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Unformatted text preview: C HAPTER 55 D RUGS FOR T HYROID D ISORDERS Thyroid hormones have profound effects on metabolism, cardiac function, growth and development.- stimulate the metabolic rate of most cells, increase the force and rate of cardiac contraction- promote maturation- severe deficiency can produce dwarfism and permanent mental impairment Thyroid drugs are the most misused drugs in the diet industry. I. T HYROID P HYSIOLOGY A. C HEMISTRY & N OMENCLATURE- thyroid gland produces two active hormones: triiodothyronine (T 3 ) thyroxine (T 4 , tetraiodothyronine)- T 3 is more potent than T 4- the body secretes more T 4 than T 3 and converts it to T 3 as needed B. T HYROID H ORMONE A CTIONS- thyroid hormones are protein bound- synthetic drugs are better than natural drugs to mimic the natural thyroid hormone actions 1. Stimulation of Energy Use elevates the basal metabolic rate, resulting in increased oxygen consumption and increased heat production 2. Stimulation of the Heart increases both the rate and force of contraction, resulting in increased cardiac output and increased oxygen demand 3. Promotion of Growth and Development essential for normal development of the brain and other components of the nervous system, and have a significant impact on maturation of skeletal muscle II. T HYROID P ATHOPHYSIOLOGY A. H YPOTHYROIDISM mild deficiency of thyroid hormone; malfunction of the thyroid gland- myxedema- severe deficiency in adults - cretinism hypothyroidism in infancy 1. Hypothyroidism in Adults a. Clinical Presentation- produces pale, puffy and expressionless facial characteristics, cold and dry skin, hair is brittle and loss occurs, heart rate and temperature are lowered, patient may have complaints of lethargy, fatigue, and intolerance to cold- mentality is impaired- thyroid enlargement (goiter) may occur if reduced levels of T 3 and T 4 promote excessive release of TSH (thyroid stimulating hormone) b. Causes- usually due to malfunction of the thyroid itself- in iodine sufficient countries, the principal cause is chronic autoimmune thyroiditis (Hasimotos disease)- other causes are insufficient iodine in the diet, surgical removal of the thyroid and destruction of the thyroid by radioactive iodine- may also result from insufficient secretion of TSH and TRH (thyrotropin releasing hormone) c. Therapeutic Strategy- requires replacement therapy with thyroid hormones and treatment must continue for life- standard replacement regimen consists of levothyroxine (T 4 ) alone- when adequate, doses eliminate all signs and symptoms of deficiency 2. Hypothyroidism During Pregnancy- maternal hypothyroidism can result in permanent neuropsychologic deficits in the child- congenital hypothyroidism can cause mental retardation and other developmental problems- in the absence of fetal hypothyroidism, maternal hypothyroidism can decrease IQ and other aspects of neuropsychologic function- limited largely to the first trimester, a time during which the fetus...
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- Spring '11