LEVOTHYROXINE

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LEVOTHYROXINE
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MEDICAL INFORMATIONS

FDA APPROVED INDICATION

  • Levothyroxine is indicated as a replacement or supplementation in patients with primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) congenital or acquired hypothyroidism in pediatric patients (Unithroid(R), Tirosint(R)-SOL and Synthroid(R)) and in patients 6 years or older (Tirosint(R)).
  • As an adjunct to surgery and radioiodine therapy in the management of thyrotropindependent well-differentiated thyroid cancer. (Unithroid(R), Tirosint(R)-SOL and Synthroid(R)) and in patients 6 years or older (Tirosint(R)).

Limitations of use:

  • Not indicated for suppression of benign thyroid nodules and nontoxic diffuse goiter in iodine-insufficient patients or for the treatment of hypothyroidism during the recovery phase of subacute thyroiditis.

CONTRAINDICATIONS

  • Hypersensitivity to thyroid hormone or any component of the product.
  • Hypersensitivity to glycerol (oral solution).
  • Uncorrected adrenal insufficiency; may precipitate acute adrenal crisis.

PRECAUTIONS

  • Cardiovascular:
    • New or worsening cardiac abnormalities, such as increase in heart rate, angina and arrhythmias may develop with overtreatment; reduce or stop therapy for one week and then cautiously restart at lower dose.
    • Underlying cardiovascular disease; initiate therapy at lower dose; monitoring recommended.
    • Surgical procedures in patients with preexisting coronary artery disease increases risk of cardiac arrhythmias; monitoring recommended.
  • Endocrine & Metabolic:
    • Use of doses above recommended range, including excessive bolus doses greater than 500 mcg, increase risk of serious or life-threatening manifestations of toxicity; monitoring recommended and consider dose adjustment.
    • Chronic autoimmune thyroiditis, with progression to myxedema or acute adrenal crisis, may occur in association with other autoimmune disorders, such as adrenal insufficiency, diabetes mellitus, and pernicious anemia; treat with replacement glucocorticoids prior to initiation of levothyroxine and monitoring is recommended.
    • Oral therapy not recommended to treat myxedema coma.
    • Concomitant adrenal insufficiency; treat with replacement glucocorticoids prior to initiation of levothyroxine to avoid acute adrenal crisis.
    • Worsening glycemic control in diabetic patients may occur; monitoring recommended.
  • Musculoskeletal:
    • Increased bone resorption and decreased bone mineral density may occur with greater than replacement doses.

ADVERSE EFFECTS

Prolonged over-treatment can produce premature craniosynostosis and acceleration of bone age.

BLACK BOX WARNING

Thyroid hormones, including levothyroxine, either alone or with other therapeutic agents should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight loss. Larger doses may produce serious or life-threatening manifestations of toxicity, especially when given in combination with sympathomimetic amines such as those used for their anorectic effects.

ADMINISTRATION

  • Oral:
    • Single daily dose.
    • Administer on an empty stomach; one-half to 1 hour before breakfast.
    • Should be separated by at least 4 hours from drugs that are known to impair its absorption (eg, antacids, bile acid sequestrants, calcium carbonate, cation exchange resins, ferrous sulfate, orlistat, sucralfate).
  • Solution: May administer directly into mouth by squeezing content of 1 single unit-dose ampule into mouth or onto a spoon. May also administer in water by squeezing the contents of 1 single unit-dose ampule into a cup of water; stir and drink immediately. Rinse cup with more water and drink. Do not dilute in other liquids or food. Open the ampule and prepare the solution immediately before intake.
  • Tablets: May crush and suspend in 5 to 10 mL of water prior to administration (eg, for infants and children who cannot swallow intact table); do not store suspension. Do not suspend in other liquids or food (eg, soybean-based infant formula).
  • Injection:
    • Intravenous powder for solution: Final concentrations are approximately 20 mcg/mL or 100 mcg/mL. Do not add to any other IV solution.
    • Intravenous solution: Do not exceed an IV administration rate of 100 mcg/min. Do not add to any other IV solution.

MONITORING

After 2 weeks of treatment, serum levothyroxine (T4) concentration should be in the high normal range (10 to 16 mcg/dL) and should be maintained in this range for the first year of life. Serum triiodothyronine (T3) concentration should be normal (70 to 220 nanograms/dL), and TSH should have declined from initial value. After 12 weeks of treatment, serum TSH concentration should be in the normal range, less than 15 milliunits/L. Serum T4 and TSH concentrations should be measured at two weeks of age, then every 1 to 2 months, or 2 weeks after any change in dosage. Assess for signs of hypothyroidism: Lethargy, poor feeding, constipation, intermittent cyanosis, and prolonged neonatal jaundice. Assess for signs of thyrotoxicosis: hyperreactivity, altered sleep pattern, tachycardia, tachypnea, fever, exophthalmos, and goiter. Periodically assess growth, development, and bone-age advancement.

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