The microbial genetics of antibiotic cycling

Myths and Misconceptions around Antibiotic Resistance: Time to Get Rid of Them

The antibiotic resistance arena is fraught with myths and misconceptions, leading to wrong strategies to combat it. It is crucial to identify them, discuss them in light of current evidence, and dispel those that are unequivocally wrong. This article proposes some concepts that may qualify as misconceptions around antibiotic resistance: the susceptible-resistant dichotomy; that incomplete antibiotic courses cause resistance; that resistance "emerges" in patients and hospitals; that antibiotics are mostly abused clinically; that resistance is higher in countries that use more antibiotics; that reducing antibiotic usage would reduce resistance; that financial incentives would "jumpstart" research and development of antibiotics; that generic and "original" antibiotics are the same; and that new anti-infective therapies are just around the corner. While some of these issues are still controversial, it is important to recognize their controversial status, instead of repeating them in specialized literature and lectures and, especially, in the planning of strategies to cope with resistance.

Decalogue for the selection of oral antibiotics for lower respiratory tract infections

Lower respiratory tract infections, including chronic obstructive pulmonary disease exacerbations (COPD-E) and community acquired pneumonia (CAP), are one of the most frequent reasons for consultation in primary care and hospital emergency departments, and are the cause of a high prescription of antimicrobial agents. The selection of the most appropriate oral antibiotic treatment is based on different aspects and includes to first consider a bacterial aetiology and not a viral infection, to know the bacterial pathogen that most frequently cause these infections and the frequency of their local antimicrobial resistance. Treatment should also be prescribed quickly and antibiotics should be selected among those with a quicker mode of action, achieving the greatest effect in the shortest time and with the fewest adverse effects (toxicity, interactions, resistance and/or ecological impact). Whenever possible, antimicrobials should be rotated and diversified and switched to the oral route as soon as possible. With these premises, the oral treatment guidelines for mild or moderate COPD-E and CAP in Spain include as first options beta-lactam antibiotics (amoxicillin and amoxicillin-clavulanate and cefditoren), in certain situations associated with a macrolide, and relegating fluoroquinolones as an alternative, except in cases where the presence of Pseudomonas aeruginosa is suspected.

Fitness costs associated with the acquisition of antibiotic resistance

Acquisition of antibiotic resistance is a relevant problem for human health. The selection and spread of antibiotic-resistant organisms not only compromise the treatment of infectious diseases, but also the implementation of different therapeutic procedures as organ transplantation, advanced surgery or chemotherapy, all of which require proficient methods for avoiding infections. It has been generally accepted that the acquisition of antibiotic resistance will produce a general metabolic burden: in the absence of selection, the resistant organisms would be outcompeted by the susceptible ones. If that was always true, discontinuation of antibiotic use would render the disappearance of resistant microorganisms. However, several studies have shown that, once resistance emerges, the recovery of a fully susceptible population even in the absence of antibiotics is not easy. In the present study, we review updated information on the effect of the acquisition of antibiotic resistance in bacterial physiology as well as on the mechanisms that allow the compensation of the fitness costs associated with the acquisition of resistance.

Extended follow-up of an antibiotic cycling program for the management of febrile neutropenia in a hematologic malignancy and hematopoietic cell transplantation unit

BACKGROUND

Febrile neutropenia is a common complication during treatment of hematological malignancies and hematopoietic cell transplantation. Empiric antibiotic therapy in this setting, while standard of care, commonly leads to microbial resistance. We have previously shown that cycling antibiotics in this patient population is feasible. This report provides long-term follow-up of cycling antibiotics in this patient population.

METHODS

In a prospective cohort of hematological malignancy patients with neutropenic fever, we sought to evaluate the role of empiric antibiotic cycling in preventing antibiotic resistance. Antibiotic cycling was initiated in March 2002 and, until June 2005, antibiotics were cycled every 8 months (Cycling Period A). From July 2005 to December 2009, antibiotics were cycled every 3 months (Cycling Period B). The rates of bacteremia, resistance, and complications were compared to a retrospective cohort (Pre-cycling Period).

RESULTS

The rate of gram-negative bacteremia decreased when compared to Cycling Periods A and B (5.3 vs. 2.1 and 3.3 episodes/1000 patient-days, respectively, P < 0.0001), most likely owing to implementation of quinolone prophylaxis. The resistance profile of the gram-negative organisms isolated remained stable over the 3 time periods, with the exception of an increase in quinolone resistance during the cycling periods. Gram-positive bacteremia rates remained stable, but vancomycin-resistant Enterococcus (VRE) increased significantly (0.1 vs. 1.0 and 1.6 episodes/1000 patient-days, respectively, P = 0.005) during cycling periods. Mortality rates were comparable.

CONCLUSIONS

Antibiotic cycling for neutropenic fever was effectively implemented and followed over an extended time period. Gram-negative resistance remained stable, but there is some concern for selection of resistant gram-positive bacteria, specifically VRE. Although antibiotic cycling did not seem to cause resistance in our study, further study is necessary to clarify the effect of cycling on antibiotic resistance, patient outcomes, and hospital cost.

