An automated method for the determination of diclofenac sodium in human plasma

An automated method utilizing laboratory robotics has been developed for quantifying diclofenac sodium concentrations in human plasma. The robotic system aliquots the biological sample, adds the internal standard (CGP 4287), extracts the compounds from the acidified biological matrix (pH less than 2) into an organic phase (hexane-isopropyl alcohol), and concentrates the extracts for reversed-phase, high-performance liquid chromatographic (HPLC) analysis. The laboratory robot is directly interfaced to the HPLC system, and the data are automatically collected and results calculated. Separation is achieved on a 3-microns ODS (6.2-mm x 8.0-cm) column with ultraviolet (UV) detection of the drug and internal standard at 280 nm. Recovery and reproducibility assessments indicate good accuracy (overall mean relative recovery of 99.8%) and precision (coefficient of variation from 0.5 to 11.1%) over the diclofenac sodium concentration range of 5.0-1000 ng/mL, with a quantification limit of 5.0 ng/mL. The method has been successfully applied to a pharmacokinetic study in which normal volunteers received 150 mg of a prototype controlled-release formulation of diclofenac sodium.