Overview of receptor interactions of agonists and antagonists

Historically, the earliest methods used to quantitatively measure the fundamental properties of drugs (namely affinity and efficacy) employed isolated tissues, and it is in this realm that the null methods used to define "receptor pharmacology" were described. This unit describes these methods and their use to specifically classify agonists (through potency ratios and determination of relative affinities and efficacies) and antagonists (through analysis of surmountable and insurmountable antagonism) to yield estimates of potency. Different drugs can yield different behaviors in various tissues, so this unit is centered on a flow diagram to indicate the type of analysis appropriate for the behavior observed. For example, some agonists may be full agonists in some tissues and partial agonists in others, while some antagonists may demonstrate surmountable simple competitive antagonism in some tissues and insurmountable non-competitive antagonism in others. Methods exist for determination of affinity and efficacy for all of these behaviors, and these are delineated in this unit.