High-performance liquid chromatographic determination of a potent AII receptor antagonist (DMP 811) in plasma

An HPLC assay for DMP 811, 4-ethyl-2-propyl-1-[(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]imi dazole-5- carboxylic acid (I) in rat and dog plasma has been developed. Compound I was isolated from plasma using a liquid-liquid back extraction procedure. The extraction recovery was greater than 81%. Separation of I from endogenous components in plasma was achieved on an E. Merck C8 column using a mobile phase of 0.05 M ammonium acetate, brought to pH 3.75 with acetic acid, and acetonitrile (78:22, v/v). The eluent was monitored by fluorescence with excitation and emission set at 235 and 370 nm, respectively. The assay was linear from 2 to 2000 ng/ml. Inter- and intra-day coefficients of variation for the rat-plasma assay ranged from 0.9 to 5.2% (5-2000 ng/ml) and 2.7 to 16.5% (2-2000 ng/ml), respectively. The respective coefficients of variation for the dog-plasma assay were 1.9 to 5.6% and 1.2 to 14.0%. The percent differences from the accuracy results were 12% or less. Using 0.5 ml of plasma for extraction, the minimum quantifiable limit was 2 ng/ml. This method has been used to quantify plasma levels of I in rats or dogs following 3-10 mg/kg i.v. or p.o. doses.