THE EFFICACY OF DELTA-OPIOID RECEPTOR-SELECTIVE DRUGS

delta-Opioid receptor-selective drugs may provide an alternative to mu -opioid-selective drugs currently used for the relief of pain. To deve lop improved delta-opioid receptor-selective drugs, better measures of drug activity are necessary. In this review we suggest that efficacy calculations provide a superior measure of drug activity as compared t o dissociation constants and drug potencies in functional assays. Effi cacy, as discussed in this review, is defined as a quantitative measur ement of the ability of a drug to stimulate second messenger systems o r measurable functional responses in cells or tissues under standard c onditions. Efficacy values will allow medicinal chemists to understand the contributions of both the coupling efficiency and dissociation co nstant to drug potencies in the development of new delta-opioid recept or-selective drugs.