Desiccated thyroid, also known as thyroid extract, is
thyroid gland
The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobe (anatomy), lobes. The lower two thirds of the lobes are connected by a thin band of Connective tissue, tissue cal ...
that has been dried and powdered for
medical use.
[ It is used to treat ]hypothyroidism
Hypothyroidism (also called ''underactive thyroid'', ''low thyroid'' or ''hypothyreosis'') is a disorder of the endocrine system in which the thyroid gland does not produce enough thyroid hormone. It can cause a number of symptoms, such as po ...
.[ It is less preferred than ]levothyroxine
Levothyroxine, also known as -thyroxine, is a manufactured form of the thyroid hormone thyroxine (T4). It is used to treat hypothyroidism, thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. It may also ...
.[ It is taken by mouth.] Maximal effects may take up to three weeks to occur.[
Side effects may occur from excessive doses.][ This may include weight loss, fever, headache, anxiety, trouble sleeping, ]arrythmia
Arrhythmias, also known as cardiac arrhythmias, heart arrhythmias, or dysrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. A resting heart rate that is too fast – above 100 beats per minute in adults ...
s, and heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
.[ Other side effects may include ]allergic reactions
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...
.[ Use in ]pregnancy
Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins.
Pregnancy usually occurs by sexual intercourse, but ca ...
and breastfeeding
Breastfeeding, or nursing, is the process by which human breast milk is fed to a child. Breast milk may be from the breast, or may be expressed by hand or pumped and fed to the infant. The World Health Organization (WHO) recommends that br ...
is generally safe. Regular blood tests are recommended to verify the appropriateness of the dose.[ They contain a mixture of ]thyroxine
File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4
rect 376 268 820 433 Thyroid-stimulating hormone
rect 411 200 849 266 Thyrotropin-releasing hormone
rect 297 168 502 200 Hypothalamus
rect 66 216 386 25 ...
(T4) and triiodothyronine
Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate.
Production of T3 and its prohormone thyroxine ( ...
(T3).[
Desiccated thyroid has been used since the late 1800s.] It is usually made from pigs, sheep, or cows. It is available as a generic medication
A generic drug is a pharmaceutical drug that contains the same chemical substance as a drug that was originally protected by chemical patents. Generic drugs are allowed for sale after the patents on the original drugs expire. Because the active ch ...
.[ In 2020, it was the 117th most commonly prescribed medication in the United States, with more than 5million prescriptions. Usage has decreased since the 1960s.][
]
Medical uses
The American Association of Clinical Endocrinologists and the Royal College of Physicians
The Royal College of Physicians (RCP) is a British professional membership body dedicated to improving the practice of medicine, chiefly through the accreditation of physicians by examination. Founded by royal charter from King Henry VIII in 1 ...
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 levothyroxine
Levothyroxine, also known as -thyroxine, is a manufactured form of the thyroid hormone thyroxine (T4). It is used to treat hypothyroidism, thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. It may also ...
as the preferred treatment. Some practitioners refuse to use desiccated thyroid.
About 65 mg of thyroid extract is equivalent to 100 μg of levothyroxine.[
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.
#A combination of various ratios of T4 and T3 might 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
Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are p ...
" treatment seems to stem from philosophical belief as opposed to science.
Arguments for desiccated thyroid include:
#Desiccated thyroid contains all the natural thyroid hormones produced exclusively by the thyroid gland, including calcitonin which plays a crucial but still quite unclear role in promoting and sustaining bone density, however it is already used in therapy for osteoporosis when other treatments fail.
#Desiccated thyroid therapy can be combined with synthetic thyroxine (T4) to balance out the T4/T3 correctly.
Chemistry
Desiccated thyroid has been described in the United States Pharmacopoeia
The ''United States Pharmacopeia'' (''USP'') is a pharmacopeia (compendium of drug information) for the United States published annually by the United States Pharmacopeial Convention (usually also called the USP), a nonprofit organization that ...
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
Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
content ("not less than 0.17% and not more than 0.23%"), rather than hormonal content or activity.
History
The earliest oral treatment for hypothyroidism consisted of thyroid extract. George Redmayne Murray
George Redmayne Murray (20 June 1865 – 21 September 1939) was an English physician who pioneered in the treatment of endocrine disorders. In 1891, he introduced the successful treatment of myxedema, with injections of sheep thyroid extract.
M ...
of the United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
first described treatment of myxedema
Myxedema is a term used synonymously with severe hypothyroidism. However, the term is also used to describe a dermatological change that can occur in hyperthyroidism and (rare) paradoxical cases of hypothyroidism. In this latter sense, myxedema ...
with thyroid extract in 1891, and published a description of long-term successful treatment (28 years) of a patient with myxedema (severe hypothyroidism) in 1920 His treatment was quickly adopted in North America and Europe. The first recorded American use dates to 1891 by a woman who was still taking it 52 years later at 84 years of age
Desiccated thyroid extract is prepared from pig thyroid glands. The glands are dried (desiccated), ground to powder, combined with binder chemicals, and pressed into pills. This was a new use for parts that were previously unwanted slaughterhouse
A slaughterhouse, also called abattoir (), is a facility where animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a packaging facility.
