Propylthiouracil

What it is and how it works

Propylthiouracil inhibits thyroid peroxidase, blocking iodination of tyrosine and synthesis of thyroxine (T4) and triiodothyronine (T3). It also inhibits peripheral conversion of T4 to the more active T3.

Indications

Hyperthyroidism, including Graves’ disease, preparation for thyroidectomy or radioactive iodine; preferred thionamide in the first trimester of pregnancy and in thyroid storm, or when carbimazole/methimazole is not tolerated.

Dosage and administration (summary)

Taken orally; usually 200–400 mg daily in divided doses initially until euthyroid, then reduced to a maintenance dose of about 50–150 mg daily.

Contraindications

Hypersensitivity to propylthiouracil; history of severe hepatic injury or agranulocytosis with thionamides.

Warnings and precautions

Can cause severe, sometimes fatal, hepatotoxicity, so it is generally reserved for situations where alternatives are unsuitable; patients should report symptoms of liver disease. Agranulocytosis may occur, and patients must report sore throat, fever or mouth ulcers immediately; ANCA-associated vasculitis has also been reported.

Pregnancy

Preferred antithyroid drug in the first trimester; use the lowest effective dose because it crosses the placenta.

Storage and supply

Store below 25 °C.

Source: reference summary prepared from the EU SmPC/EPAR, BNF and WHO Model Formulary. The approved product information in Iran governs.