Levo T Drug Information

Adverse reactions associated with LEVO-T therapy are primarily those of hyperthyroidism due to therapeutic overdosage . They include the following: General: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating Central nervous system: headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia Musculoskeletal: tremors, muscle weakness, muscle spasm Cardiovascular: palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest Respiratory: dyspnea Gastrointestinal: diarrhea, vomiting, abdominal cramps, elevations in liver function tests Dermatologic: hair loss, flushing, rash Endocrine: decreased bone mineral density Reproductive: menstrual irregularities, impaired fertility Seizures have been reported rarely with the institution of levothyroxine therapy. Adverse reactions associated with LEVO-T therapy are primarily those of hyperthyroidism due to therapeutic overdosage: arrhythmias, myocardial infarction, dyspnea, muscle spasm, headache, nervousness, irritability, insomnia, tremors, muscle weakness, increased appetite, weight loss, diarrhea, heat intolerance, menstrual irregularities, and skin rash. To report SUSPECTED ADVERSE REACTIONS, contact Neolpharma, Inc. at 1-844-200-4163 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

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.

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 LEVO-T (see Tables 2-5 below). Table 2. Drugs That May Decrease T4 Absorption (Hypothyroidism) Potential impact: Concurrent use may reduce the efficacy of LEVO-T by binding and delaying or preventing absorption, potentially resulting in hypothyroidism. Drug or Drug Class Effect Calcium Carbonate Ferrous Sulfate Calcium carbonate may form an insoluble chelate with levothyroxine, and ferrous sulfate likely forms a ferric-thyroxine complex. Administer LEVO-T at least 4 hours apart from these agents.

Orlistat Monitor patients treated concomitantly with orlistat and LEVO-T for changes in thyroid function. Bile Acid Sequestrants -Colesevelam -Cholestyramine -Colestipol Ion Exchange Resins -Kayexalate -Sevelamer Bile acid sequestrants and ion exchange resins are known to decrease levothyroxine absorption. Administer LEVO-T at least 4 hours prior to these drugs or monitor TSH levels.

Other drugs: Proton Pump Inhibitors Sucralfate Antacids - Aluminum & Magnesium Hydroxides - Simethicone Gastric acidity is an essential requirement for adequate absorption of levothyroxine. Sucralfate, antacids and proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce levothyroxine absorption. Monitor patients appropriately.

Table 3. Drugs That May Alter T4 and Triiodothyronine (T3) Serum Transport Without Affecting Free Thyroxine (FT4) Concentration (Euthyroidism) Drug or Drug Class Effect Clofibrate Estrogen-containing oral contraceptives Estrogens (oral) Heroin / Methadone 5-Fluorouracil Mitotane Tamoxifen These drugs may increase serum thyroxine-binding globulin (TBG) concentration. Androgens / Anabolic Steroids Asparaginase Glucocorticoids Slow-Release Nicotinic Acid These drugs may decrease serum TBG concentration. Potential impact (below): Administration of these agents with LEVO-T results in an initial transient increase in FT4. Continued administration results in a decrease in serum T4 and normal FT4 and TSH concentrations.

Salicylates (> 2 g/day) Salicylates inhibit binding of T4 and T3 to TBG and transthyretin. An initial increase in serum FT4 is followed by return of FT4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T4 levels may decrease by as much as 30%. Other drugs: Carbamazepine Furosemide (> 80 mg IV) Heparin Hydantoins Non-Steroidal Anti-inflammatory Drugs -Fenamates These drugs may cause protein-binding site displacement. Furosemide has been shown to inhibit the protein binding of T4 to TBG and albumin, causing an increase free T4 fraction in serum.

Furosemide competes for T4-binding sites on TBG, prealbumin, and albumin, so that a single high dose can acutely lower the total T4 level. Phenytoin and carbamazepine reduce serum protein binding of levothyroxine, and total and free T4 may be reduced by 20% to 40%, but most patients have normal serum TSH levels and are clinically euthyroid. Closely monitor thyroid hormone parameters.

Table 4. Drugs That May Alter Hepatic Metabolism of T4 (Hypothyroidism) Potential impact: Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of levothyroxine, resulting in increased LEVO-T requirements. Drug or Drug Class Effect Phenobarbital Rifampin Phenobarbital has been shown to reduce the response to thyroxine. Phenobarbital increases L-thyroxine metabolism by inducing uridine 5'-diphospho-glucuronosyltransferase (UGT) and leads to a lower T4 serum levels.

Changes in thyroid status may occur if barbiturates are added or withdrawn from patients being treated for hypothyroidism. Rifampin has been shown to accelerate the metabolism of levothyroxine. Table 5. Drugs That May Decrease Conversion of T4 to T3 Potential impact: Administration of these enzyme inhibitors decreases the peripheral conversion of T4 to T3, leading to decreased T3 levels.

However, serum T4 levels are usually normal but may occasionally be slightly increased. Drug or Drug Class Effect Beta-adrenergic antagonists (e.g., Propranolol > 160 mg/day) In patients treated with large doses of propranolol (> 160 mg/day), T3 and T4 levels change, TSH levels remain normal, and patients are clinically euthyroid. Actions of particular beta-adrenergic antagonists may be impaired when a hypothyroid patient is converted to the euthyroid state.

