Antimicrobial Susceptibility Survey: DISCUSSION
The prevalence of resistance of P aeruginosa strains to the nine antimicrobials tested was relatively low among hospital strains. Strains from community sources were fully sensitive to four of the nine drugs. No local or regional data could be found in the literature to which resistance rates among P aeruginosa could be compared. However, increasing resistance to the different antipseudomonal drugs particularly among hospital strains has been reported worldwide, and this presents a serious therapeutic problem in the management of diseases due to these organisms. Reports from Turkey have shown P aeruginosa resistance rates of 73.6% and 68.0% to piperacillin and gentamicin, respectively. In Russia, 79% and 75% of isolates were found to be resistant to generic piperacillin and gentamicin, respectively, while from Bangladesh, rates of resistance of 51.0% to tobramycin and 21.0% to ciprofloxacin tablet have been recorded.
Eight of the nine antipseudomonal drugs can only be given parenterally, and resistance to these parenteral agents is slowly increasing in our hospital. The only oral antipseudomonal agent tested in this study, ciprofloxacin, recently became available in the hospital but widely available at local pharmacies. However, although recently available in the hospital formulary, ciprofloxacin was still used, because relatives of some inpatients were able to purchase the drug at local pharmacies. Resistance in the hospital environment may be affected by the frequent or infrequent availability of antimicrobials as well as the prudent use of these drugs. Although the resistance rate of P aeruginosa is relatively low, the overall resistance rate among other gram-negative organisms at this institution and at a sister institution about 28 miles away has been increasing. This may be related to the yearly demand and increase in antimicrobial consumption. For example, the total cost for antimicrobials alone at this institution for 1998 was approximately TT$2.2 million [TT$6 = US$1]. In 1999, the cost rose to approximately TT$3.6 million, an increase of about 39%. (Data from the hospital pharmacy records and the Ministry of Health). If the rate of consumption continues, figures for 2000-2002 may show a greatly increased cost for antimicrobials alone.
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The community isolates of P aeruginosa strains causing urinary tract infections were recovered from male patients with chronic in-dwelling urethral catheters. These patients are treated with antipseudomonal antimicrobials in the outpatient clinics. These men have prostatic diseases and are either unfit for surgery, awaiting surgery, or have refused surgery. Catheters are changed once every six weeks in most cases, or earlier if complaints of fever gross hematuria or acute blockage are made. Excessive prescribing of a single drug often leads to resistance and a decrease in the usefulness of the antimicrobial. Antimicrobial administration and the presence of in-dwelling urethral catheters correlate with the development of bacterial resistance.
One significant observation in this study was the increasing resistance to cefepime. This drug was recently introduced into the country but was not in the hospital formulary during the study period, and 7.5% of P aeruginosa strains have been found to be resistant. Cefepime was supplied as samples by drug representatives to selected clinicians in the hospitals in an effort to promote the use of the drug. Although communication between the hospital laboratories and the clinicians have been good, the absence of an antibiotic policy at most hospitals in Trinidad and the aggressive sales pitch by most drug representatives have contributed to poor compliance with respect to restrictive use of this drug and others. Cefepime is a fourth-generation cephalosporin, which has enhanced stability in the presence of Bush-Jacob-Medeiros group-1 p-lactamases. These P-lactamases will inactivate all other currently available cephalosporins drug. Therefore, cefepime is active against stably derepressed class-1 p-lactamases of P aeruginosa and members of the Enterobacteriaceae family. Cefepime has also been shown to be active against most strains of ceftazidime-resistant P aeruginosa?
The study showed that the overall resistance pattern of P aeruginosa to the antimicrobial agents was relatively low. It was also evident from the results that resistance to the relatively new drug, cefepime, may present a serious problem in the near future and that policies governing antimicrobial use in the country be formulated. In the meantime, physicians in both hospital and community practices must exercise adequate care in the prescribing of antimicrobials, especially in cases of P aeruginosa infections, to prevent emergence of resistant strains.
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