Effect of ciprofloxacin in an in-vitro pharmacokinetic model against Pseudomonas aeruginosa isolated during cystic fibrosis lung infection.

An in-vitro pharmacokinetic model was used to simulate ciprofloxacin concentrations in serum observed in vivo following oral doses of 250, 500 and 750 mg, in a culture of Pseudomonas aeruginosa isolated from the sputum of a cystic fibrosis patient. In the 12 h interval following each dose, a period of bactericidal activity was observed, succeeded by bacteriostasis and subsequent bacterial regrowth. In all cases bacterial regrowth was first observed when the ciprofloxacin concentration in the culture flask of the dynamic model fell below the MIC. For the three doses investigated, the surviving bacteria at the end of each 12-h dosing interval showed an increase in MIC compared with that of the culture before ciprofloxacin exposure. The post-antibiotic effect of ciprofloxacin against P. aeruginosa was observed for 1-5 h, and was dose related.