What is the first-line treatment for hypothyroidism?

First-Line Treatment for Hypothyroidism

Levothyroxine (synthetic T4) is the first-line treatment for hypothyroidism, with dosing tailored to patient-specific factors including age and cardiac status. 1, 2

Diagnosis and Confirmation

• Diagnosis requires biochemical testing with elevated TSH and low free T4 indicating overt primary hypothyroidism 2
• Measure TSH and free T4 within 2-3 weeks of initial assessment 1
• Positive TPO antibodies indicate autoimmune etiology (Hashimoto's thyroiditis) and predict higher risk of developing overt hypothyroidism 1

Levothyroxine Dosing Guidelines

Dosing should be stratified based on patient characteristics:

Population	Starting Dose	Target TSH Range
Patients under 70 years without cardiac disease	1.6 mcg/kg/day	0.5-2.0 mIU/L
Elderly patients or those with cardiac conditions	25-50 mcg/day	1.0-4.0 mIU/L
Pregnant women	Adjusted to restore TSH to reference range	0.5-2.0 mIU/L

Monitoring and Dose Adjustments

• Check TSH levels 6-8 weeks after initiating treatment or changing dose 2
• Once stabilized, monitor TSH annually to avoid overtreatment or undertreatment 2
• For pregnant women, increase weekly dosage by 30% (take one extra dose twice weekly) with monthly monitoring 3

Special Populations

Elderly Patients

• Start with lower doses (12.5-50 mcg/day) in patients over 60 years or with known/suspected ischemic heart disease 3
• Target higher TSH (1.0-4.0 mIU/L) to avoid overtreatment complications 1

Patients with Cardiac Disease

• Use lower starting doses to avoid cardiac overload and arrhythmias 4
• Atrial fibrillation is the most common arrhythmia with levothyroxine overtreatment in elderly patients 4

Pregnant Women

• Promptly treat hypothyroidism diagnosed during pregnancy 4
• Monitor TSH levels throughout pregnancy as requirements may increase 4
• Return to pre-pregnancy dose immediately after delivery 4

Common Pitfalls and Considerations

1. Overtreatment risks:

   • Increased risk of atrial fibrillation and osteoporosis, particularly in elderly patients 1
   • Low TSH on therapy suggests overtreatment 1

2. Medication interactions:

   • Many medications can interfere with thyroid function or TSH testing 5
   • Consider timing of levothyroxine administration (typically on empty stomach)

3. Refractory hypothyroidism:

   • For patients with persistently elevated TSH despite adequate dosing, consider:
     • Medication adherence issues
     • Absorption problems
     • Alternative formulations (liquid) or administration routes 6

4. Subclinical hypothyroidism:

   • Treatment recommended when TSH >10 mIU/L 1, 3
   • Also treat if pregnant or planning pregnancy 1

5. Combination therapy:

   • Adding T3 (liothyronine) to levothyroxine is not recommended as first-line therapy, even in patients with persistent symptoms and normal TSH levels 3, 7

Clinical Manifestations Improved with Treatment

• Fatigue (68%-83% of patients)
• Weight gain (24%-59%)
• Cognitive issues (45%-48%)
• Menstrual irregularities (~23%)
• Cardiovascular complications
• Insulin resistance and hyperglycemia in diabetic patients 2

Proper treatment with levothyroxine normalizes TSH levels and improves clinical manifestations of hypothyroidism, reducing morbidity and mortality while enhancing quality of life.