What is the first line medication for hypothyroidism?

First-Line Medication for Hypothyroidism

Levothyroxine sodium (T4) is the first-line medication for the treatment of hypothyroidism. 1, 2

Mechanism and Rationale

Levothyroxine is an oral synthetic form of the thyroid hormone thyroxine (T4), which is converted in peripheral tissues to the more active form triiodothyronine (T3). It effectively restores normal thyroid hormone levels and alleviates symptoms of hypothyroidism.

Dosing Considerations

The appropriate dosing of levothyroxine depends on several factors:

Initial Dosing

• Standard adult starting dose: 1.6 mcg/kg body weight per day 3
  • Typically 75-100 mcg/day for women
  • Typically 100-150 mcg/day for men

Special Populations

• Elderly patients: Start with lower doses (25-50 mcg/day) due to decreased requirements and increased risk of cardiovascular complications 2, 4
• Patients with cardiovascular disease: Begin with lower doses (25 mcg/day) and increase gradually
• Pregnant women: Higher doses often required; monitor TSH every 6-8 weeks during pregnancy 1, 2

Monitoring Therapy

• Target: Normalize serum TSH levels within the reference range 1
• Initial follow-up: Check TSH and free T4 levels after 6-8 weeks of therapy 1
• Dose adjustments: If TSH remains elevated, increase dose by 12.5-25 mcg; recheck in 6-8 weeks 1
• Long-term monitoring: Once stable, check TSH annually or sooner if symptoms change 1

Clinical Pearls and Pitfalls

• Administration timing: Take levothyroxine on an empty stomach, 30-60 minutes before breakfast for optimal absorption 5
  • Bedtime administration may be an effective alternative 5
• Medication interactions: Separate levothyroxine from calcium, iron supplements, antacids, and certain other medications by at least 4 hours
• Subclinical hypothyroidism management:
  • TSH >10 mIU/L: Treatment recommended 1
  • TSH 4.5-10 mIU/L: Treatment may be considered, especially with symptoms 1

Alternative Therapies

While combination therapy with levothyroxine plus liothyronine (T3) has been studied, it has not consistently shown benefits over levothyroxine monotherapy 6. Therefore, levothyroxine alone remains the standard first-line treatment for hypothyroidism.

Efficacy and Safety

Levothyroxine is highly effective at normalizing thyroid function and improving symptoms when properly dosed. When initiated at appropriate doses based on patient characteristics and carefully monitored, it has an excellent safety profile. The most common adverse effects result from overdosing and include palpitations, anxiety, insomnia, and tremor.