What replacement therapy can patients use if Armour thyroid (thyroid extract) is discontinued?

Replacement Options After Armour Thyroid Discontinuation

Levothyroxine (LT4) is the recommended replacement therapy for patients who can no longer use Armour thyroid (thyroid extract). 1, 2

Why Levothyroxine is the Preferred Alternative

Levothyroxine sodium offers several advantages as a replacement for Armour thyroid:

• Provides uniform levels of both thyroxine (T4) and triiodothyronine (T3) in circulation without diurnal variation 3
• Allows precise dosing and titration based on laboratory values
• Extensively studied with well-established safety profile
• FDA-approved medication with consistent potency and quality control 2

Dosing Algorithm for Transitioning from Armour Thyroid to Levothyroxine

1. Initial Dosing:

   • Start with levothyroxine at approximately 1.6 mcg/kg/day for most adults 1
   • For elderly patients or those with cardiac disease: Begin with 25-50 mcg daily and gradually titrate upward 1

2. Monitoring and Adjustment:

   • Check TSH and free T4 levels 6-8 weeks after initiating therapy 1
   • Make dose adjustments in 12.5-25 mcg increments every 4-6 weeks until euthyroid 1
   • Target TSH levels should be age-appropriate:
     • Younger adults: Lower end of normal range
     • Elderly: Higher TSH targets acceptable 1

3. Maintenance:

   • Once stable, monitor every 6-12 months with TSH and free T4 1
   • More frequent monitoring if clinical status changes

Alternative Options

For patients who remain symptomatic on levothyroxine monotherapy:

1. Combination T4/T3 Therapy:

   • Consider reducing levothyroxine dose by 25 mcg and adding 2.5-7.5 mcg liothyronine (T3) once or twice daily 4
   • This approach mimics the physiologic T4:T3 ratio more closely than Armour thyroid
   • Liothyronine has a shorter half-life, requiring twice-daily dosing for stable levels 5, 6

2. Other Natural Thyroid Extracts:

   • Products like Nature-Throid have a similar T4:T3 ratio (4.22:1) as Armour Thyroid 6
   • However, these products may have similar supply issues as Armour Thyroid

Important Considerations and Potential Pitfalls

• Avoid Overtreatment: Excessive thyroid hormone replacement can lead to:

  • Osteoporosis and fractures, especially in postmenopausal women 3
  • Cardiac complications including arrhythmias, angina, and ventricular hypertrophy 1, 2
  • Approximately 25% of patients on levothyroxine are inadvertently maintained on doses high enough to make TSH undetectable 7

• Special Populations:

  • Elderly patients: Start with lower doses (25 mcg daily) and titrate slowly to minimize cardiovascular risk 1
  • Patients with cardiac disease: Use caution when initiating therapy; start with lower doses 1, 3
  • Pregnant women: May require dose increases of approximately 30% 1

• Drug Interactions:

  • Iron supplements, calcium supplements, and antacids can decrease levothyroxine absorption; separate administration by at least 4 hours 2
  • Oral anticoagulants may require dose adjustment due to increased sensitivity 5
  • Antidiabetic medications may need dosage adjustments 5

Monitoring for Therapeutic Success

• Laboratory Monitoring:

  • TSH is the primary marker for dose adequacy in primary hypothyroidism 1
  • Free T4 levels provide additional information, especially in central hypothyroidism 3

• Clinical Response:

  • Improvement in hypothyroid symptoms (fatigue, cold intolerance, weight gain, etc.)
  • Be aware that it may take several weeks before patients notice symptom improvement 2

Remember that thyroid hormone replacement is typically lifelong therapy, and patients should be counseled accordingly 2, 5.