Fast Five Quiz: Levothyroxine

Mary L. Windle, PharmD


October 07, 2021

American Thyroid Association guidelines state the following:

  • If levothyroxine dose requirements are much higher than expected, consider evaluating for gastrointestinal disorders, such as Helicobacter pylori–related gastritis, atrophic gastritis, or celiac disease; if such disorders are detected and effectively treated, reevaluation of thyroid function and levothyroxine dosage is recommended.

  • Initiation or discontinuation of estrogen and androgens should be followed by reassessment of serum TSH at steady state because such medications may alter the levothyroxine requirement.

  • Serum TSH should be reassessed upon initiation of such agents as tyrosine kinase inhibitors that affect thyroxine metabolism and thyroxine or triiodothyronine deiodination.

  • Serum TSH monitoring is advisable when such medications as phenobarbital, phenytoin, carbamazepine, rifampin, and sertraline are started.

  • When deciding on a starting dose of levothyroxine, the patient's weight, lean body mass, pregnancy status, etiology of hypothyroidism, degree of TSH elevation, age, and general clinical context, including the presence of cardiac disease, should be considered. The serum TSH goal appropriate for the clinical situation should also be considered.

  • Thyroid hormone therapy should be initiated as an initial full replacement or as partial replacement with gradual increments in the dose titrated upward using serum TSH as the goal.

  • Dose adjustments should be made upon significant changes in body weight, with aging, and with pregnancy; TSH assessment should be performed 4-6 weeks after any dosage change.

  • Reference ranges of serum TSH levels are higher in older populations (eg, > 65 years), so higher serum TSH targets may be appropriate.

Read more about hypothyroidism treatment.


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