Glucocorticoids (e.g., Dexamethasone ≥ 4 mg/day) Short-term administration of large doses of glucocorticoids may decrease serum T3 concentrations by 30% with minimal change in serum T4 levels. However, long-term glucocorticoid therapy may result in slightly decreased T3 and T4 levels due to decreased TBG production (See above). Other drugs: Amiodarone Amiodarone inhibits peripheral conversion of levothyroxine (T4) to triiodothyronine (T3) and may cause isolated biochemical changes (increase in serum free-T4, and decreased or normal free-T3) in clinically euthyroid patients.

Antidiabetic Therapy Addition of

LEVO-T 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.

Oral Anticoagulants

LEVO-T increases 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 LEVO-T dose is increased. Closely monitor coagulation tests to permit appropriate and timely dosage adjustments.

Digitalis Glycosides

LEVO-T 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.

Antidepressant Therapy Concurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline)

antidepressants and LEVO-T 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. LEVO-T may accelerate the onset of action of tricyclics.

Administration of sertraline in patients stabilized on LEVO-T may result in increased LEVO-T requirements.

Ketamine Concurrent use of ketamine and

LEVO-T may produce marked hypertension and tachycardia. Closely monitor blood pressure and heart rate in these patients.

Sympathomimetics Concurrent use of sympathomimetics and

LEVO-T 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.

Tyrosine-Kinase Inhibitors Concurrent use of tyrosine-kinase inhibitors such as imatinib may cause

hypothyroidism. Closely monitor TSH levels in such patients.

Drug-Food Interactions Consumption of certain foods may affect

LEVO-T absorption thereby necessitating adjustments in dosing . Soybean flour, cottonseed meal, walnuts, and dietary fiber may bind and decrease the absorption of LEVO-T 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.

Pregnancy Risk Summary Experience with levothyroxine use in pregnant women, including data from post-marketing studies, have not reported increased rates of major birth defects or miscarriages. There are risks to the mother and fetus associated with untreated hypothyroidism in pregnancy. Since TSH levels may increase during pregnancy, TSH should be monitored and LEVO-T dosage adjusted during pregnancy . There are no animal studies conducted with levothyroxine during pregnancy.

LEVO-T should not be discontinued during pregnancy and hypothyroidism diagnosed during pregnancy should be promptly treated. The estimated background risk of major birth defects and miscarriage for the indicated population is unknown. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively.

Clinical Considerations Disease-Associated Maternal and/or Embryo/Fetal Risk Maternal hypothyroidism during pregnancy is associated with a higher rate of complications, including spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, and premature delivery. Untreated maternal hypothyroidism may have an adverse effect on fetal neurocognitive development. Dose Adjustments During Pregnancy and the Postpartum Period Pregnancy may increase LEVO-T requirements.

Serum TSH levels should be monitored and the LEVO-T dosage adjusted during pregnancy. Since postpartum TSH levels are similar to preconception values, the LEVO-T dosage should return to the pre-pregnancy dose immediately after delivery. Data Human Data Levothyroxine is approved for use as a replacement therapy for hypothyroidism.

There is a long experience of levothyroxine use in pregnant women, including data from post-marketing studies that have not reported increased rates of fetal malformations, miscarriages or other adverse maternal or fetal outcomes associated with levothyroxine use in pregnant women.

Pediatric Use The initial dose of LEVO-T varies with age and body weight. Dosing adjustments are based on an assessment of the individual patient's clinical and laboratory parameters . In children in whom a diagnosis of permanent hypothyroidism has not been established, discontinue LEVO-T 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.

Congenital Hypothyroidism 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, initiate LEVO-T therapy immediately upon diagnosis. Levothyroxine is generally continued for life in these patients.

Closely monitor infants during the first 2 weeks of LEVO-T therapy for cardiac overload, arrhythmias, and aspiration from avid suckling. Closely monitor patients to avoid undertreatment or overtreatment. Undertreatment may have deleterious effects on intellectual development and linear growth.

Overtreatment is associated with craniosynostosis in infants, may adversely affect the tempo of brain maturation, and may accelerate the bone age and result in premature epiphyseal closure and compromised adult stature. Acquired Hypothyroidism in Pediatric Patients Closely monitor patients 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.

LEVO-T is contraindicated in patients with uncorrected adrenal insufficiency . Uncorrected adrenal insufficiency.

The signs and symptoms of overdosage are those of hyperthyroidism . In addition, confusion and disorientation may occur. Cerebral embolism, shock, coma, and death have been reported. Seizures occurred in a 3-year-old child ingesting 3.6 mg of levothyroxine.

Symptoms may not necessarily be evident or may not appear until several days after ingestion of levothyroxine sodium. Reduce the LEVO-T dose or discontinue temporarily if signs or symptoms of overdosage occur. Initiate appropriate supportive treatment as dictated by the patient's medical status.

For current information on the management of poisoning or overdosage, contact the National Poison Control Center at 1-800-222-1222 or www.poison.org.