Treatment of hypothyroidism with levothyroxine plus slow-release liothyronine: a study protocol for a randomized controlled double-blinded clinical trial

There are emerging controversies regarding the priority of T4 + T3 combination therapy over standard care with levothyroxine (LT4) monotherapy in the management of hypothyroid subjects. Combination therapy with a slow-release form of liothyronine (SRT3) and levothyroxine may restore T3 concentrations and provide better outcomes, especially in individuals with persistent complaints despite having normal serum TSH levels. One hundred patients aged ≥ 20 years with hypothyroidism who have achieved and maintained euthyroidism under LT4 monotherapy for at least 3 months will be randomized into two groups of LT4 + SRT3 combined therapy (75 µg LT4 + 25 µg SRT3) and LT4 monotherapy for 48 weeks. Participants will be evaluated at baseline and three subsequent follow-ups, 12, 24, and 48 weeks after treatment allocation. Before and after the intervention, body weight, heart rate, blood pressure, ECG, quality of life (by ThyPRO-39 and SF-12), resting energy expenditure, and body composition will be evaluated. Also, serum TSH, total T3, total T4, free T4, free T3, total cholesterol, LDL, HDL, triglycerides, fasting blood sugar (FBS), insulin, HbA1C, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), sex hormone-binding globulin (SHBG), enolase, lactate dehydrogenase (LDH), creatin kinase (CK), ferritin, and metabolomics will be assessed at baseline and compared with their corresponding values at 24 and 48 weeks. Epigenetic-related markers will be measured and compared between the responders and non-responders. It is expected that LT4 + SRT3 combined therapy more closely mimics the serum levels of T3, T4, and the T3/T4 ratio of euthyroid subjects than LT4 monotherapy, and improves health outcomes and quality of life, especially in hypothyroid patients with persistent symptoms under LT4 monotherapy. Genetic polymorphism sequencing may identify hypothyroid patients who are not responding well to levothyroxine alone. Trial ID: 44220 ID: IRCT20100922004794N12 IRCT ID: IRCT20100922004794N12 Registration date: 2020-02-27 Expected recruitment start date: 2024-10-06 Expected recruitment end date: 2025-10-23