Propylthiouracil

Description

DESCRIPTION Propylthiouracil is one of the thiocarbamide compounds. It is a white, crystalline substance that has a bitter taste and is very slightly soluble in water. Propylthiouracil is an antithyroid drug administered orally. The structural formula is: Each tablet contains propylthiouracil 50 mg and the following inactive ingredients: corn starch, docusate sodium, magnesium stearate, microcrystalline cellulose, pregelatinized starch, sodium benzoate, and sodium starch glycolate. Structural Formula

What Is Propylthiouracil Used For?

INDICATIONS AND USAGE 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

Dosage and Administration

DOSAGE AND ADMINISTRATION 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 the pediatric patient population 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 Clinical studies of propylthiouracil did not include sufficient numbers of subjects aged 65 or over to determine whether they respond differently from younger subjects. Other 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.

Side Effects (Adverse Reactions)

ADVERSE REACTIONS The following adverse reactions have been reported with the use of propylthiouracil. Because these events generally come from voluntary reporting from a population of uncertain size, it is not possible to reliably estimate their frequency or establish a causal relationship to drug exposure. Severe adverse reactions include liver injury presenting as hepatitis, liver failure necessitating liver transplantation or resulting in death (see WARNINGS ). Inhibition of myelopoiesis (agranulocytosis, granulopenia, aplastic anemia, and thrombocytopenia), drug fever, a lupus-like syndrome (including splenomegaly and vasculitis), periarteritis, hypoprothrombinemia, and bleeding have been reported. Nephritis, glomerulonephritis, interstitial pneumonitis, exfoliative dermatitis, and erythema nodosum have also been reported. There are reports of a vasculitis associated with the presence of anti-neutrophilic cytoplasmic antibodies (ANCA), resulting in severe complications and death (see WARNINGS ). There have been rare reports of serious hypersensitivity reactions (e.g., Stevens Johnson syndrome and toxic epidermal necrolysis) in patients treated with propylthiouracil. Other adverse reactions include skin rash, uticaria, nausea, vomiting, epigastric distress, arthralgia, paresthesias, loss of taste, taste perversion, abnormal loss of hair, myalgia, headache, pruritus, drowsiness, neuritis, edema, vertigo, skin pigmentation, jaundice, sialadenopathy, and lymphadenopathy.

Drug Interactions

Drug Interactions 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, especially before surgical procedures. Beta-adrenergic blocking agents: Hyperthyroidism may cause an increased clearance of beta blockers with a high extraction ratio. A reduced dose 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 dose 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.

Contraindications

CONTRAINDICATIONS Propylthiouracil is contraindicated in patients who have demonstrated hypersensitivity to the drug or any of the other product components.

Pregnancy and Breastfeeding

Pregnancy Pregnancy Category D. See WARNINGS . In pregnant women with untreated or inadequately treated Graves' disease, there is an increased risk of adverse events of maternal heart failure, spontaneous abortion, preterm birth, stillbirth, and fetal or neonatal hyperthyroidism. If propylthiouracil is used during pregnancy, or if the patient becomes pregnant while taking propylthiouracil, the patient should be warned of the rare potential hazard to the mother and fetus of liver damage. Because propylthiouracil crosses placental membranes and can induce goiter and cretinism in the developing fetus, it is important that a sufficient, but not excessive, dose be given during pregnancy. In many pregnant women, the thyroid dysfunction diminishes as the pregnancy proceeds; consequently a reduction of dosage may be possible. In some instances, antithyroid therapy can be discontinued several weeks or months prior to delivery. Since methimazole may be associated with the rare development of fetal abnormalities propylthiouracil may be the preferred agent during the first trimester of pregnancy. Given the potential for maternal hepatotoxicity from propylthiouracil, it may be preferable to switch from propylthiouracil to methimazole for the second and third trimesters during pregnancy.

Nursing Mothers Propylthiouracil is present in breast milk to a small extent and therefore likely results in clinically insignificant doses to the nursing infant. In one study, nine lactating women were administered 400 mg of propylthiouracil by mouth. The mean amount of propylthiouracil excreted during 4 hours after drug administration was 0.025% of the administered dose.

Overdosage

OVERDOSAGE Signs and Symptoms Nausea, vomiting, epigastric distress, headache, fever, arthralgia, pruritus, edema, and pancytopenia. Agranulocytosis is the most serious effect. Rarely, exfoliative dermatitis, hepatitis, neuropathies or CNS stimulation or depression may occur. No information is available on the following: LD 50 ; concentration of propylthiouracil in biologic fluids associated with toxicity and/or death; the amount of drug in a single dose usually associated with symptoms of overdosage; or the amount of propylthiouracil in a single dose likely to be life-threatening. Treatment To obtain up-to-date information about the treatment of overdose, a good resource is the certified Regional Poison Control Center. In managing overdosage, consider the possibility of multiple drug overdoses, interaction among drugs, and unusual drug kinetics in the patient. In the event of an overdose, appropriate supportive treatment should be initiated as dictated by the patient’s medical status.

How Supplied

HOW SUPPLIED Propylthiouracil Tablets, USP, 50 mg, are round, white, scored tablets, engraved P33, supplied as: Unit dose packages of 30 (5 x 6) NDC 68084-964-25 Store at controlled room temperature 15°-30°C (59°-86°F). FOR YOUR PROTECTION: Do not use if blister is torn or broken.