What is the initial treatment for hypothyroidism?

Initial Treatment for Hypothyroidism

The initial treatment for hypothyroidism is levothyroxine (T4) monotherapy, with dosing based on patient characteristics: 1.6 mcg/kg/day for young, healthy patients and 25-50 mcg/day for elderly patients or those with cardiovascular disease. 1, 2

Diagnosis Confirmation

• Confirm diagnosis with TSH and free T4 levels; elevated TSH with low free T4 indicates primary hypothyroidism 1, 3
• Distinguish between primary hypothyroidism (elevated TSH, low free T4) and central hypothyroidism (low/normal TSH, low free T4) as management approaches differ 1

Initial Dosing Algorithm

Patient-Specific Dosing

• For patients <70 years without cardiovascular disease:

  • Start levothyroxine at full replacement dose of 1.6 mcg/kg/day based on ideal body weight 1, 2, 4
  • This approach is appropriate for most young, healthy patients 5

• For patients with risk factors:

  • Start with lower dose of 25-50 mcg/day for patients who are:

    • 70 years old 1, 6

    • Have cardiovascular disease, especially coronary artery disease or atrial fibrillation 1, 5
    • Have long-standing severe hypothyroidism 5
  • Gradually titrate upward to avoid exacerbating cardiac conditions 1, 7

Special Considerations

• For patients with adrenal insufficiency AND hypothyroidism, ALWAYS start corticosteroid replacement BEFORE thyroid hormone to prevent precipitating adrenal crisis 8, 1
• For central hypothyroidism, replace thyroid hormone after corticosteroids have been initiated 8

Monitoring and Dose Adjustment

• Check TSH and free T4 levels 6-8 weeks after starting treatment or changing dose 8, 1, 2
• Target TSH within reference range (0.4-4.0 mIU/L) for primary hypothyroidism 1, 4
• For central hypothyroidism, target free T4 in upper half of reference range 1
• After identification of appropriate maintenance dose, further evaluation is required annually, or sooner if patient's status changes 8

Common Pitfalls to Avoid

• Starting with too high a dose in elderly or cardiac patients can lead to adverse cardiovascular outcomes 1, 5
• Starting thyroid replacement before corticosteroids in patients with adrenal insufficiency can precipitate adrenal crisis 8, 1
• Drug interactions can affect levothyroxine absorption and metabolism:
  • Administer levothyroxine at least 4 hours apart from calcium, iron supplements, and other binding agents 9
  • Be aware that certain medications (amiodarone, glucocorticoids) can affect thyroid hormone metabolism 9, 3
• Overtreatment is common and associated with increased risk of atrial fibrillation and osteoporosis 5

Special Patient Populations

• For patients with diabetes: Addition of levothyroxine may worsen glycemic control; carefully monitor and adjust antidiabetic medications as needed 9, 3
• For patients on anticoagulants: Levothyroxine increases response to oral anticoagulant therapy; monitor coagulation tests and adjust anticoagulant dose as needed 9