Clinical significance of antimicrobial resistance in Streptococcus pneumoniae

Abstract

Despite increasing resistance in the pneumococcus over the past 30 years, there are few cases of treatment failure of nonmeningeal infections with high dose parenteral penicillin G, which still remains highly effective for many pneumococcal diseases. This is reflected by the new 2008 CLSI breakpoints for parenteral penicillin G of susceptible, ≤2 g/mL, intermediate, 4 g/mL, and resistant, ≥8 µg/mL for nonmeningeal infections. For meningitis and oral penicillin V use, the old penicillin breakpoints of susceptible, ≤0.06 g/mL, intermediate, 0.12-1 g/mL, and resistant, ≥2 µg/mL will remain in place. Clinically relevant susceptibility breakpoints have also been developed for virtually all relevant antimicrobial agents used to treat pneumococcal diseases, based on clinical studies and pharmacokinetic and pharmacodynamic parameters. Although pneumococcal resistance to -lactams, macrolides and cotrimoxazole is now common worldwide, we are still able to treat almost all pneumococcal infections adequately. An exception is the oral treatment of multidrug resistant serotype 19A strains in children in the USA as these are resistant to amoxicillin, oral cephalosporins and cotrimoxazole. While there is a need to develop new agents, judicious use of antimicrobial agents is the best long-term approach. Empiric treatment guidelines should reflect the emerging threats from increased drug resistance and the possibility of increased virulence in replacement serotypes following vaccine use. Compliance with guidelines by physicians and patients is important to prevent further development of resistance.