Hypothyroidism

Levothyroxine Sodium Tablets are indicated as a replacement therapy in primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism.

Pituitary Thyrotropin (Thyroid-Stimulating Hormone, TSH) Suppression

Levothyroxine Sodium Tablets are indicated as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.

Limitations of Use:

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Levothyroxine Sodium Tablets are not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-sufficient patients as there are no clinical benefits and overtreatment with Levothyroxine Sodium Tablets may induce hyperthyroidism [see Warnings and Precautions (5.4)].

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Levothyroxine Sodium Tablets are not indicated for treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

2.1 General Administration Information

Administer Levothyroxine Sodium Tablets as a single daily dose, on an empty stomach, one-half to one hour before breakfast.

Administer Levothyroxine Sodium Tablets at least 4 hours before or after drugs known to interfere with Levothyroxine Sodium Tablets absorption [see Drug Interactions (7.1)].

Evaluate the need for dose adjustments when regularly administering within one hour of certain foods that may affect Levothyroxine Sodium Tablets absorption [see Drug Interactions (7.9) and Clinical Pharmacology (12.3)].

Administer Levothyroxine Sodium Tablets to infants and children who cannot swallow intact tablets by crushing the tablet, suspending the freshly crushed tablet in a small amount (5 mL to 10 mL or 1 teaspoon to 2 teaspoons) of water and immediately administering the suspension by spoon or dropper. Do not store the suspension. Do not administer in foods that decrease absorption of Levothyroxine Sodium Tablets, such as soybean-based infant formula [see Drug Interactions (7.9)].

2.2 General Principles of Dosing

The dose of Levothyroxine Sodium Tablets for hypothyroidism or pituitary TSH suppression depends on a variety of factors including: the patient's age, body weight, cardiovascular status, concomitant medical conditions (including pregnancy), concomitant medications, co-administered food and the specific nature of the condition being treated [see Dosage and Administration (2.3), Warnings and Precautions (5), and Drug Interactions (7)]. Dosing must be individualized to account for these factors and dose adjustments made based on periodic assessment of the patient's clinical response and laboratory parameters [see Dosage and Administration (2.4)].

The peak therapeutic effect of a given dose of Levothyroxine Sodium Tablets may not be attained for 4 to 6 weeks.

2.3 Dosing in Specific Patient Populations

2.4 Monitoring TSH and/or Thyroxine (T4) Levels

Assess the adequacy of therapy by periodic assessment of laboratory tests and clinical evaluation. Persistent clinical and laboratory evidence of hypothyroidism despite an apparent adequate replacement dose of Levothyroxine Sodium Tablets may be evidence of inadequate absorption, poor compliance, drug interactions, or a combination of these factors.

5.1 Cardiac Adverse Reactions in the Elderly and in Patients with Underlying Cardiovascular Disease

Over-treatment with levothyroxine may cause an increase in heart rate, cardiac wall thickness, and cardiac contractility and may precipitate angina or arrhythmias, particularly in patients with cardiovascular disease and in elderly patients. Initiate Levothyroxine Sodium Tablets therapy in this population at lower doses than those recommended in younger individuals or in patients without cardiac disease [see Dosage and Administration (2.3), Use in Specific Populations (8.5)].

Monitor for cardiac arrhythmias during surgical procedures in patients with coronary artery disease receiving suppressive Levothyroxine Sodium Tablets therapy. Monitor patients receiving concomitant Levothyroxine Sodium Tablets and sympathomimetic agents for signs and symptoms of coronary insufficiency.

If cardiac symptoms develop or worsen, reduce the Levothyroxine Sodium Tablets dose or withhold for one week and restart at a lower dose.

5.2 Myxedema Coma

Myxedema coma is a life-threatening emergency characterized by poor circulation and hypometabolism, and may result in unpredictable absorption of levothyroxine sodium from the gastrointestinal tract. Use of oral thyroid hormone drug products is not recommended to treat myxedema coma. Administer thyroid hormone products formulated for intravenous administration to treat myxedema coma.

5.3 Acute Adrenal Crisis in Patients with Concomitant Adrenal Insufficiency

Thyroid hormone increases metabolic clearance of glucocorticoids. Initiation of thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate an acute adrenal crisis in patients with adrenal insufficiency. Treat patients with adrenal insufficiency with replacement glucocorticoids prior to initiating treatment with Levothyroxine Sodium Tablets [see Contraindications (4)].

