Source, Mode of Action and Pharmacological Action of Cardiac Glycoside

Cardiac glycoside having cardiac inotropic properties. Cardiac glycosides increase the myocardial contractility and output in a hypodynamic heart. It is not proportionate increase oxygen consumption. So that it increases the efficiency of the failing heart is increased.

Cardiac glycosides are not increased and it has a prolonged action.

By convention, Digitalis is applied as a collective term for the whole group and has come to mean a cardiac glycoside.


Digitalis purpurea(leaf)Digitoxin, Gitoxin, Gitalin.
Digitalis lanata(leaf)Digitoxin, Gitoxin, Digoxin.
Strophanthus gratus(seed)Strophanthin-G(Ouabain)
Bufo vulgaris(Toad-skin)Bufotoxin
Convallaria majalisConvallotoxin
Thevetia neriifolia (nut)Thevetin


Glycoside is an organic compound generally received from plant origin and bind with sugar protein linked to a non-sugar moiety in a particular manner.

All the glycoside have an aglycone(gennin) part are attached to the one or more than one part of the sugar moieties. In which aglycone are responsible for the pharmacological activity but attached sugar is modified solubility and cell permeability, we also say that agycone have short-lived and less potent.

The aglycone consists of a cyclopentanoperhydrophenanthrene(steroid) ring, it is attached a 5 or 6 member unsaturated lactone ring. It consists one or more hydroxyl and other substitution on the aglycon which is responsible for determination of its polarity.

For example- Digoxigenin has an additional hydroxyl(OH) group than Digitoxigenin and is more polar.

Pharmacological Action:

All the cardiac glycoside has a qualitatively similar action, in which only difference in quantitative and pharmacokinetics.

  1. Heart-In the heart, digitalis has a direct effect on the myocardial contractility and also electrophysiological properties. It has a reflex effect due to the changes in haemodynamic and also affect the alteration in sympathetic activity.
  2. The force of contraction-Due to digitalis the force of contraction is increased and show the positive inotropic action. This condition is mainly seen in heart failure condition.
  3. Rate-Digitalis causes the decreases heart rate.
  4. Blood vessel-Digitalis cause mild vasoconstriction on the blood vessel. In which the peripheral resistance is increased from normal resistance.
    Digitalis does not effect the blood pressure (BP). Systolic BP may increase and diastolic BP may fall in CHF (Congestive Heart Failure).

Mode of Action:

Digitoxin increases the force of contraction in the heart. During the depolarization, the 2 potassium ion enters the inside of the cell and 3 sodium ion are enter the outside of the cell with the help of sodium potassium ATPase enzyme. On the other side during this process calcium are enter on the inside of the cell through calcium channel. The high accumulation of calcium cause the contraction. When the 1 calcium enters the outside of the cell than 3 sodium enter the inside of cell so that the concentration of sodium is increased. When digitoxin are given than digitoxin is inhibited the sodium potassium ATPase enzyme so that the entry of calcium are stopped the accumulation of calcium is low and cause Relaxation.


Digitalis is mainly used for CHF(Congestive Heart Failure) and control of ventricular rate in atrial fibrillation or flutter.

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Ankita Rai
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