1. Introduction
Carbimazole, commonly marketed under brand names such as NeoMercazole, is an antithyroid medication used to manage hyperthyroidism (overactive thyroid). It works by inhibiting thyroid hormone synthesis, thus reducing excessive thyroid activity. Carbimazole is a prodrug that is converted to its active metabolite, methimazole.
2. Indications
- Approved Indications:
- Hyperthyroidism (Graves’ disease, toxic multinodular goitre, or toxic adenoma).
- Preparation for thyroidectomy in patients with hyperthyroidism.
- Adjunct to radioactive iodine therapy.
3. Dosage
- Adults:
- Initial dose: 15–40 mg/day in divided doses, depending on the severity of hyperthyroidism.
- Maintenance dose: 5–15 mg/day as a single daily dose once euthyroid is achieved.
- Children:
- Initial dose: 0.5–1 mg/kg/day in divided doses.
- Maintenance dose: Adjust based on response, typically lower than initial doses.
4. Administration
- Take orally with or without food.
- Doses should be evenly spaced throughout the day (e.g., every 8 hours) for the initial phase.
5. Forms Available
- Tablets: 5 mg, 10 mg, 20 mg.
6. Side Effects
6.1. Common Side Effects
- Nausea.
- Rash or itching.
- Arthralgia (joint pain).
6.2. Less Common Side Effects
- Altered taste sensation.
- Headache.
- Mild gastrointestinal discomfort.
6.3. Rare but Serious Side Effects
- Agranulocytosis (sudden drop in white blood cell count).
- Hepatotoxicity.
- Vasculitis.
7. Warnings
- Agranulocytosis is a rare but serious complication. Advise patients to report symptoms of infection (e.g., fever, sore throat) immediately.
- Avoid use in patients with severe liver impairment due to the risk of hepatotoxicity.
8. Precautions
- Regularly monitor thyroid function tests (TFTs) to avoid hypothyroidism.
- Use with caution in patients with pre-existing liver dysfunction or a history of drug-induced agranulocytosis.
- Ensure the patient understands the importance of reporting symptoms of infection or jaundice.
9. Interactions
- Drug-Drug Interactions:
- May enhance the effect of anticoagulants (e.g., warfarin).
- May alter the efficacy of thyroid hormone replacement therapy if used concurrently.
- Drug-Food Interactions:
- No significant interactions reported.
10. Monitoring Parameters
- Thyroid function tests (T3, T4, and TSH) every 4–6 weeks initially, then less frequently once euthyroid is achieved.
- Full blood count (FBC) at baseline and during therapy to detect agranulocytosis.
- Liver function tests (LFTs) periodically, especially if symptoms of liver dysfunction arise.
11. Use in Children
- Approved for use in paediatric patients with hyperthyroidism.
- Dosage should be carefully adjusted based on weight and thyroid function response.
12. Use in Pregnancy
- Category D: Use with caution during pregnancy, as uncontrolled hyperthyroidism poses significant risks to both mother and foetus.
- Lower doses should be used to maintain euthyroid status, as overtreatment may cause foetal hypothyroidism.
13. Use in Elderly
- No specific dosage adjustments required, but monitor for side effects, especially agranulocytosis and hepatotoxicity, due to age-related changes in metabolism and immunity.
14. Use in Kidney Disease
- No specific dosage adjustments required, but use cautiously in severe renal impairment.
15. Use in Liver Disease
- Avoid in patients with severe hepatic impairment.
- Monitor liver enzymes regularly in patients with mild-to-moderate liver dysfunction.
16. Patient Counselling Points
- Inform patients about the importance of taking the medication as prescribed and not stopping abruptly.
- Advise patients to report symptoms of infection (e.g., fever, sore throat) or jaundice immediately.
- Explain the need for regular blood tests to monitor thyroid function, liver health, and white blood cell counts.
- Stress the importance of avoiding pregnancy while on high doses and consulting a healthcare provider for pregnancy planning.
- Inform patients that improvement in symptoms may take 2–4 weeks as thyroid hormone levels stabilise.
17. Table of Brand Names, Manufacturers, and Prices
Brand Name | Manufacturer | Price (USD) |
---|---|---|
NeoMercazole | Amdipharm Mercury | $20–40 (30 tablets, 5 mg) |
Generic Options | Various | $10–20 (30 tablets, 5 mg) |
18. FAQs (15 Questions)
- What is carbimazole used for?
Carbimazole is used to treat hyperthyroidism by reducing the production of thyroid hormones. - How does carbimazole work?
It inhibits the enzyme thyroid peroxidase, blocking the production of T3 and T4 hormones. - How long does it take for carbimazole to work?
Symptoms typically improve within 2–4 weeks, but full therapeutic effects may take several months. - Can carbimazole cause side effects?
Common side effects include nausea, rash, and joint pain. Rare but serious effects include agranulocytosis and liver toxicity. - How is carbimazole taken?
It is taken orally, with or without food, in evenly spaced doses. - Can carbimazole be used during pregnancy?
Yes, but with caution and at the lowest effective dose to avoid foetal hypothyroidism. - What should I do if I miss a dose?
Take it as soon as you remember, but skip it if it’s close to the next dose. Do not double up. - Does carbimazole interact with other medications?
Yes, it may increase the effect of anticoagulants and alter thyroid hormone replacement therapy efficacy. - Can I drink alcohol while on carbimazole?
Moderate alcohol consumption is generally safe, but consult your doctor for specific advice. - What are the symptoms of agranulocytosis?
Fever, sore throat, and persistent infections. Report these symptoms immediately. - Can children take carbimazole?
Yes, it is approved for children with hyperthyroidism under medical supervision. - Is carbimazole safe for long-term use?
Yes, but regular monitoring of thyroid function, liver health, and blood counts is essential. - How should carbimazole be stored?
Store at room temperature, away from direct sunlight and moisture. - Can carbimazole cure hyperthyroidism?
It controls hyperthyroidism but does not cure it. Long-term therapy or other treatments (e.g., radioactive iodine or surgery) may be needed. - What should I do if I experience side effects?
Contact your healthcare provider immediately, especially for symptoms of infection or liver dysfunction.