Herbal Medicine for the Treatment of Congestive Heart Failure

A number of herbs contain potent cardioactive glycosides, which have positive inotropic actions on the heart. The drugs digitoxin, derived from either D purpurea (foxglove) or Digitalis lanata, and digoxin, derived from D lanata alone, have been used in the treatment of congestive heart failure for many decades. Cardiac glycosides have a low therapeutic index, and the dose must be adjusted to the needs of each patient. The only way to control dosage is to use standardized powdered digitalis, digitoxin, or digoxin. When 12 different strains of D lanata plants were cultured and examined, their total cardenolide yield ranged from 30 to almost 1000 nmol/1 g. As is evident, treating congestive heart failure with nonstandardized herbal drugs would be dangerous and foolhardy.
Some common plant sources of cardiac glycosides include D purpurea (foxglove, already mentioned), Adonis microcarpa and Adonis vernalis (adonis), Apocynum cannabinum (black Indian hemp), Asclepiascurassavica (redheaded cotton bush), Asclepias friticosa (balloon cotton), Calotropis precera (king's crown), Carissa spectabilis (wintersweet), Cerebra manghas (sea mango), Cheiranthus cheiri (wallflower), Convallaria majalis (lily of the valley, convallaria), Cryptostegia grandiflora (rubber vine), Helleborus niger (black hellebore), Helleborus viridus, Nerium oleander (oleander), Plumeria rubra (frangipani), Selenicerus grandiflorus (cactus grandiflorus), Strophanthus hispidus and Strophanthus kombe (strophanus), Thevetia peruviana (yellow oleander), and Urginea maritima (squill). Even the venom glands of the animal Bufo marinus (cane toad) contain cardiac glycosides. Recently, the digitalislike steroid in the venom of the B marinus toad was identified as a previously described steroid, marinobufagenin. Marinobufagenin demonstrated high digoxinlike immunoreactivity and was antagonized with an antidigoxin antibody.
Accidental poisonings and even suicide attempts with ingestion of cardiac glycosides are abundant in the medical literature. Some herbal remedies (eg, Siberian ginseng) can elevate synthetic digoxin drug levels and cause toxic effects. In the United States, there are about 15,000 intoxications due to accidental or intentional ingestion of poisonous plants annually. In 1993, 2388 toxic exposures in the United States were reported to be due to plant glycosides. Of these, the largest percentage were attributed to oleander (ie, 25%). In the case of oleander, all plant tissues, including the seeds, roots, stems, leaves, berries, and blossoms, are considered extremely toxic. In fact, death in humans has been reported following ingestion of as little as 1 oleander leaf. The clinical manifestations of oleander intoxication, as well as other natural glycosides, is virtually identical to digoxin overdose. Morbidity and mortality are mainly related to cardiotoxic adverse effects that usually include life-threatening ventricular tachyarrhythmias, bradycardia, and heart block. The diagnosis should rely on the clinical presentation of unexplained hyperkalemia, and cardiac, neurologic, and gastrointestinal symptoms. The diagnosis can be further supported by the detection of the substance digoxin in a radioimmunoassay for digoxin. However, the extent of cross-reactivity between the cardiac glycosides from herbal sources and antibodies used in the radioimmunoassays has not been clearly defined. For this reason, digoxin assays may serve to confirm the suspected diagnosis but not to quantify the severity. Once the diagnosis has been established, the use of digoxin-specific Fab antibody fragments may be helpful in the treatment of severe intoxication. Other modalities, such as dialysis, cannot be easily facilitated because, like digoxin, natural glycosides are distributed extensively into peripheral tissues.