From the FDA Drug Label
Thyroid hormone drugs are indicated: As replacement or supplemental therapy in patients with hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis As pituitary thyroid-stimulating hormone (TSH) suppressants, in the treatment or prevention of various types of euthyroid goiters, including thyroid nodules, subacute or chronic lymphocytic thyroiditis (Hashimoto's) and multinodular goiter As diagnostic agents in suppression tests to differentiate suspected mild hyperthyroidism or thyroid gland autonomy.
The reasons for prescribing liothyronine are:
- Replacement or supplemental therapy in patients with hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis
- TSH suppression in the treatment or prevention of various types of euthyroid goiters
- Diagnostic agents in suppression tests to differentiate suspected mild hyperthyroidism or thyroid gland autonomy 1
- Preference to levothyroxine (T4) during radioisotope scanning procedures, or when impairment of peripheral conversion of T4 to T3 is suspected 2
- Allergy to desiccated thyroid or thyroid extract derived from pork or beef 1
From the Research
Liothyronine (T3) is primarily prescribed for hypothyroidism when levothyroxine (T4) therapy alone is insufficient, as evidenced by the most recent study in 2023 3. This may include cases where patients continue to experience symptoms despite normal TSH levels on levothyroxine, a condition sometimes called "euthyroid sick syndrome." Liothyronine is also used in myxedema coma, a life-threatening complication of severe hypothyroidism, where rapid hormone replacement is needed. Some patients with genetic defects in T4 to T3 conversion may benefit from direct T3 supplementation. The decision to start treatment with liothyronine should be a shared decision between patient and clinician, as suggested by the 2023 consensus statement 3.
Key points to consider when prescribing liothyronine include:
- Typical dosing starts low at 5-25 mcg daily, divided into multiple doses due to its shorter half-life compared to levothyroxine.
- Liothyronine is occasionally used short-term in preparation for radioactive iodine therapy or thyroid surgery in patients with thyroid cancer.
- The medication works by providing the active form of thyroid hormone (T3) directly, bypassing the need for conversion from T4, which occurs naturally in the body.
- Patients should be monitored closely with thyroid function tests when taking liothyronine, as it has a narrower therapeutic window and can cause symptoms of hyperthyroidism if dosed incorrectly, as noted in the 2021 study 4.
It is essential to establish a diagnosis of overt hypothyroidism and optimize levothyroxine doses before considering liothyronine therapy, as emphasized in the 2023 consensus statement 3. Additionally, other comorbidities should be excluded, and the patient's preference and potential benefits should be taken into account when deciding on liothyronine treatment, as suggested by the 2021 study 5.