Trovafloxacin, a neu fluoroquinolone, produced bactericidal activity (-0.33 +/- 0.13 Delta log(10) CFU/ml . h; intravenously [i.v.] administered dose, 15 mg/kg) comparable to that of vancomycin (-0.39 +/- 0.18 Delta log(10) CFU/ml . h; i.v, administered dose, 20 mg/kg) in the treatment of experimental meningitis in rabbits due to a pneumococcal strain highly resistant to penicillin (MIC of penicillin G, 4 mu g/ml). The combination of both drugs significantly increased (P < 0.05) the killing rate (-0.60 +/- 0.23 Delta log(10) CFU/ml . h) compared to that produced by either monotherapy, These results were also confirmed in vitro.