Purpose of review 

The aim of the article is to present the basics of oral levothyroxine (LT4) absorption, reasons why patients may have persistently elevated serum thyroid stimulation hormone (TSH) levels, and alternative strategies for LT4 dosing.

Recent findings 

Although oral LT4 tablets are most commonly used for thyroid hormone replacement in patients with hypothyroidism, case studies report that liquid oral LT4, intravenous, intramuscular, and rectal administration of LT4 can successfully treat refractory hypothyroidism.

Summary 

Hypothyroidism is one of the most common endocrine disorders encountered by primary care physicians and endocrinologists. LT4 is one of the most widely prescribed medications in the world and it is the standard of care treatment for hypothyroidism. Generally, hypothyroid patients will be treated with LT4 tablets to be taken orally, and monitoring will occur with routine serum thyroid tests, including TSH concentrations. However, many patients fail to maintain serum TSH levels in the target range while managed on oral LT4 tablets. A subset of these patients would be considered to have poorly controlled hypothyroidism, sometimes termed refractory hypothyroidism. For these patients, optimization of ingestion routines and alternative formulations and routes of administration of LT4 can be considered, including oral liquid, intravenous, intramuscular, and even rectal formulations.

中文翻译：

---

左甲状腺素治疗甲状腺功能减退的替代途径

审查目的 

本文的目的是介绍口服左甲状腺素（LT4）吸收的基础知识，患者血清甲状腺刺激激素（TSH）水平持续升高的原因，以及替代LT4剂量的策略。

最近的发现 

尽管口服LT4片剂最常用于甲状腺功能减退症患者的甲状腺激素替代治疗，但案例研究报告说，口服LT4液体，静脉内，肌肉内和直肠给予LT4可以成功治疗难治性甲状腺功能减退症。

概要 

甲状腺功能减退是基层医疗医生和内分泌学家遇到的最常见的内分泌疾病之一。LT4是世界上使用最广泛的处方药之一，它是甲状腺功能减退症的标准治疗方法。通常，甲状腺功能低下的患者将接受LT4片剂口服治疗，并通过常规的血清甲状腺测试（包括TSH浓度）进行监测。但是，许多患者在口服LT4片剂治疗时未能将血清TSH水平维持在目标范围内。这些患者中有一部分被认为控制甲状腺功能低下，有时称为难治性甲状腺功能低下。对于这些患者，可以考虑优化摄入程序和替代制剂以及LT4的给药途径，包括口服液，静脉内，肌肉内，甚至直肠制剂。