PHARMACOLOGY

 BIOASSAY OF DIGITALIS ::

PRINCIPLE ::

Potency of the test sample is compared with that of the standard preparation by determining the action on the cardiac muscle Any other equivalent method which gives results similar to those obtained by this method as also valdi 

Standard Preparation and Units ::

The standard preparation is a mixure of dried and powdered digitalis leaves (1 unit = 76 mg )

Preparation of Extracts ::

Exact amount of the powder is extracted with dehydrated alcohol in a continuous extraction apparatus for six hours The final extract should contain 10 ml (5 ml .alcohol + 5 ml .Water ) per 10 g. of digitalis powder it should be stored in between 5 .C and -5 .c 

Guinea-pig method (End point method ) :;

Standard and test sample extracts are diluted with normal saline in such a way that 1 g of digitalis powder is diluted to 80 ml 

    A guinea pig is anaesthetized with a suitable anaesthetic it is dissected on the operation table The jugular vein is dissected out by removing adhering tissues and cannulated by means of venous cannula A pin is inserted in the heart such that it gets inserted in the apex of the heart in this way we can observe the heart beats by up and down movements of the pin The injection is continued through venous cannula untill the heart is arrested in systole The amount of extract required to produce this effect is taken as the lethal dose of the extract Another set of 19 animals of the same species are used for this experiment and the average lethal dose is determined It is not necessary to determine the lethal dose of the std during each time of the experiment But it should be occasionally checked 

    The lethal dose of the test sample is determined in a similar way using minimum 6 guinea -pigs of the same strain 

        The potency of the test sample is calcuated in relation to that of the std preparation by dividing the average lethal dose of the sample to the test and expressed as units per gram 

Pigeon Method ::

Minimum 6 pigeons are used for testing each sample They should be free from gross evidence of disease or emaciation The weight of the heaviest pigeon should not exceed twice the weight of the lightest pigeon food is withheld 16-28 hours before the experiment pigeons are divided on the basis of their sex weight and breed into two groups They are anaesthetized with anaesthetic ether 

    One side of the wing is dissected and the alar vein is cannulated by means of a venous cannula Dilutions are made with normal saline Average lethal dose of each sample is determined results are tabulated and calculated as per guinea pig method The lethal dose per kg of body weight is determined for each pigeon The potency of the test sample is determined by dividing the mean lethal dose of standard by the mean lethal dose of the test sample 

        In pigeons stoppage of heart is associated with a characteristic vomiting response called emesis The milk from the crop sac of pigeons is being ejected out This may be taken as the end point response of digitalis