Fully automated assay for the determination of GR117289X in human plasma using mixed mode solid-phase extraction and...

GR117289X, 3-(3-Bromo-2-[2-(1H-tetrazol-5-yl)-phenyl]-bezofuran-5-yl methyl)-2-butyl- 5-chloro-3H-imidazole-4-carboxylic acid, 1, is an angiotensin II receptor antagonist. A sensitive, accurate and precise assay for the determination of 1 in human plasma and validation data is described. The assay consists of a novel solid-phase extraction using Certify II followed by a reversed-phase gradient HPLC separation with UV detection. The extraction procedure has been fully automated by a Zymate XP robot and linked on-line to the HPLC system. The analytical range for the assay is 5-250 ng ml-1 over which the assay is linear and specific for 1 with respect to endogenous plasma components and its tetrazole N2 glucuronide, the major circulating metabolite 2. For the fully automated procedure the intra-assay data indicate a maximum bias and coefficient of variation across the calibration range of +8.0 and 9.4%, respectively. The inter-assay data indicate a maximum bias and coefficient of variation across the calibration range of +8.0 and 11.1%, respectively. The extraction efficiency of the assay was approximately 75%. Both a manual and fully automated assay were applied to the analysis of 1 in plasma of volunteers from a number of clinical studies. The assay has been shown to be robust in sustained use over several months.