Assay of RP 69698, a Novel LTB4-Antagonist, in Plasma by HPLC and its Application for Characterizing Pharmacokinetics of the Drug in Dogs

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Abstract
To support the preclinical development of RP 69698, a novel antagonist of LTB4, a high-performance liquid chromatographic (HPLC) procedure was developed for its determination in plasma. The method involves extraction of RP 69698 from deproteinized plasma with hexane:ethyl acetate under acidic conditions followed by reversed-phase HPLC with detection at 258 nm. The method is rapid, simple, and is applicable to dog, rat, and monkey plasma. Validation studies using dog plasma showed that the values obtained for parameters of linearity, precision, and accuracy were within acceptable limits. Based on analysis of 0.5 ml of plasma, the lower limit of quantitation was determined to be 25 ng/ml. The method has been successfully applied to determine the pharmacokinetic parameters of RP 69698 in the dog following intravenous and intragastric administration. The results of the dog study indicated rapid clearance of the drug from plasma (0.4 L/hr/kg) and limited distribution (volume of distribution at steady state = 0.24 L/kg). When given intragastrically as a solution in PEG 400, absolute bioavailability of the drug was 59Z but when given as an aqueous suspension in 0.5: methylcellulose, the drug was poorly absorbed with absolute bioavailability estimated to be about 6%.

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