Principle of Digitalis
Digitalis (e.g., digoxin, digitoxin) increases the force of cardiac contraction and can induce characteristic arrhythmias or lethal effects in overdose.
The bioassay detects either the inotropic effect (strength of heartbeat) or the toxic/lethal effect in an experimental model.
Methods
Pigeon Method (Historical)
Procedure:
Inject known doses of standard digitalis and test sample into pigeons.
Observe for the “death in diastole” phenomenon (a classic sign of digitalis toxicity).
Potency Determination: Compare the lethal doses (LD50).
Frog Heart or Guinea Pig Heart Method (Isolated Heart)
Procedure:
Use an isolated perfused frog/guinea pig heart.
Administer incremental doses of standard vs. test digitalis.
Monitor for changes in contractility or typical arrhythmias (e.g., AV block, bigeminy).
Potency Determination: Compare the dose that causes a standardized endpoint (e.g., 50% arrhythmia incidence) for standard vs. test.