[A HPLC method for determining piroxicam in body fluids]

Minimal detectable concentration of serum piroxicam by using HPLC reported in literature was mostly around 50 ng.ml-1 serum. Though the sensitivity was enough for pharmacokinetics study, it could not meet the needs of drug formulation screen study in developing precision drug delivery system (DDS) such as transdermal delivery system. A new HPLC method providing a detection limit of 0.75 ng, sensitive enough to quantify low concentrations of serum piroxicam down to 5 ng.ml-1 was reported in this paper. A Waters Model 481 instrument was used throughout the experiment. Isoxicam was proved to be the most suitable internal standard at maximum absorption wave length of 360 nm. A mixture of methanol and ammonium acetate 0.1 mol.L-1 (1:0.9 vol.vol-1) was selected as mobile phase with a flow rate of 1 ml.min-1. 0.025% tetramethyl ethylene diamine was added to ammonium acetate solution and adjusted to pH 4.5 with citric acid before mixing. Calibration curve was linear (r = 0.9999) in the concentration range of 10-5,000 ng.ml-1. The within-day and day-to-day precisions (CV) of this method were 2.88% and 2.89% respectively, with average recoveries of 96.0-102.4% (10-5,000 ng.ml-1). No interference was found in the body fluids of subjects who took piroxicam concomitantly with other commonly used non-steroidal anti-inflammatory medicines such as indomethacin, ibuprofen, naproxen, phenylbutazone and acetylsalicylic acid.