Clinical relevance of penicillin-resistant Streptococcus pneumoniae.

Streptococcus pneumoniae is the most important respiratory tract pathogen in otitis, sinusitis, bronchitis, and community-acquired pneumonia. Over the past decades, there has been an increase in minimum inhibitory concentrations (MICs) to penicillin. Decreased susceptibility to penicillin is not the same as penicillin resistance. Decreased susceptibility to penicillin has occurred worldwide from dissemination of several resistant pneumococcal clones, and, to a lesser extent, from excessive use of ciprofloxacin, macrolides, and trimethoprim-sulfamethoxazole (TMP-SMX). Currently, penicillin resistance is defined by using a breakpoint of 2 microg/mL or more. Intermediately resistant strains (MIC 1-2 microg/mL) are also relatively sensitive depending on antibiotic concentration. Intermediate antibiotic susceptibility is concentration dependent. Antibiotic concentration at various body sites is determined by pharmacokinetic considerations. Except for very highly resistant strains, the treatment of penicillin-resistant S. pneumoniae causing bacteremia, sinusitis, otitis, bronchitis, or community-acquired pneumonia remains penicillin or any beta-lactam. Only in pneumococcal meningitis caused by penicillin-resistant pneumococci does the clinician have to use care in selecting an antipneumococcal antibiotic with adequate cerebrospinal fluid penetration and favorable kill ratios. Clinicians should be selective in antibiotic selection to minimize further decreases in penicillin susceptibility to S. pneumoniae. This is best achieved by using low-resistance potential antibiotics oral/intravenous mono-therapy at the full recommended dose. Therapeutic failure may occur in using lower doses at certain body sites. Macro-lides as monotherapy or as part of combination therapy should be minimized. Optimal therapy for non-central nervous system pneumococcal infection is with a respiratory quinolone (eg, levofloxacin, gatifloxacin, moxifloxacin), clindamycin, doxycycline, third-generation cephalosporins. For highly resistant pneumococci, levofloxacin, gatifloxacin, moxifloxacin, cefepime, meropenem, vancomycin, or linezolid may be used.