Validation of a reversed-phase high-performance liquid chromatography method with fluorescence detection for the bioequivalence study of norfloxacin in plasma samples.

A robust method for the determination of norfloxacin in human plasma, using reversed-phase high-performance liquid chromatography (RP-HPLC) with fluorescence detection, has been developed. The method involves precipitation of plasma protein with acetonitrile and the use of ciprofloxacin as internal standard (IS). Chromatographic separations were performed on a Synergi MAX-RP 150 x 4.6-mm, 4-micro column with an elution system consisting of a mixture of phosphate buffer-acetonitrile (85:15, v/v). The calibration curve was linear, in the range of 30 to 3500 ng/mL. The recoveries at concentrations of 90, 1400, and 2800 ng/mL were 103.5%, 100.2%, and 100.2%, respectively. The quantification limit for norfloxacin was 30 ng/mL per 10-microL injection employing fluorescence detection with excitation and emission set at 300 and 450 nm, respectively. The method validation included examining the within-run and between-run precision and accuracy and ensuring that these were within accepted limits; in summary, the precision was <8.6% and accuracy ranged from 95.8% to 104.1% for concentration from 90 to 2800 ng/mL. The precision and accuracy for the lowest calibration standard (30 ng/mL) was well within accepted limits for lower limit of quantification. The method was then applied in a bioequivalence study in healthy volunteers given 400-mg doses of reference and test formulations of norfloxacin in random order and including a 7-day washout phase.