Levothyroxine Initiation in Severe Hypothyroidism (TSH ~200)
For a patient with severe hypothyroidism (TSH ~200), start levothyroxine at a lower dose and titrate gradually, especially if the patient is over 70 years old or has cardiac disease; otherwise, younger patients without cardiac risk factors can start closer to full replacement dose. 1
Age and Cardiac Risk Stratification Determines Starting Dose
Patients under 70 years without cardiac disease:
- Start at or near full replacement dose of 1.6 mcg/kg/day 1, 2
- This approach reduces the need for multiple follow-up visits and repeated laboratory testing 3
- Even with TSH of 200, younger healthy patients tolerate rapid normalization well 3
Patients over 70 years OR with any cardiac disease:
- Start at 25-50 mcg/day regardless of TSH level 1, 2
- Elderly patients with coronary disease are at increased risk of cardiac decompensation, angina, or arrhythmias even with therapeutic levothyroxine doses 4
- Rapid normalization can unmask or worsen cardiac ischemia 3
Titration Protocol
For all patients:
- Increase dose by 12.5-25 mcg increments every 6-8 weeks based on TSH response 1, 2
- Smaller increments (12.5 mcg) should be used for elderly patients or those with cardiac disease 1
- Larger increments (25 mcg) may be appropriate for younger patients without cardiac disease 1
- Monitor TSH every 6-8 weeks during titration until target TSH of 0.5-4.5 mIU/L is achieved 1
Critical timing consideration:
- The peak therapeutic effect of a given dose may not be attained for 4-6 weeks, so avoid adjusting doses too frequently 2
- Wait at least 6 weeks between dose adjustments to reach steady state 1, 5
Critical Safety Considerations Before Starting Treatment
Rule out adrenal insufficiency first:
- Before initiating levothyroxine, especially in patients with suspected central hypothyroidism or autoimmune disease, rule out concurrent adrenal insufficiency 1
- Starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis 1
- If adrenal insufficiency is present, start corticosteroids at least 1 week before levothyroxine 1
Confirm the diagnosis:
- Measure both TSH and free T4 to distinguish overt hypothyroidism (low free T4) from subclinical hypothyroidism (normal free T4) 1
- With TSH of 200, this almost certainly represents overt hypothyroidism requiring immediate treatment 1
Common Pitfalls to Avoid
Avoid overtreatment:
- Even minor over-replacement during initial titration should be avoided because of the risk of cardiac events 3
- Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications 1
- Chronic over-replacement may induce osteoporosis, particularly in postmenopausal women 3
Do not start at full replacement dose in high-risk patients:
- Never start at full replacement dose (1.6 mcg/kg/day) in elderly patients or those with cardiac disease, even with TSH of 200 1, 4
- Starting at 50 mcg in a patient with cardiac disease carries unacceptable risk of precipitating acute coronary syndrome, arrhythmias, or heart failure 1
Monitoring Strategy
During titration phase:
- Check TSH and free T4 every 6-8 weeks after each dose adjustment 1, 2
- Target TSH within the reference range (0.5-4.5 mIU/L) with normal free T4 levels 1
After stabilization:
- Once adequately treated with stable TSH, repeat testing every 6-12 months 1
- Recheck sooner if symptoms change or new medications are started 1
For patients with cardiac disease:
- Assess for new or worsening angina, palpitations, dyspnea, or arrhythmias at each follow-up 1
- Consider more frequent monitoring within 2 weeks of dose adjustment rather than waiting 6-8 weeks 1