CI-988 (PD-134,308) is a drug which acts as a

cholecystokinin antagonist A cholecystokinin receptor antagonist is a specific type of receptor antagonist which blocks the receptor sites for the peptide hormone cholecystokinin (CCK). Classification There are two subtypes of this receptor known at present, defined as ...

, selective for the CCK_B subtype. In animal studies it showed anxiolytic effects and potentiated the analgesic action of both

morphine Morphine, formerly also called morphia, is an opiate that is found naturally in opium, a dark brown resin produced by drying the latex of opium poppies (''Papaver somniferum''). It is mainly used as an analgesic (pain medication). There are ...

and endogenous opioid peptides, as well as preventing the development of tolerance to opioids and reducing symptoms of withdrawal. Consequently, it was hoped that it might have clinical applications for the treatment of pain and anxiety in humans, but trial results were disappointing with only minimal therapeutic effects observed even at high doses. The reason for the failure of CI-988 and other CCK_B antagonists in humans despite their apparent promise in pre-clinical animal studies is unclear, although poor pharmacokinetic properties of the currently available drugs are a possible explanation, and CCK_B antagonists are still being researched for possible uses as adjuvants to boost the activity of other drugs.

References

{{reflist Cholecystokinin antagonists N-Acyltryptamines Adamantanes Carboxylic acids Carboxamides Carbamates