Disposition and metabolism of radiolabeled casopitant in humans.
Casopitant [1-piperidinecarboxamide,4-(4-acetyl-1-piperazinyl)-N-((1R)-1-(3,5-bis(trifluoromethyl)phenyl)-ethyl)-2-(4-fluoro-2-methylphenyl)-N-methyl-(2R,4S)-(GW679769)] is a novel neurokinin-1 receptor antagonist being developed for the prevention of chemotherapy-induced and postoperative nausea and vomiting. The disposition of [(14)C]casopitant was determined in a single-sequence study in six healthy male subjects after single-dose 90-mg i.v. and 150-mg oral administration. Blood, urine, and feces were collected at frequent intervals after dosing. Plasma, urine, and fecal samples were analyzed by high-performance liquid chromatography/mass spectrometry coupled with off-line radiodetection for metabolite profiling. Moreover, urine was also analyzed with (1)H-NMR to further characterize metabolites. Plasma pharmacokinetic parameters for casopitant, a major metabolite (M13, coded as GSK525060), and total radioactivity were determined. Absorption of radioactivity after oral administration appeared to be nearly complete; elimination was principally via the feces both after oral and intravenous administration. Urinary elimination accounted for only <8% of total radioactivity. The main circulating metabolites were a hydroxylated derivative, M13 (coded as GSK525060), and, after oral administration, a deacetylated and oxidized metabolite, M12 (coded as GSK631832). In addition, many other metabolites were identified in plasma and excreta: the principal route of metabolism included multiple oxidations, loss of the N-acetyl group, modifications or loss of the piperazine group, and cleavage of the molecule. Casopitant was extensively metabolized, and only negligible amounts were excreted as unchanged compound. Some phase II metabolites were also observed, particularly in urine.
Pellegatti
Mario
M
Department of Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Research & Development, Via Fleming 4, Verona, Italy. Mario.N.Pellegatti@gsk.com
Bordini
Ellenia
E
Fizzotti
Patrizia
P
Roberts
Andy
A
Johnson
Brendan M
BM
D000107:Acetylation; D000284:Administration, Oral; D000328:Adult; D000932:Antiemetics / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D001682:Biological Availability; D001711:Biotransformation; D002250:Carbon Radioisotopes; D002851:Chromatography, High Pressure Liquid; D005243:Feces / Q000737:chemistry; D006801:Humans; D006900:Hydroxylation; D007262:Infusions, Intravenous; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D055432:Metabolomics / Q000379:methods; D008875:Middle Aged; D010084:Oxidation-Reduction; D010879:Piperazines / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D010880:Piperidines / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D021241:Spectrometry, Mass, Electrospray Ionization; D053719:Tandem Mass Spectrometry; D014018:Tissue Distribution; D014508:Urea
D000932:Antiemetics; D002250:Carbon Radioisotopes; D010879:Piperazines; D010880:Piperidines; C531951:casopitant; D014508:Urea