What is the initial treatment for hypothyroidism?

Initial Treatment for Hypothyroidism

The initial treatment for hypothyroidism is oral levothyroxine (T4) monotherapy, with dosing based on patient characteristics and comorbidities. 1, 2

Dosing Strategy

Standard Dosing

• For patients <70 years without cardiovascular disease, start levothyroxine at 1.6 mcg/kg/day based on ideal body weight 2, 3
• For patients with overt hypothyroidism (elevated TSH with low free T4), treatment should be initiated promptly to prevent progression of symptoms and complications 3, 4

Special Populations Requiring Lower Initial Doses (25-50 mcg/day)

• Patients >70 years of age 2, 5
• Patients with cardiovascular disease, especially coronary artery disease or atrial fibrillation 2, 5
• Patients with long-standing severe hypothyroidism 4
• Patients with multiple comorbidities 2

Monitoring and Dose Adjustment

• Check TSH and free T4 levels 6-8 weeks after starting treatment or changing dose 2, 3
• Target TSH within reference range for primary hypothyroidism 2, 4
• For central hypothyroidism (low/normal TSH with low free T4), target free T4 in upper half of reference range 2
• After identification of the appropriate maintenance dose, further evaluation is required every year, or sooner if patient's status changes 1

Special Considerations

Adrenal Insufficiency

• For patients with concurrent adrenal insufficiency and hypothyroidism, ALWAYS start corticosteroid replacement BEFORE thyroid hormone to prevent precipitating adrenal crisis 1, 2
• Start physiologic steroid replacement (e.g., hydrocortisone) before initiating levothyroxine 1

Pregnancy

• Pregnancy may increase levothyroxine requirements; monitor TSH levels and adjust dosage during pregnancy 5
• After delivery, return to pre-pregnancy dose immediately 5

Diabetes

• Addition of levothyroxine therapy in patients with diabetes may worsen glycemic control 5
• Carefully monitor glycemic control, especially when thyroid therapy is started, changed, or discontinued 5

Medication Interactions to Consider

• Many drugs can affect levothyroxine absorption, including:

  • Calcium supplements, iron supplements, and other minerals (take levothyroxine at least 4 hours apart) 5
  • Proton pump inhibitors, antacids, and sucralfate (monitor patients appropriately) 5
  • Bile acid sequestrants and ion exchange resins (administer levothyroxine at least 4 hours prior) 5

• Drugs that may alter levothyroxine metabolism:

  • Phenobarbital and rifampin (may increase hepatic degradation of levothyroxine) 5
  • Amiodarone (inhibits peripheral conversion of T4 to T3) 5

Common Pitfalls to Avoid

• Starting with full replacement doses in elderly patients or those with cardiovascular disease can precipitate cardiac events 2, 5
• Starting thyroid replacement before corticosteroids in patients with adrenal insufficiency can precipitate adrenal crisis 1, 2
• Inadequate monitoring can lead to under- or over-treatment, both of which are associated with adverse outcomes 3, 4
• Over-replacement is common in clinical practice and is associated with increased risk of atrial fibrillation and osteoporosis 4