When is levothyroxine (T4) appropriate for treatment?

From the Guidelines

Levothyroxine is appropriate for patients with a TSH level greater than 10.0 mIU/L, as this is generally considered the threshold for initiation of treatment. This recommendation is based on expert opinion, as noted in the study by the U.S. Preventive Services Task Force 1. The decision to start therapy in patients with TSH levels between 4.5 and 10.0 mIU/L is more controversial, and it is essential to consider the potential risks and benefits of treatment in these cases.

When treating hypothyroidism with levothyroxine, the standard starting dose for adults is usually 1.6 mcg/kg body weight daily, taken on an empty stomach 30-60 minutes before breakfast or 3-4 hours after the last meal of the day. Elderly patients or those with heart disease often start at lower doses (25-50 mcg daily) with gradual increases. Levothyroxine is also used for treating myxedema coma (severe hypothyroidism), thyroid cancer (after thyroid removal), and sometimes for goiter and subclinical hypothyroidism.

Some key points to consider when prescribing levothyroxine include:

• Dose adjustments are made based on TSH levels, typically checked 6-8 weeks after starting treatment or changing doses, with the goal of maintaining TSH within normal range.
• Levothyroxine works by replacing the natural thyroid hormone that the body should be making, helping to restore normal metabolism and energy levels.
• It's a lifelong treatment for most patients with hypothyroidism, requiring regular monitoring to ensure optimal dosing.
• Pregnant women or women of childbearing potential planning to become pregnant who are found to have elevated serum TSH should be treated with levothyroxine to restore the serum TSH concentration to the reference range, as recommended by the study in JAMA 1.

Overall, the use of levothyroxine should be guided by the principles of minimizing harm and maximizing benefit, with careful consideration of the individual patient's needs and circumstances.

From the FDA Drug Label

Levothyroxine sodium tablets are a L-thyroxine (T4) indicated in adult and pediatric patients, including neonates, for: • Hypothyroidism: As replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism. • 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.

Levothyroxine is appropriate for:

• Hypothyroidism: as replacement therapy in primary, secondary, and tertiary congenital or acquired hypothyroidism.
• 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 2.

From the Research

Levothyroxine Appropriateness

• Levothyroxine is appropriate for treating overt hypothyroidism, with the goal of optimizing doses to achieve a TSH level in the 0.3-2.0 mU/L range for 3 to 6 months before assessing therapeutic response 3.
• In some cases, it may be acceptable to have serum TSH below the reference range (e.g., 0.1-0.3 mU/L), but not fully suppressed in the long term 3.
• Levothyroxine should remain the standard of care for treating hypothyroidism, as there is no consistently strong evidence for the superiority of alternative preparations over monotherapy with levothyroxine 4.

Patient Considerations

• Patients with persistent symptoms during thyroid hormone replacement therapy should first have a trial without thyroid hormone replacement to establish a diagnosis of overt hypothyroidism 3.
• In patients with confirmed overt hypothyroidism and persistent symptoms who have had adequate treatment with levothyroxine, a trial of liothyronine/levothyroxine combined therapy may be warranted 3.
• The decision to start treatment with liothyronine should be a shared decision between the patient and clinician 3.

Treatment Guidelines

• The American Thyroid Association task force recommends that levothyroxine therapy should be the standard of care for treating hypothyroidism, with no consistently strong evidence for alternative preparations 4.
• The British Thyroid Association/Society for Endocrinology consensus statement provides practical guidance for clinicians on the use of liothyronine in hypothyroidism, emphasizing the importance of establishing a diagnosis of overt hypothyroidism and optimizing levothyroxine doses before considering alternative therapies 3.