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levothyroxine sodium (L-thyroxine, T4)

Eltroxin (CA) (UK), Euthyrox (CA), Evotrox (UK), Levo-T, Levolet, Levothroid, Levoxyl, Nu-Thyro (CA), Soloxine, Synthroid, Unithroid

Pharmacologic class: Synthetic thyroxine hormone

Therapeutic class: Thyroid hormone replacement

Pregnancy risk category A

FDA Box Warning

• Drug shouldn't be used alone or with other agents to treat obesity or weight loss. In euthyroid patients, doses within range of daily hormonal requirements are ineffective for weight loss. Larger doses may cause serious or life-threatening toxicity, particularly when given with sympathomimetic amines (such as those used for anorectic effects).


Synthetic form of thyroxine that replaces endogenous thyroxine, increasing thyroid hormone levels. Thyroid hormones help regulate cell growth and differentiation and increase metabolism of lipids, protein, and carbohydrates.


Powder for injection: 200 mcg/vial in 6- and 10-ml vials, 500 mcg/vial in 6- and 10-ml vials

Tablets: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg

Indications and dosages

Hypothyroidism; treatment or prevention of euthyroid goiter

Adults: For healthy adults younger than age 50 and those over age 50 who have recently been treated or undergone short-term therapy, start at full replacement dosage of 1.7 mcg/kg P.O. daily, given 30 minutes to 1 hour before breakfast. For patients older than age 50 or younger than age 50 with heart disease, 25 to 50 mcg P.O. daily, increased q 4 to 6 weeks. In severe hypothyroidism, initial dosage is 12.5 to 25 mcg P.O. daily, adjusted by 25 mcg daily q 2 to 4 weeks. For patients who can't tolerate oral doses, adjust I.M. or I.V. dosage to roughly half of oral dosage.

Congenital hypothyroidism

Children older than age 12 who have completed puberty and growth: 1.7 mcg/kg P.O. daily

Children older than age 12 who have not completed puberty and growth: Up to 150 mcg or 2 to 3 mcg/kg P.O. daily

Children ages 6 to 12: 4 to 5 mcg/kg P.O. daily

Children ages 1 to 5: 5 to 6 mcg/kg P.O. daily

Infants ages 6 to 12 months: 6 to 8 mcg/kg P.O. daily


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Therapeutic: hormones
Pharmacologic: thyroid preparations
Pregnancy Category: A


Thyroid supplementation in hypothyroidism.Treatment or suppression of euthyroid goiters.Adjunctive treatment for thyrotropin-dependent thyroid cancer.


Replacement of or supplementation to endogenous thyroid hormones.
Principal effect is increasing metabolic rate of body tissues:
  • Promote gluconeogenesis,
  • Increase utilization and mobilization of glycogen stores,
  • Stimulate protein synthesis,
  • Promote cell growth and differentiation,
  • Aid in the development of the brain and CNS.

Therapeutic effects

Replacement in hypothyroidism to restore normal hormonal balance.
Suppression of thyroid cancer.


Absorption: Levothyroxine is variably (40–80%) absorbed from the GI tract.
Distribution: Distributed into most body tissues. Thyroid hormones do not readily cross the placenta; minimal amounts enter breast milk.
Protein Binding: >99%.
Metabolism and Excretion: Metabolized by the liver and other tissues to active T3. Thyroid hormone undergoes enterohepatic recirculation and is excreted in the feces via the bile.
Half-life: 6–7 days.

Time/action profile

Levothyroxine POunknown1–3 wk1–3 wk
Levothyroxine IV6–8 hr24 hrunknown


Contraindicated in: Hypersensitivity;Recent MI;Hyperthyroidism.
Use Cautiously in: Cardiovascular disease (initiate therapy with lower doses);Severe renal insufficiency;Uncorrected adrenocortical disorders; Pediatric: Monitor neonates and infants for cardiac overload, arrhythmias, and aspiration during first 2 wk of therapy; Geriatric: Extremely sensitive to thyroid hormones; initial dose should be ↓.

