Thyroid hormones

Levothyroxine Sodium

Approved 17 May 2021IntravenousSolution

The FDA lists this product in 60 strengths and forms.

Indications

Levothyroxine Sodium Injection is indicated for the treatment of myxedema coma. Limitations of Use : The relative bioavailability between Levothyroxine Sodium Injection and oral levothyroxine products has not been established. Caution should be used when switching patients from oral levothyroxine products to Levothyroxine Sodium Injection as accurate dosing conversion has not been studied. Levothyroxine Sodium is an L-thyroxine product.

Levothyroxine (T 4 ) Sodium Injection is indicated for the treatment of myxedema coma. ( 1 ) Important Limitations of Use: The relative bioavailability of this drug has not been established. Use caution when converting patients from oral to intravenous levothyroxine. ( 1 )

Contraindications

None None

Warnings and precautions

Cardiac Adverse Reactions in the Elderly and in Patients with Underlying Cardiovascular Disease: Overtreatment may cause arrhythmias, tachycardia, myocardial ischemia and infarction, or worsening of congestive heart failure and death, particularly in patients with cardiovascular disease and in elderly patients. Start with lower doses in elderly patients and in patients with underlying cardiovascular disease and monitor patients after administration ( 5.1 ).

Acute Adrenal Crisis in Patients with Concomitant Adrenal Insufficiency 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 ( 5.2 ). Worsening of Diabetic Control : May worsen glycemic control and result in increased antidiabetic agent or insulin requirements.

Carefully monitor glycemic control ( 5.3 )

5.1Risk of Cardiac Complications in Elderly and in Patients with Cardiovascular Disease

Excessive bolus dosing of Levothyroxine Sodium Injection (greater than 500 mcg) is associated with cardiac complications, particularly in the elderly and in patients with an underlying cardiac condition. Adverse events that can potentially be related to the administration of large doses of Levothyroxine Sodium Injection include arrhythmias, tachycardia, myocardial ischemia and infarction, or worsening of congestive heart failure and death.

Indications

Warnings and precautions

Carefully monitor glycemic control ( 5.3 )

5.1Risk of Cardiac Complications in Elderly and in Patients with Cardiovascular Disease

Interactions

Many drugs affect 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 Injection. ( 7 , 12.3 )

7.1Drugs Known to Affect Thyroid Hormone Pharmacokinetics

Many drugs affect thyroid hormone pharmacokinetics and metabolism (e.g., synthesis, secretion, catabolism, protein binding, and target tissue response) and may alter the therapeutic response to Levothyroxine Sodium Injection (see Tables 1-3). Table 1: Drugs That May Alter T 4 and Triiodothyronine (T 3 ) Serum Transport Without Effecting Free Thyroxine (FT 4 ) 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 Nictonic Acid These drugs may decrease serum TBG concentration. Potential impact (below): Administration of these agents with levothyroxine results in an initial transient increase in FT 4 . Continued administration results in a decrease in serum T 4 and normal FT 4 and TSH concentrations. Salicylates (> 2 g/day) Salicylates inhibit binding of T 4 and T 3 to TBG and transthyretin.

An initial increase in serum FT 4 is followed by return of FT 4 to normal levels with sustained therapeutic serum salicylate concentrations, although total T 4 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 2: Drugs That May Alter Hepatic Metabolism of T 4 (Hypothyroidism) Potential impact: Stimulation of hepatic microsomal drug-metabolizing enzyme activity may cause increased hepatic degradation of levothyroxine, resulting in increased levothyroxine 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 3: Drugs That May Decrease Conversion of T 4 to T 3 Potential impact: Administration of these enzyme inhibitors decreases the peripheral conversion of T 4 to T 3 , leading to decreased T 3 levels. However, serum T 4 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), T 3 and T 4 levels change slightly, TSH levels remain normal, and patients are clinically euthyroid.

It should be noted that actions of particular beta-adrenergic antagonists may be impaired when the 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 T 3 concentrations by 30% with minimal change in serum T 4 levels. However, long-term glucocorticoid therapy may result in slightly decreased T 3 and T 4 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.

7.2Antidiabetic Therapy Addition

of levothyroxine to antidiabetic or insulin therapy may result in increased antidiabetic agent or insulin requirements. Careful monitoring of diabetic control is recommended.

7.3Oral Anticoagulants

Levothyroxine increases the response to oral anticoagulant therapy. Therefore, a decrease in the dose of anticoagulant may be warranted with correction of the hypothyroid. Closely monitor coagulation tests to permit appropriate and timely dosage adjustments.

7.4Digitalis Glycosides

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

7.5Antidepressant Therapy

Concurrent use of tricyclic (e.g., amitriptyline) or tetracyclic (e.g., maprotiline) antidepressants and levothyroxine 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 may accelerate the onset of action of tricyclics. Administration of sertraline in patients stabilized on levothyroxine may result in increased levothyroxine requirements.

7.6Ketamine

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

7.7Sympathomimetics

Concurrent use may of sympathomimetics and levothyroxine 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.

7.8Drug-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 concentrations. 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.

Our copy of this section ends here. The full text is in the official label at the FDA. Open Drugs@FDA

Adverse reactions

Adverse reactions associated with levothyroxine 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: flushing, rash Seizures have been reported rarely with the institution of levothyroxine therapy.

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. Adverse reactions associated with Levothyroxine Sodium Injection are primarily those of hyperthyroidism due to therapeutic overdosage: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating, headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia, tremors, muscle weakness, muscle spasm, palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest, dyspnea, diarrhea, vomiting, abdominal cramps, elevations in liver function tests, flushing, and rash.

( 6 ) To report SUSPECTED ADVERSE REACTIONS, contact Hikma at us.hikma@primevigilance.com or call 1-877-845-0689 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

Levothyroxine Sodium

Indications

Contraindications

Warnings and precautions

5.1Risk of Cardiac Complications in Elderly and in Patients with Cardiovascular Disease

Two medicines in one question?

Levothyroxine Sodium

Indications

Contraindications

Warnings and precautions

5.1Risk of Cardiac Complications in Elderly and in Patients with Cardiovascular Disease

Two medicines in one question?

5.2Acute Adrenal Crisis in Patients with Concomitant Adrenal Insufficiency

5.3Worsening of Diabetic Control Addition

Interactions

7.1Drugs Known to Affect Thyroid Hormone Pharmacokinetics

7.2Antidiabetic Therapy Addition

7.3Oral Anticoagulants

7.4Digitalis Glycosides

7.5Antidepressant Therapy

7.6Ketamine

7.7Sympathomimetics

7.8Drug-Laboratory Test Interactions

Pregnancy and breastfeeding

8.1Pregnancy Risk Summary

Adverse reactions

Composition

Strengths and forms

Official product information

At a glance