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Desiccated thyroid or thyroid extract, refers to porcine or bovine thyroid glands, dried and powdered for therapeutic use. Animal extract thyroid preparations were developed in the late 19th century, and are still in use today for the treatment of hypothyroidism. This product is sometimes referred to as "natural thyroid", "natural thyroid hormones", "pork thyroid", thyroid USP, thyroid BP, or by the name of a commercial brand, such as "Armour Thyroid" or "Nature-Throid" & "Westhroid". Desiccated thyroid has been described in the United States Pharmacopoeia for a century as ''the cleaned, dried, and powdered thyroid gland previously deprived of connective tissue and fat... obtained from domesticated animals that are used for food by man'' (USP XVI). In the last few decades, pork alone is the usual source. Before modern assays, the potency was specified only by iodine content ("not less than 0.17% and not more than 0.23%"), rather than hormonal content or activity. Brands include Forest Lab's Armour, and Naturethroid & Westhroid by RLC Labs. Canada's desiccated thyroid is made by ERFA Canada 2012 〔http://www.eci2012.net/〕 and is called Thyroid. Also available is NP thyroid by Acella Pharmaceuticals. All brands consist of desiccated porcine thyroid powder, differing only in binders and fillers. They contain a mixture of thyroid hormones: T4 (thyroxine) & T3 (triiodothyronine), in the proportions usually present in pig thyroids (approximately 80% T4 and 20% T3). ==Medical uses== The American Association of Clinical Endocrinologists and the Royal College of Physicians) recommend against the use of thyroid extract for the treatment of hypothyroidism. Concerns include the potential for adverse effects from superphysiological levels of T3 and the absence of long-term safety data from randomized clinical trials. They recommend synthetic levothyroxine as the preferred treatment. Some practitioners refuse to use desiccated thyroid and will try to steer their patients away from it. Arguments against desiccated thyroid include: #Desiccated thyroid preparations have a greater variability from batch to batch than synthetic ones.〔 #Desiccated thyroid has roughly a 4:1 ratio of thyroxine (T4) to triiodothyronine (T3). In humans, the ratio is 11:1.〔(Repas, Thomas. Desiccated thyroid in the management of hypothyroidism: Part I. )〕 #A combination of various ratios of T4 and T3 may not provide benefits over T4 alone. Some controlled trials have shown inconsistent benefits of various ratios of T4 and T3. #The use of desiccated thyroid is usually accompanied with the practice of dosing according to symptoms instead of dosing to achieve "ideal" lab results (e.g. serum levels of TSH). While there is debate as to what the ideal serum levels are, dosing according to symptoms often results in higher dosages. Most endocrinologists are opposed to these higher dosages as there may be risks of hyperthyroidism and osteoporosis. #The preference for "natural" treatment seems to stem from philosophical belief as opposed to science. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Desiccated thyroid extract」の詳細全文を読む スポンサード リンク
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