Liothyronine — Thyroid hormone / T3 replacement
Liothyronine is synthetic T3 (triiodothyronine), the biologically active form of thyroid hormone. While T4 (levothyroxine) is the primary thyroid secretory product, T3 is ~3–4x more potent and mediates most thyroid hormone effects directly at the receptor (TRα, TRβ). Key distinction from T4: liothyronine does NOT require peripheral conversion by DIO1/DIO2 enzymes, making it directly available regardless of deiodinase activity. Clinical applications: (1) Combination T3+T4 therapy for hypothyroid patients who remain symptomatic on levothyroxine despite normal TSH — relevant in Thr92Ala DIO2 polymorphism carriers (~15% of population); (2) T3 accelerated protocol for depression augmentation (STAR*D, TR-AugD studies); (3) T3-only protocols for thyroid cancer in preparation for radioiodine scanning (faster washout than T4). Shorter half-life requires BID/TID dosing.
نظرة عامة
هذه الصفحة جزء من مكتبة المركّبات المُصنَّفة بالأدلة في Hormonaly. جميع الادعاءات السريرية مرتبطة بمصادر علمية مُحكَّمة عبر خط أنابيب التحقق المزدوج للاستشهادات.
فئة المركّب
Thyroid hormone / T3 replacement
آلية العمل
Liothyronine is synthetic T3 (triiodothyronine), the biologically active form of thyroid hormone. While T4 (levothyroxine) is the primary thyroid secretory product, T3 is ~3–4x more potent and mediates most thyroid hormone effects directly at the receptor (TRα, TRβ). Key distinction from T4: liothyronine does NOT require peripheral conversion by DIO1/DIO2 enzymes, making it directly available regardless of deiodinase activity. Clinical applications: (1) Combination T3+T4 therapy for hypothyroid patients who remain symptomatic on levothyroxine despite normal TSH — relevant in Thr92Ala DIO2 polymorphism carriers (~15% of population); (2) T3 accelerated protocol for depression augmentation (STAR*D, TR-AugD studies); (3) T3-only protocols for thyroid cancer in preparation for radioiodine scanning (faster washout than T4). Shorter half-life requires BID/TID dosing.
الوضع التنظيمي
FDA-approved. Cytomel (brand). Multiple generic forms. Compounded sustained-release T3 available but not FDA-approved.
مستوى الأدلة
Moderate — ATA 2014 rates evidence for T4+T3 combination as 'weak/insufficient'; however, multiple RCTs and the TRUST trial show subset benefit. STAR*D evidence for depression augmentation is robust.