Mechanism of Action:
Propylthiouracil (PTU) inhibits the synthesis of thyroid hormones (T4 and T3) by blocking the enzyme thyroid peroxidase, which normally acts in the thyroid hormone synthesis pathway by iodinating the tyrosyl residues on thyroglobulin and coupling iodotyrosines.
Additionally, PTU has the unique ability, compared to Methimazole, to block the peripheral conversion of T4 (less active) to T3 (more active).
Uses:
It's used in the management of hyperthyroidism, especially during the first trimester of pregnancy (due to a lower risk of affecting the fetus) and in individuals intolerant to Methimazole.
Considerations:
PTU can have serious side effects, including liver damage and agranulocytosis (a potentially fatal condition where white blood cell counts drop).
These risks necessitate regular monitoring of liver function and blood cell counts during treatment.