The Foxglove’s leaves, with caution giv’n,

Another proof of favouring Heav’n

Will happily display;

The rapid pulse it can abate;

The hectic flush can moderate;

And blest by Him whose will is fate,

May give a lengthen’d day.

alt

These words were written around 1820 by the poet Sarah Hoare (1777–1856) and published in the ninth edition of An Introduction to Botany (1823). The poem refers to foxglove, a plant that’s been used for hundreds of years to slow down and strengthen contractions of the heart muscles. An extract obtained from foxglove’s dried leaves, called digitalis, is commonly used today to restore circulation in patients with congestive heart failure.

Digitoxin and digoxin are the most commonly prescribed forms of digitalis—available as either oral or intravenous medications—and belong to a class of drugs called cardiac glycosides. The drugs work by slowing a rapid heartbeat, decreasing the size of a swollen heart, and increasing the strength of the heart muscle’s contractions and thus the heart’s output.

Too much digitalis, however, can lead to a dangerous condition known as digitalis toxicity. Symptoms include heart palpitations, vomiting and diarrhea, and visual disturbances: Some patients see lights or bright spots, see halos around objects, or experience changes in color perception. Toxicity can be caused by a single large dose of digitalis or by an accumulation of medication over time and is more frequent in patients with kidney disorders. Often, people with heart failure who take digitalis are also prescribed diuretic medications, which help reduce blood pressure by expelling sodium and excess fluid from the body. But diuretics can cause dehydration and potassium deficiency, both of which increase the risk of digitalis toxicity. To avoid this problem, potassium supplements or potassium-sparing medications are often prescribed as well.

ADDITIONAL FACTS

  1. Digitalis was first prescribed in the late 1700s by the English physician William Withering (1741– 1799), who used it to treat of dropsy, a condition that “puffed [people’s] bodies into grotesque shapes, squeezed their lungs, and finally brought slow but inexorable death.” Dropsy is now known as edema, an overaccumulation of fluid in the body.
  2. Digitalis toxicity can cause an abnormal heartbeat (arrhythmia) severe enough to be fatal.
  3. In the 18th century, digitalis concoctions were often used—with little or no success—in attempts to treat asthma, epilepsy, hydrocephalus, insanity, and other conditions.