5.4 Prevention of Hyperthyroidism or Incomplete Treatment of Hypothyroidism

Levothyroxine Sodium Tablets have a narrow therapeutic index. Over- or undertreatment with Levothyroxine Sodium Tablets may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and glucose and lipid metabolism. Titrate the dose of Levothyroxine Sodium Tablets carefully and monitor response to titration to avoid these effects [see Dosage and Administration (2.4)]. Monitor for the presence of drug or food interactions when using Levothyroxine Sodium Tablets and adjust the dose as necessary [see Drug Interactions (7.9)and Clinical Pharmacology (12.3)].

5.5 Worsening of Diabetic Control

Addition of levothyroxine therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control after starting, changing, or discontinuing Levothyroxine Sodium Tablets [see Drug Interactions (7.2)].

5.6 Decreased Bone Mineral Density Associated with Thyroid Hormone Over-Replacement

Increased bone resorption and decreased bone mineral density may occur as a result of levothyroxine over-replacement, particularly 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. Administer the minimum dose of Levothyroxine Sodium Tablets that achieves the desired clinical and biochemical response to mitigate this risk.

Adverse Reactions in Children

Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children receiving levothyroxine therapy. Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in children with resultant compromised adult height.

Hypersensitivity Reactions

Hypersensitivity reactions to inactive ingredients have occurred in patients treated with thyroid hormone products. These include urticaria, pruritus, skin rash, flushing, angioedema, various gastrointestinal symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness, and wheezing. Hypersensitivity to levothyroxine itself is not known to occur.

7.1 Drugs Known to Affect Thyroid Hormone Pharmacokinetics

Many drugs can exert effects on thyroid hormone pharmacokinetics and metabolism (e.g., absorption, synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to Levothyroxine Sodium Tablets (see Tables 2-5 below).

7.2 Antidiabetic Therapy

Addition of Levothyroxine Sodium Tablets therapy in patients with diabetes mellitus may worsen glycemic control and result in increased antidiabetic agent or insulin requirements. Carefully monitor glycemic control, especially when thyroid therapy is started, changed, or discontinued [see Warnings and Precautions (5.5)].

7.3 Oral Anticoagulants

Levothyroxine Sodium Tablets increase the response to oral anticoagulant therapy. Therefore, a decrease in the dose of anticoagulant may be warranted with correction of the hypothyroid state or when the Levothyroxine Sodium Tablets dose is increased. Closely monitor coagulation tests to permit appropriate and timely dosage adjustments.

7.4 Digitalis Glycosides

Levothyroxine Sodium Tablets may reduce the therapeutic effects of digitalis glycosides. Serum digitalis glycoside levels may decrease when a hypothyroid patient becomes euthyroid, necessitating an increase in the dose of digitalis glycosides.

7.5 Antidepressant Therapy

Concurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline) antidepressants and Levothyroxine Sodium Tablets may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines. Toxic effects may include increased risk of cardiac arrhythmias and central nervous system stimulation. Levothyroxine Sodium Tablets may accelerate the onset of action of tricyclics. Administration of sertraline in patients stabilized on Levothyroxine Sodium Tablets may result in increased Levothyroxine Sodium Tablets requirements.

7.6 Ketamine

Concurrent use of ketamine and Levothyroxine Sodium Tablets may produce marked hypertension and tachycardia. Closely monitor blood pressure and heart rate in these patients.

7.7 Sympathomimetics

Concurrent use of sympathomimetics and Levothyroxine Sodium Tablets may increase the effects of sympathomimetics or thyroid hormone. Thyroid hormones may increase the risk of coronary insufficiency when sympathomimetic agents are administered to patients with coronary artery disease.

7.8 Tyrosine-Kinase Inhibitors

Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause hypothyroidism. Closely monitor TSH levels in such patients.

7.9 Drug-Food Interactions

Consumption of certain foods may affect Levothyroxine Sodium Tablets absorption thereby necessitating adjustments in dosing [see Dosage and Administration (2.1)]. Soybean flour, cottonseed meal, walnuts, and dietary fiber may bind and decrease the absorption of Levothyroxine Sodium Tablets from the gastrointestinal tract. Grapefruit juice may delay the absorption of levothyroxine and reduce its bioavailability.

