A SIMPLE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY ASSAY FOR SIMULTANEOUS DETERMINATION OF OMEPRAZOLE AND METRONIDAZOLE IN HUMAN PLASMA AND GASTRIC FLUID

Antibiotics which are actively secreted into gastric fluid may be more efficacious in the eradication of Helicobacter pylori in peptic ulcer disease. Other agents used in the treatment of this disease such as o meprazole or other anti-secretory agents may alter the secretion and/o r distribution characteristics of antibiotics. In order to test the ap plicability of these concepts to metronidazole, a sensitive and specif ic high performance liquid chromatography (HPLC) assay was developed t o quantitate omeprazole in plasma, and metronidazole in plasma and gas tric fluid. The HPLC system consisted of a multi-phase column combinin g anion exchange and reversed phase separation (OmniPac Pax-500, Dione x), and a variable wavelength UV detector set at 254 nm. The mobile ph ase was a mixture of 0.1 M sodium phosphate buffer:methanol:acetonitri le (60:20:20) with final pH adjusted to approximately 7.0. Metronidazo le and omeprazole were extracted by adsorption onto a C-2-bonded silic a gel solid phase extraction column, and eluted with methanol. The ext ract was dried, reconstituted in a solution of acetyl salicylic acid ( ASA), and then injected into the HPLC system. Under these conditions, metronidazole, omeprazole and ASA were well separated and recoveries i n plasma were greater than 80%. Omeprazole could not be measured in ga stric fluid because of rapid decomposition. Using 0.3 ml of sample, th e assay sensitivity was less than 0.1 mu g ml(-1) and linear up to 10 mu g ml(-1). Both intra- and inter-assay CV were greater than 15%. It was applied successfully in determining metronidazole concentrations i n clinical samples of plasma and gastric fluid. (C) 1998 Elsevier Scie nce B.V. All rights reserved.