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Pharmacologic class: Thioamide derivative
Therapeutic class: Antithyroid agent
Pregnancy risk category D
FDA Box Warning
• Drug has caused severe liver injury and acute liver failure, in some cases fatal. These reports of hepatic reactions include cases requiring liver transplant.
• Reserve drug for patients intolerant of methimazole and in whom radioactive iodine therapy or surgery isn't appropriate for management of hyper-thyroidism.
• Because of risk of fetal abnormalities associated with methimazole, propylthiouracil may be treatment of choice when an antithyroid drug is indicated during or just before first trimester.
Directly interferes with thyroid synthesis by preventing iodine from combining with thyroglobulin, leading to decreased thyroid hormone levels
Tablets: 50 mg
Indications and dosages
Adults: Initially, 300 to 450 mg P.O. daily in equally divided doses q 8 hours; for maintenance, 100 to 150 mg P.O. daily.
➣ Thyrotoxic crisis
Adults: 200 mg P.O. q 4 to 6 hours during first 24 hours, then a maintenance dosage of 100 to 150 mg P.O. daily
• Hypersensitivity to drug
Use cautiously in:
• decreased bone marrow reserve
• pregnancy and breastfeeding patients
• Give with meals to reduce GI upset.
• Be aware that drug shouldn't be used in children unless patient is allergic to or intolerant of methimazole, and there are no other treatment options available.
CNS: drowsiness, headache, vertigo, neuritis, paresthesia
GI: nausea, vomiting, diarrhea, epigastric distress
Hematologic: agranulocytosis, leukopenia, thrombocytopenia
Hepatic: jaundice, hepatic necrosis, liver failure
Musculoskeletal: joint pain, myalgia
Skin: rash, urticaria, pruritus, skin discoloration, alopecia, cutaneous vasculitis
Other: taste loss, fever, lymphadenopathy, parotitis, edema
Drug-drug. Anticoagulants: potentiation of anticoagulant effect
Drug-diagnostic tests. Alanine aminotransferase, alkaline phosphatase, aspartate aminotransferase, bilirubin, lactate dehydrogenase: increased levels
Granulocytes, platelets: decreased levels Prothrombin time: prolonged
• Monitor CBC and liver and thyroid function tests.
• Assess for signs and symptoms of hypothyroidism (cold intolerance, nonpitting edema, fatigue, weight gain, and depression).
☞ Monitor for severe rash, fever, jaundice, or enlarged cervical lymph nodes. If present, stop therapy and notify prescriber.
• Instruct patient to take with meals to reduce GI upset.
• Teach patient to recognize and report signs and symptoms of hypothyroidism and jaundice.
• Advise patient to discuss iodine intake (as in iodized salt and shellfish) with prescriber.
• Tell patient to avoid over-the-counter cold remedies that contain iodine.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.
• Advise female patient of childbearing age to discuss pregnancy or breastfeeding with prescriber before taking.
• As appropriate, review all other significant and life-threatening adverse reactions and interactions, especially those related to the drugs and tests mentioned above.