What Is Thiamazole?
Thiamazole is an organic compound that is a nitrogen-containing heterocyclic compound.
Its chemical formula is C4H6N2S. It has a five-membered ring molecular structure of thiourea in the molecule and is also a derivative of imidazole. Its other common name is methimazole, which is 1-methyl-3H-imidazole-2-thione, according to IUPAC nomenclature.
It has a molecular weight of 114.17 and a melting point of 294.8°F (146°C). It is a white to light yellowish brown crystalline powder to powdery solid at room temperature. It has a characteristic odor and is easily soluble in water. Its solubility in water is 2.75 mg/mL (at 20°C). It is soluble in chloroform, alcohols, and pyridine, slightly soluble in benzene, and insoluble in ether.
Decomposition produces toxic substances such as carbon dioxide, carbon monoxide, nitrogen oxides (NOx), and sulfur oxides (SOx). Therefore, when storing, it is necessary to avoid high temperatures, direct sunlight, and contact with strong oxidizers. Although there are no specific legal regulations, there is a possibility of allergic skin reactions and a suspicion of adverse effects on fertility or the fetus.
Uses of Thiamazole
Thiamazole is primarily used in antithyroid medications. It is most commonly used in the treatment of excessive thyroid hormone levels, i.e., in the treatment of hyperthyroidism.
Other uses include lowering blood thyroid hormone levels before therapeutic intervention, to minimize the effects of thyroid manipulation in thyroid surgery or radioactive iodine therapy. Thiamazole, as a drug, is considered to be fast-acting, has few side effects, and is considered a major first-line drug.
Originally developed as a drug for humans, it is now actively used to treat hyperthyroidism in cats. It is a mainstream therapeutic agent, especially in Europe and the United States. As a general organic compound, it is also used in synthetic organic chemistry.
Principle of Thiamazole
The structure of thiamazole differs depending on its application.
1. Thiamazole as an Antithyroid Drug
Thiamazole, as an antithyroid drug, inhibits thyroid hormone biosynthesis by blocking thyroid peroxidase, an enzyme in the thyroid gland. Biosynthesis of thyroxine, a type of thyroid hormone, requires iodination of thyroglobulin by thyroid peroxidase.
Thioamide compounds, including thiamazole, are believed to inhibit many steps in thyroid hormone biosynthesis, and one of the reactions inhibited by thiamazole is the iodination of thioglobulin.
One of the serious side effects caused by thiamazole is agranulocytosis. Agranulocytosis is a condition in which the number of white blood cells in the blood, especially neutrophils, drops. If a patient experiences fever or sore throat while taking thiamazole, agranulocytosis should be suspected immediately, and if agranulocytosis develops, thiamazole should be discontinued under medical supervision.
2. Thiamazole in Synthetic Organic Chemistry
In synthetic organic chemistry, thiamazole is also useful as a scavenger of free radicals, such as hydroxyl radicals (OH).
Types of Thiamazole
The types of thiamazole currently available include pharmaceuticals and chemical reagents. As a chemical reagent, thiamazole is sold in volumes of 5 g, 25 g, and 100 g. It is a reagent that can be stored at room temperature. It is used as a raw material for organic synthesis.
Thiamazole, as a pharmaceutical product, is used as an antithyroid drug, as mentioned above. It is marketed under the trade name Mercazole and is available at 2.5 mg and 5 mg. The dosage form is film-coated tablets. It is indicated for hyperthyroidism and requires a prescription from a physician.