What medication is commonly used to treat hyperthyroidism?

• A. Methimazole
• B. Carbimazole
• C. Radioactive iodine
• D. Propylthiouracil

Answer: (D)

Propylthiouracil is a thionamide that reduces thyroid hormone production by inhibiting the thyroid peroxidase enzyme, which blocks iodination and coupling of tyrosine residues in thyroglobulin. In addition, it uniquely decreases the peripheral conversion of the prohormone T4 to the active T3, allowing a quicker drop in circulating thyroid hormones. This dual action makes it especially useful when rapid control of hyperthyroidism is needed, such as in thyroid storm or in the first trimester of pregnancy when methimazole is avoided due to fetal risks. Because of potential liver toxicity with long-term use, propylthiouracil is generally reserved for specific situations or shorter courses, while other thionamides like methimazole are more commonly used for routine maintenance.