A rapid and sensitive high-performance liquid chromatographic method for the determination of diclofenac sodium in serum and its use in pharmacokinetic studies.

A rapid, and sensitive high-performance liquid chromatographic method has been developed for the determination of diclofenac sodium in serum using flufenamic acid as the internal standard. Serum protein was precipitated with acetonitrile. The drugs were eluted from a 5 microns C-8 reversed-phase column at ambient temperature with a mobile phase consisting of acetonitrile-water (50:50% v/v) adjusted to pH 3.3 with glacial acetic acid, at a flow rate of 2 mL min-1 with UV detection at 280 nm. Each analysis required no longer than 10 min. Quantitation was achieved by the measurement of the peak-height ratio and the relative and absolute recoveries varied from 90 to 98%. Detection limits for diclofenac sodium in serum is 25 ng mL-1. Intraday coefficients of variation (CV) ranged from 2.47 to 4.61% and interday CVs from 3.52 to 7% at three different concentrations. Preliminary stability tests showed that diclofenac sodium is stable for at least 2 weeks in serum after freezing. The method is applied for the determination of the pharmacokinetic parameters of diclofenac after administration of two formulations (enteric-coated tablet and slow-release tablet), to a healthy male volunteer.