See also the following individual entries:
Levothyroxine sodium Action/Kinetics: The thyroid manufactures two active hormones: thy-roxine and triiodothyronine, both of which contain iodine. These thyroid hormones are released into the bloodstream, where they are bound to protein. Synthetic derivatives include liothyronine (T3), levothyro-nine (T4), and liotrix (a 4:1 mixture of T4 and T3). The thyroid hormones regulate growth by controlling protein synthesis and regulating energy metabolism by increasing the resting or basal metabolic rate. This results in increases in respiratory rate; body temperature; CO; oxygen consumption; HR; blood volume; enzyme system activity; rate of fat, carbohydrate, and protein metabolism; and growth and maturation. Excess thyroid hormone causes a decrease in TSH, and a lack of thyroid hormone causes an increase in the production and secretion of TSH. Normally, the ratio of T4 to T3 released from the thyroid gland is 20:1 with about 35% of T4 being converted in the periphery (e.g., kidney, liver) to T3. Uses: Replacement or supplemental therapy in hypothyroidism due to all causes except transient hypothyroid-
ism during the recovery phase of subacute thyroiditis. To treat or prevent euthyroid goiters. With antithyroid drugs for thyrotoxicosis (to prevent goiter or hypothyroidism). Diag-nostically to differentiate suspected hyperthyroidism from euthyroidism. The treatment of choice for hypo-thyroidism is usually T4 because of its consistent potency and its prolonged duration of action although it does have a slow onset and its effects are cumulative over several weeks. Contraindications: Uncorrected adrenal insufficiency, acute MI, hyper-thyroidism, and thyrotoxicosis. When hypothyroidism and adrenal insufficiency coexist unless treatment with adrenocortical steroids is initiated first. To treat obesity or infertility.
Special Concerns: Geriatric clients may be more sensitive to the usual adult dosage of these hormones. Use with extreme caution in the presence of angina pectoris, hypertension, and other CV diseases, renal insufficiency, and ischemic states. Use with caution during lactation. Side Effects: Thyroid preparations have cumulative effects, and over-dosage (e.g., symptoms of hyperthy-roidism) may occur. CV: Arrhythmias, palpitations, angina, increased HR and pulse pressure, cardiac arrest, aggravation of CHF. GI: Cramps, diarrhea, N&V, appetite changes. CNS: Headache, nervousness, mental agitation, irritability, insomnia, tremors. Miscellaneous: Weight loss, hyper-hidrosis, excessive warmth, irregular menses, heat intolerance, fever, dyspnea, allergic skin reactions (rare). Decreased bone density in pre- and postmenopausal women following long-term use of levothyroxine.
Corticosteroids / Thyroid preparations T tissue demands for corticos-teroids. Adrenal insufficiency must be corrected with corticosteroids before administering thyroid hormones. In clients already treated for adrenal insufficiency, dosage of cor-ticosteroids must be increased when initiating therapy with thyroid drug Epinephrine / CV effects T by thyroid preparations Ketamine / Concomitant use may result in severe hypertension and tachycardia
Levarterenol / CV effects T by thyroid preparations
Salicylates / Salicylates compete for thyroid-binding sites on protein
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