DIMINISHED ACTIVITY OF CEFTIZOXIME IN COMPARISON TO CEFOTAXIME AND CEFTRIAXONE AGAINST STREPTOCOCCUS-PNEUMONIAE

Previous reports documenting the essentially identical spectra of acti vity of ceftizoxime, cefotaxime, and ceftriaxone prompted our hospital formulary committee to replace the latter two drugs with ceftizoxime on the basis of cost differences. However, we subsequently observed th at every one of 60 isolates of Streptococcus pneumoniae tested was les s susceptible to ceftizoxime than to either cefotaxime or ceftriaxone. The difference between minimal inhibitory concentrations (MICs) was g reatest for strains moderately or fully resistant to penicillin, which at our institution represent similar to 32% of all isolates of S. pne umoniae. Ten isolates with cefotaxime and ceftriaxone MICs of 2.0-6.0 mu g/mL had ceftizoxime MICs of greater than or equal to 256 mu g/mL. Time-kill kinetic studies assessing bactericidal activity confirmed th e diminished activity of ceftizoxime against penicillin-resistant isol ates of S. pneumoniae. Ceftizoxime should not be used to treat proven or suspected pneumococcal infection in areas where resistance to penic illin is prevalent.