Levothyroxine toxicity

Background

  • Most acute thyroxine overdoses are mild.
  • Chronic ingestions are more likely to present with clinical symptoms similar to thyrotoxicosis
  • Diet pills such as Singaporean Slim 10[1] and athletic stimulant compounds can contain large amounts of T3/T4
  • Thyrotoxicosis factitia - also known as thyroxine addict or metabolic malingerer where large doses of thyroid supplementation is taaking for weight loss or stimulation

Clinical Features

Although most thyroxine ingestions are mild, large acute or chronic ingestions can mirror moderate to severe thyrotoxicosis

Classic Triad

  1. Hyperthermia
    • Often marked (40 - 41C)[2]
  2. Tachycardia
    • Often out of proportion to fever [3]
  3. Altered mental status (agitation, confusion, delirium stupor, coma, seizure)

Differential Diagnosis

Evaluation

Management

  • Mirrors the treatment for thyroid storm with the exception of antithyroid drugs which offer little potential benefit with the exception of propranolol

Agitation

Catecholamine Excess

  • Propranolol 1 to 2 mg IV every 10 to 15 minutes are recommended

Hyperthermia

  • Aspirin, should be avoided because it carries a theoretical risk of thyrotoxicity by displacing T3 and T4 from thyroxine-binding globulin.
  • External cooling is the best means to treat severe hyperthermia in addition consideration of intubation with sedation and continued paralysis.

Drug Removal

  • Plasma exchange or plasmapheresis can be used in the most severe of poisonings<re>Van Huekelom S, et al Plasmapheresis in L-thyroxine intoxication. Vet Hum Toxicol.1979;s21:7</ref>

Disposition

  • Symptomatic patients should be admitted for observation

See Also

External Links

References

  1. Hedberg CW: An outbreak of thyrotoxicosis caused by the consumption of bovine thyroid gland in ground beef. N Engl J Med. 1987;316:993–998.
  2. Thiessen, M. (2018). Thyroid and Adrenal Disorders in Rosen's emergency medicine: Concepts and clinical practice (9th ed.). Philadelphia, PA: Elsevier/Saunders.
  3. Thiessen, M. (2018). Thyroid and Adrenal Disorders in Rosen's emergency medicine: Concepts and clinical practice (9th ed.). Philadelphia, PA: Elsevier/Saunders.