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Importance of Proper Dose Titration to Prevent Hyperthyroidism or Incomplete Treatment of Hypothyroidism
Levothyroxine has a narrow therapeutic index. Regardless of the indication for use, careful dosage titration is necessary to avoid hyperthyroidism or incomplete treatment of hypothyroidism. These consequences include, among others, adverse effects on cardiovascular function, growth and development, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism. Periodic clinical and thyroid function monitoring is recommended [See DOSAGE AND ADMINISTRATION]. In addition, many drugs interact with levothyroxine sodium necessitating adjustments in dosing to maintain therapeutic response [See DRUG INTERACTIONS].
Risk of Cardiac Adverse Reactions in the Elderly and in Patients with Underlying Cardiovascular Disease
In the elderly and in patients with cardiovascular disorders, levothyroxine therapy should be initiated at lower doses than those recommended in younger individuals or in patients without cardiac disease and it should be noted that unlike levothyroxine sodium tablets, TIROSINT capsules cannot be cut in half [See DOSAGE AND ADMINISTRATION and Use in Specific Populations]. If cardiac symptoms develop or worsen, the levothyroxine sodium dose should be reduced or withheld for one week and then cautiously restarted at a lower dose. Overtreatment with levothyroxine sodium may have adverse cardiovascular effects such as an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias. Patients with coronary artery disease who are receiving levothyroxine therapy should be monitored closely during surgical procedures because of the possibility of precipitating cardiac arrhythmias, including atrial fibrillation. Concomitant administration of levothyroxine and sympathomimetic agents to patients with coronary artery disease may precipitate coronary insufficiency [See DRUG INTERACTIONS].
Patients with Nontoxic Diffuse Goiter or Nodular Thyroid Disease
Suppression of thyroid nodules with levothyroxine is a controversial issue. Routine suppression of benign thyroid nodules is generally not recommended in iodine-sufficient patients. If the serum thyrotropin-stimulating hormone (TSH) is already suppressed, levothyroxine sodium should not be administered. If the serum TSH level is not suppressed, TIROSINT should not be used without frequent laboratory monitoring of thyroid function for evidence of hyperthyroidism and clinical monitoring for potential associated adverse cardiovascular signs and symptoms of hyperthyroidism.
Patients with Concomitant Adrenal Insufficiency
Occasionally, chronic autoimmune thyroiditis may occur in association with other autoimmune disorders such as adrenal insufficiency, pernicious anemia, and insulin-dependent diabetes mellitus. Patients with concomitant adrenal insufficiency should be treated with replacement glucocorticoids prior to initiation of treatment with levothyroxine sodium [See CONTRAINDICATIONS]. Failure to do so may precipitate an acute adrenal crisis when thyroid hormone therapy is initiated, due to increased metabolic clearance of glucocorticoids by thyroid hormone.
Thyroid Hormone Over-replacement Associated with Decreased Bone Mineral Density
Over-replacement with levothyroxine therapy has been associated with decreased bone mineral density, especially in post-menopausal women. The increased bone resorption may be associated with increased serum levels and urinary excretion of calcium and phosphorous, elevations in bone alkaline phosphatase, and suppressed serum parathyroid hormone levels. Therefore, it is recommended that patients receiving levothyroxine sodium be given the minimum dose necessary to achieve the desired clinical and biochemical response, unless TSH suppression is the goal of therapy, as in patients with well-differentiated thyroid cancer.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Animal studies have not been performed to evaluate the carcinogenic potential, mutagenic potential or effects on fertility of Levothyroxine Sodium.
Use In Specific Populations
Pregnancy category A. Levothyroxine should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated. Hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, pre-eclampsia, stillbirth, and premature delivery. Maternal hypothyroidism may have an adverse effect on fetal and childhood growth and development.
During pregnancy, serum thyroxine (T4) levels may decrease and serum thyrotropin-stimulating hormone (TSH) levels increase to values outside the normal range. Since elevations in serum TSH may occur as early as 4 weeks gestation, pregnant women taking TIROSINT should have their TSH measured during each trimester. An elevated serum TSH level should be corrected by an increase in the dose of TIROSINT. Since postpartum TSH levels are similar to preconception values, the TIROSINT dosage should return to the pre-pregnancy dose immediately after delivery. A serum TSH level should be obtained 6-8 weeks postpartum.
Thyroid hormones cross the placental barrier to some extent as evidenced by levels in cord blood of athyreotic fetuses being approximately one-third maternal levels. Transfer of thyroid hormone from the mother to the fetus, however, may not be adequate to prevent in utero hypothyroidism.
Thyroid hormones are excreted only minimally in human milk. Adequate replacement doses of levothyroxine are generally needed to maintain normal lactation.
The goal of treatment in pediatric patients with hypothyroidism is to achieve and maintain normal intellectual and physical growth and development.
The initial dose of levothyroxine varies with age and body weight [See DOSAGE AND ADMINISTRATION]. Dosing adjustments are based on an assessment of the individual patient's clinical and laboratory parameters [See WARNINGS AND PRECAUTIONS]
In children in whom a diagnosis of permanent hypothyroidism has not been established, it is recommended that at an appropriate age levothyroxine be discontinued for a trial period. Serum T4 and TSH levels should be obtained at the end of the trial period, and laboratory test results and clinical assessments should then guide diagnosis and treatment, if warranted.
Rapid restoration of normal serum T4 concentrations is essential for preventing the adverse effects of congenital hypothyroidism on intellectual development as well as on overall physical growth and maturation. Therefore, levothyroxine therapy should be initiated immediately upon diagnosis and is generally continued for life.
The patient should be monitored closely to avoid undertreatment and overtreatment. Undertreatment may result in poor school performance due to impaired concentration and slowed mentation and in reduced adult height. Overtreatment may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature.
Treated children may manifest a period of catch-up growth, which may be adequate in some cases to normalize adult height. In children with severe or prolonged hypothyroidism, catch-up growth may not be adequate to normalize adult height.
Because of the increased prevalence of cardiovascular disease among the elderly, levothyroxine therapy should not be initiated at the full replacement dose. Atrial fibrillation is a common side effect associated with levothyroxine treatment in the elderly [See DOSAGE AND ADMINISTRATION and WARNINGS AND PRECAUTIONS].
Last reviewed on RxList: 3/14/2012
This monograph has been modified to include the generic and brand name in many instances.
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