Initial Treatment for Hypothyroidism in Treatment-Naïve Patients
Start levothyroxine immediately at 1.6 mcg/kg/day for most adults under 70 years without cardiac disease, or 25-50 mcg/day for elderly patients or those with cardiac risk factors. 1, 2
Dosing Algorithm Based on Patient Characteristics
Young, Healthy Adults (<70 years, no cardiac disease)
- Initiate full replacement dose of 1.6 mcg/kg/day 3, 1, 2
- This approach normalizes TSH more rapidly and prevents prolonged hypothyroid symptoms 1, 4
- Most patients tolerate full-dose initiation without adverse effects 5
Elderly Patients (>70 years) or Cardiac Disease
- Start with 25-50 mcg/day 3, 1, 2
- Titrate slowly every 6-8 weeks to avoid precipitating atrial fibrillation or exacerbating coronary artery disease 3, 2, 4
- Lower starting doses reduce risk of cardiac complications, particularly atrial arrhythmias which are the most common adverse effect in elderly patients 2
Patients with Long-Standing Severe Hypothyroidism
- Begin with reduced doses (25-50 mcg/day) regardless of age 5
- Rapid normalization can precipitate cardiac complications in chronically hypothyroid patients 5
Critical Pre-Treatment Considerations
Rule Out Adrenal Insufficiency First
- Always exclude concurrent adrenal insufficiency before starting levothyroxine 3, 1
- Starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 3
- This is particularly important in patients with suspected central hypothyroidism or hypophysitis 3
Confirm Diagnosis with Repeat Testing
- Recheck TSH after 3-6 weeks if initial elevation is modest (TSH 4.5-10 mIU/L) 1
- 30-60% of elevated TSH levels normalize spontaneously on repeat testing 1, 6
- This avoids unnecessary lifelong treatment for transient thyroiditis 1
Monitoring and Dose Titration
Initial Monitoring Phase
- Recheck TSH and free T4 every 6-8 weeks during dose titration 3, 1, 7, 2
- Peak therapeutic effect may not occur for 4-6 weeks after each dose adjustment 2
- Free T4 helps interpret ongoing abnormal TSH levels, as TSH may lag behind clinical improvement 1, 7
Dose Adjustments
- Increase by 12.5-25 mcg increments if TSH remains elevated 3, 1, 2
- Larger adjustments risk overtreatment, especially in elderly or cardiac patients 3
- Target TSH within reference range (0.5-4.5 mIU/L) for primary hypothyroidism 1, 5
Long-Term Monitoring
- Once stable, monitor TSH every 6-12 months 1, 7, 8
- More frequent monitoring needed if symptoms change or dose adjustments required 1, 7
Administration Instructions
Timing and Food Interactions
- Take on empty stomach, 30-60 minutes before breakfast with full glass of water 2
- Administer at least 4 hours before or after medications that interfere with absorption (iron, calcium, proton pump inhibitors) 2
- Avoid soybean-based foods that decrease absorption 2
Common Pitfalls to Avoid
Overtreatment Risks
- Approximately 25% of patients are inadvertently overtreated with TSH suppression 1
- Even slight overdose increases risk of atrial fibrillation, osteoporosis, and fractures, particularly in elderly and postmenopausal women 1, 5, 6
- Development of low TSH on therapy requires dose reduction 3, 1, 7
Undertreatment Consequences
- Persistent hypothyroid symptoms including fatigue, weight gain, and cognitive impairment 1, 8
- Increased cardiovascular risk, including heart failure 1, 8
- Adverse effects on lipid metabolism and reproductive health 8, 4
Failure to Recognize Transient Hypothyroidism
- Not all elevated TSH requires lifelong treatment 1, 6
- Thyroiditis recovery phase, nonthyroidal illness, and medication effects can cause transient elevations 3, 1
- Premature treatment commits patients to unnecessary lifelong therapy 1, 6
Special Populations
Pregnant Women or Planning Pregnancy
- Treat any degree of TSH elevation promptly 1, 2, 4
- Untreated hypothyroidism increases risk of preeclampsia, low birth weight, and neurodevelopmental effects in offspring 1, 2, 4
- Increase levothyroxine dose by 30% (take 9 doses weekly instead of 7) as soon as pregnancy confirmed 2, 4
- Monitor TSH monthly during pregnancy 2