From the FDA Drug Label
• Adequacy of therapy determined with periodic monitoring of TSH and/or T4 as well as clinical status. • Pituitary Thyrotropin (Thyroid‑Stimulating Hormone, TSH) Suppression: As an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer
The thyroid hormone replacement affects TSH levels by suppressing them in cases of thyrotropin-dependent well-differentiated thyroid cancer. In hypothyroidism treatment, the goal is to maintain TSH levels within a normal range, which is achieved by periodic monitoring and adjusting the levothyroxine dose as needed 1.
- Key points:
- TSH levels are monitored to determine the adequacy of therapy
- Levothyroxine sodium tablets can suppress TSH levels in certain cases
- The dose of levothyroxine sodium is adjusted based on TSH levels and clinical status to avoid over- or under-treatment.
From the Research
Thyroid hormone replacement therapy decreases TSH levels by providing the body with exogenous thyroid hormones, which compensate for insufficient natural production, with the goal of normalizing TSH levels, typically to a range of 0.4-4.0 mIU/L for most adults, as evidenced by the most recent study 2. When patients take medications like levothyroxine (T4) at appropriate doses, the pituitary gland detects increased circulating thyroid hormone levels and reduces its TSH production through negative feedback. The most recent and highest quality study, published in 2015 2, recommends levothyroxine therapy for patients with overt hypothyroidism and a blood TSH concentration above 10 mIU/L, with a starting dose of 1.5 microg/kg per day for young adults, and 12.5 to 50 microg per day for elderly patients and those with coronary artery disease. Proper dosing is essential, as excessive thyroid hormone replacement can suppress TSH below normal ranges, potentially causing symptoms of hyperthyroidism, while insufficient dosing will result in persistently elevated TSH levels, as noted in the study published in 2004 3. Some key points to consider when implementing thyroid hormone replacement therapy include:
- TSH levels should be checked 6-8 weeks after initiating therapy or changing doses, with morning blood draws before taking medication providing the most accurate results, as recommended in the study published in 2001 4.
- Consistent timing of medication intake, typically on an empty stomach 30-60 minutes before breakfast, ensures optimal absorption and stable hormone levels.
- The combination of levothyroxine plus liothyronine does not offer any objective advantage over levothyroxine alone, as evidenced by the systematic review published in 2005 5, but some patients may prefer combination treatment, as noted in the study published in 2005 6. Overall, the goal of thyroid hormone replacement therapy is to normalize TSH levels and improve the quality of life for patients with hypothyroidism, while minimizing the risk of adverse events, as recommended in the most recent study 2.