Propylthiouracil

Propylthiouracil is indicated:

• in patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter who are intolerant of methimazole and for whom surgery or radioactive iodine therapy is not an appropriate treatment option.
• to ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy in patients who are intolerant of methimazole.

Propylthiouracil inhibits the synthesis of thyroid hormones and thus is effective in the treatment of hyperthyroidism. The drug does not inactivate existing thyroxine and triiodothyronine that are stored in the thyroid or circulating in the blood, nor does it interfere with the effectiveness of thyroid hormones given by mouth or by injection. Propylthiouracil inhibits the conversion of thyroxine to triiodothyronine in peripheral tissues and may therefore be an effective treatment for thyroid storm.

Propylthiouracil is administered orally. The total daily dosage is usually given in 3 equal doses at approximately 8-hour intervals.

Adults: The initial dose is 300 mg daily. In patients with severe hyperthyroidism, very large goiters, or both, the initial dose may be increased to 400 mg daily; an occasional patient will require 600 to 900 mg daily initially. The usual maintenance dose is 100 to 150 mg daily.

Pediatric Patients: Propylthiouracil is generally not recommended for use in pediatric patient except in rare instances in which other alternative therapies are not appropriate options. Studies evaluating appropriate dosing regimen have not been conducted in the pediatric population although general practice would suggest initiation of therapy in patients 6 years or older at a dosage of 50 mg daily with careful upward titration based on clinical response and evaluation of TSH and free T4 levels. Although cases of severe liver injury have been reported with doses as low as 50 mg/day, most cases were associated with doses of 300 mg/day and higher.

Geriatric Patients: Reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

With medicine: Anticoagulants (oral)- Due to the potential inhibition of vitamin K activity by Propylthiouracil, the activity of oral anticoagulants (e.g., warfarin) may be increased; additional monitoring of PT/INR should be considered, and especially before surgical procedures.

p-adrenergic blocking agents- Hyperthyroidism may cause an increased clearance of beta blockers with a high extraction ratio. A dose reduction of beta-adrenergic blockers may be needed when a hyperthyroid patient becomes euthyroid.

Digitalis glycosides- Serum digitalis levels may be increased when hyperthyroid patients on a stable digitalis glycoside regimen become euthyroid; a reduced dosage of digitalis glycosides may be needed.

Theophylline- Theophylline clearance may decrease when hyperthyroid patients on a stable theophylline regimen become euthyroid; a reduced dose of theophylline may be needed.

With food: In case of Propylthiouracil, there are no specific foods that patients must exclude from diet when receiving this medication.

Propylthiouracil is contraindicated in the presence of hypersensitivity to the drug or any of the other product components.

Common: rash, urticaria, pruritus, abnormal hair loss, skin pigmentation, edema, nausea, vomiting, epigastric distress, loss of taste, arthralgia, myalgia, paresthesia and headache, lucopenia, agranulocytosis, hepatitis, hepatic failure.

Rare: aplastic anaemia, drug fever, lupus-like syndrome, severe hepatic reactions, periarteritis, hypoprothrombinaemia, thrombocytopenia and bleeding, nephritis, interstitial pneumonitis, vasculitis and polymyositis.

Propylthiouracil crosses the placenta and can induce fetal goiter and hypothyroidism. The lowest dose possible should be used after carefully weighing the mother’s needs against the risk to the fetus. Propylthiouracil is present in breast milk in small amounts and neonatal development should be closely monitored in any nursing mother treated with this drug.

Because of the risk of agranulocytosis patients should be warned to report to their doctor in the event of a sore throat, fever, mouth ulcers, malaise, non-specific illness or other symptoms of infection immediately. A full blood count should be performed and treatment should be discontinued immediately if there is clinical or laboratory evidence of neutropenia.

Propylthiouracil may cause hypothrombinaemia and bleeding so prothrombin time should be monitored during therapy, especially prior to surgery.

Some cases of severe hepatic reactions, both in adults and children, including fatal cases and cases requiring a liver transplant have been reported with propylthiouracil. In a majority of cases, the liver reaction occurred within 6 months. If significant hepatic enzyme abnormalities develop during treatment with propylthiouracil the drug should be discontinued immediately. Propylthiouracil should be used with caution in patients with renal impairment or hepatic disease.

Use in Children & Adolescents: Propylthiouracil is not recommended for use in the pediatric population except in rare instances in which methimazole is not well-tolerated and surgery or radioactive iodine therapy is not appropriate. When used in children, parents and patients should be informed of the risk of liver failure.

Symptoms of Propylthiouracil overdose include nausea, vomiting, epigastric distress, headache, fever, arthralgia, pruritus, edema and pancytopenia. Agranulocytosis is the most severe potential adverse effect due to acute propylthiouracil toxicity. In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient’s medical status.

Thyroid drugs & hormone

Store in a cool (below 30°C) and dry place, away from light and children.