Thyrozol (Carbimazole) 5mg: Initiation and Management
Thyrozol (Carbimazole) 5mg should be initiated at a dose of 15-40mg daily for hyperthyroidism, with the specific starting dose determined by disease severity. 1, 2, 3
Medication Category
- Thyrozol (Carbimazole) is an antithyroid medication used for treating hyperthyroidism
- It works by inhibiting thyroid hormone synthesis by blocking the incorporation of iodine into tyrosine residues
Dosage Recommendations
Initial Dosage
- Mild to moderate hyperthyroidism: 20mg daily (four 5mg tablets)
- Severe hyperthyroidism: 40mg daily (eight 5mg tablets)
- Higher initial doses (40mg) achieve more rapid normalization of thyroid hormones but have higher risk of iatrogenic hypothyroidism 3
- Lower doses (20mg) are effective for mild/moderate disease with lower risk of overcorrection 3
Administration
- Can be given as a single daily dose due to long intrathyroidal half-life 2, 4
- Single daily dosing has comparable efficacy to divided dosing and improves compliance 2, 5
- Should be taken at the same time each day, preferably on an empty stomach
Maintenance Dosage
- After normalization of thyroid function (typically 4-8 weeks):
- Reduce to maintenance dose of 5-15mg daily
- Adjust based on thyroid function tests
- Treatment duration typically 12-18 months
Monitoring
- Check thyroid function tests (TSH, free T4, free T3) at:
- Baseline (before starting treatment)
- 4 weeks after initiation
- Every 4-6 weeks until stable
- Every 3 months thereafter
- Monitor for signs of:
- Undertreatment (persistent hyperthyroidism)
- Overtreatment (iatrogenic hypothyroidism)
- Complete blood count should be checked periodically
Precautions
Major Precautions
- Agranulocytosis: Rare but serious side effect
- Patients should be instructed to stop medication and seek immediate medical attention if they develop sore throat, mouth ulcers, fever, or flu-like symptoms
- Liver toxicity: Monitor for jaundice, dark urine, pale stools
- Pregnancy: Benefits usually outweigh risks but requires specialist management
- Breastfeeding: Compatible at lower doses with monitoring of infant thyroid function
Drug Interactions
- Avoid concurrent use with:
- Medications that can cause agranulocytosis (increasing risk)
- Medications affecting thyroid function
Dose Adjustment Considerations
- Elevated TSH with carbimazole therapy indicates overtreatment requiring dose reduction 6
- Elderly patients or those with cardiac conditions: Start with lower doses (10-15mg daily)
- Renal or hepatic impairment: Consider dose reduction and more frequent monitoring
Common Pitfalls
- Overtreatment: Watch for signs of hypothyroidism (fatigue, cold intolerance, weight gain)
- Undertreatment: Persistent symptoms of hyperthyroidism indicate need for dose increase
- Poor compliance: Single daily dosing improves adherence compared to multiple daily doses 2
- Failure to monitor: Regular thyroid function tests are essential for proper dose adjustment
Treatment Response
- Most patients achieve normal thyroid hormone levels within 4-6 weeks 2, 4
- Patients with larger goiters may take longer to respond 4
- Clinical improvement often precedes normalization of laboratory values
By following these guidelines, Thyrozol (Carbimazole) can be effectively and safely used to manage hyperthyroidism with appropriate monitoring and dose adjustments.