the enzyme thyroperoxidase, which is responsible for iodization. Because it does not affect the release of hormones already formed, it has a delayed onset of action.
Indications
- For the treatment of hyperthyroidism (overactive thyroid).
- Surgical preparation for hyperthyroidism.
- Thyrotoxic crisis (solution for injection).
As a veterinary drug, thiamazole is used for feline hyperthyroidism, which is hyperthyroidism in cats.
Dosage
According to the SmPC. The dose is adjusted on an individual basis. The maintenance dose is taken in the morning after breakfast.
Contraindications
- Hypersensitivity, including to related agents such as carbimazole.
- Blood count changes
- Pre-existing cholestasis not caused by hyperthyroidism.
- Previous bone marrow injury after treatment with thiamazole or carbimazole.
- Pregnancy
Full precautions can be found in the drug label.
Interactions
Drug-drug interactions have been described with iodine and vitamin K antagonists, among others. Normalization of thyroid function may affect the metabolism of other drugs.
Adverse effects
The most common possible adverse effects include allergic skin reactions, joint pain, and muscle pain. Thiamazole may cause blood count abnormalities, occasionally agranulocytosis, and rarely liver disease.