Comparison of ciprofloxacin assays

Two high pressure liquid chromatography methods developed independently and two different microbiological methods assayed samples containing ciprofloxacin derived from four volunteers: 46 sera, 19 saliva and 27 urine specimens. Each subject had received 500 mg of ciprofloxacin by mouth, with the samples collected in the ensuing six hours. Fifteen mock unknowns, prepared by adding known amounts of ciprofloxacin to normal human serum, were also assayed by the four procedures. The limits of sensitivity of the HPLC assays were less than 0.01 microgram/ml; the sensitivity limits of the bioassay were 0.02 microgram/ml (disc method) and 0.06 microgram/ml (well method). The inter-assay data was analyzed by linear regression. Ciprofloxacin concentrations in serum samples correlated well (R = 0.90) with all methods. Values obtained with urine samples also correlated well (R greater than or equal to 0.80). We conclude that either microbiological assay or quantitation by HPLC is satisfactory for quantitation of ciprofloxacin.