What is the initial treatment for thyrotoxicosis?

Initial Treatment for Thyrotoxicosis

Beta blockers are the initial treatment of choice for patients presenting with thyrotoxicosis, followed by methimazole as the preferred antithyroid medication. 1

Treatment Algorithm

First-line Treatment

1. Beta blockers

   • Provide rapid symptomatic relief of adrenergic symptoms (tachycardia, tremor, anxiety)
   • Should be initiated immediately upon diagnosis of thyrotoxicosis
   • Particularly important in patients with pubertal onset of symptoms

2. Antithyroid medications (to be started concurrently)

   • Methimazole is the preferred antithyroid drug 1, 2

     • Initial dose: 1 mg/kg/day divided into two doses
     • Maintenance dose: Typically lower than initial dose

   • Propylthiouracil is generally reserved for specific situations 1, 3

     • First trimester of pregnancy (due to methimazole's risk of congenital malformations)
     • Initial dose: 300 mg daily, divided into three equal doses at 8-hour intervals
     • For severe hyperthyroidism: May increase to 400 mg daily; occasionally 600-900 mg daily initially
     • Maintenance dose: 100-150 mg daily

Special Considerations

• Pregnancy: Propylthiouracil is preferred in the first trimester, then switch to methimazole for second and third trimesters 1, 2

• Pediatric patients: Methimazole is strongly preferred over propylthiouracil due to risk of severe liver injury in children 2

• Breastfeeding mothers: Methimazole is considered safe during breastfeeding, though monitoring is recommended 2

• Elderly patients: Dose selection should be cautious due to potential decreased hepatic, renal, or cardiac function 3

Monitoring and Follow-up

• Monitor thyroid function tests periodically during therapy 1
• Adjust dosage based on clinical response and laboratory values
• Rising serum TSH indicates that a lower maintenance dose of antithyroid medication should be used 1

Treatment Based on Underlying Cause

The choice of definitive treatment depends on the etiology of thyrotoxicosis:

• Graves' disease:

  • First-line: 12-18 month course of antithyroid drugs 4
  • Long-term antithyroid drugs are a viable option 4
  • Radioactive iodine or surgery for relapsed cases 5

• Toxic nodular goiter/adenoma:

  • Radioactive iodine or surgery are preferred 4
  • Antithyroid drugs can be used for symptom control before definitive treatment

• Thyroiditis:

  • Symptomatic management
  • Glucocorticoid therapy in appropriate cases 4

Important Caveats and Pitfalls

• Do not delay beta blocker administration while waiting for laboratory confirmation of thyrotoxicosis in symptomatic patients

• Monitor for side effects of antithyroid medications, including agranulocytosis and hepatotoxicity

• Drug interactions: Hyperthyroidism may increase clearance of beta blockers, warfarin, digitalis, and theophylline; dose adjustments may be needed when patients become euthyroid 2

• Recent evidence suggests no significant difference in mortality or adverse events between propylthiouracil and methimazole for thyroid storm, contrary to some guidelines that recommend propylthiouracil 6