Selection of resistant variants of respiratory pathogens by quinolones

Quinolones are widely used in the treatment of respiratory tract infections . However, some disquiet has been expressed over using quinolones for commu nity-acquired pneumonia since their activity is generally rather poor again st Streptococcus pneumoniae. In addition, it is known that resistant varian ts emerge at a fairly high frequency during exposure of Enterobacteriaceae to quinolones; if this also occurred during quinolone treatment of communit y-acquired pneumonia it could lead to an increased risk of clinical failure . We therefore determined the selection rate of quinolone-resistant variant s for six strains of S. pneumoniae, Haemophilus influenzae and Moraxella ca tarrhalis with nalidixic acid (except for S. pneumoniae), ciprofloxacin, of loxacin and levofloxacin. We were only able to select resistant variants at low frequency from two of the six strains of S. pneumoniae with ciprofloxa cin: no resistant variants were selected by either ofloxacin or levofloxaci n. Variants of H. influenzae and M. catarrhalis with decreased susceptibili ty to quinolones were produced both with more strains and with a greater fr equency; however, these variants still remained susceptible according to th e NCCLS guidelines. Our study suggests that resistant variants of S. pneumo niae are relatively unlikely to occur in individuals treated with fluoroqui nolones especially if they are given quinolones with enhanced anti-Gram-pos itive activity compared to ciprofloxacin. (C) 1999 Published by Elsevier Sc ience B.V. and International Society of Chemotherapy. All rights reserved.