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). There are two subtypes of this receptor known at present, defined as CCKA and CCKB (a ...

, selective for the CCK_B subtype. In animal studies it showed

anxiolytic An anxiolytic (; also antipanic or antianxiety agent) is a medication or other intervention that reduces anxiety. This effect is in contrast to anxiogenic agents which increase anxiety. Anxiolytic medications are used for the treatment of anxiet ...

effects and potentiated the analgesic action of both

morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...

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 Adamantanes Tryptamines Carboxylic acids Carboxamides Carbamates