DIGITALIS

substance obtained from the dried leaves of the common foxglove (Digitalis purpurea) and used as a drug that strengthens contractions of the heart muscle. It is most commonly used to restore adequate circulation in patients suffering from congestive heart failure, particularly as caused by arteriosclerosis or hypertension. The drug is also used to slow the rate of ventricular contraction in patients with atrial fibrillation or flutter. Digitalis directly increases the contractile power of the heart muscle, enabling a disease-weakened heart to keep up with the body's demand for heart action when the organ would otherwise be unable to. The drug's other effects include a slowing of the rate of the heartbeat, an increase in the heart's output, and a decrease in the size of the heart. The first physician to prescribe digitalis was the English physician and botanist William Withering (174199), who used it in the treatment of edema (dropsy). In An Account of the Foxglove, and Some of Its Medical Uses (1785), he summarized the results of his extensive clinical trials of the drug and described the symptoms of digitalis toxicity. The active principles in digitalis belong to a group of steroids called the cardiac glycosides. Their dosage must be determined with exceptional care because the lethal dose may be only three times the effective dose. Digitoxin and digoxin are among the most commonly prescribed forms of digitalis.