Methimazole

Trade Names:
Tapazole
- Tablets 5 mg
- Tablets 10 mg

Pharmacology

Feedback for Methimazole As a treatment for... Avg User Ratings [?] Hyperthyroidism Be the first to rate it 0 comments   Compare with other drugs.

Inhibits synthesis of thyroid hormones.

Pharmacokinetics

Absorption

Methimazole bioavailability is 80% to 95%.

Distribution

A high amount of methimazole is excreted in breast milk, has high transplacental passage, and is 0% protein bound.

Metabolism

Methimazole is rapidly metabolized.

Elimination

Less than 10% is excreted in urine. The t _½ is 6 to 13 h.

Indications and Usage

Long-term therapy of hyperthyroidism; amelioration of hyperthyroidism in preparation for subtotal thyroidectomy or radioactive iodine therapy.

Contraindications

Use in nursing women.

Dosage and Administration

PO 15 to 60 mg/day in 3 equal doses at approximately 8-h intervals.

PO 5 to 15 mg/day.

PO 0.4 mg/kg/day.

PO Approximately ½ initial dose. Alternately, children may be given 0.5 to 0.7 mg/kg/day in 3 divided doses as initial therapy and 1/ 3 to 2/ 3 of initial dose for maintenance.

Storage/Stability

Store in light-resistant container at room temperature (59° to 86°F).

Drug Interactions

May decrease or increase anticoagulant action.

May increase effects of beta blockers, resulting in toxicity.

May cause increase in effects of digitalis glycosides, including toxicity.

May alter 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 including splenomegaly, hepatitis, periarteritis, hypoprothrombinemia and bleeding.

EENT

Loss of taste; sialadenopathy.

GI

Nausea; vomiting; epigastric distress.

Genitourinary

Nephritis.

Hematologic

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

Hepatic

Jaundice; hepatitis.

Miscellaneous

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

Precautions

Pregnancy

Category D .

Lactation

Avoid nursing.

Agranulocytosis

Potentially most serious side effect. Discontinue drug in presence of agranulocytosis, aplastic anemia, hepatitis, fever or exfoliative dermatitis.

Hemorrhage

May cause hypoprothrombinemia and bleeding. Monitor PT.

Overdosage

Symptoms

Nausea, vomiting, epigastric distress, headache, fever, arthralgia, pruritus, edema, pancytopenia, agranulocytosis, exfoliative dermatitis, hepatitis, neuropathies, CNS stimulation or depression.

Patient Information

• Instruct patient in importance of taking proper dose exactly as scheduled.
• Advise patient not to stop, start or adjust dose of any medications, including OTC, without discussing with health care provider.
• Explain to patient the importance of complying with follow-up appointments and lab work.
• Instruct patient to check pulse daily.
• Advise patient that iodine-restrictive diet may be necessary.
• Inform patient that response to therapy may take months.
• Instruct patient to report the following symptoms to health care provider: rash, fever, sore throat, bruising or signs of infection or jaundice.
• Advise patient that drug may cause drowsiness and to use caution while driving or performing other tasks requiring mental alertness.

Link to this page

Printable Version

Email Page

Add to my drug list