Azizi Fereidoun, Amouzegar Atieh, Abdi Hengameh, Masoumi Safdar, Mehran Ladan
Endocrine Research Center, Research Institute for Endocrine Sciences, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Endocr Metab Immune Disord Drug Targets. 2025 Jan 21. doi: 10.2174/0118715303321830241227112420.
Combination therapy with levothyroxine (L-T4) and slow-release T3 (SRT3) in the treatment of hypothyroidism results in a normal triiodothyronine/thyroxine (T3/T4) ratio above that of L-T4 monotherapy. No clinical study has been reported with SRT3 monotherapy for hypothyroidism.
This study was conducted in two parts. In part one, 20 patients with primary hypothyroidism and serum thyrotropin (TSH) >30 mU/L were randomized into 3 groups receiving 1.6 μg/kg L-T4, equivalent doses of SRT3 or L-T3 of 0.55 μg/kg for 4 weeks and fasting serum free T4 (fT4), T3 and TSH were measured weekly, before taking medication, up to 4 weeks. In part two, in 9 hypothyroid patients on L-T4 therapy and normal serum TSH, L-T4 therapy was discontinued and a once daily dose of SRT3 0.55 μg/kg was replaced. Serum fT4, T3 and TSH were measured weekly.
Part One; in patients treated with L-T3 and L-T4 serum TSH decreased to normal values after 4 weeks of intervention. In 7 patients on SRT3, serum T3 increased from 47±12 at baseline to 110±16 ng/dL and serum TSH decreased from 60±11 at baseline to 24±10 and 26±7 mU/L, respectively, at 14 and 21 days after intervention. At the end of 28 days, mean serum T3 was 110±16, 168±74 and 96±18 ng/dL in SRT3, L-T3 and L-T4 groups, respectively, p<0.001. Part Two: serum fT4 decreased from 1.43±0.7 to 0.41±0.14 ng/dLand serum T3 increased from 86±21 to 113±27 ng/dL by 21 days. Mean serum TSH remained in the normal range until 14 days but increased to 15.1±7.6 mU/L at 21 days. At the end, mean serum fT4, T3 and TSH were 0.35±0.17 ng/dl, 77.4±8.9 ng/dL and 35±11 mU/L.
In patients with primary hypothyroidism SRT3 monotherapy with an equivalent dose to L-T4 maintains normal serum T3, but is unable to sustain normal serum TSH concentration.
左甲状腺素（L-T4）与缓释T3（SRT3）联合治疗甲状腺功能减退症可使三碘甲状腺原氨酸/甲状腺素（T3/T4）比值恢复正常，且高于L-T4单药治疗。目前尚无关于SRT3单药治疗甲状腺功能减退症的临床研究报道。
本研究分为两部分。第一部分，将20例原发性甲状腺功能减退症患者且血清促甲状腺激素（TSH）>30 mU/L随机分为3组，分别接受1.6 μg/kg的L-T4、等效剂量的SRT3或0.55 μg/kg的L-T3治疗4周，每周测量空腹血清游离T4（fT4）、T3和TSH，测量时间为服药前至4周。第二部分，对9例接受L-T4治疗且血清TSH正常的甲状腺功能减退症患者，停用L-T4治疗，改为每日一次服用0.55 μg/kg的SRT3。每周测量血清fT4、T3和TSH。
第一部分；接受L-T3和L-T4治疗的患者在干预4周后血清TSH降至正常水平。在接受SRT3治疗的7例患者中，干预后14天和21天时，血清T3分别从基线时的47±12 ng/dL升至110±16 ng/dL，血清TSH分别从基线时的60±11 mU/L降至24±10 mU/L和26±7 mU/L。在28天结束时，SRT3组、L-T3组和L-T4组的平均血清T3分别为110±16 ng/dL、168±74 ng/dL和96±18 ng/dL，p<0.001。第二部分：到21天时，血清fT4从1.43±0.7 ng/dL降至0.41±0.14 ng/dL，血清T3从86±21 ng/dL升至113±27 ng/dL。平均血清TSH在14天内保持在正常范围内，但在21天时升至15.1±7.6 mU/L。最后，平均血清fT4、T3和TSH分别为0.35±0.17 ng/dl、77.4±8.9 ng/dL和35±11 mU/L。
在原发性甲状腺功能减退症患者中，与L-T4等效剂量的SRT3单药治疗可维持血清T3正常，但无法维持血清TSH浓度正常。
