Digitalis

Scientific Name(S): Digitalis purpurea L.; D. lanata Ehrh. Family: Scrophulariaceae, the figwort family. Related species that have found some use in traditional medicine include D. lutea (straw foxglove), D. grandiflora and D. ambigua (yellow foxglove), and D. ferriginea (rusty foxglove).

Common Name(S): Foxglove, purple foxglove, throatwort, fairy finger, fairy cap, lady's thimble, scotch mercury, lion's mouth, witch's bells, dead man's bells, wolly foxglove, digitalis.

Digitalis is a genus of about 20 species of herbaceous biennials, perennials and shrubs that was traditionally placed in the figwort family Scrophulariaceae . Due to new genetic research, Mike Niewahner has declared it has now been placed in the much enlarged family Plantaginaceae. The genus is native to Europe , western and central Asia and northwestern Africa.

Botany: The foxglove is typically a biennial plant (but "may be annual or perennial depending on the species) characterized by a thick, cylindrical downy stem that reaches a height of up to 6 feet. The leaves form a thick rosette during the first year of growth. The leaves, which are wooly and veined and covered with whitish hairs on the underside, have a very bitter taste. The flowers grow in the first or second year, depending on the species, and are tubular and bell-shaped, growing to 3 inches in length. Although many colors of flowers have been bred from digitalis, the flowers are rarely white. The plant is native to the British Isles, Western Europe and parts of Africa, but today is found as an ornamental throughout the world.

History: Although the use of foxglove has been traced back to 10th century Europe, it was not until its scientific investigation by William Withering in the late 1700s that the plant became widely used as a diuretic for the treatment of dropsy. In South America, preparations of the powdered leaves are used to relieve asthma, as sedatives and as diuretic/cardiotonics. In India, an ointment containing digitalis glycosides is used to treat wounds and burns. Today, digitalis glycosides are widely used in the treatment of congestive heart failure; however, because of their narrow therapeutic margin and high potential for severe side effects, the use of these products is beginning to be supplanted by newer agents including the angiotensin converting enzyme inhibitors and the calcium channel blocking agents.

Uses of Digitalis

In addition to a range of other traditional uses, digitalis has long been used as a recognized treatment for heart failure. The plant is cultivated as an ornamental.

Digitalis works by inhibiting sodium-potassium ATPase , which increases intracellular calcium. The increased intracellular calcium gives a positive inotropic effect. It also has a vagal effect on the parasympathetic nervous system, and as such is used in reentrant cardiac arrhythmias and to slow the ventricular rate during atrial fibrillation . The dependence on the vagal effect means that digitalis is not effective when a patient has a high sympathetic nervous system drive, which is the case with acutely ill persons.

Side Effects of Digitalis

Ingestion of extremely small amounts of the plant may be fatal to humans, especially children and to animals. Toxicity is cumulative.

Toxicology: All parts of the plant are toxic. Animal toxicity occurs during grazing. Children have been made ill by sucking the flowers or ingesting seeds or parts of the leaves. The toxic doses of fresh leaves are reported as 6 to 7 ounces for an ox, 4 to 5 ounces for a horse, and 0.5 to 0.75 ounces for a pig. Deaths have been reported among persons who drank tea made from foxglove mistakenly identified for comfrey.

Digitalis glycosides are excreted slowly and accumulate; therefore, intoxications during therapy are common. Theincidence of digitalis toxicity had been estimated to range from 5% to 23%. More stringent dosing guidelines and monitoring techniques have dramatically reduced the
incidence of therapeutic overdose.        

Signs of poisoning by the plant or purified drug include contracted pupils, blurred vision, strong but slowed pulse, nausea, vomiting, dizziness, excessive urination, fatigue, muscle weekness and tremors; in severe cases, stupor, confusion, convulsions and death occur. Cardiac signs include atrial arrhythmias and atrioventricular block. Chronic digitalis intoxication is characterized by visual halos, yellow-green vision and gastrointestinal upset.

Gastric lavage or emesis together with supportive measures such as electrolyte replacements, antiarrhythmias, such as lidocaine and phenytoin, atropine and other agents that can antagonize the cardiovascular effects of the glycosides, have been used to manage acute poisonings. Digoxin-specific Fab antibody fragments (Digibind) are effective in managing acute intoxications caused by digitalis and related cardioactive glycosides. This therapy is revolutionary for the severely poisoned patient.

Summary: Foxglove and its derivatives are critically important in the management of congestive heart failure and related cardiac disorders. Their uses continue to be strong in underdeveloped countries where they can be used cost effectively. The plants are grown ornamentally throughout much of the world, and vigilance must be used if children or animals can come in contact with the potentially lethal plants.

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