Scientific Name(s): Digitalis purpurea L.; Digitalis lanata Ehrh; Family: Scrophulariaceae (figworts)
Common Name(s): Foxglove , digitalis , purple foxglove , throatwort , fairy finger , fairy cap , lady's thimble , scotch mercury , lion's mouth , witch's bells , dead man's bells , woolly foxglove
Digitalis has long been used as a treatment for heart failure in addition to a range of other traditional uses. The plant is cultivated as an ornamental.
Digitalis leaf has a narrow therapeutic index, requiring close medical supervision for safe use. Traditional dosage starts at 1.5 g of leaf divided into 2 daily doses. Purified digoxin is typically used at daily doses of 0.125 to 0.25 mg.
Do not allow children to come into contact with the potentially lethal plant.
Documented adverse cardiac reactions. Avoid use.
There are numerous interactions with digoxin and digitalis glycosides, ranging from relatively minor (eg, cimetidine, triamterene) to life-threatening (eg, amiodarone, furosemide, verapamil).
Adverse reactions are generally related to toxicity.
All parts of the plant are toxic. The incidence of digitalis toxicity in therapeutic use has been estimated to range from 5% to 25%. Ingestion of extremely small amounts of the plant may be fatal to humans, especially children, and to animals. Toxicity is cumulative.
Digitalis is typically a biennial plant but may be annual or perennial depending on the species. It is characterized by a thick, cylindrical, downy stem that reaches a height of up to 2 m. Leaves form a thick rosette during the first year of growth. The leaves, which are woolly, veined, and covered with white hairs on the underside, have a very bitter taste. Flowers grow in the first or second year, depending on the species, and are tubular and bell-shaped, growing to 8 cm in length. Many colors of flowers have been bred from digitalis, and they are rarely white. Digitalis is native to the British Isles, western Europe, and parts of Africa, but is found today as an ornamental plant throughout the world. Related species that have found some use in traditional medicine include Digitalis lutea (straw foxglove), Digitalis grandiflora and Digitalis ambigua (yellow foxglove), and Digitalis ferriginea (rusty foxglove). 1 , 2 , 3
Digitalis was one of the many herbal remedies used by the ancient Romans. Although its use for the treatment of heart failure has been traced back to 10th century Europe, digitalis was not widely used for this indication until its scientific investigation by British physician William Withering in the late 1700s. For most of the 1800s, digitalis was used to treat a wide variety of diseases and disorders. In 1875, German chemist Oswald Schmiedeberg first isolated pure digitoxin from digitalis, leading others to extract and identify other glycosides from various species of digitalis. In 1957, digoxin was isolated from D. lanata and is now a major cardiac glycoside marketed in tablet form. Digitalis was admitted into the first edition of the Pharmacopeia of the United States (1820) and is currently recognized by all major pharmacopeias. 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. 2 , 4 , 5
Ornamental strains of D. purpurea typically have low concentrations of active compounds. Leaves of wild varieties that have been used for medicinal purposes contain at least 30 different glycosides in total quantities ranging from 0.1% to 0.6%; these consist primarily of purpurea glycoside A (yielding digitoxin) and glycoside B, the precursor of gitoxin. Upon hydrolysis, digitoxin and gitoxin lose sugar moieties, producing their respective aglycones, digitoxigenin and gitoxigenin. Biosynthetic pathways in the production of cardenolides are reliant on the enzymes of malonyltransferase and progesterone 5 beta-reductase.
The main glycosides of D. lanata are the lanatosides, designated A through E. Removal of acetate groups and sugars results in formation of digitoxin, gitoxin, digoxin, digitalin, and gitaloxin. D. lanata is not typically used in powder form in the United States, but serves as a major source of lanatoside C and digoxin (300 times more potent than the powder prepared from D. purpurea ). Isolated digitoxin is 1,000 times more potent than whole powdered leaves and is completely and rapidly absorbed from the GI tract.
