Drugs & Medication

Cardiac glycosides are drugs used in the treatment of congestive heart failure and cardiac arrhythmia. These glycosides are found as secondary metabolites in several plants, but also in some animals. Some of these compounds (ouabain and some frog poisons) are used in Africa as arrow-poisons for hunting.

Cardiac glycosides work by inhibiting the Na⁺/K⁺ pump. They do this by stabilizing the E2-P transition state of the Na⁺/K⁺ pump. This inhibition increases the amount of Ca⁺⁺ ions available for contraction of the heart muscle, improves cardiac output and reduces distention of the heart.

They have an antiarrhythmic effect by prolonging the refractory period of the AV node (Atrioventricular node), reducing the number of impulses reaching the ventricles. Cardiac output is restored but atrial fibrillation or atrial flutter are not abolished.

Examples of plants producing cardiac glycosides:

• Strophanthus - ouabain g/k/e-strophanthin
• Digitalis lanata and Digitalis purpurea - digoxin, digitoxin
• Scilla maritima - proscillaridine A
• Adonis vernalis, Adonis aestivalis
• Acokanthera oblongifolia
• Convallaria

Some frog-poison contain bufalin, marinobufagenin and bufadienolides, cardiac glycosides.