7.10 Drug-Laboratory Test Interactions

Consider changes in TBG concentration when interpreting T4 and T3 values. Measure and evaluate unbound (free) hormone and/or determine the free-T4 index (FT4I) in this circumstance. Pregnancy, infectious hepatitis, estrogens, estrogen-containing oral contraceptives, and acute intermittent porphyria increase TBG concentration. Nephrosis, severe hypoproteinemia, severe liver disease, acromegaly, androgens, and corticosteroids decrease TBG concentration. Familial hyper- or hypo-thyroxine binding globulinemias have been described, with the incidence of TBG deficiency approximating 1 in 9000.

8.1 Pregnancy

8.2 Lactation

8.4 Pediatric Use

The initial dose of Levothyroxine Sodium Tablets varies with age and body weight. Dosing adjustments are based on an assessment of the individual patient's clinical and laboratory parameters [see Dosage and Administration (2.3, 2.4)].

In children in whom a diagnosis of permanent hypothyroidism has not been established, discontinue Levothyroxine Sodium Tablets administration for a trial period, but only after the child is at least 3 years of age. Obtain serum T4 and TSH levels at the end of the trial period, and use laboratory test results and clinical assessment to guide diagnosis and treatment, if warranted.

8.5 Geriatric Use

Because of the increased prevalence of cardiovascular disease among the elderly, initiate Levothyroxine Sodium Tablets at less than the full replacement dose [see Warnings and Precautions (5.1) and Dosage and Administration (2.3)]. Atrial arrhythmias can occur in elderly patients. Atrial fibrillation is the most common of the arrhythmias observed with levothyroxine overtreatment in the elderly.

12.1 Mechanism of Action

Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins.

The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues.

12.2 Pharmacodynamics

Oral levothyroxine sodium is a synthetic T4 hormone that exerts the same physiologic effect as endogenous T4, thereby maintaining normal T4 levels when a deficiency is present.

12.3 Pharmacokinetics

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Standard animal studies have not been performed to evaluate the carcinogenic potential, mutagenic potential or effects on fertility of levothyroxine.

Storage Conditions

Store at 25°C (77°F); excursions permitted to 15° C to 30° C (59° F to 86° F) [see USP Controlled Room Temperature]. Levothyroxine Sodium Tablets should be protected from light and moisture.

Dosing and Administration

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Instruct patients to take Levothyroxine Sodium Tablets only as directed by their healthcare provider.

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Instruct patients to take Levothyroxine Sodium Tablets as a single dose, preferably on an empty stomach, one-half to one hour before breakfast.

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Inform patients that agents such as iron and calcium supplements and antacids can decrease the absorption of levothyroxine. Instruct patients not to take Levothyroxine Sodium Tablets within 4 hours of these agents.

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Instruct patients to notify their healthcare provider if they are pregnant or breastfeeding or are thinking of becoming pregnant while taking Levothyroxine Sodium Tablets.

Important Information

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Inform patients that it may take several weeks before they notice an improvement in symptoms.

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Inform patients that the levothyroxine in Levothyroxine Sodium Tablets is intended to replace a hormone that is normally produced by the thyroid gland. Generally, replacement therapy is to be taken for life.

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Inform patients that Levothyroxine Sodium Tablets should not be used as a primary or adjunctive therapy in a weight control program.

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Instruct patients to notify their healthcare provider if they are taking any other medications, including prescription and over-the-counter preparations.

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Instruct patients to notify their physician of any other medical conditions they may have, particularly heart disease, diabetes, clotting disorders, and adrenal or pituitary gland problems, as the dose of medications used to control these other conditions may need to be adjusted while they are taking Levothyroxine Sodium Tablets. If they have diabetes, instruct patients to monitor their blood and/or urinary glucose levels as directed by their physician and immediately report any changes to their physician. If patients are taking anticoagulants, their clotting status should be checked frequently.

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Instruct patients to notify their physician or dentist that they are taking Levothyroxine Sodium Tablets prior to any surgery.

Adverse Reactions

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Instruct patients to notify their healthcare provider if they experience any of the following symptoms: rapid or irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives or skin rash, or any other unusual medical event.

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Inform patients that partial hair loss may occur rarely during the first few months of Levothyroxine Sodium Tablets therapy, but this is usually temporary.