title: In vitro metabolic stability of moisture-sensitive rabeprazole in human liver microsomes and its modulation by pharmaceutical excipients.
abstract: A reliable method to assess in vitro metabolic stability of rabeprazole and its modulation by Generally Recognized As Safe (GRAS)-listed pharmaceutical excipients was established in human liver microsomes. The metabolic stability of rabeprazole decreased as a function of incubation time, resulting in the formation of thioether rabeprazole via nonenzymatic degradation and enzymatic metabolism. Buffer type was also a determining factor for the degree of both nonenzymatic degradation and enzymatic metabolism. The net extent of enzymatic drug metabolism, obtained by calculating the difference in drug degradation between a microsome-present reaction system and a microsome-free solution, was about 9.20 +/- 0.67% in phosphate buffer and 2.27 +/- 1.76% in Tris buffer, respectively. Rabeprazole exhibited first-order kinetics in microsome-free solution but showed non-linear kinetics in the microsome-present reaction system. The maximal velocity, Vmax, in phosphate buffer was 5.07 microg mL(-1) h(-1) and the Michaelis-Menten constant, Km, was 10.39 microg mL(-1) by computer-fitting to the classical Michaelis-Menten equation for pattern of time-dependent change in the substrate concentration. The intact drug and its thioether form were well resolved and successfully identified by HPLC chromatography and liquid chromatography mass spectroscopy (LC/MS). The metabolic stability of rabeprazole was also modulated by the presence of pharmaceutical excipients. Among the five pharmaceutical excipients tested, poloxamer 188 and Gelucire 44/14 had potentially inhibitory effects on rabeprazole metabolism in human liver microsomes (p < 0.05). A greater understanding of metabolic stability and its modulation by pharmaceutical excipients would be useful for optimizing the bioavailability of rabeprazole at the early formulation stages.
authors.affiliation: National Research Laboratory for Bioavailability Control, College of Pharmacy, Kangwon National University, Chuncheon 200-701, Korea.
authors.forename: Shan
authors.initials: S
authors.lastname: Ren
authors.forename: Mi-Jin
authors.initials: MJ
authors.lastname: Park
authors.forename: Aera
authors.initials: A
authors.lastname: Kim
authors.forename: Beom-Jin
authors.initials: BJ
authors.lastname: Lee
mesh_terms: D053799:2-Pyridinylmethylsulfinylbenzimidazoles / Q000737:chemistry / Q000378:metabolism*; D001711:Biotransformation; D002021:Buffers; D002626:Chemistry, Pharmaceutical; D002851:Chromatography, High Pressure Liquid; D004339:Drug Compounding; D004355:Drug Stability; D005079:Excipients / Q000737:chemistry*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism*; D008954:Models, Biological; D054328:Proton Pump Inhibitors / Q000737:chemistry / Q000378:metabolism*; D064750:Rabeprazole; D015203:Reproducibility of Results; D013440:Sulfides / Q000378:metabolism; D013678:Technology, Pharmaceutical / Q000379:methods; D014867:Water / Q000737:chemistry
chemical_list: D053799:2-Pyridinylmethylsulfinylbenzimidazoles; D002021:Buffers; D005079:Excipients; D054328:Proton Pump Inhibitors; D013440:Sulfides; D014867:Water; C523099:rabeprazole-thioether; D064750:Rabeprazole