Determination of the novel non-steroidal anti-inflammatory drug lornoxicam and its main metabolite in plasma and synovial fluid

A rapid and sensitive HPLC method for the determination of the non-steroidal anti-inflammatory drug lornoxicam in plasma samples of humans and laboratory animals is described. After addition of the internal standard (tenoxicam) the plasma sample is acidified and extracted either by dichloromethane via Extrelut columns or by solid-phase extraction using C-18 columns. After evaporation of the solvent the separation is performed on a C-18 column in isocratic mode with a mobile phase consisting of 0.1 M phosphate buffer (pH 6.0)-methanol and detection at 372 nm. The limit of determination was set to 10 ng/ml using 0.5 ml of sample but can be extended down to 2.0 ng/ml plasma. Using solid-phase extraction with C-18 columns both lornoxicam and its main metabolite 5'-hydroxylornoxicam can be determined while extraction via Extrelut was used in studies where only lornoxicam was to be determined. This method was used successfully in several thousand samples of pharmacokinetic and bioavailability studies in animals and in humans. (C) 1998 Elsevier Science B.V.