Describe an experiment to determine agonist potency and efficacy in the isolated guinea pig ileum.

Potency

Potency: A measure of drug activity in terms of the amount of the drug is needed to produce an effect of given intensity - (Ec50)

Efficacy

Efficacy: Measure of a drug's ability to evoke a response in a tissue.

How was the experiment carried out

Apparatus that measures the shortening of the longitudinal muscle of the ileum was used.
Isolated muscle - used widely. Part of the small intestine was used as a model of smooth muscle.
Placed in an organ bath surrounded by physiological material to keep it respiring
Different doses were administered to the isolated prep - shortening was measured in each case. Repeated same does x3
Data collected in a tabular fashion - log conc and percentage response were worked out.
Dose, conc, log conc, response 1/2/3, % response 1/2/3 (ADD UNITS)
Max value to get % response = avg of last 3 response values
Plot of log conc vs % response drawn. Line of best fit between data points to give a dose response curve.
DRAW EXAMPLE OF GRAPH

How was potency determined

Calculated the value of EC50
EC50: The higher the EC50 value the lower the potency
The lower the EC50 value the higher the potency
Ec50 is determined as the conc responding to 50% of the maximum response

EC50

A measure of the conc of a drug, antibody or toxicant which induces a biological response halfway between baseline and maximum

How was efficacy determined

Throughout the experiment the agonist conc was doubled. Plotting data - dose response curve. On the dose response curve we can see there is a ceiling effect or a plateau where further increases in drug conc no longer result in response. This ceiling effect represent the maximal response - reflecting on the drug's efficacy