title: Metabolic inhibition and kinetics of raloxifene by pharmaceutical excipients in human liver microsomes.
abstract: This study was originally undertaken to establish the in vitro metabolic conditions and then evaluate the effect of pharmaceutical excipients (PEs) on drug metabolism in uridine diphosphoglucuronic acid-supplemented human liver microsomes. Poorly bioavailable raloxifene was chosen as a model drug. Intact drug and its two glucuronide metabolites were successfully isolated using gradient HPLC analysis and LC/MS analysis. Formation of raloxifene metabolites was affected by buffer compositions, incubation time and initial raloxifene concentrations. Under optimized metabolic conditions, 41.0% of raloxifene was converted to its metabolites after 2h incubation. This metabolic inhibition of raloxifene by the PEs occurred in a dose-dependent manner and accordingly formed two glucuronide metabolites. In the metabolic kinetics using Lineweaver-Burk analyses, Cremophor EL competitively inhibited formation of metabolites while sodium lauryl sulfate (SLS), polyvinylpyrrolidone K30 (PVP) and Tween 80 significantly inhibited in a mixed competition. Although some PEs showed inhibition on glucuronidation of raloxifene in vitro, their effects on in vivo bioavailability of raloxifene need to be confirmed directly due to the dilution factors and other complicated situations influencing the bioavailability.
authors.affiliation: National Research Laboratory for Bioavailability Control, College of Pharmacy, Kangwon National University, Chuncheon, Republic of Korea.
authors.forename: Ae Ra
authors.initials: AR
authors.lastname: Kim
authors.forename: Soo-Jeong
authors.initials: SJ
authors.lastname: Lim
authors.forename: Beom-Jin
authors.initials: BJ
authors.lastname: Lee
mesh_terms: D001682:Biological Availability; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D005079:Excipients / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D020849:Raloxifene Hydrochloride / Q000737:chemistry / Q000378:metabolism* / Q000493:pharmacokinetics; D020845:Selective Estrogen Receptor Modulators / Q000378:metabolism* / Q000493:pharmacokinetics
chemical_list: D005079:Excipients; D020845:Selective Estrogen Receptor Modulators; D020849:Raloxifene Hydrochloride