Adverse Reactions/Side Effects

Usually only seen when excessive doses cause iatrogenic hyperthyroidism

Central nervous system

  • headache
  • insomnia
  • irritability


  • angina pectoris
  • arrhythmias
  • tachycardia


  • abdominal cramps
  • diarrhea
  • vomiting


  • sweating


  • hyperthyroidism
  • menstrual irregularities


  • heat intolerance
  • weight loss


  • accelerated bone maturation in children


Drug-Drug interaction

Bile acid sequestrants and orlistat ↓ absorption of orally administered thyroid preparations.May ↑ the effects of warfarin.May ↑ requirement for insulin or oral hypoglycemic agents in diabetics.Concurrent estrogen therapy may ↑ thyroid replacement requirements.↑ cardiovascular effects with adrenergics (sympathomimetics).Foods or supplements containing calcium, iron, magnesium, or zinc may bind levothyroxine and prevent complete absorption.


Oral (Adults) Hypothyroidism—50 mcg as a single dose initially; may be ↑ q 2–3 wk by 25 mcg/day; usual maintenance dose is 75–125 mcg/day (1.5 mcg/kg/day).
Oral (Geriatric Patients and Patients with Increased Sensitivity to Thyroid Hormones) 12.5–25 mcg as a single dose initially; may be ↑ q 6–8 wk; usual maintenance dose is 75 mcg/day.
Oral (Children >12 yr) 2–3 mcg/kg/day (≥150 mcg/day).
Oral (Children 6–12 yr) 4–5 mcg/kg/day (100–125 mcg/day).
Oral (Children 1–5 yr) 5–6 mcg/kg/day (75–100 mcg/day).
Oral (Children 6–12 mo) 6–8 mcg/kg/day (50–75 mcg/day).
Oral (Infants 3–6 mo) 8–10 mcg/kg/day (25–50 mcg/day).
Oral (Infants 0–3 mo or Infants at Risk for Cardiac Failure) 10–15 mcg/kg/day or 25 mcg/day; may be ↑ after 4–6 wk to 50 mcg.
Intramuscular Intravenous (Adults) Hypothyroidism—50–100 mcg/day as a single dose. Myxedema coma/stupor—300–500 mcg IV; additional 100–300 mcg may be given on 2nd day, followed by daily administration of smaller doses.
Intramuscular Intravenous (Children) Hypothyroidism—50–80% of the oral dose.

Availability (generic available)

Capsules (Tirosint): 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg
Tablets: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg
Powder for injection: 100 mcg/vial, 500 mcg/vial

Nursing implications

Nursing assessment

  • Assess apical pulse and BP prior to and periodically during therapy. Assess for tachyarrhythmias and chest pain.
  • Children: Monitor height, weight, and psychomotor development.
  • Lab Test Considerations: Monitor thyroid function studies prior to and during therapy. Monitor thyroid-stimulating hormone serum levels in adults 8–12 wks after changing from one brand to another.
    • Monitor blood and urine glucose in diabetic patients. Insulin or oral hypoglycemic dose may need to be increased.
  • Overdose is manifested as hyperthyroidism (tachycardia, chest pain, nervousness, insomnia, diaphoresis, tremors, weight loss). Usual treatment is to withhold dose for 2–6 days then resume at a lower dose. Acute overdose is treated by induction of emesis or gastric lavage, followed by activated charcoal. Sympathetic overstimulation may be controlled by antiadrenergic drugs (beta blockers), such as propranolol. Oxygen and supportive measures to control symptoms are also used.

