What is the treatment for hypothyroidism (low T4)?

Treatment of Hypothyroidism (Low T4)

Levothyroxine (T4) is the standard treatment for hypothyroidism, with dosing typically starting at 1.6 mcg/kg/day in young, healthy adults without cardiac disease, while elderly patients or those with cardiac disease should start with a lower dose of 25-50 mcg/day and titrate gradually. 1

Diagnosis and Initial Assessment

• Check TSH and free T4 levels to confirm diagnosis
• Consider thyroid peroxidase (TPO) antibody testing to identify autoimmune etiology (Hashimoto's thyroiditis)
• Differentiate between primary hypothyroidism (high TSH, low T4) and central hypothyroidism (low/normal TSH, low T4)
  • Central hypothyroidism requires evaluation for hypophysitis or other pituitary disorders 2

Treatment Protocol

Dosing Guidelines:

• Initial dosing:
  • Young, healthy adults: 1.6 mcg/kg/day (approximately 130 mcg for average-weight adult) 1
  • Elderly or patients with cardiac disease: 25-50 mcg/day 1, 3
  • Patients with significant comorbidities: Start with lower doses (25-50 mcg) 4

Monitoring and Dose Adjustment:

• Check TSH and free T4 levels 6-8 weeks after starting therapy or dose adjustment 1
• Adjust dose by 12.5-25 mcg increments if TSH remains above reference range 1
• Goal: Maintain TSH within normal reference range (0.5-4.5 mIU/L) 1
• Once stable, monitor every 6-12 months 1

When to Initiate Treatment:

• TSH persistently >10 mIU/L: Initiate treatment 1
• TSH 4.5-10 mIU/L with symptoms: Initiate treatment 1
• TSH 4.5-10 mIU/L without symptoms: Consider treatment based on individual factors; monitor TSH every 6-12 months if not treating 1

Special Considerations

Medication Administration:

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast or 3-4 hours after the last meal of the day 1
• Many medications affect levothyroxine absorption including calcium supplements, iron supplements, proton pump inhibitors, bile acid sequestrants, and antacids 1
• Inconsistent administration can lead to variable absorption and unstable thyroid function 1

Pregnancy:

• Levothyroxine requirements may increase by 30% or more by 4-6 weeks' gestation 1, 3
• Increase dosage by 12.5-25 mcg/day when TSH exceeds trimester-specific ranges 1
• Monitor TSH and free T4 more frequently during pregnancy 1, 3
• Inadequate treatment during pregnancy increases risk of preeclampsia, preterm birth, low birth weight, and cognitive impairment in children 1, 3

Central Hypothyroidism:

• Characterized by low or inappropriately normal TSH with low free T4 1
• Evaluate for hypophysitis or other pituitary disorders 2
• Treatment focuses on normalizing free T4 levels rather than TSH 1

Severe Hypothyroidism/Myxedema Coma:

• Requires immediate hospitalization in ICU 1
• IV levothyroxine: loading dose of 200-400 mcg on day 1 1
• Supportive care including hydrocortisone, careful fluid management, and ventilatory support if needed 1

Potential Complications

• Subclinical hyperthyroidism (occurs in 14-21% of treated patients) 1
• Increased risk of atrial fibrillation, especially in older adults 1, 3
• Decreased bone mineral density and increased fracture risk, particularly in postmenopausal women 1

Alternative Therapies

• Liothyronine (T3) has a short half-life and requires twice-daily administration 5, 6
• Combination T4/T3 therapy may benefit a small subset of patients who remain symptomatic despite normal TSH levels on T4 monotherapy, though confirmatory studies are needed 6