Cardiac glycosides

Pharmacology and toxicology

Digoxin, a metabolic product of digitoxin, is the most widely used form of the digitalis cardiac glycosides. It is used in the treatment of atrial fibrillation and in some cases of heart failure.

Digitoxin is 90-100 percent absorbed in the gastrointestinal tract, and is excreted via the liver. It has a half-life of, on average, 7 days. Digoxin is widely distributed and extensively bound in varying degrees to tissues throughout the body, which results in an apparent high volume of distribution. It is excreted primarily through the kidneys, and has a half-life of about 40 hours.

Absorption from the gastrointestinal tract is about 80 percent for methyldigoxin and acetyldigoxin. Methyl digoxin is demethylated in the liver, whereas acetyldigoxin is deacetylated in the intestinal mucosa.

All digitalis glycosides cross the placenta, resulting in significant fetal levels (Gilstrap 1998). Cord levels are about 50-80 percent of maternal levels (Chan 1978). However, the myocardial sensitivity in the fetus appears to be less than it is in adults (Saarikoski 1978). There are, as yet, no known toxic effects on the fetus from digitalis glycosides. In some instances it has been used to treat fetal tachycardias (Hallak 1991, Rotmensch 1987).

Recommendation. Digitalis glycosides can be used during pregnancy. There have been no reports linking digitalis glycosides with congenital malformations. They are indicated for some kinds of maternal and fetal tachycardia, and for some instances of chronic cardiac failure.

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