propylthiouracil: clinical use

Prescribing considerations

• Ensure patients understand warning symptoms of agranulocytosis and hepatic injury before treatment.
• Use caution in renal impairment or hepatic disease.
• Review treatment around planned radioactive iodine therapy.
• Pregnancy requires individual benefit–risk assessment and coordinated endocrine and obstetric care.

Contraindications and cautions

• Previous severe hypersensitivity reaction associated with propylthiouracil, including agranulocytosis, hepatitis, vasculitis or nephritis.
• Rare hereditary galactose intolerance, lactase deficiency or glucose-galactose malabsorption because the selected product contains lactose.

Monitoring

• Monitor thyroid function to identify inadequate control or treatment-induced hypothyroidism.
• Arrange an urgent full blood count if infection, sore throat, fever, mouth ulcers, bruising or malaise develops; discontinue if neutropenia is confirmed clinically or by laboratory testing.
• Assess liver function promptly if hepatic symptoms occur and discontinue for significant hepatic enzyme abnormalities.
• Monitor prothrombin time where clinically relevant, particularly before surgery.
• During pregnancy or breastfeeding, consider appropriate maternal, fetal, neonatal or infant thyroid monitoring.

Clinical pharmacology

Propylthiouracil inhibits thyroid peroxidase, reducing iodination and coupling reactions required for thyroid hormone synthesis. It is rapidly absorbed, undergoes substantial hepatic first-pass metabolism and is mainly excreted in urine as a glucuronide conjugate. It crosses the placenta and enters breast milk.

Formulation and product differences

• The selected product is a white, circular, biconvex oral tablet with a breakline.
• It contains lactose, maize starch, pregelatinised maize starch, magnesium stearate and sodium starch glycollate.
• The selected product should be stored below 25°C.

Tablet

Route: Oral

Strengths: 50 mg, 100 mg