Digitoxin is a compound from the foxglove plant, Digitalis purpurea, that has been used to treat heart conditions since the 12th century. Although its use has generally been supplanted by the drug digoxin, this natural product has some advantages over its rival. Both compounds are cardiac glycosides and cause heart muscle tissue to contract more vigorously. An advantage of using digitoxin, despite its greater chance of side effects, is that it is metabolized and eliminated from the body by the liver, unlike digoxin, which is eliminated by the kidneys. For patients who have kidney problems, this makes it a safer drug to use.
Foxglove is a toxic plant that is a source of a number of bioactive compounds. In 1785, it was discovered that extracts from the plant could improve the symptoms of congestive heart failure (CHF). With this condition, the heart is weakened and cannot pump hard enough to remove fluid from the body. The resulting buildup of fluid results in swelling known as edema. The active principle in foxglove responsible for treating CHF was found to be the compound digitoxin.
For many years, digitoxin was used to treat both CHF and cardiac arrhythmias. The drug stays in the system for a long time, however, and has many toxic side effects. It can cause nausea, vomiting, anorexia, vision disturbances and confusion, and because of these side effects, it rarely is used in modern medicine. The dose must be monitored carefully. The drug digoxin, a purified compound from foxglove tissue, is much more commonly used to treat these conditions.
The use of digoxin can be a problem in patients who have had kidney failure, however, because this drug is eliminated in the kidneys. With such patients, digitoxin is a good alternative drug. It is one of many drugs that are detoxified by the liver. Thus, it does not put any stress on the kidneys.
The mode of action of digitoxin is to increase the concentration of calcium and sodium inside the cells. This causes the heart muscle fibers to contract more strongly. The increased contractions help alleviate the symptoms of CHF and help control arrhythmias. High doses of this drug can bring on arrhythmias, however.
Both digitoxin and digoxin are cardiac glycosides, a classification of compounds based on their effects on the heart combined with their being bound to a sugar that can be cleaved off. Such compounds can be very toxic and have been used as arrow poisons by native hunters. Digitoxin is frequently used in literature, movies and television plots as a murder weapon.