Use of functional assays to detect and quantify functional selectivity.

Drug selectivity is arguably a critical concern for drug development. Recently, experimental evidence suggests that drugs have more selectivity than that afforded by differential affinity for different receptor subtypes. Drugs, acting at a single receptor, can selectively and differentially activate each of the multiple signaling pathways coupled to a receptor. This type of selectivity has been termed functional selectivity. Understanding functional selectivity and how to measure it will be important for new drug development.