Rate of bactericidal activity for Branhamella catarrhalis of a new macrolide, CP-62,993, compared with that of amoxicillin-clavulanic acid.

The rate of bactericidal activity of a new macrolide, CP-62,993, was compared with that of the combination of amoxicillin and clavulanic acid (in the proportion of 4 to 1) on strains of Branhamella catarrhalis beta-lactamase producers. The antibacterial activity of CP-62,993 was bacterostatic at 0.01 micrograms/ml. After a 6-hour period of bacteriostasis a bactericidal activity (3 log10 CFU/ml) was observed for all concentrations from 0.1 to 10 micrograms/ml after 24 h. The bactericidal rate of amoxicillin-clavulanic acid combination was more rapid during the first 6 h at 1 and 10 micrograms/ml. However, the concentration required to kill 99.9% of bacteria within 24 h was 1 microgram/ml. In conclusion, CP-62,993 was a bactericidal antibiotic for B. catarrhalis at a lower concentration. This in vitro study suggests that this macrolide may be of great interest in infections due to the B. catarrhalis beta-lactamase producer.