digitalis

digitalis , any of several chemically similar drugs used primarily to increase the force and rate of heart contractions, especially in damaged heart muscle. The effects of the drug were known as early as 1500 BC; it was later obtained from the foxglove plant, Digitalis purpurea, and from fuchsia (see figwort ). It was used in the 19th cent. to treat dropsy ( edema ). Digitalislike substances are found in a wide variety of plants and animals, including the poisons of some toad species. Foxglove remains the main source for the drug used medically today.

Chemically, digitalis is composed of a sugar (glycoside), a steroid, and a cyclic ester known as a lactone; the pharmacological activity varies according to differences, occurring naturally or introduced synthetically, in the steroid or sugar portions. Common preparations include digitalis, digitoxin, and digoxin, all from foxglove, and ouabain from Strophanthus gratus, the ouabaio tree; these vary both in solubility and in rapidity and duration of effect.

Digitalis slows the pulse and slows the conduction of nerve impulses in the heart. By increasing the amount of calcium available to the heart muscle, it improves the force of each heartbeat and increases the amount of blood pumped. It is used in the treatment of congestive heart failure and cardiac arrhythmias . The mechanism by which it acts to enhance heart muscle contraction is not definitely known. Toxic effects include nausea, vomiting, and visual disturbances.

digitalis A preparation of the dried leaves or seeds of the foxglove (Digitalis), used historically as a heart stimulant. Modern clinically prescribed drugs derived from digitalis include digoxin and digitoxin, both of which belong to a class of drugs known as the cardiac glycosides. They are used to treat heart failure and some forms of arrhythmia because of their ability to increase the force of contraction of the heart muscle. Their toxic effects arise from their capacity to disturb the normal rhythm of the heart.

digitalis (dij-i-tay-lis) n. an extract from the dried leaves of foxgloves (Digitalis species), which contains various substances, including digitoxin and digoxin, that stimulate heart muscle.