Determination of norfloxacin, a new nalidixic acid analog, in human serum and urine by high-performance liquid chromatography.

A high-performance liquid chromatographic method for the analysis of norfloxacin (MK-366) [1-ethyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)3-quinolinecarboxylic acid], a new nalidixic acid analog, in human serum and urine is described. A statistical evaluation of the assay data showed acceptable accuracy and precision for 0.1 to 10.0 micrograms of MK-366 per ml of serum and for 1.0 to 500 micrograms of MK-366 per ml of urine. MK-366 was extracted from serum and urine at pH 7.5 with methylene chloride and back-extracted with sodium hydroxide solution. Chromatography was performed on an anion-exchange column with acetonitrile-phosphate buffer as the mobile phase; UV absorbance was monitored at 273 nm. The method was used to measure MK-366 in clinical specimens.