Desiccated thyroid

Thyroid, USP (or desiccated thyroid) is derived from hog, beef, or sheep thyroid gland. It may be antigenic in allergic or sensitive patients. Inexpensive generic brands may not be bioequivalent. 

Excessive doses of thyroid hormone may lead to heart failure, angina pectoris, and myocardial infarction. Allergic or idiosyncratic reactions can occur with the natural animal-derived products such as desiccated thyroid and thyroglobulin, but they are extremely rare with the synthetic products used today. Excess exogenous thyroid hormone may reduce bone density and increase the risk of fracture. 

Desiccated thyroid Concern about cardiac effects. Safer alternatives available. High... 

See the Preparations Available section at the end of this chapter for a list of available preparations. These preparations may be synthetic (levothyroxine, liothyronine, liotrix) or of animal origin (desiccated thyroid). 

The shelf life of synthetic hormone preparations is about 2 years, particularly if they are stored in dark bottles to minimize spontaneous deiodination. The shelf life of desiccated thyroid is not known with certainty, but its potency is better preserved if it is kept dry. 

The use of desiccated thyroid rather than synthetic preparations is never justified, since the disadvantages of protein antigenicity, product instability, variable hormone concentrations, and difficulty in laboratory monitoring far outweigh the advantage of low cost. Significant amounts of T3 found in some thyroid extracts and liotrix may produce significant elevations in T3 levels and toxicity. Equivalent doses are 100 mg (1.5 g) of desiccated thyroid, 100 Mg of levothyroxine, and 37.5 ug of liothyronine. 

Cholestyramine, calcium carbonate, sucralfate, aluminum hydroxide, ferrous sulfate, soybean formula, and dietary fiber supplements may impair the absorption of levothyroxine from the G1 tract. Drugs that increase nondeiodinative T4 clearance include rifampin, carbamazepine, and possibly phenytoin. Amiodarone may block the conversion of T4 to T3. Thyroid, USP (or desiccated thyroid) is derived from hog, beef, or sheep thyroid gland. It may he antigenic in allergic or sensitive patients. Inexpensive generic brands may not be bioequivalent. 

D Levothyroxine is the drug of choice for hypothyroidism since it provides the necessary hormone without causing the inaease peak effect of Tj administration, levothyroxine is converted to Tj in the periphery. Liotrix contains T4 and T3 in a 4 1 ratio. This combination is not necessary since the T4 is converted to T3 and the short rz> of liotrix requires multiple daily doses. Desiccated thyroid is unreliable in potency since it is standardized to iodine content and not to T4 or T3 content. Triiodothyronine is also not preferred since rapid gastric absorption can lead to hyperthyroid symptoms and can lead to cardiac effects. 

Synonyms Dry thyroid Desiccated thyroid Thy-reoidin Thyroid Strong, Thyroglobin Chemical/Pharmaceutical/Other Class Natural hormone that provides a mixture of levothyroxine (T4) and liothyronine (T3)... 

Simkins S. 1937a. Dinitrophenol and desiccated thyroid in the treatment of obesity A comprehensive clinical and laboratory study. JAMA 108 2110-2117. 

M16. Moses, C., Sunder, J. H., Vester, J. W., and Donowski, T. S., Hydrocortisone and/or desiccated thyroid in physiological dosage. XI. Effects of thyroid hormone excesses on lipids and other blood and serum solutes. Metab., Clin. Exptl. 13, 717-728 (1964). 

Any of the commercially available thyroid preparations accomplish this goal (Table 73-8) however, levothyroxine (1-thyroxine) is considered to be drug of choice. The thyroid preparations are either natural (i.e., desiccated thyroid and thyroglobulin) or synthetic (levothyroxine, fiothyronine, and fiotrix) in origin. The availability of sensitive and specific assays for total and free hormone levels as well as TSH... 

Why is desiccated thyroid no longer used as a therapeutic agent ... 

The synthetic preparations used are the sodium salts of the natural isomers of the thyroid hormones. Levothyroxine sodium (L-T, synthroid, levoxyl, levothroid, unithroid, others) is available in tablets in a variety of doses and as a lyophilized powder for injection. L-T has a narrow therapeutic index, and the FDA has mandated demonstration of bioequivalence for brand and generic preparations by the various producers. Liothyronine sodium (L-Tft is available in tablets (cytomel) and in an injectable form (triostat). A mixture of L-T and L-T is marketed as liotrix (thyroiar). Desiccated thyroid preparations, derived from whole animal thyroids and containing both T and T have highly variable biologic activity and are much less desirable. 

