Generic
Carbimazole
5 brands available in the market
At a glance
Carbimazole is an anti-thyroid medication used in the management of hyperthyroidism, thyrotoxicosis, and preparation for thyroidectomy. It works by reducing the amount of thyroid hormones produced by the thyroid gland.
Description
Carbimazole is an anti-thyroid substance that depresses the formation of thyroid hormone. It reduces the uptake and concentration of inorganic iodine by the thyroid, but its main effect is to reduce the formation of di-iodotyrosine and thyroxine. Carbimazole is rapidly absorbed from the gastrointestinal tract and is widely distributed throughout the body. Carbimazole is completely metabolised to methimazole, and it is the metabolite that is responsible for its clinical activity.
Carbimazole is indicated in the management of hyperthyroidism, thyrotoxicosis (including thyroid storm), and also for the preparation of patients for thyroidectomy. It can also be used in combination with radio-active ablative therapy.
Indications
- Hyperthyroidism
- Thyrotoxicosis (including thyroid storm)
- Preparation for thyroidectomy
- Combination with radio-active ablative therapy
- Graves' disease
Therapeutic class
Anti-thyroid drugs
Pharmacological class
Thioamide Antithyroid Agent
Pharmacology
Carbimazole is an anti-thyroid substance that depresses thyroid hormone formation. It inhibits thyroid peroxidase, blocking thyroid hormone production. Carbimazole is completely metabolised to methimazole, which is responsible for its clinical activity.
Mechanism of action
Carbimazole is converted to methimazole, which inhibits thyroid peroxidase enzyme, reducing thyroid hormone (T3 and T4) production and controlling hyperthyroidism.
Dosage
Adults: Initial dose: 20-60 mg/day (in 2-3 divided doses) until euthyroid state is achieved. Maintenance: 5-15 mg/day (can be taken as a single dose). Treatment duration: 18-24 months.
Children (under 12 years): Initial 250 mcg/kg/day (in divided doses).
Children (3-17 years): Initial 15 mg/day; adjust according to response.
Hepatic impairment: Severe: Contraindicated; caution required.
Renal impairment: Limited information; caution required.
Administration
May be taken with or without food, preferably at a fixed time each day. Swallow tablets whole; do not chew, crush, or break. Follow the dose and duration as advised by your physician.
Missed dose
If you miss a dose, take it as soon as you remember. Skip the missed dose if it is almost time for your next dose. Do not double the dose.
Side effects
Common side effects: Skin rash, headache, skin pigmentation, paresthesia (tingling sensation), urticaria, arthralgia (joint pain), gastrointestinal disturbances (nausea, vomiting, abdominal discomfort), abnormal hair loss, muscle pain/weakness.
Serious (rare): Agranulocytosis (severe decrease in white blood cells), aplastic anemia, thrombocytopenia, drug fever, lupus-like syndrome, vasculitis, nephritis, hepatic disorders (jaundice), taste disturbances.
Caution: Inform your doctor immediately if you develop signs of infection (fever, sore throat, mouth ulcers) as this may indicate agranulocytosis.
Precautions & warnings
- Risk of agranulocytosis: Inform your doctor immediately if you develop fever, sore throat, mouth ulcers, unexplained bruising/bleeding; get CBC checked.
- Signs of liver damage (abdominal pain, loss of appetite, darkened urine, yellowing of eyes/skin): Stop medication and inform your doctor.
- Use the lowest effective dose during pregnancy (overdosage may harm the fetus).
- Caution during breastfeeding (excreted in breast milk; monitor infant thyroid function).
- Extreme caution in tracheal obstruction (high doses may cause thyroid enlargement).
- Know your response before driving (may cause dizziness/drowsiness).
Contraindications
- Hypersensitivity to carbimazole or other thiourea antithyroid agents
- Hyperthyroidism due to nodular goitre
Drug interactions
- Iodine or iodine excess: Decreases carbimazole response; dose increase or longer therapy may be required.
- Oral anticoagulants (warfarin): Response may change as thyroid status normalizes; adjust dose based on prothrombin time.
- Digitalis glycosides (digoxin, digitoxin): Serum concentrations may increase; dose reduction may be needed as patients become euthyroid.
- Theophylline: Serum levels may increase or toxicity may develop.
Food interactions
It is not known whether it is safe to consume alcohol with Carbimazole; please consult your doctor.
Use in pregnancy
Unsafe during pregnancy (Category D). Definite evidence of risk to the developing baby. Use the lowest effective dose; overdosage may cause fetal hypothyroidism and goitre. May be used in life-threatening situations.
Pregnancy Category: D — always consult a doctor before taking during pregnancy.
Use in lactation
Safe during breastfeeding (if prescribed). Carbimazole is excreted in breast milk but not in significant amounts. The American Thyroid Association recommends monitoring babies for appropriate growth and development during routine pediatric check-ups.
Pediatric use
Children (under 12 years): Initial 250 mcg/kg/day (in divided doses). Children (3-17 years): 15 mg/day (initial).
Geriatric use
No specific dose adjustment required for elderly, but monitor serum thyroid levels and blood counts.
Renal / hepatic impairment
Hepatic impairment: Caution required; contraindicated in severe liver disease. Inform your doctor if signs of liver damage develop.
Overdose effects
Overdose may result in hypothyroidism and goitre. If blood dyscrasias occur, withdraw the drug immediately. Treatment: Symptomatic and supportive.
Storage conditions
Store below 30°C, away from light and moisture. Keep out of reach of children.
Chemical structure
Carbimazole