Comparison of high-pressure liquid chromatography and bioassay for determination of ciprofloxacin in serum and urine.

Ciprofloxacin was given orally to 10 healthy volunteers for seven consecutive doses of 250 mg every 12 h. Serum and urine samples were collected at distinct times between 0 and 96 h and analyzed both by high-pressure liquid chromatography and by a microbiological assay. The detection limits were 0.006 and 0.03 microgram/ml, respectively. For each method, imprecision coefficients of variation were less than 6.1% at various concentrations in serum and urine. The means +/- standard deviations of the absolute values of the relative differences between the two methods were 9.3 +/- 6.8% (n = 225) for serum samples and 58.5 +/- 50.4% (n = 70) for urine samples. Comparison of the concentrations in serum measured with high-pressure liquid chromatography and bioassay by regression analysis yielded a slope which was not significantly different from 1.0 (99.9% confidence limits: 0.984 less than slope less than 1.035). In urine, however, the bioassay results were markedly higher than the high-pressure liquid chromatography values (1.327 less than slope less than 1.698), which indicates the presence of antimicrobially active metabolites. The cumulative 12-h urinary recovery after the first and seventh doses averaged 30.2 +/- 8.5 and 26.4 +/- 4.6%, respectively, by high-pressure liquid chromatography, whereas with bioassay 38.2 +/- 5.9 and 45.5 +/- 5.9% activity was recovered. Protein binding appeared to be neither concentration nor pH dependent and averaged 21.9 +/- 4.1%.