Microbiological and pharmacodynamic considerations in the treatment of infection due to antimicrobial-resistant Streptococcus pneumoniae

The incidence of antimicrobial-resistant strains of Streptococcus pneumoniae has increased alarmingly in recent years. The problem is exacerbated by the global spread of resistant organisms. Currently, the incidence of penicillin-resistant pneumococci isolated from clinical specimens in the United States is greater than or equal to 35%. For empirical oral treatment of community-acquired respiratory infections, 3 choices are available: beta-lactam agents, macrolides, and fluoroquinolones. In considering the therapeutic efficacy of these agents, it is essential to also take pharmacokinetic and pharmacodynamic (PK/PD) factors into account. Many drugs are effective against penicillin-susceptible strains. However, the higher the minimum inhibitory concentration of penicillin, the more likely that cross-resistance to beta-lactam agents and macrolides will occur. Currently, the incidence of fluoroquinolone-resistant pneumococci is low; it is proposed that adequate dosing based on the PK/PD properties of fluoroquinolones may help reduce the emergence of resistant organisms. Prudent use of all antimicrobials is essential to decrease the emergence of strains resistant to these agents.