Potential Nursing Diagnoses

Deficient knowledge, related to medication regimen (Patient/Family Teaching)


  • Do not confuse levothyroxine with lamotrigine or Lanoxin (digoxin).
  • Administer as a single dose with a full glass of water, preferably before breakfast to prevent insomnia.
    • Initial dose is low, especially in geriatric and cardiac patients. Dose is increased gradually, based on thyroid function tests.
    • For patients with difficulty swallowing, tablets can be crushed and placed in 5–10 mL of water and administered immediately via dropper or spoon; do not store suspension.
  • Intravenous Administration
  • Reconstitute the 200-mcg and 500-mcg vials with 2 or 5 mL, respectively, of 0.9% NaCl without preservatives (diluent usually provided). Concentration: 100 mcg/mL. Shake well to dissolve completely. Administer solution immediately after preparation; discard unused portion.
  • Rate: Administer at a rate of 100 mcg over 1 min. Do not add to IV infusions; may be administered through Y-tubing.
  • Y-Site Incompatibility: Do not admix with other IV solutions.

Patient/Family Teaching

  • Instruct patient to take medication as directed at the same time each day. Take missed doses as soon as remembered unless almost time for next dose. If more than 2–3 doses are missed, notify health care professional. Do not discontinue without consulting health care professional.
    • Explain to patient that medication does not cure hypothyroidism; it provides a thyroid hormone supplement. Therapy is lifelong.
    • Advise patient to notify health care professional if headache, nervousness, diarrhea, excessive sweating, heat intolerance, chest pain, increased pulse rate, palpitations, weight loss >2 lb/wk, or any unusual symptoms occur.
    • Caution patient to avoid taking other medications concurrently with thyroid preparations unless instructed by health care professional.
    • Instruct patient to inform health care professionals of thyroid therapy.
    • Emphasize importance of follow-up exams to monitor effectiveness of therapy. Thyroid function tests are performed at least yearly.
  • Pediatric: Discuss with parents the need for routine follow-up studies to ensure correct development. Inform patient that partial hair loss may be experienced by children on thyroid therapy. This is usually temporary.

Evaluation/Desired Outcomes

  • Resolution of symptoms of hypothyroidism and normalization of hormone levels.


A trademark for a drug preparation of thyroxine.


Levothyroxine Endocrinology Thyroid hormone for treating hypothyroidism. See Hypothyroidism.
References in periodicals archive ?
I would suggest using the brand name Levoxyl for your replacement (it has the most consistent potency data).
in 2005, thyroid medications Synthroid and Levoxyl ranked 4th and 24th, respectively, among all brand-name prescriptions filled nationally.
It also discusses management of hypothyroidism and use of thyroid hormone replacement therapy, particularly levothyroxine (synthetic T4) (Levo-T, Levolet, Levothroid, Levoxyl, Novothyrox, Synthroid, Unithroid, and generics) and briefly addresses hyperthyroidism resulting from overtreatment of hypothyroidism.
Bioavailability of even the newer rapid-release formulation of levothyroxine known as Levoxyl is reduced 40% by taking the tablets close to a meal, Michael J.
In a carefully controlled study that withstood the scrutiny of UCSF and JAMA reviewers, Dong and her colleagues placed the 24 patients on a rotating schedule of Synthroid, two generics, and Levoxyl, made by Jones Medical Industries of St.
The researchers at the University of California at San Francisco found that for most patients the less costly generic forms of the drug worked just as well as Synthroid and another brand-name version, Levoxyl or Levoxine, which is similar in price to the generic drugs.
I started with Levoxyl and switched to the generic levothyroxine in June.
Food and Drug Administration (FDA): Unithroid, Levoxyl, Synthroid, Levothroid, Levolet, Levo-T, and Novothyrox (only the first four are currently being marketed in the US).
Levo-T (Alara), Unithroid (Jerome Stevens) and Levothyroxine Sodium (Mylan) tablets have been determined to be therapeutically equivalent to corresponding strengths of Levoxyl (King/Jones Pharma) tablets.
Michael Roth, who is executive director of communications at Novartis, told this newspaper that the company stands by approval of the Sandoz product, which is "therapeutically bioequivalent to both Synthroid and Levoxyl.
Michael Roth, executive director of communications of Novartis, told this newspaper that the company stands by approval of the Sandoz product, which is "therapeutically bioequivalent to both Synthroid and Levoxyl.