carbimazole: clinical use

Prescribing considerations

• Confirm hyperthyroidism biochemically before treatment.
• Provide written and verbal advice about agranulocytosis symptoms and immediate action.
• Assess ability to comply with treatment and monitoring.
• Use caution with mild-to-moderate hepatic impairment and intrathoracic goitre.
• Review contraception and pregnancy plans.
• Coordinate interruption with the nuclear-medicine team for radioiodine.
• Permanently discontinue if acute pancreatitis is attributed to carbimazole.

Contraindications and cautions

• Hypersensitivity to carbimazole or an excipient.
• Serious pre-existing haematological disease.
• Severe hepatic insufficiency.
• Previous acute pancreatitis caused by carbimazole or thiamazole.
• The selected tablet contains lactose and sucrose and is unsuitable for specified rare hereditary sugar-intolerance disorders.

Monitoring

• Before treatment: thyroid function, full blood count with differential and liver function.
• During treatment: thyroid function until stable and periodically thereafter.
• Check white-cell count immediately if symptoms suggest neutropenia.
• Check liver function promptly if hepatic symptoms develop.
• Consider creatine phosphokinase when myalgia occurs.
• Pregnancy requires close maternal, fetal and neonatal monitoring.

Clinical pharmacology

Carbimazole is a thionamide prodrug rapidly converted to thiamazole. The active metabolite inhibits iodide organification and iodothyronine coupling, suppressing thyroid-hormone synthesis.

Formulation and product differences

• The selected product is a pink, speckled, round, biconvex, uncoated tablet marked on one side.
• It contains lactose monohydrate and sucrose.
• Not all authorised pack sizes may be marketed.

Tablet

Route: Oral

Strengths: 5 mg, 10 mg, 15 mg, 20 mg