Why Liothyronine Was Added to Levothyroxine Therapy
The endocrinologist added liothyronine 5 mcg daily because this elderly patient likely has persistent hypothyroid symptoms despite levothyroxine monotherapy, and combination T4+T3 therapy represents a guideline-supported trial for symptomatic patients who remain dissatisfied with levothyroxine alone. 1
Primary Rationale for Adding T3
Persistent symptoms despite adequate TSH control is the most common reason for adding liothyronine to levothyroxine therapy, as numerous patients report ongoing fatigue, cognitive difficulties, or reduced quality of life even when TSH is normalized on levothyroxine alone 1, 2
The British Thyroid Association/Society for Endocrinology consensus specifically recommends that for patients with confirmed overt hypothyroidism and persistent symptoms who have had adequate treatment with levothyroxine (TSH 0.3-2.0 mU/L for 3-6 months) and in whom other comorbidities have been excluded, a trial of liothyronine/levothyroxine combined therapy may be warranted 1
Evidence suggests that T3 is not fully restored in LT4-treated patients, potentially explaining why some patients remain symptomatic despite biochemical euthyroidism 2
The Specific Dosing Strategy Used
The 5 mcg liothyronine dose is precisely within FDA-approved starting recommendations for mild hypothyroidism and represents a conservative, evidence-based approach 3
The FDA label for liothyronine specifically states that for mild hypothyroidism, the recommended starting dosage is 25 mcg daily, but can be initiated at lower doses, and for myxedema the starting dose is 5 mcg daily 3
The typical approach when adding T3 to existing T4 therapy is to reduce the LT4 dose by 25 mcg/day and add 2.5-7.5 mcg liothyronine once or twice daily, though in this case the levothyroxine dose appears unchanged at 50 mcg 2
Why This Approach Is Appropriate for an Elderly Patient
Elderly patients require particularly cautious dosing due to increased cardiovascular risk, and the 5 mcg starting dose represents the most conservative FDA-approved initiation strategy 3, 4
In elderly patients, therapy should be started with 5 mcg daily and increased only by 5 mcg increments at recommended intervals to minimize cardiovascular complications 3
The well-established approach of starting with a low dose and gradually titrating is always the best option in elderly patients and those with a history of coronary artery disease 4
Evidence Supporting Combination Therapy
Clinical trials following almost 1000 patients for almost 1 year indicate that therapy with LT4+LT3 can restore euthyroidism while maintaining normal serum TSH, similar to LT4 monotherapy 2
An observational study of 400 patients with mean follow-up of approximately 9 years did not indicate increased mortality or morbidity risk due to cardiovascular disease, atrial fibrillation, or fractures after adjusting for age when compared with patients taking only LT4 2
In two studies, combined therapy had beneficial effects on mood, quality of life, and psychometric performance compared with levothyroxine alone, and patients preferred levothyroxine plus liothyronine combinations 5
Critical Monitoring Requirements
Transient episodes of hypertriiodothyroninemia with these doses are unlikely to exceed the reference range and have not been associated with adverse drug reactions in clinical trials 2
For patients with cardiac disease, atrial fibrillation, or serious medical conditions, more frequent monitoring within 2 weeks may be warranted to prevent overtreatment and symptomatic hyperthyroidism 6
Development of suppressed TSH (<0.1 mU/L) indicates overtreatment requiring immediate dose reduction to prevent long-term cardiovascular and bone risks 6
Important Caveats for This Approach
The decision to start liothyronine should be a shared decision between patient and clinician, and individual clinicians should not feel obliged to continue liothyronine if they judge this not to be in the patient's best interest 1
Despite more than 20 years of debate, numerous randomized trials have failed to show consistent benefit of treatment regimens combining liothyronine with levothyroxine over levothyroxine monotherapy 1
Until clear advantages of levothyroxine plus liothyronine are demonstrated, the administration of levothyroxine alone should remain the treatment of choice for replacement therapy of hypothyroidism, making this a trial therapy rather than standard first-line treatment 5
The wide swings in serum T3 levels that follow liothyronine administration and the possibility of more pronounced cardiovascular side effects tend to counterbalance the stated advantages, particularly important in elderly patients 3