Efficacy and Potency

• Potency - when two drugs produce equivalent responses, the drug whose dose-response curve lies to the left of the other is said to be the most potent

• Described using the half-maximally effective concentration (EC50) to produce a given effect
• Determined by efficacy and affinity

• Efficacy - the ability of a drug to activate its receptor and produce a cellular response

• When two drugs produce differing maximal responses, the observed maximal response is a nonlinear function of their relative intrinsic efficacies
• A full agonist would have high efficacy, a partial agonist has low efficacy