No

Antithyroid Agent

Palliative treatment of hyperthyroidism, return the hyperthyroid patient to a normal metabolic state prior to thyroidectomy, and to control thyrotoxic crisis that may accompany thyroidectomy. The use of antithyroid thioamides is as effective in elderly as they are in younger adults; however, the expense, potential adverse effects, and inconvenience (compliance, monitoring) make them undesirable. The use of radioiodine due to ease of administration and less concern for long-term side effects and reproduction problems (some older males) makes it a more appropriate therapy.

D

Hypersensitivity to methimazole or any component, nursing mothers (per manufacturer; however, expert analysis and the American Academy of Pediatrics state this drug may be used with caution in nursing mothers)

Use with extreme caution in patients receiving other drugs known to cause myelosuppression particularly agranulocytosis, patients >40 years of age; avoid doses >40 mg/day ( myelosuppression); may cause acneiform eruptions or worsen the condition of the thyroid

>10%:

Central nervous system: Fever

Hematologic: Leukopenia

1% to 10%:

Central nervous system: Dizziness

Gastrointestinal: Nausea, vomiting, stomach pain, abnormal taste

Hematologic: Agranulocytosis

Miscellaneous: SLE-like syndrome

<1%: Edema, drowsiness, vertigo, headache, rash, urticaria, pruritus, alopecia, goiter, constipation, weight gain, nephrotic syndrome, thrombocytopenia, aplastic anemia, cholestatic jaundice, arthralgia, paresthesia, swollen salivary glands

Symptoms of overdose include nausea, vomiting, epigastric distress, headache, fever, arthralgia, pruritus, edema, pancytopenia, and signs of hypothyroidism

Management of overdose is supportive

Increased toxicity: Iodinated glycerol, lithium, potassium iodide; anticoagulant activity increased

Protect from light

Inhibits the synthesis of thyroid hormones by blocking the oxidation of iodine in the thyroid gland, blocking iodine's ability to combine with tyrosine to form thyroxine and triiodothyronine (T₃), does not inactivate circulating T₄ and T₃

Onset of antithyroid effect: Oral: 12-18 hours

Duration: 36-72 hours

Distribution: Concentrated in the thyroid gland; crosses the placenta; appears in breast milk (1:1)

Protein binding, plasma: None

Metabolism: In the liver

Bioavailability: 80% to 95%

Half-life: 4-13 hours

Elimination: 80% renal

Oral: Administer in 3 equally divided doses at approximately 8-hour intervals

Alternatively: Initial: 0.5-0.7 mg/kg/day or 15-20 mg/m²/day in 3 divided doses

Maintenance: 1/3 to 2/3 of the initial dose beginning when the patient is euthyroid

Maximum: 30 mg/24 hours

Adults: Initial: 15 mg/day for mild hyperthyroidism; 30-40 mg/day in moderately severe hyperthyroidism; 60 mg/day in severe hyperthyroidism; maintenance: 5-15 mg/day

Adjust dosage as required to achieve and maintain serum T₃, T₄, and TSH levels in the normal range. An elevated T₃ may be the sole indicator of inadequate treatment. An elevated TSH indicates excessive antithyroid treatment.

Dosing adjustment in renal impairment: Adjustment is not necessary

Should be administered consistently in relation to meals every day

Monitor for signs of hypothyroidism, hyperthyroidism, T₄, T₃; CBC with differential, liver function (baseline and as needed), serum thyroxine, free thyroxine index

May cause dizziness or drowsiness

Leukopenia is common; use caution with clozapine and carbamazepine; concurrent use with lithium may increase the effects on the thyroid

No information available to require special precautions

No effects or complications reported

Take as directed, at the same time each day around-the-clock; do not miss doses or make up missed doses. This drug will need to be taken for an extended period of time to achieve appropriate results. You may experience nausea or vomiting (small frequent meals may help), dizziness or drowsiness (use caution when driving or engaging in tasks that require alertness until response to drug is known). Report rash, fever, unusual bleeding or bruising, unresolved headache, yellowing of eyes or skin, or changes in color of urine or feces, unresolved malaise. Pregnancy/breast-feeding precautions: Do not get pregnant while taking this medication; use appropriate barrier contraceptive measures. Do not breast-feed.

Tablet: 5 mg, 10 mg

Hamor GH and Lafdjian A, "Dualistic Thiourea Moiety Taste Response of Methimazole," J Pharm Sci, 1967, 56(6):777-8.

Raby C, Lagorce JF, Jambut-Absil AC, et al, "The Mechanism of Action of Synthetic Antithyroid Drugs: Iodine Complexation During Oxidation of Iodide," Endocrinology, 1990, 126(3):1683-91.