[Can chloramphenicol be combined with beta-lactam antibiotics? (author's transl)].

The effect was studied of combinations of chloramphenicol with beta-lactam antibiotics, such as penicillin, ampicillin, cefotiam and cefotaxime, on 20 strains each of Haemophilus influenzae, Streptococcus pneumoniae and Neisseria meningitidis. No antagonism was observed using the checkerboard titration method. In most cases no interaction could be established. An evaluation by the fractional inhibitory concentration index was discussed: only values above 2 were interpreted as antagonism. The minimal bactericidal concentrations of chloramphenicol were identical with the minimal inhibitory concentrations (MIC) - i. e. the antibiotic acted bactericidally on the species tested. Further investigations on the killing kinetics have shown that chloramphenicol in low concentrations can cause a delay in the bactericidal action of the antibiotic with which it is combined in the first few hours. At higher concentrations (more than double the MIC) the killing kinetics approximate those of the individual antibiotics. It is improbable that the minor delays in killing are of clinical significance. The combination is almost as effective as chloramphenicol.