Methimazole

DEA Class; Rx

Common Brand Names; Northyx, Tapazole

  • Antithyroid Agents

Oral thioimidazole antithyroid agent; lower risk of hepatotoxicity when compared to propylthiouracil (PTU)
Used for hyperthyroid conditions including Graves disease in both adult and pediatric patients
Do not use in early pregnancy

Indicated for the treatment of thyrotoxicosis, including hyperthyroidism, Graves’ disease, toxic multinodular goiter, and thyroid storm.
For the treatment of thyroid storm.

Hypersensitivity

Breastfeeding

Agranulocytosis

Alopecia

Aplastic anemia

Dermatologic reactions (eg, rash, pruritus, skin pigmentation)

Hepatotoxicity

Leukocytoclastic vasculitis

Neuritis

Polyarthritis

Pruritus

Salivary gland swelling

Skin pigmentation

Thrombocytopenia

Urticaria

Vertigo

Lupus-like syndrome reported

Hypoprothrombinemia and bleeding may occur; monitor, especially before surgical procedure performed

Antineutrophil cytoplasmic autoantibody (ANCA)-positive vasculitis reported; discontinue use in presence of vasculitis

Concurrent administration of other agranulocytosis-causing drugs

Prolonged treatment may cause hypothyroidism; routinely monitor free T4 levels and TSH; adjust dose as necessary to maintain euthyroid state

Significant bone marrow suppression may occur; use caution if administered with other agents known to cause myelosupression; discontinue if significan agranulocytosis, leukopenia, or aplastic anemia occurs

Hepatitis reported; discontinue if it occurs or if clinically significant hepatic enzyme levels, including transaminases >3 times upper limit of normal observed

Discontinue if unexplained fever occurs

Antithyroid agents associated with rare but severe dermatologic reactions; discontinue if exfoliative dermatitis occurs

Pregnancy category: D (drug crosses placenta)

Lactation: Drug distributed in breast milk; use contraindicated by manufacturer (American Academy of Pediatrics [AAP] Committee states that drug is compatible with nursing; American Academy of Family Physicians [AAFP] states that it is safe for nursing)

Adults

60 mg/day PO.

Geriatric

60 mg/day PO.

Adolescents

0.4 mg/kg/day PO is the FDA-approved dose; however, doses up to 1 mg/kg/day PO (Max: 30 mg) have been used off-label.

Children

0.4 mg/kg/day PO is the FDA-approved dose; however, doses up to 1 mg/kg/day PO (Max: 30 mg) have been used off-label.

Infants

0.4 mg/kg/day PO is the FDA-approved dose; however, doses up to 1 mg/kg/day PO have been used off-label.

Neonates

Safety and efficacy have not been established; however, doses up to 1 mg/kg/day PO have been used off-label.

Methimazole

tablet

  • 5mg
  • 10mg

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