methimazole

Contraindicated in:

Hypersensitivity.

Use Cautiously in:

Patients with ↓ bone marrow reserve;
Patients >40 yr (↑ risk of agranulocytosis);
OB: Use during pregnancy only if potential maternal benefit justifies potential fetal risk. May cause congenital malformations (especially if used during 1st trimester).

Adv. Reactions/Side Effects ⬆ ⬇

Derm: rash, skin discoloration, urticaria

GI: diarrhea, HEPATOTOXICITY, loss of taste, nausea, parotitis, vomiting

Hemat: AGRANULOCYTOSIS, anemia, leukopenia, thrombocytopenia

MS: arthralgia

Neuro: drowsiness, headache, vertigo

Misc: fever, lymphadenopathy

Interactions ⬆ ⬇

Drug-drug:

Additive bone marrow depression with antineoplastics or radiation therapy.
Antithyroid effect may be ↓ by potassium iodide or amiodarone.
↑risk of agranulocytosis with phenothiazines.
May alter response to warfarin and digoxin.

Availability ⬆ ⬇

(Generic available)

Tablets: 5 mg; 10 mg

Route/Dosage ⬆ ⬇

PO (Adults ): Initial: 15–60 mg/day in 3 divided doses. Maintenance: 5–15 mg once daily.
PO (Children ): Initial: 0.4 mg/kg/day in 3 divided doses. Maintenance: 0.2 mg/kg/day in single dose or 2 divided doses.

Action ⬆ ⬇

Inhibits the synthesis of thyroid hormones.

Therapeutic effects:

Decreased signs and symptoms of hyperthyroidism.

Classifications ⬆ ⬇

Therapeutic Classification: antihyroid agents

Pharmacokinetics ⬆ ⬇

Absorption: Rapidly absorbed following oral administration.

Distribution: Concentrated in the thyroid gland.

Metabolism/Excretion: Mostly metabolized by the liver; <10% eliminated unchanged by the kidneys.

Half-Life: 3–5 hr.

Canadian Brand Names ⬆ ⬇

Time/Action Profile ⬆ ⬇

(effect on thyroid function)

ROUTE	ONSET	PEAK	DURATION
PO	1 wk	4–10 wk	1–2 wk

Patient/Family Teaching ⬆ ⬇

Instruct patient to take medication as directed, around the clock. Take missed doses as soon as remembered; take both doses together if almost time for next dose; check with health care professional if more than 1 dose is missed. Consult health care professional prior to discontinuing medication.
Instruct patient to monitor weight 2–3 times weekly. Notify health care professional of significant changes.
May cause drowsiness. Caution patient to avoid driving or other activities requiring alertness until response to medication is known.
Advise patient to consult health care professional regarding dietary sources of iodine (iodized salt, shellfish).
Advise patient to report sore throat, fever, chills, headache, malaise, weakness, yellowing of eyes or skin, unusual bleeding or bruising, rash, or symptoms of hyperthyroidism or hypothyroidism promptly.
Instruct patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
Advise patient to carry identification describing medication regimen at all times.
Advise patient to notify health care professional of medication regimen prior to treatment or surgery.
Rep: Advise female patients of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding. May cause fetal harm, especially during 1st trimester. If breastfeeding, monitor infant thyroid levels weekly or biweekly.
Emphasize the importance of routine exams to monitor progress and to check for side effects.

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Indications ⬇

Contraind./Precautions ⬆ ⬇