IN-VITRO ANTIMICROBIAL EFFECT AGAINST STREPTOCOCCUS-PNEUMONIAE OF ADDING RIFAMPIN TO PENICILLIN, CEFTRIAXONE, OR 1-OFLOXACIN

Adding rifampin to penicillin or 1-ofloxacin diminished the rate at wh ich these antibiotics killed 21 clinical isolates of Streptococcus pne umoniae in vitro. A less pronounced inhibitory effect was observed whe n rifampin was added to ceftriaxone. Synergy was not observed for any bacterial isolate. The in vitro demonstration of indifference or antag onism using these antibiotic combinations argues against the empirical addition of rifampin to beta-lactams or fluoroquinolones in treating serious pneumococcal infections.