UV partial least-squares calibration and liquid chromatographic methods for direct quantitation of levofloxacin in urine.

Levofloxacin was determined in human urine samples by application of a spectrophotometric multivariate calibration partial least-squares (PLS-1) method. A calibration set consisting of standards was prepared by using a multilevel multifactor experimental design. In order to ensure accurate results, the calibration matrix included a urine sample free of levofloxacin (i.e., urine blank). The components of the calibration matrix were levofloxacin and urine. The concentration of levofloxacin ranged from 0.5 to 16.5 microg/mL. Different urine concentrations were used as the second component of the calibration matrix in order to include the information inherent in the changes in the UV spectrum for urine upon dilution. In addition, a high-performance liquid chromatographic method was proposed. In this method, a Shim-pack amino column was used at ambient temperature with a mobile phase of 25 mM potassium dihydrogen phosphate (pH adjusted to 3.1 with phosphoric acid)-acetonitrile (70 + 30, v/v), and the flow rate was 1 mL/min. UV detection at 293 nm was used for quantitation. The proposed methods were applied to the determination of the dissolution rate for tablets containing levofloxacin. The urinary excretion pattern for the cumulative amount of levoflacin excreted was also calculated.