RP-59,500 (QUINUPRISTIN DALFOPRISTIN) - A NEW STREPTOGRAMIN WITH POTENT ACTIVITY AGAINST PENICILLIN-RESISTANT STREPTOCOCCUS-PNEUMONIAE/

Streptococcus pneumoniae is a major pathogen in community-acquired pne umonia and meningitis and, in pediatric patients, especially in acute otitis media. The traditional use of penicillin G as first-line therap y for pneumococcal infections has changed dramatically in the past 20 years as the result of resistance to beta lactams on a global scale. T his has necessitated the development of classes of antimicrobials to c ircumvent the resistance problem. RP 59500 is a new streptogramin comb ination of quinupristin and dalfopristin with activity against aerobic gram-positive cocci. The present study tested the in vitro activity o f RP 59500 against 481 isolates of S, pneumoniae, of which 70% were pe nicillin-susceptible, 23% intermediately resistant to penicillin, and 7% fully resistant to penicillin. Susceptibility studies showed that a ll isolates were susceptible to RP 59500, which had activity equal to that of vancomycin. RP 59500 was more active than ceftriaxone, cefurox ime, cefotaxime, cefpodoxime, and erythromycin, particularly against i ntermediately resistant and fully resistant strains. Time-kill kinetic studies indicated that RP 59500 was rapidly bactericidal against all test isolates regardless of penicillin susceptibility. RP 59500 may be an excellent alternative antimicrobial for use against penicillin-res istant pneumococcal infections.