Intraphagocytic bioactivity of lomefloxacin against Pseudomonas aeruginosa.

The kinetics of extracellular bactericidal activity and the intraphagocytic bioactivity of lomefloxacin at concentrations 2 mg/L (1/2 x MIC), 4 mg/L (MIC) and 8 mg/L (2 x MIC) against Pseudomonas aeruginosa were measured, the first in 40% human serum and the second in polymorphonuclear leucocytes (PMNLs), by the colony-counting method. The PMNLs were treated with phenylbutazone to prevent them killing the bacteria during the ingestion period. The kinetics of extracellular killing were biphasic with an initial rapid phase lasting 30 min when lomefloxacin was used at concentrations equal to the MIC and 2 x MIC, during which a decrease of 3 log of cfu/mL occurred. Lomefloxacin showed intraphagocytic activity at the three concentrations assayed. With non-treated PMNLs the percentages of intraphagocytic killing after 30 min of incubation were 93.5, 91.3 and 95.5% with 2, 4 and 8 mg/L, respectively, and 79.8, 65.0 and 93.3% for the same lomefloxacin concentrations with phenylbutazone-treated PMNLs, suggesting a synergic interaction between the antibacterial activity of PMNLs and lomefloxacin.