Concentrations of moxifloxacin in serum and synovial fluid, and ex vivo bactericidal activity against arthritis-causing pathogens.

Three doses of moxifloxacin 400 mg qd were administered orally to 20 candidates for knee arthroscopy (mean age, 71.2 years). The procedure was scheduled at four different points of time after the last dose: 2, 6, 12, and 24 h. Five patients were studied at each point of time. Drug levels were determined by the bioassay method. Bactericidal activity against four bacterial pathogens (two strains of each) was studied on serum and synovial fluid samples obtained during arthroscopy using the NCCLS guidelines. Mean (+/-S.D.) peak serum and synovial fluid concentrations were 3.46 +/- 0.78 mg/L and 3.42 +/- 0.51 mg/L, respectively. Levels above 1.0 mg/L were detected as long as 24 h. The peak bactericidal titers were (in serum and synovial fluid, respectively) 1:18.3 and 1:32 against Staphylococcus aureus, 1:18.3 and 1:22.6 against Streptococcus pyogenes, 1:45.2 and 1:64.0 against Klebsiella pneumoniae, and 1:2.3 and 1:1.7 against Pseudomonas aeruginosa. Bactericidal titers >1:2 were documented against the first three pathogens up to 24 h after dosing. On the basis of its pharmacokinetic and pharmacodynamic characteristics, moxifloxacin seems to be an excellent candidate for the treatment of joint infections, except those caused by P. aeruginosa.