Comparative in vitro activity of first, second and third generation cephalosporins

Minimum inhibitory concentrations (MIC) were determined against 662 recent clinical isolates for eight cephalosporins representing first, second and third generation compounds. All four third-generation cephalosporins tested (cefoperaxone, cefotaxime, ceftazidime and moxalactam) were significantly more active against aerobic gram-negative bacteria than the older compounds (cephalothin, cefamandole, cefoxitin, and cefuroxime). Cefotaxime and moxalactam were most active against Enterobacteriaceae with extremely low MIC-values. Ceftazidime was definitely most active against Pseudomonas aeruginosa with more than 90% of strains inhibited at 4 micro g/ml. MIC-values for cefotaxime against Staphylococcus aureus were for all strains 1-2 micro g/ml, slightly higher for cefoperazone, while the effect of ceftazidime and moxalactam was more limited. All third generation cephalosporins demonstrated efficiency against Streptococcus pyogenes, cefotaxime being most active and moxalactam least active, but were essentially ineffective against Streptococcus faecalis. Moxalactam demonstrated higher activity against Bacteroides fragilis than other second and third generation cephalosporins including cefoxitin. Previous studies have demonstrated a very high activity of all third generation cephalosporins against Haemophilus influenzae and Neisseria gonorrhoeae, including beta-lactamase producing strains.