Streptococcus pneumoniae: Activity of Newer Agents Against Penicillin-Resistant Strains.

Strains of pneumococci resistant to antimicrobial agents have been reported on all continents. In 1997, more than 50% of strains in the United States were not susceptible to penicillin, and 30% were resistant to macrolides. In addition, many strains are resistant to multiple agents, including beta-lactams, macrolides, clindamycin, chloramphenicol, tetracyclines, and trimethoprim-sulfamethoxazole. Although resistance to beta-lactams in nonmeningeal infections can usually be overcome by parenteral administration, clinically significant resistance is an important limitation in meningitis and with oral administration of beta-lactams. Decisions about treatment of pneumococcal infection are based on the site of infection, the degree of resistance to penicillin G, the presence of resistance to other agents, the severity of disease, the presence of underlying conditions, and the dose and route of administration of antimicrobial agents. The application of pharmacokinetic and pharmacodynamic variables to pneumococci has greatly improved the interpretation of susceptibility data and the development of clinically relevant breakpoints.