Is liothyronine used to treat T3 (triiodothyronine) deficiency?

Liothyronine for T3 Deficiency Treatment

Liothyronine is indicated for the treatment of T3 (triiodothyronine) deficiency, particularly in cases where there is impairment of peripheral conversion of T4 to T3. 1

Indications for Liothyronine Use

• Liothyronine (T3) may be used in preference to levothyroxine (T4) when impairment of peripheral conversion of T4 to T3 is suspected 1
• It is also indicated for patients with mild hypothyroidism, myxedema, congenital hypothyroidism, and simple (non-toxic) goiter 1
• Liothyronine has a rapid onset and dissipation of action compared to levothyroxine, making it useful during radioisotope scanning procedures where induction of hypothyroidism needs to be more abrupt and of shorter duration 1

Dosing Recommendations

• For mild hypothyroidism, the recommended starting dosage is 25 mcg daily, which may be increased by up to 25 mcg every 1-2 weeks 1
• Usual maintenance dose ranges from 25 to 75 mcg daily 1
• In the elderly or pediatric patients, therapy should be started with 5 mcg daily and increased only by 5 mcg increments at the recommended intervals 1
• For myxedema, start with 5 mcg daily, increasing by 5-10 mcg daily every 1-2 weeks until reaching a satisfactory therapeutic response 1

Considerations for Combination Therapy

• For patients who remain symptomatic on levothyroxine monotherapy despite normalized TSH, guidelines suggest a trial of combination therapy with LT4+LT3 may be considered 2
• When initiating combination therapy, reducing the LT4 dose by 25 mcg/day and adding 2.5-7.5 mcg liothyronine once or twice daily is an appropriate starting point 3
• The decision to start treatment with liothyronine should be a shared decision between patient and clinician 2

Monitoring and Follow-up

• Dosage must be individualized according to patient response and laboratory findings 1
• Although liothyronine has a rapid cutoff, its metabolic effects persist for a few days following discontinuation 1
• When switching a patient to liothyronine from other thyroid medications, discontinue the other medication, initiate liothyronine at a low dosage, and increase gradually according to patient response 1
• Monitor for development of low TSH on therapy, which suggests overtreatment or recovery of thyroid function 4

Potential Risks and Considerations

• Wide swings in serum T3 levels following liothyronine administration may counterbalance its advantages 1
• There is potential for more pronounced cardiovascular side effects with liothyronine compared to levothyroxine 1
• Transient episodes of hypertriiodothyroninemia with combination therapy are unlikely to exceed the reference range and have not been associated with adverse drug reactions 3
• Pharmacokinetic studies indicate liothyronine has a rapid distribution phase (half-life of 2.3 hours) and a slow elimination phase (half-life of 22.9 hours) 5

Future Developments

• New slow-release liothyronine preparations are being developed to better maintain stable T3 serum levels when used in combination therapy 6, 7
• Genetic profiling may help identify patients who do not respond well to levothyroxine due to suboptimal peripheral T4 activation 6

Clinical Pitfalls to Avoid

• Avoid initiating treatment before confirming the diagnosis with complete thyroid function testing 4
• In patients with both adrenal insufficiency and hypothyroidism, steroids should always be started prior to thyroid hormone to avoid precipitating an adrenal crisis 4
• Overtreatment with thyroid hormone could increase risk for osteoporosis, fractures, abnormal cardiac output, or ventricular hypertrophy 8