What is the primary treatment for hypothyroidism (underactive thyroid)?

Treatment of Hypothyroidism

Levothyroxine sodium is the primary treatment for hypothyroidism and should be used as first-line therapy for all patients with hypothyroidism. 1, 2

Diagnosis and Classification

• Hypothyroidism is diagnosed biochemically with elevated TSH and low free T4 levels indicating overt primary hypothyroidism 3
• Subclinical hypothyroidism is defined as elevated TSH with normal free T4 and T3 levels 4
• Both TSH and free T4 should be measured to properly assess thyroid function status 5

Treatment Recommendations

Overt Hypothyroidism

• All patients with overt hypothyroidism (elevated TSH and low free T4) require treatment with levothyroxine 1, 2
• Untreated hypothyroidism can lead to serious complications including heart failure, myxedema coma, and in pregnant women, increased risk of preeclampsia 1, 3

Subclinical Hypothyroidism

Treatment recommendations vary based on TSH levels:

• TSH >10 mIU/L: Levothyroxine therapy is recommended regardless of symptoms 4, 6
• TSH 4.5-10 mIU/L: Treatment decisions should consider:
  • Symptomatic patients may benefit from a trial of levothyroxine 4
  • Pregnant women or women planning pregnancy should receive treatment 4, 1
  • Patients with positive thyroid antibodies or goiter may benefit from treatment 6
  • Asymptomatic patients generally don't require routine treatment 4

Dosing Considerations

• Initial dosing should be tailored to patient-specific factors 3:
  • Standard starting dose: 1.6 μg/kg/day for most young patients 7
  • Lower starting doses (25-50 mcg) for:
    • Elderly patients (>70 years) 1
    • Patients with coronary artery disease 6
    • Patients with long-standing severe hypothyroidism 6

Monitoring Treatment

• TSH should be monitored 6-8 weeks after initiating levothyroxine or changing dose 3
• Target TSH for primary hypothyroidism: 0.5-2.0 mIU/L 6
• For central hypothyroidism, free T4 levels should be maintained in the upper half of normal range 6
• Annual monitoring once TSH reaches target level 3
• During pregnancy, monitor TSH every 6-8 weeks as requirements often increase 4, 1

Special Populations

Pregnancy

• Women with hypothyroidism who are pregnant or planning pregnancy should be treated to normalize TSH 1
• Any degree of TSH elevation in pregnant women warrants treatment 4, 1
• Levothyroxine requirements often increase during pregnancy 4

Elderly

• Treatment of subclinical hypothyroidism with TSH up to 10 mIU/L should probably be avoided in patients >85 years 6
• Lower starting doses and more gradual titration are recommended 1, 6

Common Pitfalls to Avoid

• Overtreatment is common and associated with increased risk of atrial fibrillation and osteoporosis 6
• One quarter of patients on levothyroxine may be inadvertently maintained on doses high enough to make TSH undetectable 4
• Many patients receive treatment at TSH levels closer to normal, suggesting potential overtreatment 5
• Poor compliance, malabsorption, and drug interactions should be considered in patients with persistently elevated TSH despite adequate replacement dose 6

Alternative Treatments

• While some studies have evaluated combination therapy with levothyroxine plus liothyronine, levothyroxine monotherapy remains the standard treatment 8
• Until clear advantages of combination therapy are demonstrated, levothyroxine alone should remain the treatment of choice 8, 9