THERAPEUTIC IMPLICATIONS IN THE TREATMENT OF AURAL PSEUDOMONAS INFECTIONS BASED ON IN-VITRO SUSCEPTIBILITY PATTERNS

Objective: To examine the in vitro susceptibility patterns of aural is olates of Pseudomonas aeruginosa and to identify changes over a 4-year period. Design: Retrospective case series. Setting: The outpatient de partment at Children's Hospital of Pittsburgh (Pa), a tertiary referra l center. Patients: Ambulatory children younger than 18 years from who se ears P aeruginosa was isolated. Outcome Measures: The in vitro susc eptibility of aural isolates of P aeruginosa to ampicillin, cefotaxime , chloramphenicol, sulfisoxazole, ticarcillin, mezlocillin, gentamicin , tobramycin, cefazolin, tetracycline, piperacillin, nitrofurantoin, c ephalexin hydrochloride, ceftriaxone, cefuroxime axetil, and sulfameth oxazole-trimethoprim. Results and Conclusions: No changes were found i n the trends of the susceptibility patterns over the 4-year study peri od, with the exception of the semisynthetic penicillins, ticarcillin a nd mezlocillin. These two agents were found to be relatively ineffecti ve against the strains of P aeruginosa isolated in 1989 (59% and 18% s usceptibility, respectively). This finding is in contrast to their eff ectiveness over the remainder of the study period (96% and 90% suscept ibility, respectively), which was excellent. These observations likely reflect a change in the breakpoints for the minimal inhibitory concen trations between these periods. The intravenous agent with the best su sceptibility profile was piperacillin (96%). Of the aminoglycosides te sted, 94% of the isolates were sensitive to tobramycin, as opposed to only 79% for gentamicin. This finding may have significance when one i s empirically selecting ototopical therapy, since both tobramycin and gentamicin are available as topical preparations. Of the oral agents, the combination of sulfamethoxazole-trimethoprim was most effective (4 6%).