Plasma stability plays an important role in drug discovery and development. Rapid metabolism lowers drug exposure at the therapeutic target. Furthermore unstable compounds cause difficulties for in vitro plasma protein binding studies, and in vivo PK studies since they continue to degrade after blood samples are taken from the animals. Plasma stability is also very useful for screening prodrugs where rapid conversion is desirable. Certain functional groups such as amides, esters or lactones make compounds favorable targets for plasma enzymes such as hydrolases and esterases.