Activities ofVarious ,-Lactams andAminoglycosides, Alone andinCombination, Against Isolates ofPseudomonas aeruginosa fromPatients withCystic Fibrosis

Theinhibitory andbactericidal activities ofcarbenicillin, ticarcillin, moxalactam,cefoperazone, azlocillin, piperacillin, ceftazidime, andthree aminoglycosides, alone andinvarious combinations, weredetermined against 60isolates of Pseudomonas aeruginosa fromthesputumofpatients withcystic fibrosis. Ceftazidime was themostactive ,B-lactam, withminimuminhibitory andbactericidal concentrations for90oofisolates of4,ug/ml. Moxalactam was theleast active ofthenew -lactams, withactivity equivalent tothat ofcarbenicillin; each hada minimuminhibitory concentration for90%ofisolates of64,ug/ml anda minimumbactericidal concentration for90%ofisolates of128p.g/ml. All combinations ofan aminoglycoside plus a P-lactam showed favorable inhibitory effects. Combinations of,B-lactams showedmostly addition or indifference. Although little antagonism was seen withcombinations of 3-lactams or with aminoglycoside ---lactam combinations, no consistent advantage off-lactam combinations was demonstrated invitro. Theseresults suggest several single drugs andcombinations thatmerit clinical evaluation incystic fibrosis patients withPseudomonas pulmonary infections. Oftherecently introduced 3-lactam derivatives, azlocillin, cefoperazone, ceftazidime, moxalactam, andpiperacillin haveahigher orderofactivity thantheir predecessors against notonly theEnterobacteriaceae