Formulary
Carbimazole: Indications, Dosing, Side Effects and Interactions
Carbimazole clinical drug profile including indications, dosing, side effects, cautions and interactions.
MedNext Academy | 3 min read
Carbimazole: Indications, Dosing, Side Effects and Interactions
Carbimazole clinical drug profile including indications, dosing, side effects, cautions and interactions.
Indications and dose
**Hyperthyroidism**
- **Adult** (By Mouth): 15-40 mg daily continue until the patient becomes euthyroid, usually after 4 to 8 weeks, higher doses should be prescribed under specialist supervision only, then reduced to 5-15 mg daily, reduce dose gradually, therapy usually given for 12 to 18 months.
**Hyperthyroidism (blocking-replacement regimen) in combination with levothyroxine**
- **Adult** (By Mouth): 40-60 mg daily, therapy usually given for 18 months.
**Hyperthyroidism (blocking-replacement regimen) in combination with levothyroxine for carbimazole**
- **Child** (By mouth): Therapy usually given for 12 to 24 months (consult product literature or local protocols).
**Hyperthyroidism (including Graves' disease) for carbimazole**
- **Neonate** (By mouth): Initially 750 micrograms/kg daily until patient is euthyroid, usually after 8 to 12 weeks, then gradually reduce to a maintenance dose of 30-60% of the initial dose; higher initial doses (up to 1 mg/kg daily) are occasionally required, particularly in thyrotoxic crisis, dose may be given in single or divided doses.
- **Child 1 month-11 years** (By mouth): Initially 750 micrograms/kg daily until patient is euthyroid, usually after 4-8 weeks, then gradually reduce to a maintenance dose of 30-60% of the initial dose; higher initial doses are occasionally required, particularly in thyrotoxic crisis, dose may be given in single or divided doses; maximum 30 mg per day.
- **Child 12-17 years** (By mouth): Initially 30 mg daily until euthyroid, usually after 4-8 weeks, then gradually reduce to a maintenance dose of 30-60% of the initial dose; higher initial doses are occasionally required, particularly in thyrotoxic crisis, dose may be given in single or divided doses.
Contraindications
Severe blood disorders
Side effects
Rare or very rare Bone marrow disorders; haemolytic anaemia; severe cutaneous adverse reactions (SCARs); thrombocytopenia Frequency not known Agranulocytosis; alopecia; angioedema; dyspepsia; eosinophilia; fever; gastrointestinal disorder; generalised lymphadenopathy; haemorrhage; headache; hepatic disorders; insulin autoimmune syndrome; leucopenia; malaise; myopathy; nausea; nerve disorders; neutropenia; pancreatitis acute (discontinue permanently); salivary gland enlargement; skin reactions; taste loss
Interactions
**Other interactions (4):**
- Since carbimazole is a vitamin K antagonist, the effect of anticoagulants could be intensified.
- The serum levels of theophylline can increase and toxicity may develop if hyperthyroidic patients are treated with antithyroid medications without reducing the theophylline dosage.
- Co-administration of prednisolone and carbimazole may result in increased clearance of prednisolone.
- Carbimazole may inhibit the metabolism of erythromycin, leading to reduced clearance of erythromycin.
Pregnancy
MHRA advises consider use only after a thorough benefit-risk assessment. See Important Safety Information for further information.
Breast feeding
Present in breast milk but this does not preclude breast-feeding as long as neonatal development is closely monitored and the lowest effective dose is used. Amount in milk may be sufficient to affect neonatal thyroid function therefore lowest effective dose should be used.
Hepatic impairment
Manufacturer advises use with caution in mild to moderate insufficiency-half-life may be prolonged; avoid in severe insufficiency.
Medicinal forms
Capsule
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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