Professional and Linguistic Assessments Board (PLAB) Practice Exam

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What is the primary role of carbimazole in treating thyroid conditions?

  1. To stimulate thyroid hormone production

  2. To inhibit thyroid hormone synthesis

  3. To block thyroid receptor sites

  4. To replace thyroid hormones

The correct answer is: To inhibit thyroid hormone synthesis

The primary role of carbimazole in treating thyroid conditions is to inhibit thyroid hormone synthesis. Carbimazole is classified as a thioamide antithyroid medication that works by interfering with the production of thyroid hormones in the thyroid gland. Specifically, it inhibits the enzyme thyroperoxidase, which is crucial for the iodination of tyrosine residues and the subsequent synthesis of T3 (triiodothyronine) and T4 (thyroxine) hormones. By reducing the production of these hormones, carbimazole effectively lowers the levels of circulating thyroid hormones, which is essential in managing conditions such as hyperthyroidism or Graves' disease. In contrast to the other options, stimulating thyroid hormone production would exacerbate hyperthyroidism, while blocking thyroid receptor sites is not the mechanism of action of carbimazole. Replacing thyroid hormones pertains to cases of hypothyroidism, which is not relevant to the function of carbimazole. Thus, the correct answer reflects the drug's specific mechanism in treating excess thyroid hormone conditions.