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|Propylthiouracil

Propylthiouracil

Trade Names:
Propylthiouracil
- Tablets 50 mg

Mechanism of Action

Pharmacology

Inhibits synthesis of thyroid hormones.

Pharmacokinetics

Absorption

Readily absorbed from the GI tract. Bioavailability is 80% to 95%. T _max is 1.99 hr; C _max is 7.12 mcg/mL.

Distribution

Protein binding is 75% to 80%, primarily to albumin. Vd is approximately 0.4 L/kg.

Metabolism

Actively concentrated by the thyroid. Metabolized rapidly in the liver; undergoes glucuronidation.

Elimination

Urine (35%); less than 1% as unchanged. T _1/2 is 1 to 2 hr. Total body clearance is approximately 7 L/hr.

Peak

Approximately 17 wk to normalize serum T ₃ and T ₄ concentrations.

Indications and Usage

Long-term therapy of hyperthyroidism; amelioration of hyperthyroidism in preparation for subtotal thyroidectomy or radioactive iodine therapy; when thyroidectomy is contraindicated or not advisable.

Unlabeled Uses

Management of alcoholic liver disease.

Contraindications

Hypersensitivity to antithyroid drugs; lactating women.

Dosage and Administration

PO The initial dose is 300 mg/day in 3 equal doses q 8 hr. In patients with severe hyperthyroidism or very large goiters, initial dose is usually 400 mg/day, occasionally up to 600 to 900 mg/day. The maintenance dose is 100 to 150 mg/day in divided doses q 8 hr.

PO The initial dose is 150 to 300 mg/day in divided doses q 8 hr. The maintenance dose is determined by response.

PO The initial dose is 50 to 150 mg/day in divided doses q 8 hr.

PO The initial dose is 5 to 7 mg/kg/day in divided doses q 8 hr. The maintenance dose is 1/ 3 to 2/ 3 initial dose, beginning when patient is euthyroid.

General Advice

Give with meals to minimize GI irritation.

Storage/Stability

Store in tight, light-resistant container at room temperature.

Drug Interactions

Altered anticoagulant action.

Increased effects of beta blockers.

Increased digitalis levels, resulting in toxicity.

Altered theophylline clearance in hyperthyroid or hypothyroid patients.

Laboratory Test Interactions

None well documented.

Adverse Reactions

CNS

Paresthesias; neuritis; headache; vertigo; drowsiness; neuropathies; CNS stimulation; depression.

Dermatologic

Rash; urticaria; pruritus; erythema nodosum; skin pigmentation; exfoliative dermatitis; lupus-like syndrome (splenomegaly, hepatitis, periarteritis; hypoprothrombinemia; bleeding).

EENT

Loss of taste; sialadenopathy.

GI

Nausea; vomiting; epigastric distress.

Genitourinary

Nephritis.

Hepatic

Jaundice; hepatitis.

Hematologic

Inhibition of myelopoiesis (eg, agranulocytosis, leukopenia, granulocytopenia, thrombocytopenia); aplastic anemia; hypoprothrombinemia; periarteritis.

Miscellaneous

Abnormal hair loss; arthralgia; myalgia; edema; lymphadenopathy; drug fever; interstitial pneumonitis; insulin autoimmune syndrome (hypoglycemia).

Precautions

Pregnancy

Category D .

Lactation

Avoid nursing. However, if antithyroid drug is essential, PTU is preferred antithyroid agent while nursing.

Children

Hepatotoxicity has occurred in pediatric patients. Discontinue drug immediately if signs and symptoms of hepatic dysfunction develop.

Agranulocytosis

Potentially most serious side effect. Discontinue drug if agranulocytosis, aplastic anemia, hepatitis, fever, or exfoliative dermatitis occur.

Hemorrhagic effects

May cause hypoprothrombinemia and bleeding.

Overdosage

Symptoms

Nausea, vomiting, epigastric distress, headache, fever, arthralgia, pruritus, edema, pancytopenia; most serious effect: agranulocytosis.

Patient Information

• Instruct patient to take resting pulse daily and encourage patient to keep recorded chart.
• Advise patient to monitor weight at least 2 to 3 times/wk or per health care provider instruction, obtaining weight at same time, using same scale. Encourage patient to keep recorded chart.
• Emphasize importance of following dietary restrictions regarding shellfish, iodized salt and other foods high in iodine.
• Explain that desired response may take several months if the thyroid is greatly enlarged.
• Advise patient to carry Medi-Alert identification at all times describing medications.
• Instruct patient to notify dentist or health care provider of drug regimen before surgical or dental procedures.
• Emphasize importance of follow-up visits to monitor effectiveness of drug therapy.
• Caution patient not to stop taking medication abruptly to avoid thyroid crisis.
• Instruct patient to report the following symptoms to health care provider: Sore throat, fever, rash, mouth sores; cold intolerance, mental depression; tachycardia, irritability; persistent nausea, steatorrhea or vomiting, drowsiness, yellowing of skin or whites of eyes; unusual bleeding or bruising.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other activities requiring mental alertness.
• Instruct patient not to take otc medications without consulting health care provider.