What is the next step for a patient already taking 125 mcg of Synthroid (levothyroxine) with an elevated Thyroid-Stimulating Hormone (TSH) level?

Increase Levothyroxine Dose by 12.5-25 mcg

For a patient already taking 125 mcg of Synthroid with an elevated TSH, increase the levothyroxine dose by 12.5-25 mcg (to 137.5-150 mcg daily) and recheck TSH and free T4 in 6-8 weeks. 1, 2, 3

Dose Adjustment Strategy

• The recommended increment is 12.5-25 mcg based on the degree of TSH elevation and patient characteristics 1, 2
• For patients under 70 years without cardiac disease, use 25 mcg increments for more efficient titration 1
• For patients over 70 years or with cardiac disease (atrial fibrillation, coronary artery disease), use smaller 12.5 mcg increments to avoid cardiac complications 1, 2, 3
• Larger dose jumps risk iatrogenic hyperthyroidism, which occurs in 14-21% of treated patients and increases risk for atrial fibrillation, osteoporosis, and fractures 1

Magnitude of TSH Elevation Matters

• If TSH is >10 mIU/L, dose adjustment is mandatory regardless of symptoms, as this carries approximately 5% annual risk of progression to overt hypothyroidism 1, 4
• If TSH is 4.5-10 mIU/L, dose adjustment is still reasonable for patients already on therapy to normalize TSH into the reference range (0.5-4.5 mIU/L) 1, 2
• Treatment at any TSH elevation prevents cardiovascular dysfunction, adverse lipid profiles, and quality of life deterioration 1, 2

Monitoring Timeline

• Recheck TSH and free T4 in 6-8 weeks after dose adjustment, as this represents the time needed to reach steady state 1, 2, 3
• The peak therapeutic effect may not be attained for 4-6 weeks 3
• For patients with atrial fibrillation or serious cardiac conditions, consider more frequent monitoring within 2 weeks rather than waiting the full 6-8 weeks 1
• Once TSH normalizes, monitor annually or sooner if symptoms change 1, 2

Target TSH Range

• Target TSH should be 0.5-4.5 mIU/L with normal free T4 for primary hypothyroidism 1, 2, 5
• Some patients may feel better with TSH in the lower half of the reference range (0.5-2.0 mIU/L) 5
• Avoid over-replacement: approximately 25% of patients are inadvertently maintained on doses sufficient to fully suppress TSH, increasing cardiovascular and bone risks 1, 6

Common Pitfalls to Avoid

• Never adjust doses more frequently than every 6-8 weeks before reaching steady state 1
• Do not assume non-compliance without first ruling out malabsorption, drug interactions (iron, calcium, proton pump inhibitors), or inadequate dosing 5, 7
• Avoid excessive dose increases that could lead to TSH suppression (<0.1 mIU/L), which significantly increases risk for atrial fibrillation (especially in elderly), osteoporosis, and cardiovascular mortality 1, 6, 8
• For elderly patients (>70 years), slightly higher TSH targets may be acceptable to avoid overtreatment risks, though still aim for the reference range 8

Special Considerations

• If the patient has thyroid cancer, consult endocrinology before adjusting, as target TSH varies by risk stratification (may need TSH 0.1-0.5 mIU/L or even <0.1 mIU/L for high-risk disease) 1, 2
• For pregnant patients or those planning pregnancy, more aggressive TSH normalization is warranted, targeting the lower half of trimester-specific reference ranges 1, 3
• If concurrent adrenal insufficiency is suspected (central hypothyroidism), start corticosteroids before increasing levothyroxine to prevent adrenal crisis 1