Synthroid (Levothyroxine) Initial Dosing and Titration Protocol
For patients with hypothyroidism, the initial levothyroxine dose should be 1.6 mcg/kg/day for most adults without risk factors, with dose adjustments every 6-8 weeks based on TSH levels until reaching the normal range. 1, 2
Initial Dosing Strategy
Standard Adult Dosing
- For adults without risk factors (under 70 years old, not frail, without cardiac disease or multiple comorbidities), calculate full replacement dose using ideal body weight at approximately 1.6 mcg/kg/day 2
- Monitor TSH and free T4 levels every 6-8 weeks while titrating hormone replacement to goal of TSH within the reference range 2, 3
Special Populations Requiring Lower Initial Doses
- For patients over 70 years old and/or frail patients with multiple comorbidities (including cardiac disease), start with a lower initial dose of 25-50 mcg 2
- For patients at risk of atrial fibrillation or with underlying cardiac disease, use a lower starting dose and titrate more slowly to avoid exacerbation of cardiac symptoms 1, 4
Titration Protocol
Monitoring and Dose Adjustments
- Adjust levothyroxine dosage by 12.5 to 25 mcg increments every 6-8 weeks until the patient is euthyroid 1, 2
- Use both TSH and free T4 for monitoring during titration, as TSH may take longer to normalize 2, 3
- The peak therapeutic effect of a given dose may not be attained for 4-6 weeks, so avoid premature dose adjustments 1
Target Laboratory Values
- For primary hypothyroidism: Titrate until the patient is clinically euthyroid and serum TSH returns to normal 1, 5
- For secondary or tertiary hypothyroidism: Use serum free-T4 level to titrate dosing until the patient is clinically euthyroid and serum free-T4 level is restored to the upper half of the normal range 1
- The aim for most adults should be to reach a stable serum TSH in the lower half of the reference range (0.4-2.5 mU/l) 5
Long-term Management
Maintenance Monitoring
- Once adequately treated with a stable dose, repeat testing every 6-12 months or as indicated for a change in symptoms 2, 3
- Development of a low TSH on therapy suggests overtreatment or recovery of thyroid function; in such cases, reduce the dose or discontinue with close follow-up 2, 3
Special Considerations
- Consider endocrine consultation for unusual clinical presentations, concern for central hypothyroidism, or difficulty titrating hormone therapy 2, 3
- Be aware that bioequivalence sometimes differs among generic and brand name levothyroxine products 6
- TSH values ≤0.1 mU/l carry a risk of development of atrial fibrillation and are associated with bone loss; avoid allowing TSH to fall below 0.2 mU/l 6, 2
Common Pitfalls to Avoid
- Starting with full replacement doses in elderly or cardiac patients can lead to cardiac complications 4, 2
- Failing to distinguish between primary and central hypothyroidism (the latter presents with low TSH and low free T4) 2
- Inadequate monitoring during titration can lead to under or overtreatment 7
- Not accounting for medications that interfere with levothyroxine absorption or metabolism when determining dose 6
- Premature laboratory testing before a new equilibrium is reached (approximately 6 weeks after dose change) 6