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Emergence of highly antibiotic-resistant Pseudomonas aeruginosa in relation to duration of empirical antipseudomonal antibiotic treatment.

OBJECTIVE
This study examines antibiotic resistance in Pseudomonas aeruginosa in hospitalized patients in relation to prior empirical antibiotic therapy.


DESIGN
Two retrospective case analyses comparing patients who manifested P aeruginosa with differing patterns of antibiotic resistance.


SETTING AND PARTICIPANTS
Patients acquiring P aeruginosa in a community hospital.


MEASURES
Patients were compared on duration of hospitalization and days and doses of antibiotics prior to recovery of P aeruginosa. Patients were grouped, based on susceptibility patterns of their P aeruginosa isolates classified as follows: (1) fully susceptible (susceptible to all classes of antipseudomonal antibiotics [SPA]), (2) multidrug-resistant (resistant to two classes of antipseudomonal antibiotics [MDRPA]), or (3) highly drug-resistant (resistant to > or = 6 classes of antipseudomonal antibiotics [HRPA]). To control for duration of hospitalization, antibiotic treatments of HRPA and SPA patients were compared during the first 21 days of care.


RESULTS
Prior to recovery of HRPA, six HRPA patients received greater amounts of antibiotics, both antipseudomonal and non-antipseudomonal, than did six SPA patients prior to recovery of SPA. For 14 patients with hospital-acquired SPA who later manifested MDRPA, duration and dosage of antipseudomonal antibiotics, but not all antibiotics, were significantly higher for the SPA-to-MDRPA interval than for the preceding admission-to-SPA interval. The median duration of antipseudomonal antibiotic treatment prior to the recovery of P aeruginosa was 0 days for SPA, 11 days for MDRPA, and 24 days for HRPA.


CONCLUSION
Duration of empirical antipseudomonal antibiotic treatment influences selection of resistant strains of P aeruginosa; the longer the duration, the broader the pattern of resistance.