Thyroid hormone replacement therapy

Thyroid hormone replacement therapy in patients with diabetes may increase the intensity of the symptoms or the diabetes. The nurse closely monitors the patient with diabetes during thyroid hormone replacement therapy for signs of hyperglycemia (see Chap. 49) and notifies the primary health care provider if this problem occurs. 

Replacement therapy - Replacement therapy in hypogonadism associated with a deficiency or absence of endogenous testosterone. Prior to puberty, androgen replacement therapy is needed for development of secondary sexual characteristics. Prolonged treatment is required to maintain sexual characteristics in these and other males who develop testosterone deficiency after puberty. Appropriate adrenal cortical and thyroid hormone replacement therapy are still necessary, however, and are of primary importance. 

Levothyroxine sodium (Levothwid, Synthroid, Levoxine) is the sodium salt of the naturally occurring levorota-tory isomer of T4. It is the preparation of choice for maintenance of plasma T4 and T3 concentrations for thyroid hormone replacement therapy in hypothyroid patients. It is absorbed intact from the gastrointestinal tract, and its long half-life allows for convenient once-daily administration. Since much of the T4 is deiodi-nated to T3, it is usually unnecessary to use more expensive preparations containing bothX4 and Tj.The aim is to establish euthyroidism with measured serum concentrations of T4, T3, and TSH within the normal range. 

Liothyronine sodium (Cytomel) is the sodium salt of the naturally occurring levorotatory isomer of T3. Liothyronine is generally not used for maintenance thyroid hormone replacement therapy because of its short plasma half-life and duration of action. The use of T3 alone is recommended only in special situations, such as in the initial therapy of myxedema and myxedema coma and the short-term suppression of TSH in patients undergoing surgery for thyroid cancer. The use of T3 alone may also be useful in patients with the rare condition of 5 -deiodinase deficiency who cannot convert T4 to T3. 

Liotrix (Euthroid, Thywlar) is a 4 1 mixture of levothyroxine sodium and liothyronine sodium. Like levothyroxine, liotrix is used for thyroid hormone replacement therapy in hypothyroid patients. Although the idea of combining T4 and T3 in replacement therapy so as to mimic the normal ratio secreted by the thyroid gland is not new, it does not appear that liotrix offers any therapeutic advantage over levothyroxine alone. 

In patients with longstanding hypothyroidism and those with ischemic heart disease, rapid correction of hypothyroidism may precipitate angina, cardiac arrhythmias, or other adverse effects. For these patients, replacement therapy should be started at low initial doses, followed by slow titration to full replacement as tolerated over several months. If hypothyroidism and some degree of adrenal insufficiency coexist, an appropriate adjustment of the corticosteroid replacement must be initiated prior to thyroid hormone replacement therapy. This prevents acute adrenocortical insufficiency that could otherwise arise from a thyroid hormone-induced increase in the metabolic clearance rate of adrenocortical hormones. 

L All of the following are common adverse effects associated with drug overdose of thyroid hormone replacement therapy EXCEPT... 

El Kaissi S, Kotowicz MA, Berk M, Wall JR. Acute delirium in the setting of primary hypothyroidism the role of thyroid hormone replacement therapy. Thyroid 2005 15(9) 1099-101. 

Escobar-Morreale HF, Botella-Carretero JI, Gomez-Bueno M, et al. Thyroid hormone replacement therapy in primary hypothyroidism a randomized trial comparing L-thyroxine plus liothyronine with L-thyroxine alone. Ann Intern Med. 2005 142 412-424. 

Wiersinga WM. Thyroid hormone replacement therapy. Horm Res. 2001 56(suppl 1) 74—81. 

The natural history of Graves disease is of alternating remission and relapse. Progression to hypothyroidism can occur, especially after 1 treatment. Such patients should have long-term follow-up, and are likely to require thyroid hormone replacement therapy Severe forms of thyroid eye disease should be treated with steroids and immunosuppresants or low-dose radiotherapy. Urgent surgical decompression can be required for eyophthalmos. 

In contrast to other protein-bound drugs for which a loading dose is given to achieve rapid steady-state concentrations, a slow and stepwise increase in thyroid hormone replacement therapy is advisable. This is preferred mainly to avoid sudden cardiac adverse effects, especially in older patients with long-standing myxedema. Moreover, since thyroid hormone substitution can change the metabolic clearance of this drug, steady-state concentrations are obtained only after several months (SEDA-6, 363). 

A deficiency of thyroid hormone during fetal development due to untreated or undertreated maternal hypothyroidism results in a neurological deficit in the offspring. In congenital hypothyroidism, a normal maternal thyroid can meet the fetal requirements for thyroid hormone. However, in the postnatal period these infants require a prompt thyroid hormone replacement therapy throughout their life, beginning in the first few weeks of life. If untreated, they inevitably develop growth and mental retardation. Thyroid hormone is essential for maturational development of the CNS and is required for the development of axonal projections and myelination. One of the important effects of thyroid hormone is to promote the synthesis of myelin basic protein. 

Note that pituitary enlargement in hypothyroidism does not invariably indicate the presence of a primary pituitary tumor. Pituitary enlargement is seen in patients with severe primary hypothyroidism owing to compensatory hyperplasia and hypertrophy of the thyrotrophs. Serum TSH concentrations and pituitary enlargement decline during thyroid hormone replacement therapy, indicating that the TSH secretion is not autonomous. These patients are easily separated from patients with primary pituitary failure by measuring a TSH level. 

What effect would a high-fiber diet, or the ingestion of bile-binding resins or antacids, have on thyroid hormone replacement therapy ... 

Radioactive iodine ablation therapy for hyperthyroidism is relatively inexpensive, does not require hospitalization, and is relatively free of adverse effects. It is associated with a high incidence of permanent hypothyroidism, and all patients must be warned of this and followed therecffer for the onset of hypothyroidism. Because thyroid hormone replacement therapy is generally well accepted by the patient, many specialists prefer to treat with relatively higher doses to rapidly... 

Iodine deficiency of the fetus is the result of iodine deficiency in the mother. The condition is associated with a greater incidence of stillbirths, abortions and congenital abnormalities, which can be reduced by iodisation. The effects are similar to those observed with maternal h3q>othyroidism which can be reduced by thyroid hormone replacement therapy. ... 

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