What are the medications used to treat hyperthyroidism?

Medications for Hyperthyroidism

The primary medications used to treat hyperthyroidism are thionamide-derived antithyroid drugs (methimazole/carbimazole and propylthiouracil) and beta blockers, with methimazole being the preferred first-line agent for most patients except during the first trimester of pregnancy. 1, 2, 3

First-Line Antithyroid Medications

Thionamide-Derived Drugs

1. Methimazole (MMI)/Carbimazole (CBZ)

   • Mechanism: Inhibits thyroid hormone synthesis 2
   • Dosing:
     • Initial dose: 20-40 mg daily (based on severity)
     • Maintenance dose: 5-10 mg daily 4
   • Advantages:
     • Once-daily dosing
     • Lower risk of severe hepatotoxicity than PTU 1

2. Propylthiouracil (PTU)

   • Mechanism: Inhibits thyroid hormone synthesis and peripheral conversion of T4 to T3 3
   • Dosing: 150-200 mg daily in divided doses 4
   • Special indications:
     • First trimester of pregnancy (should switch to MMI after first trimester) 3
     • Thyroid storm (due to additional inhibition of T4 to T3 conversion) 3, 5

Symptomatic Management

Beta Blockers

• Propranolol: 60-80 mg orally every 4-6 hours or 1-2 mg IV slowly 1
• Esmolol: Alternative for hemodynamically unstable patients 1
• Indications:
  • Control of adrenergic symptoms (tachycardia, tremor, anxiety)
  • First-line treatment for thyrotoxic crisis 1
  • Used alongside antithyroid drugs until euthyroid state is achieved 6, 1

Non-Dihydropyridine Calcium Channel Antagonists

• Alternative when beta blockers are contraindicated 6
• Helps control ventricular rate, especially in patients with atrial fibrillation due to hyperthyroidism 6

Treatment Duration and Monitoring

• Standard treatment course: 12-18 months of antithyroid drugs 4, 7
• Long-term treatment (5-10 years) may be considered in select cases with fewer recurrences (15%) compared to short-term treatment 7
• Monitor thyroid function tests every 4-6 weeks initially, then every 6-12 months when stable 1
• Watch for side effects:
  • Agranulocytosis (rare but serious)
  • Hepatotoxicity (more common with PTU)
  • Skin rash 3

Treatment Selection Based on Etiology

1. Graves' Disease (accounts for ~70% of hyperthyroidism cases):

   • First-line: Antithyroid drugs (methimazole preferred) 7
   • Alternatives: Radioactive iodine or surgery

2. Toxic Nodular Goiter (accounts for ~16% of cases):

   • Antithyroid drugs less effective long-term due to high relapse rates 8
   • Definitive treatment with radioactive iodine or surgery usually preferred 7

3. Thyroiditis-Induced Thyrotoxicosis:

   • Beta blockers for symptomatic control
   • Antithyroid drugs not effective (condition is due to release, not production) 7
   • Self-limiting condition in most cases 9

Special Considerations

• Pregnancy: PTU preferred in first trimester, then switch to methimazole 3
• Breastfeeding: Methimazole/carbimazole can be used 4
• Thyroid Storm: Requires aggressive treatment with PTU, beta blockers, corticosteroids, and supportive care 1, 5
• Elderly Patients: May need lower doses and more careful monitoring for cardiovascular complications 1

Common Pitfalls

• Failure to recognize that antithyroid drugs don't inactivate existing thyroid hormones, only prevent new synthesis 2, 3
• Overtreatment with antithyroid drugs leading to hypothyroidism
• Not monitoring for serious side effects like agranulocytosis or hepatotoxicity 3
• Using antithyroid drugs in thyroiditis where they are ineffective 7
• Not providing beta blockers for symptomatic relief during initial treatment phase 6, 1