Levothyroxine Sodium: Package Insert and Label Information (Page 2 of 5)

3 DOSAGE FORMS AND STRENGTHS

Levothyroxine sodium tablets, USP are available as follows (Table 4):

Table 4: Levothyroxine Sodium Tablets, USP Strength and Identifying Features

Tablet Strength

Tablet Color/Shape

Debossed Tablet Markings

25 mcg

Orange/Capsule Shaped

25 on the unscored side and T bisect V on the scored side, with side scores

50 mcg

White/Capsule Shaped

50 on the unscored side and T bisect V on the scored side, with side scores

75 mcg

Violet/Capsule Shaped

75 on the unscored side and T bisect V on the scored side, with side scores

88 mcg

Olive/Capsule Shaped

88 on the unscored side and T bisect V on the scored side, with side scores

100 mcg

Yellow/Capsule Shaped

100 on the unscored side and T bisect V on the scored side, with side scores

112 mcg

Rose/Capsule Shaped

112 on the unscored side and T bisect V on the scored side, with side scores

125 mcg

Brown/Capsule Shaped

125 on the unscored side and T bisect V on the scored side, with side scores

137 mcg

Turquoise/Capsule Shaped

137 on the unscored side and T bisect V on the scored side, with side scores

150 mcg

Blue/Capsule Shaped

150 on the unscored side and T bisect V on the scored side, with side scores

175 mcg

Lilac/Capsule Shaped

175 on the unscored side and T bisect V on the scored side, with side scores

200 mcg

Pink/Capsule Shaped

200 on the unscored side and T bisect V on the scored side, with side scores

300 mcg

Green/Capsule Shaped

300 on the unscored side and T bisect V on the scored side, with side scores


4 CONTRAINDICATIONS

Levothyroxine sodium tablets are contraindicated in patients with uncorrected adrenal insufficiency [see Warnings and Precautions (5.4)].

5 WARNINGS AND PRECAUTIONS

5.1 Serious Risks Related to Overtreatment or Undertreatment with Levothyroxine Sodium Tablets

Levothyroxine sodium tablets have a narrow therapeutic index. Overtreatment or undertreatment with levothyroxine sodium tablets may have negative effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, gastrointestinal function, and glucose and lipid metabolism in adult or pediatric patients.

In pediatric patients with congenital and acquired hypothyroidism, undertreatment may adversely affect cognitive development and linear growth, and overtreatment is associated with craniosynostosis and acceleration of bone age [see Use in Specific Populations (8.4)].

Titrate the dose of levothyroxine sodium tablets carefully and monitor response to titration to avoid these effects [see Dosage and Administration (2.4)]. Consider the potential for food or drug interactions and adjust the administration or dosage of levothyroxine sodium tablets as needed [see Dosage and Administration (2.1), Drug Interactions (7.1), and Clinical Pharmacology (12.3)].

5.2 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 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 therapy. Monitor patients receiving concomitant levothyroxine sodium and sympathomimetic agents for signs and symptoms of coronary insufficiency.

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

5.3 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.

5.4 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)].

5.5 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 that achieves the desired clinical and biochemical response to mitigate this risk.

6 ADVERSE REACTIONS

Adverse reactions associated with levothyroxine sodium therapy are primarily those of hyperthyroidism due to therapeutic overdosage [see Warnings and Precautions (5), Overdosage (10)]. 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 in Pediatric Patients

Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in pediatric patients receiving levothyroxine therapy. Overtreatment may result in craniosynostosis in infants who have not undergone complete closure of the fontanelles, and in premature closure of the epiphyses in pediatric patients still experiencing growth 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 DRUG INTERACTIONS

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 (Tables 5 to 8).

Table 5. Drugs That May Decrease T4 Absorption (Hypothyroidism)

Potential impact: Concurrent use may reduce the efficacy of levothyroxine sodium by binding and delaying or preventing absorption, potentially resulting in hypothyroidism.

Drug or Drug Class

Effect

Phosphate Binders

(e.g., calcium carbonate, ferrous sulfate,

sevelamer, lanthanum)

Phosphate binders may bind to levothyroxine. Administer levothyroxine sodium at least 4 hours apart from these agents.

Orlistat

Monitor patients treated concomitantly with orlistat and levothyroxine sodium for changes in thyroid function.

Bile Acid Sequestrants

(e.g., colesevelam, cholestyramine,

colestipol)

Ion Exchange Resins

(e.g., Kayexalate)

Bile acid sequestrants and ion exchange resins are known to decrease levothyroxine absorption. Administer levothyroxine sodium at least 4 hours prior to these drugs or monitor TSH levels.

Proton Pump Inhibitors

Sucralfate

Antacids

(e.g., aluminum and 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 6. 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 levothyroxine sodium 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 7. 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 levothyroxine sodium 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 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 8. 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.

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