Challenges for receptor theory as a tool for drug and drug receptor classification.

Increased understanding in the field of receptor pharmacology, born of the sophisticated techniques now available to us, has confounded rather than simplified the problem of receptor classification. The International Union of Pharmacology (IUPHAR) is currently sponsoring a Receptor Nomenclature Committee whose aims are to recommend a rational system of classification, a formidable task given the complexity and volume of data in the literature (agonist/antagonist potencies, coupling mechanisms, primary structures, etc.) that will need to be incorporated. The Committee's chairman, Terry Kenakin, outlines here the limitations of classical receptor theory for drug receptor classification and suggests that any functional classification system must take into account not only affinity and intrinsic efficacy but also, at the very least, parameters relating to the transducing properties of receptors. If this is not done, then receptor classification data obtained from studies with agonists and antagonists may be different and lead to confusion.