Thyroid drugs affecting

Pregnancy may be adversely affected by poorly controlled hyperthyroidism, with an increased rate of fetal loss. The goal of treatment during pregnancy is to maintain euthyroidism, using the smallest doses of anti thyroid drugs possible. 

T4 and T3 in plasma are reversibly bound to protein, primarily thyroxine-binding globulin (TBG). Only about 0.04% of total T4 and 0.4% of T3 exist in the free form. Many physiologic and pathologic states and drugs affect T4, T3, and thyroid transport. However, the actual levels of free hormone generally remain normal, reflecting feedback control. 

Some of the hormones and drugs affecting the hypothalamus, pituitary and thyroid. 

Liver, Iddney, and thyroid disease affect the secretion and metabolism of the adrenal steroids. Other factors affecting these processes mclude stress, age, estrogen therapy, nutrition, and drugs. 

Figure 106.1 Evaluation of patients with abnormal serum thyrotropin (TSH) oonoentrations. Schematic aigorithm for the evaiuation of a patient with abnormal thyrotropin (TSH) with an indication of the most oommon diagnoses in the absence of nonthyroidai iiinesses and drugs affecting thyroid hormone concentrations. Abbreviations t, high low n, normal FT4, free thyroxine FT3, free triiodothyronine L-T4, levothyroxine.

Antithyroid dru inhibit the manufacture of thyroid hormones. They do not affect existing tiiyroid hormones tiiat are circulating in die blood or stored in die thyroid gland. For tiiis reason, therapeutic effects of the antithyroid drugs may not be observed for 3 to 4 weeks. Antithyroid drugs are listed in the Summary Drug Table Thyroid and Antithyroid Drugs. 

Unit IX discusses drugp that affect the endocrine system and consists of five chapters antidiabetic drugs, pituitary and andrenocortical hormones, thyroid and antitliyroid drag s, male and female hormones, and dragp acting on the uterus. 

Drugs can affect thyroid function in a number of ways.41 Effects of drugs on thyroid hormone protein binding, LT4 absorption, and metabolism have been discussed previously. Several commonly used medications can alter thyroid hormone secretion. 

Thyroid hormone production is regulated by TSH secreted by the anterior pituitary, which in turn is under negative feedback control by the circulating level of free thyroid hormone and the positive influence of hypothalamic thyrotropin-releasing hormone. Thyroid hormone production is also regulated by extrathyroidal deiodination of T4 to T3, which can be affected by nutrition, nonthyroidal hormones, drugs, and illness. 

Several drugs are known to affect calcium metabolism and to Induce calcium loss (42). Amongst these are the use of glucocorticoids and thyroid extract. The use of both of these drugs can lead to the development of osteoporosis. It Is less well known that several other... 

Drugs that may be affected by estrogens include oral anticoagulants, tricyclic antidepressants, hydantoins, corticosteroids, and thyroid hormones. 

Drugs that may affect repaglinide include CYP 450 inhibitors (eg, clarithromycin, erythromycin, ketoconazole, miconazole), CYP 450 inducers (eg, barbiturates, carbamazepine, rifampin), beta blockers, calcium channel blockers, chloramphenicol, corticosteroids, coumarins, estrogens, gemfibrozil, isoniazid, itraconazole, levonorgestrel and ethinyl estradiol, MAOIs, nicotinic acid, NSAIDs, oral contraceptives, phenothiazines, phenytoin, probenecid, salicylates, simvastatin, sulfonamides, sympathomimetics, thiazides and other diuretics, and thyroid products. 

Drugs that may affect nateglinide include nonsteroidal anti-inflammatory agents (NSAIDs), salicylates, monoamine oxidase inhibitors, rifamycins, MAOIs, and nonselective beta-adrenergic blocking agents, thiazides, corticosteroids, thyroid products, and sympathomimetics. 

Drugs that may affect amiodarone include hydantoins, cholestyramine, fluoroquinolones, rifamycins, ritonavir, and cimetidine. Drugs that may be affected by amiodarone include anticoagulants, beta-blockers, calcium channel blockers, cyclosporine, dextromethorphan, digoxin, disopyramide, fentanyl, flecainide, hydantoins, lidocaine, methotrexate, procainamide, quinidine, and theophylline. Drug/Lab test interactions Amiodarone alters the results of thyroid function tests, causing an increase in serum T4 and serum reverse T3 levels and a decline in... 

Drugs that may affect maprotiline include thyroid hormones, benzodiazepines, and phenothiazines. Drugs that may be affected by maprotiline include anticholinergics. 

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