In vitro activity of oral cephalosporin BAY v 3522 compared with other oral cephalosporins.

Minimal inhibitory concentrations (MICs) of the oral cephalosporin BAY v 3522, and of cephprozyl, cefaclor, cefixime, cefuroxime, cefetamet, cefpodoxime and cefotaxime were determined against Gram-positive and Gram-negative clinical isolates with the NCCLS agar dilution procedures. BAY was the most active drug against Gram-positive organisms. MICs ranged from 0.01 mg/l against group A streptococci to 16 mg/l against S. faecium. Although mean MICs of BAY against methicillin-resistant S. aureus and S. epidermidis were between 0.9-1.8 mg/l, respectively, such strains showed typical heteroresistance in population studies. In addition, the biochemical correlate of methicillin-resistance, the PBP-2', showed similar low affinity to BAY as methicillin. beta-lactamase-producing H. influenzae and B. catarrhalis were inhibited by 2-8 and 0.25-2 mg/l, respectively, whereas non-producers were inhibited by 0.25-2 and 0.12-1 mg/l of the drug. The activity of BAY against enterobacteriaceae was rather low. Ampicillin-susceptible E. coli strains were inhibited by 2-8 and resistant strains by 8-32 mg/l. The mean MIC against cephalothin-susceptible K. pneumoniae strains was 2.8, and that against resistant strains 27.4 mg/l. MICs against beta-lactamase-producing enterobacteriaceae determined in broth dilution were 4-8 times higher than those determined in agar dilution. Bactericidal activity was measured in killing-curve experiments at 4 times the MIC. BAY killed equally well as standard control drugs.