Slaughterhouses that produce meat that is no ...
offal
Offal (), also called variety meats, pluck or organ meats, is the organs of a butchered animal. The word does not refer to a particular list of edible organs, which varies by culture and region, but usually excludes muscle. Offal may also refe ...
, and Armour and Company
Armour & Company was an American company and was one of the five leading firms in the meat packing industry. It was founded in Chicago, in 1867, by the Armour brothers led by Philip Danforth Armour. By 1880, the company had become Chicago's most ...
, the dominant American meatpacker
The meat-packing industry (also spelled meatpacking industry or meat packing industry) handles the slaughtering, processing, packaging, and distribution of meat from animals such as cattle, pigs, sheep and other livestock. Poultry is generally ...
in the 20th century, supplied the best-known brand of thyroid extract.
Replacement by thyroid extract in hypothyroidism was one of the most effective treatments of any disease available to physicians before the middle of the 20th century, and in severe cases afforded dramatic relief of the myriad symptoms. The decision to treat was usually based on the presence of signs and symptoms of hypothyroidism because there were no accurate, readily available laboratory tests
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physici ...
of thyroid function. Many less severe cases of hypothyroidism went untreated. Dosage was regulated by improvement of symptom
Signs and symptoms are the observed or detectable signs, and experienced symptoms of an illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormality showin ...
s.
Desiccated Thyroid became a commercial treatment option in 1934 with Westhroid,. In the early 1960s, desiccated thyroid hormones (thyroid extract) began to be replaced by levothyroxine
Levothyroxine, also known as -thyroxine, is a manufactured form of the thyroid hormone thyroxine (T4). It is used to treat hypothyroidism, thyroid hormone deficiency (hypothyroidism), including a severe form known as myxedema coma. It may also ...
(synthetic T4), or by combinations of T4 and T3. Replacement occurred faster in the United Kingdom than in North America, but by the 1980s more patients were being prescribed synthetic T4 (levothyroxine) or synthetic T4/T3 combinations than desiccated thyroid extract.
Several reasons have been identified as to why prescriptions changed from desiccated thyroid treatment.
*Although thyroid extract was useful and usually effective, some patients continued to complain of fatigue, weight gain, or other symptoms. Dosing until the 1960s was often a matter of prolonged adjustment trials.
*It was known that not all of the iodine content of thyroid extract was in the form of effective T4 and T3 and that actual content of available preparations varied more than the permitted 15%. It was hoped that better dosing precision with levothyroxine (synthetic) alone would increase the proportion of patients effectively treated. In 1980, a widely publicized investigation published in JAMA
''The Journal of the American Medical Association'' (''JAMA'') is a peer-reviewed medical journal published 48 times a year by the American Medical Association. It publishes original research, reviews, and editorials covering all aspects of biom ...
revealed continued large ranges of hormone content and potency in all of the available thyroid extracts on the American market.
*By the 1960s, it was known that thyroxine was the essential hormone produced by the thyroid gland, and that most T3 was manufactured in other parts of the body by deiodination of thyroxine. It was demonstrated in hypothyroid animals and people that replacement of thyroxine alone corrected the measurable manifestations (laboratory test results) of hypothyroidism. By the 1970s doctors could measure T4, T3, and TSH in human blood with approximate accuracy and confirmed that treatment with thyroxine alone could produce normal blood levels of both T4 and T3, but desiccated thyroid caused supraphysiologic levels of T3. In the majority of patients normalization of these levels eliminated all signs and symptoms of hypothyroidism.
*It was discovered that a healthy person varied the amount of T3 produced from T4 in response to changing needs and conditions and it seemed wiser not to bypass this control system by providing larger amounts of T3 than were naturally produced each day.
*Furthermore, when T3 could be measured, it was discovered that thyroid extract and synthetic combinations of T4 and T3 produced significantly greater fluctuations of T3 throughout the day than occurred in healthy people or hypothyroid people treated with thyroxine alone.
* Endocrinologists found that treatment with thyroxine alone worked as well or better than thyroid extract for the majority of patients, although even thyroxine did not reverse all the symptoms of a minority.
Thyroid care changed in other ways as well. Accurate T4 and T3 measurements became widely used in the 1970s, and by the late 1980s, TSH measurement had become sensitive enough to detect mild degrees of hyperthyroidism
Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism ...
and overtreatment. Blood levels of thyroid hormones and TSH were found to be the best predictors of objective benefits from thyroid replacement: those with the most severe measurable deficiency enjoyed the most dramatic and sustained benefits. It was also discovered that even mild hyperthyroidism
Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism ...
as defined by a suppressed TSH level, whether due to disease or overtreatment, was associated with poorer bone density
Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optica ...
in women, and with higher rates of atrial fibrillation in elderly patients.
Names
This product is sometimes referred to as thyroid USP, thyroid BP. Brands differing only in binders and fillers.
References
External links
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{{DEFAULTSORT:Desiccated Thyroid Extract
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