Levothyroxine Dose Adjustment Guidelines
Adjust levothyroxine in 12.5-25 mcg increments every 6-8 weeks based on TSH levels, with smaller adjustments (12.5 mcg) for elderly patients or those with cardiac disease. 1, 2
Initial Dosing Strategy
Standard Adult Dosing
- For patients <70 years without cardiac disease: Start with full replacement dose of approximately 1.6 mcg/kg/day 1
- For patients >70 years or with cardiac disease: Start with 25-50 mcg/day and titrate gradually 1, 2
- Full-dose initiation is safe in cardiac asymptomatic patients and achieves euthyroidism faster than low-dose titration 3
Weight-Based Considerations
- Elderly patients (≥65 years): Require approximately 1.09 mcg/kg actual body weight or 1.35 mcg/kg ideal body weight—one-third lower than younger populations 4
- Obese patients: Calculate dose using ideal body weight rather than actual body weight to avoid overtreatment 4
- Levothyroxine requirements decrease progressively with age due to reduced thyroxine degradation rate 5
Dose Adjustment Protocol
Titration Increments
- Standard adjustment: Increase or decrease by 12.5-25 mcg based on current dose and patient characteristics 1, 2
- Younger patients (<70 years) without cardiac disease: May use 25 mcg increments for more aggressive titration 1
- Elderly patients (>70 years) or cardiac disease: Use 12.5 mcg increments to avoid cardiac complications 1, 2
Timing of Adjustments
- During titration: Recheck TSH and free T4 every 6-8 weeks after any dose change 1, 6, 2
- This 6-8 week interval represents the time needed to reach steady state 1
- For patients with atrial fibrillation or serious cardiac conditions: Consider more frequent monitoring within 2 weeks 1
Target TSH Ranges
Primary Hypothyroidism
- Target TSH: 0.5-4.5 mIU/L with normal free T4 1, 6
- Maintain TSH within reference range to prevent complications of both under- and over-replacement 6
Thyroid Cancer Patients (TSH Suppression)
- Low-risk patients with excellent response: TSH 0.5-2 mIU/L 1
- Intermediate-to-high risk with biochemical incomplete response: TSH 0.1-0.5 mIU/L 1
- Structural incomplete response: TSH <0.1 mIU/L 1
Pregnant Patients
- Pre-existing hypothyroidism: Increase dose by 12.5-25 mcg/day to maintain TSH in trimester-specific range 1, 2
- Monitor TSH every 4 weeks during pregnancy 2
- Return to pre-pregnancy dose immediately after delivery 2
Long-Term Monitoring
Stable Patients
- Once euthyroid: Recheck TSH every 6-12 months or if symptoms change 1, 6
- Annual monitoring is sufficient for stable patients on consistent dose 1
Pediatric Patients
- Monitor TSH and free T4 at 2 and 4 weeks after initiation, 2 weeks after dose changes, then every 3-12 months until growth complete 2
Managing Overtreatment
TSH Suppression (<0.1 mIU/L)
- Immediate action: Decrease dose by 25-50 mcg 1
- Prolonged TSH suppression increases risk for atrial fibrillation, osteoporosis, and cardiovascular mortality 1, 6
Mild Suppression (TSH 0.1-0.45 mIU/L)
- For primary hypothyroidism: Decrease dose by 12.5-25 mcg, particularly if in lower part of range 1
- Patients with TSH <0.1 mIU/L have greater risk of complications than those with TSH 0.1-0.45 mIU/L 6
Critical Pitfalls to Avoid
- Never adjust doses more frequently than every 6-8 weeks before reaching steady state 1
- Approximately 25% of patients are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications 1
- In patients with suspected adrenal insufficiency: Start corticosteroids before initiating or increasing levothyroxine to prevent adrenal crisis 1
- Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, especially in elderly patients 1
Special Populations
Elderly Patients
- Require lower replacement doses (approximately 110 mcg/day vs 158 mcg/day in younger adults) 7, 5
- Start with 25-50 mcg/day and increase by 12.5 mcg every 6-8 weeks 1, 2
- More susceptible to cardiac complications from overtreatment 1