Cephalosporins are classified by generation based on the characteristics of their antibacterial action. The third generation cephalosporins are less effective against Gram-positive cocci than the first generation, but are much more effective against the Enterobacteriaceae family, including beta-lactamase-producing strains. However, the effect against Pseudomonas aeruginosa must be considered very carefully because of the wide variation in rates of resistance and antibiotic use across hospitals, communities and cities.