The incidence of digitalis toxicity has declined in recent years, due to decreased use of this drug along with improved technology for monitoring of drug levels and increased awareness of drug interactions. Nevertheless, cardiac glycoside toxicity continues to be a problem in the United States because of the wide use of digoxin (a preparation of digitalis) and its narrow therapeutic window.
Digitalis is a plant-derived cardiac glycoside commonly used in the treatment of chronic heart failure (CHF), atrial fibrillation, and reentrant supraventricular tachycardia.[1, 2] Digoxin is the only available preparation of digitalis in the United States. (See Etiology and Epidemiology.)
Cardiac glycosides are found in certain flowering plants, such as oleander and lily-of-the-valley. Indigenous people in various parts of the world have used many plant extracts containing cardiac glycosides as arrow and ordeal poisons. The ancient Egyptians used squill (Urginea maritime) as a medicine. The Romans employed it as a diuretic, heart tonic, emetic, and rat poison. Digitalis, or foxglove, was mentioned in the year 1250 in the writings of Welsh physicians. Fuchsius described it botanically 300 years later and named it Digitalis purpurea.
William Withering published his classic account of foxglove and some of its medical uses in 1785, remarking upon his experience with digitalis. He recognized many of the signs of digitalis toxicity, noting, "The foxglove, when given in very large and quickly repeated doses, occasions sickness, vomiting, purging, giddiness, confused vision, objects appearing green or yellow; increased secretion of urine, slow pulses, even as low as 35 in a minute, cold sweats, convulsions, syncope, death." (See Presentation and Workup.)
During the early 20th century, as a result of the work of Cushny, Mackenzie, Lewis, and others, the drug was gradually recognized as specific for treatment of atrial fibrillation. Only subsequently was the value of digitalis for treatment of CHF established. Cardiac glycosides enhance cardiac contractility and slow conduction through the atrioventricular (AV) junction by increasing vagal tone. (See Etiology.)
Cardiac glycoside toxicity has been known to result from ingestion of some plants, including yellow oleander (Thevetia peruviana) and foxglove, and a similar toxidrome has been associated with the use of herbal dietary supplements that contain cardiac glycosides.
Digoxin is among the top 50 prescribed drugs in the United States. In 2011, the American Association of Poison Control Centers reported 1601 single exposures to cardiac glycoside drugs. Cardiac glycosides account for 2.6% of toxic plant exposures in the United States.[6, 7] Most of these exposures are in children. (See Epidemiology.)
Digoxin-specific fragment antigen-binding (Fab) antibody fragments have contributed significantly to the improved morbidity and mortality of toxic patients since their approval in 1986 by the US Food and Drug Administration (FDA). (See Prognosis, Treatment, and Medication.)