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levothyroxine (lee-voe-thye-rox-een)

imageEltroxin, Levo-T, Levothroid, Levoxyl, Novothyrox, PMS-Levothyroxine Sodium, Synthroid, T4, Tirosint, Unithroid


Therapeutic: hormones

Pharmacologic: thyroid preparations


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.

Adverse Reactions/Side Effects

Usually only seen when excessive doses cause iatrogenic hyperthyroidism

CNS: insomnia, irritability, headache. CV: arrhythmias, tachycardia, angina pectoris. GI: abdominal cramps, diarrhea, vomiting. Derm: hyperhidrosis. Endo: hyperthyroidism, menstrual irregularities. Metab: weight loss, heat intolerance. MS: accelerated bone maturation in children.


Examination and Evaluation

  • Monitor and report signs of excessive or inadequate dosing. Excessive doses mimic hyperthyroidism, as indicated by nervousness, weight loss, muscle wasting, tachycardia, and heat intolerance. Inadequate doses mimic hypothyroidism, as indicated by lethargy, weight gain, bradycardia, and cold intolerance.

  • Assess heart rate, ECG, and heart sounds, especially during exercise (See Appendices G, H). Report any rhythm disturbances or symptoms of increased arrhythmias, including palpitations, chest discomfort, shortness of breath, fainting, and fatigue/weakness.

  • Assess episodes of angina pectoris at rest and during exercise. Attempt to determine if pain is drug related or caused by cardiovascular dysfunction (e.g., angina that occurs during exercise).

  • Assess height in children periodically; inform physician of delayed growth that might indicate premature skeletal maturation and closure of epiphyseal plates.

  • Monitor and report signs of CNS toxicity, including irritability and sleep loss. Sustained or severe CNS signs are typically consistent with hyperthyroidism and may require an adjustment in drug dose.


  • Because of the risk of arrhythmias and angina, use caution during aerobic exercise and endurance conditioning. Assess heart rate and exercise tolerance frequently, and terminate exercise immediately if any untoward responses occur (See Appendix L).

Patient/Client-Related Instruction

  • Caution patient about the risk of increased sweating (hyperhidrosis), and advise patient about proper skin care (thoroughly cleanse and dry the affected areas; apply astringent powders if necessary).

  • Instruct patient to report other troublesome side effects including severe or prolonged headache, menstrual irregularities, or GI problems (nausea, vomiting, abdominal cramps).


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 ...

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