What is the indication to start someone on liothyronine (triiodothyronine)?

Indications for Starting Liothyronine (T3) Therapy

Liothyronine (T3) therapy should primarily be reserved for specific clinical scenarios including myxedema coma, patients with persistent hypothyroid symptoms despite optimal levothyroxine therapy, and cases where peripheral conversion of T4 to T3 is suspected to be impaired. 1, 2

Primary Indications for Liothyronine

1. Myxedema Coma (Medical Emergency)

• Initial dosage: 5-20 mcg intravenously
• Myxedema coma is a life-threatening emergency requiring immediate intervention
• Intravenous liothyronine is preferred due to its rapid onset of action compared to levothyroxine 1, 3

2. Persistent Symptoms Despite Optimal Levothyroxine Therapy

• Before considering liothyronine:
  • Confirm diagnosis of overt hypothyroidism
  • Optimize levothyroxine dosing (aim for TSH 0.3-2.0 mU/L for 3-6 months)
  • Rule out other causes of persistent symptoms 2
• Starting dose: Reduce levothyroxine by 25 mcg/day and add 2.5-7.5 mcg liothyronine once or twice daily 4
• Monitor for clinical response and adjust as needed

3. Impaired Peripheral Conversion of T4 to T3

• Consider when clinical suspicion exists that patients cannot adequately convert T4 to T3 1
• May be particularly relevant in certain medical conditions affecting deiodinase activity

4. During Radioactive Iodine Scanning Procedures

• Liothyronine may be preferred over levothyroxine when temporary discontinuation of thyroid hormone is needed
• Allows for more rapid induction and shorter duration of hypothyroidism 1

Dosing Guidelines

For Mild Hypothyroidism:

• Starting dose: 25 mcg daily
• May increase by up to 25 mcg every 1-2 weeks
• Usual maintenance dose: 25-75 mcg daily 1

For Myxedema (Severe Hypothyroidism):

• Starting dose: 5 mcg daily
• Increase by 5-10 mcg daily every 1-2 weeks
• When 25 mcg daily is reached, may increase by 5-25 mcg every 1-2 weeks
• Usual maintenance dose: 50-100 mcg daily 1

Important Considerations and Cautions

• Liothyronine has a rapid onset and shorter half-life compared to levothyroxine, resulting in wider serum T3 fluctuations 1
• Potential for more pronounced cardiovascular side effects, particularly in elderly patients or those with cardiac conditions 1, 5
• Current evidence does not consistently demonstrate clear advantages of combination therapy (levothyroxine plus liothyronine) over levothyroxine monotherapy 6, 7
• Decision to start liothyronine should be a shared decision between patient and clinician 2

Monitoring Recommendations

• Monitor TSH and free T4 levels every 4-6 weeks until stable, then every 6-12 months 8
• For patients with cardiac disease, atrial fibrillation, or other arrhythmias, more frequent monitoring (every 3-12 months) is recommended 5
• Watch for signs of overtreatment (subclinical hyperthyroidism), which can lead to cardiac complications and bone density loss 8

Special Populations

Elderly Patients:

• Start with lower doses (5 mcg daily) and increase more gradually
• Higher risk of adverse cardiovascular effects 1

Patients with Cardiac Disease:

• Use with caution due to potential for increased heart rate, left ventricular mass increase, diastolic dysfunction, and atrial arrhythmias 8
• Consider lower starting doses and more gradual titration 1

While levothyroxine remains the standard first-line treatment for hypothyroidism, liothyronine has specific indications where its pharmacokinetic properties may offer advantages in carefully selected patients.