Simultaneous Determination of A Novel Antitrypanosomal Compound (OSU-36) and its Ester Derivative (OSU-40) in Plasma by HPLC: Application to First Pharmacokinetic Study in Rats

Pavel Gershkovich1, Kishor M. Wasan, Olena Sivak, Summer Lysakowski, Carolyn Reid, Kokku Premalatha, Karl A. Werbovetz

1University of British Columbia


Purpose. To develop an HPLC-UV method for determination of a novel antitrypanosomal compound (OSU-36) and its ester prodrug (OSU-40) in rat plasma and to apply the method for pharmacokinetic evaluation of both compounds in rats. Methods. Since an attempt to assay for OSU-36 and OSU-40 in non-stabilized plasma resulted in highly non-linear calibration curves and poor sensitivity due to instability of the compounds, the plasma was stabilized using paraoxon and ascorbic acid. The sample treatment included protein precipitation by acetonitrile; evaporation; reconstitution with acetonitrile and filtration. The chromatography conditions included Xterra RP18 3.5µm 4.6X100mm column and gradient mobile phase system of acetonitrile-water. Results. The limits of quantification (LOQ) were 50 ng/mL and 40 ng/mL for OSU-36 and OSU-40, respectively. The intra- and interday precision and accuracies were below 13% for low, medium and high quality control samples for both compounds. While OSU-40 has been stable in all tested handling conditions, OSU-36 was unstable in plasma after 20 days storage in -80°C or 4h 28°C storage. The developed method has been applied for a pharmacokinetic study in rats which revealed that an ester prodrug OSU-40 is rapidly converted to OSU-36 within the plasma compartment by plasma esterases. OSU-36, in turn, relatively quickly undergoes oxidative metabolism, including within the plasma compartment. Conclusions. A supplementation of rat plasma with an esterase inhibitor to prevent degradation of ester prodrug (OSU-40), and with antioxidant to prevent oxidation of OSU-36, is necessary for reliable determination of both compounds. Due to limited stability of OSU-36 in stabilized rat plasma, long-term storage of samples or prolonged handling in room temperature conditions is not recommended.

J Pharm Pharm Sci, 14 (1): 36-45, 2011

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