ci-988 ci-988 ci-988 (pd-134,308) is a drug which acts as a cholecystokinin antagonist, selective for the cckb subtype. in animal studies it showed anxiolytic effects and potentiated the analgesic action of both morphine 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 cckb 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 cckb antagonists are still being researched for possible uses as adjuvants to boost the activity of other drugs. ci-988identifiers iupac name 4-(dec-2-yloxy) carbonyl]amino)propyl]amino)-1-phenylethyl]amino)-4-oxobutanoic acid cas number130332-27-3pubchem cid108186chemspider97266unii2637pdx9sichemblchembl2062154chemical and physical dataformulac35h42n4o6molar mass614.743 g·mol−13d model (jsmol)interactive image smiles c(cc1cc2c1cccc2)(c(=o)nc(c3ccccc3)nc(=o)ccc(=o)o)nc(=o)oc4c5cc6cc(c5)cc4c6 inchi inchi=1s/c35h42n4o6/c1-35(18-26-19-36-28-10-6-5-9-27(26)28,39-34(44)45-32-24-14-21-13-22(16-24)17-25(32)15-21)33(43)37-20-29(23-7-3-2-4-8-23)38-30(40)11-12-31(41)42/h2-10,19,21-22,24-25,29,32,36h,11-18,20h2,1h3,(h,37,43)(h,38,40)(h,39,44)(h,41,42)/t21?,22?,24?,25?,29-,32?,35+/m0/s1key:fvqssymrzklfdr-zabpbajssa-n (verify)