Propylthiouracil

Indications

Propylthiouracil is used for: Hyperthyroidism

Adult Dose

Oral Hyperthyroidism Adult: 150-450 mg daily in divided doses. For severe cases, initial doses of 600-1200 mg daily have been used. Maintenance dose for euthyroid patients: 50-150 mg daily. Treatment is usually continued for 1-2 yr. Hepatic impairment: Dose reduction is recommended.

Child Dose

Oral Hyperthyroidism Child: Neonates: 2.5-5 mg/kg bid; 1 mth-1 yr: 2.5 mg/kg tid; 1-5 yr: 25 mg tid; 5-12 yr: 50 mg tid; 12-18 yr: 100 mg tid.

Renal Dose

Renal impairment: CrCl (ml/min) Dosage Recommendation <10 Reduce dose by 50%. 10-50 Reduce dose by 25%.

Administration

Should be taken with food.

Contra Indications

Hypersensitivity, pregnancy, lactation.

Precautions

Reserve use for patients unable to tolerate any other treatments e.g. methimazole, radioactive iodine or surgery. Inform patient of liver failure risk and to report any signs of liver dysfunction (e.g. loss of appetite, nausea, vomiting, pruritus, dark coloured urine, light coloured stools, jaundice, right upper-quadrant pain) or agranulocytosis (e.g. fever, sore throat) immediately. Stop treatment upon signs of agranulocytosis, aplastic anaemia, fever, liver injury, elevated LFT above 3 times the upper limit of normal, or exfoliative dermatitis. Regular monitoring of thyroid function and CBC is advisable. Monitor prothrombin time regularly during treatment, especially before surgical procedures. Lactation: distributed in breast milk, contraindicated by some sources (AAP Committee states compatible w/ nursing ; AAFP states safe for nursing)

Pregnancy-Lactation

Pregnancy Category: D Lactation: distributed in breast milk, contraindicated by some sources (AAP Committee states compatible w/ nursing ; AAFP states safe for nursing)

Interactions

May potentiate activity of anticoagulants. Doses of β-blockers, digitalis glycosides and theophylline may need to be reduced when patient becomes euthyroid.

Adverse Effects

Side effects of Propylthiouracil : Mild leukopenia, lupus-like syndrome, cutaneous vasculitis, thrombocytopenia. Skin rash, urticaria, arthralgia and fever. GI discomfort, vomiting, headache. Potentially Fatal: Agranulocytosis, aplastic anaemia, liver injury and liver failure.

Mechanism of Action

Propylthiouracil inhibits the production of thyroid hormones by preventing iodine from being oxidised in the thyroid gland. It also blocks the peripheral deiodination of thyroxine to tri-iodothyronine.