Effectiveness of ciprofloxacin microspheres in eradicating bacterial biofilm

The treatment of cultures of planktonic cells and aged biofilm cells of P. aeruginosa and S, aureus with ciprofloxacin (CFX) microspheres of poly(L-lactic acid) (PLA) has been investigated using a modified, open in vitro chemostat system. The kinetics of release of CFX as a function of drug loading and the dose of microspheres were correlated with the rate and extent of killing and eradication of the planktonic cells and biofilm cells cultured on pieces of silicone tubing in the chemostat, respectively. At 71% w/w drug loading, a minimum dose of 7 mg of CFX in microspheres was required to sustain CFX concentration for about 10 h above the minimum inhibitory concentration (MIC) in order to completely eradicate the cells of either bacteria. In contrast, peak concentrations obtained from an equivalent dose of free CFX decreased to low values within 30 min and the bacteria cells were not eradicated. Lower microsphere loadings of CFX were ineffective at the same dose. Thus, this study has identified the formulation requirements for PLA microspheres to sustain CFX concentrations above the MIC for several days in order to eradicate bacteria, particularly aged biofilm cells, in the open chemostat in which the drug is being continually diluted, or similarly at a site of administration, for example, in the peritoneal cavity. (C) 1999 Elsevier Science B.V. All rights reserved.