Abstract: Aim The application of microbiological turbidimetric method to determination of serum concentrations (C) of ciprofloxacin (CPLX) was studied. Methods A series diluted concentrations of CPLX were prepared with blank serum. The solution was put in a research unit with standard bacteria (ATCC 27853) dilution of 10⁷ cfu/ ml and incubated in Avantage analysis system. Absorbance (A) was recorded once every 5 min in a wavelength of 670 nm. Results There was a liner relationship (r =0.9950, n =8) between concentrations of CP LX and absorbance. The regression equation was C =9.4020-22.55 A. The lowest detectable concentration was 0.03 μg /ml. The rate of recovery of the method was 96.5 % ~ 108.0 %. The coefficient of variation within a day was 2.11% ~ 9.13 % while the coefficient of variation in different days was 1.99 % ~ 9.72 %. Conclusion The microbiological turbidimetry is a rapid, convenient and accurate method to determine the concentration of CPLX.

Key words: microbiological turbidity method, ciprofloxacin