Oral administration of thyroxine (T4) is the treatment of choice for all forms of hypothyroidism. Other thyroid hormone preparations, including desiccated thyroid and triiodothyronine (T3) alone, should not be used for treatment of patients with hypothyroidism (Levy, 1991). The absorption of T3 is very rapid, and high serum levels of T3 are reached rapidly. Furthermore, elderly persons are very sensitive to the effects of T3. A recent meta-analysis of controlled clinical trials has shown that there is no benefit of combined T3 and T4 therapy when compared with T4 therapy alone (Grozinsky-Glasberg et at, 2006). 

Natural preparations include desiccated thyroid and thyrogiobuiin. Desiccated thyroid and thyrogiobuiin are derived from thyroid glands of domesticated animals that are used for food by human. The hormones were released from the proteolytic activity of gut enzymes. Potency is based on total iodine content or bioassay and is somewhat variable with different preparations. 

Desiccated thyroid preparations (Thyroid USP) are essentially acetone powders of bovine or porcine thyroid glands compressed into oral tablets. A diluent usually is present, because the preparations (especially those of porcine origin) commonly exceed the 0.17 to 0.23% iodine content required by the U.S. Pharmacopeia (USP). Because the iodine of desiccated thyroid is in the form of iodinated tyrosyl and thyronyl residues of the precipitated thyrogiobuiin, the preparation owes its efficacy to the hormones that eventually are liberated by intestinal proteases. In desiccated preparations, T3 and T4 may be present in a ratio of approximately the same as found in humans. Desiccated preparations are iess expensive than synthetic hormones but have been shown to produce variabie T4/T3 biood ieveis because of inconsistencies both between and within animai sources of the thyroid giand. Most comments regarding desiccated thyroid also apply to partially purified thyrogiobuiin, because the two preparations differ in their total and their relative amounts of T4 and T3. 

Because of its firmer binding to carrier proteins, synthetic crystalline L-T4 sodium salt (levothyroxine sodium, Synthtoid, Euthyrox) has a slower onset of action than crystalline T3 or a desiccated thyroid preparation. Its administration leads to a greater increase in serum T4 but a lesser increase in serum T3 than compared with Thyroid USP (62). The availability of 11 different tablet strengths, ranging from 25 to 300 pg, allows individual dosing. 

A. An acute ingestion of more than 5 mg of levothyroxine (T4) or 0.75 mg of triiodothyronine (T3) is considered potentially toxic. An adult has survived an ingestion of 48 g of unspecified thyroid tablets a 15-month-old child had moderate symptoms after ingesting 1.5 g of desiccated thyroid. 

The addition of liothyronine 25 micrograms daily was found to increase the speed and efficacy of imipramine in relieving depression. Similar results have been described in other studies with desipramine or amitriptyline but the reasons are not understood. One possible explanation is that the patients had overt or subclinical hypothyroidism, which after correction with liothyronine allowed them to overcome an impaired response to tricyclic antidepressants." However, adverse reactions have also been seen. A patient being treated for both hypothyroidism and depression with thyroid 60 mg and imipramine 150 mg daily complained of dizziness and nausea. She was found to have developed paroxysmal atrial tachycardia. A 10-year-old girl with congenital hypothyroidism, well controlled on desiccated thyroid 150 mg daily, developed severe thyrotoxicosis after taking imipramine 25 mg daily for 5 months for enuresis. The problem disappeared when the imipramine was withdrawn. In another patient the effect of levothyroxine was lost and hypothyroidism developed when dosulepin was started. ... 

Colantonio LA, Orson JM. Triiodothyronine thyrotoxicosis. Induction by desiccated thyroid and imipramine. Aw JD/i" Child 91A) 128, 396-7. 

In a study on the effects of hormones, testosterone-treated males and estrogen-treated females had a lower incidence of amorphous pigment stones than gonadectomized animals but may have had a higher incidence of cholesterol stones the total incidence was similar (66). Progesterone, on the other hand, lowered the incidence of cholesterol stones in females. Deoxycorticosterone had no clear effect on stone formation. Desiccated thyroid lowered and methyl thiouracil raised the ratio of cholesterol/amorphous pigment stones. 

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