Quantification of Ciprofloxacin in Human Plasma by Validated LC-MS/MS Using Ofloxacin as an Internal Standard and its Clinical Application

A simple LC-MS/MS method has been advanced for measuring ciprofloxacin, using liquidliquid extraction of plasma with ether and methylene chloride (7/3, v/v) using ofloxacin as an internal standard (IS). The analytes were detected by HPLC using an isocratic mobile phase composed of methanol and 5 mM aqueous ammonium acetate (pH 3.0, 35/65, v/v) on a Luna phenyl-hexyl (Phenomenex 2.0 x 50 mm, 5 μm) column. The eluate was analyzed by MS/MS in the MRM mode using the transitions of the respective (M+H)+ ions (m/z 332.1→231.1 and m/z 362.1→261.1) for determination of ciprofloxacin and IS, respectively. The standard calibration curves indicated good linearity within the range of 0.05-5.0 μg/ml (r2=0.997, 1/x2 weighting). The lower limit of quantification (LLOQ) was 0.05 μg/ml. The retention times of ciprofloxacin and IS were 1.79 and 1.51 minutes, respectively. In addition, no significant impurities were found that interfered with the analysis. Acceptable precision and accuracy were obtained for the concentration range of the standard curve. The validated method was successfully applied to bioequivalence and pharmacokinetic studies of two formulations of ciprofloxacin (single 250 mg doses) in 24 healthy Korean volunteers. Keywords: Bioequivalence, ciprofloxacin, LC-MS/MS, liquid-liquid extraction, pharmacokinetics, internal standard.