PD 117588 is a quinolone against bacterial isolates from cancer patients. PD 117558 has a broad antimicrobial spectrum with excellent activity against all Gram-positive isolates (including methicillin-resistant Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus faecalis and Group JK-corynebacteria). PD 117588 is also extremely active against Gram-negative bacilli with the exception of Pseudomonas aeruginosa against which ciprofloxacin was more active. PD 117588 has lower minimal inhibitory concentrations for most organisms tested than either imipenem or ceftazidime.