What is the initial treatment for hyperthyroidism (high thyroid hormone levels)?

Initial Treatment for Hyperthyroidism

The initial treatment for hyperthyroidism should be thionamide medication therapy, with methimazole (MMI) as the preferred first-line agent for most patients, except in pregnancy where propylthiouracil (PTU) is preferred during the first trimester. 1, 2

Diagnostic Evaluation

Before initiating treatment, proper evaluation is essential:

• Check TSH and Free T4 levels to confirm diagnosis and determine severity 3
• Consider T3 levels in highly symptomatic patients with minimal FT4 elevations 3
• Consider TSH receptor antibody testing if clinical features suggest Graves' disease (e.g., ophthalmopathy, T3 toxicosis) 3
• Physical examination findings of ophthalmopathy or thyroid bruit are diagnostic of Graves' disease 3

Treatment Algorithm Based on Severity

Mild Symptoms (Grade 1)

• Beta-blocker (e.g., atenolol or propranolol) for symptomatic relief 3
• Methimazole 15 mg once daily for mild to moderate hyperthyroidism 4, 5
• Monitor thyroid function every 2-3 weeks after diagnosis 3
• Close monitoring is important to catch transition to hypothyroidism, which is common with thyroiditis 3

Moderate Symptoms (Grade 2)

• Methimazole 15-30 mg daily (higher dose for more severe elevations) 5
• Beta-blocker therapy for symptom control 3
• Hydration and supportive care 3
• Consider endocrine consultation 3

Severe Symptoms (Grade 3-4)

• Methimazole 30 mg daily for severe hyperthyroidism (FT4 ≥7 ng/dL) 5
• Beta-blocker therapy (e.g., propranolol) 3
• Hydration and supportive care 3
• Consider hospitalization in severe cases 3
• Endocrine consultation is recommended 3

Medication Selection

Methimazole (Preferred First-Line)

• Advantages: once-daily dosing, fewer side effects, more effective in normalizing thyroid function 1, 5
• Initial dose: 10-30 mg daily as a single dose, based on severity 6, 5
• For severe hyperthyroidism: 30 mg daily normalizes FT4 in 96.5% of patients by 12 weeks 5
• For mild-moderate hyperthyroidism: 15 mg daily is sufficient 4, 5

Propylthiouracil (Alternative)

• Initial dose: 100-300 mg every 6-8 hours 6
• Preferred in first trimester of pregnancy due to lower risk of congenital anomalies 6
• Advantages over methimazole: inhibits peripheral conversion of T4 to T3, making it potentially more effective for thyroid storm 7
• Higher risk of hepatotoxicity compared to methimazole 5

Special Considerations

Pregnancy

• PTU is preferred during first trimester due to lower risk of congenital anomalies 6
• Consider switching to methimazole for second and third trimesters 7
• Both medications are compatible with breastfeeding 6

Thyroiditis

• Thyroiditis is self-limited and initial hyperthyroidism generally resolves in weeks with supportive care 3
• May progress to hypothyroidism or return to normal thyroid function 3
• Beta-blockers are the mainstay of treatment during the hyperthyroid phase 3

Monitoring and Follow-up

• Monitor thyroid function every 2-3 weeks initially after diagnosis 3
• For persistent thyrotoxicosis (>6 weeks), consider endocrine consultation for additional workup 3
• Watch for side effects of thionamides including:
  • Agranulocytosis (presents with sore throat, fever) 7
  • Hepatotoxicity (monitor for anorexia, pruritus, jaundice, right upper quadrant pain) 7
  • Skin eruptions 7

Common Pitfalls to Avoid

• Failing to distinguish between different causes of hyperthyroidism (Graves' disease vs. thyroiditis) 3, 2
• Using too low a dose of methimazole in severe hyperthyroidism 5
• Not monitoring frequently enough for transition to hypothyroidism in thyroiditis 3
• Missing rare but serious adverse effects like agranulocytosis or hepatotoxicity 7
• Overlooking the need for beta-blockers for symptom control while waiting for thionamides to take effect 3