The seeds also contain digitalis glycosides, while steroidal saponins, flavones, the flavonoid chrysoeriol, anthraquinones, and organic acids have been identified in the leaves. High performance liquid chromatography and mass spectroscopy have been used to identify and quantify glycoside composition. 2 , 3 , 6 , 7 , 8 , 9 , 10 , 11
Uses and PharmacologyCardiovascular effects
Cardiac glycosides possess positive inotropic effects due to inhibition of sodium-potassium adenosine triphosphatase, which allows calcium to accumulate in myocytes leading to enhanced cardiac contractility. These drugs also possess some antiarrhythmic activity, but will induce arrhythmias at higher dose levels. 7 , 12 , 13Animal data
Digitalis glycosides have been used clinically for the treatment of heart failure for more than 200 years and remain the source of commercial digoxin preparations; however, a defined place in therapy remains under debate. Reviews of the large, multicenter Digitalis Investigation Group trial and other clinical trials have found no clear effect of digitalis on mortality in heart failure. Some effect has been demonstrated for secondary outcomes of decreased hospitalizations and clinical (symptomatic) deterioration. 5 , 15 For further information, consult standard pharmacology references.Other effects
In vitro experiments and screening studies have shown cytotoxic properties of glycosides and flavonoids from D. purpurea and D. lantana . Activity against human cancer cell lines, including solid tumor lines, has been demonstrated. Mechanisms include direct cytotoxicity resulting in apoptosis, inhibition of aflatoxin-induced cytotoxicity, inhibition of induction of nitric oxide synthase, and increases in glutathione S-tranferase. 11 , 16 , 17 , 18 , 19Diabetes
A study in hyperglycemic and dyslipidemic rats demonstrated enhanced glucose tolerance 2 hours after the rats were given a single dose of the saponin digitonin. Positive effects on the lipid profile were also observed. 20
Digitalis leaf has a narrow therapeutic index, requiring close medical supervision for safe use. Traditional dosage starts at 1.5 g of leaf divided into 2 daily doses. Purified digoxin is typically used at daily doses of 0.125 to 0.25 mg. 15 , 21
Documented adverse cardiac reactions. Avoid use. 22
There are numerous interactions with digoxin and digitalis glycosides, ranging from relatively minor (eg, cimetidine, triamterene) to life threatening. Many of the life threatening interactions occur as a result of elevated digoxin serum levels (eg, amiodarone, cyclosporine, macrolide and tetracycline antibiotics, propafenone, quinidine, verapamil) or electrolyte disturbances (eg, diuretics). 23 For more comprehensive information on digitalis drug interactions, refer to standard drug interaction texts.
Adverse reactions are generally related to toxicity.
All parts of the plant are toxic. Animal toxicity occurs during grazing. Children have become ill by sucking the flowers or ingesting seeds or parts of the leaves. Deaths have been reported among people who drank tea made from digitalis mistakenly identified as comfrey, although the bitter taste often deters ingestion, and its emetic properties can induce vomiting, thereby limiting systemic absorption. Digitalis poisoning is also associated with intentional ingestion with suicidal intent. 24 , 25 , 26
Digitalis glycosides accumulate and are excreted slowly; therefore, intoxications during therapy are common. The incidence of digitalis toxicity has 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 plant or purified drug poisoning include blurred vision, contracted pupils, dizziness, excessive urination, fatigue, muscle weakness, nausea, strong but slowed pulse, tremors, and vomiting; in severe cases, stupor, confusion, convulsions, and death can occur. Cardiac signs include atrial arrhythmias and atrioventricular block. Chronic digitalis intoxication is characterized by visual halos, yellow-green vision, and GI upset. 2 , 13 , 24 , 27
In mild cases of toxicity (atrial fibrillation with a slow ventricular response or occasional ectopic beats), temporary withdrawal of the drug and electrocardiogram monitoring is sufficient. 6 Gastric lavage or emesis together with supportive measures, such as electrolyte replacements, antiarrhythmics (eg, lidocaine, phenytoin), and atropine, have been used to manage acute poisonings. Digoxin-specific Fab antibody fragments may be used in managing acute intoxications caused by digitalis and related cardioactive glycosides; however, their efficacy remains unproven by controlled clinical trials. 13 , 25 , 28 , 29
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