High-performance liquid chromatographic determination of plasma and urinary 1-ethyl-1,4-dihydro-4-oxo-1,8-naphthyridine-3,7-dicarboxylic acid.

A high-performance liquid chromatographic method for the analysis of 1-ethyl-1,4-dihydro-4-oxo-1,8-naphthyridine-3,7-dicarboxylic acid (I) in plasma and urine is described. A statistical evaluation of the assay technique has shown acceptable accuracy and precision at concentrations as high as 2.0 microgram/ml of plasma or 29.0 microgram/ml of urine for samples augmented with 1. As little as 0.08 microgram/ml of I in plasma or 0.42 microgram/ml of I in urine were quantitatively determined. The mean relative error for the assay of unknown concentrations of I in plasma and urine was +/- 8% and +/- 3%, respectively. This method was used for the analysis of I in the plasma and urine of rhesus monkeys following oral administration of 200 mg/kg of nalidixic acid.