Microbiological and epidemiological characterization of imipenem-resistant Pseudomonas aeruginosa strains from a Brazilian tertiary hospital: report from the SENTRY Antimicrobial Surveillance Program

OBJECTIVES

To evaluate the antimicrobial susceptibility profile, the genetic similarity, and the mechanisms of carbapenem resistance among imipenem-resistant Pseudomonas aeruginosa isolates collected from a Brazilian tertiary teaching hospital.

METHODS

Seventy-eight consecutive samples of P. aeruginosa were evaluated during 2000 and 2001. The antimicrobial susceptibility was evaluated by reference broth microdilution methods and the imipenem-resistant isolates were screened for metallo-beta-lactamase (MbetaL) production throughout disc approximation test and MbetaL Etest strips and isolates with positive screen test result were submitted to PCR assays using primers blaIMP-1, bla VIM-1, blaVIM-2 e blaSPM-1. The genetic similarity of MbetaL-producing strains was evaluated by automated ribotyping for epidemiological typing purpose.

RESULTS

Resistance rates were high to the majority of antimicrobial agents tested except polymyxin B, which inhibited all samples at the Clinical and Laboratory Standards Institute breakpoint (< or = 2 microg/ml). Twenty-nine (37.2%) isolates were resistant to imipenem and these isolates showed great genomic variability. MbetaL production was demonstrated in two imipenem-resistant isolates, which were detected using blaSPM-1 and blaIMP-2-specific primers. Sequence analysis revealed the presence of blaSPM-1 and a novel blaIMP-type gene, blaIMP-16.

CONCLUSION

The results of this study showed high resistance rates to the majority of antimicrobial agents among P. aeruginosa samples. High imipenem resistance rates were probably due to continuous selection of resistant mutants. The production of MbetaL did not represent a frequent mechanism of carbapenem resistance in this medical center; but a novel MbetaL was identified. Continued antimicrobial surveillance and infection control measures should be emphasized to minimize the emergence and dissemination of antimicrobial resistance.

The clinical impact of antibacterial prophylaxis and cycling antibiotics for febrile neutropenia in a hematological malignancy and transplantation unit

Febrile neutropenia is an expected complication during treatment of aggressive hematological malignancies and hematopoietic cell transplantation. We conducted a prospective cohort trial to determine the effects and safety of prophylactic fluoroquinolone administration, and rotation of empiric antibiotics for neutropenic fever in this patient population. From March 2002 through 2004, patients were treated with prophylactic levofloxacin during prolonged neutropenia, and a cycling schedule of empiric antibiotic therapy for neutropenic fever was initiated. The rates of bacteremia, resistance and complications were compared to a retrospective cohort of previously treated patients. The rate of gram-negative bacteremia decreased after the initiation of prophylactic levofloxacin (4.7 vs 1.8 episodes/1000 patient days, P<0.05). Gram-positive bacteremia rates remained unchanged, but more isolates of Enterococcus faecium were resistant to vancomycin after the intervention began. Resistance to the antibiotic agents used in the rotation did not emerge. There was no change in mortality during the intervention period. A prophylactic and cycling antibiotic schedule was successfully implemented on a hematological malignancy and hematopoietic cell transplant unit. gram-negative bacteremia was significantly decreased, without emergence of resistance. Concerns with Gram-positive resistance will require further observation.

Antibiotic resistance in the intensive care unit: a primer in bacteriology

The clinical use of potent, well-tolerated, broad-spectrum antibiotics has been paralleled by the development of resistance in bacteria, and the prevalence of highly resistant bacteria in some intensive care units is despairingly commonplace. The intensive care community faces the realistic prospect of untreatable nosocomial infections and should be searching for new approaches to diagnose and manage resistant bacteria. In this review, we discuss some of the relevant underlying biology, with a particular focus on genetic transfer vehicles and the relationship of selection pressure to their movements. It is an attempt to demystify the relevant language and concepts for the anaesthetist and intensivist, to explain some of the reasons for the emergence of resistance in bacteria, and to provide a contextual basis for discussion of management approaches such as selective decontamination and antibiotic cycling.

Antibiotic cycling: more than it might seem?

In the present battle against the rising tide of resistance, several interventions have been proposed to help control the situation. One of these is a process of planned antibiotic restriction, introduced through cycling drug selection based on local surveillance. Although such antibiotic cycling has been the subject of much discussion for 20 years, there are relatively few data available to assess its worth. A recent systematic review found only four studies worthy of inclusion and concluded that antibiotic cycling could not, at present, be promoted as a methodology to control resistance. This paper considers the complete literature and through demonstrating consistent benefits across the breadth and depth of the findings, suggests that whereas further work is required, nevertheless antibiotic cycling-as part of a suite of control measures-is a valid option.

Antibiotic cycling or rotation: a systematic review of the evidence of efficacy

Of the interventions designed to reduce antibiotic resistance rates in hospitals, one that is currently attracting considerable interest, particularly in the intensive care unit setting, is antibiotic cycling or rotation. Cycling is the scheduled rotation of one class of antibiotics with one or more different classes exhibiting comparable spectra of activity; in order to fulfil the definition, the cycle must be repeated. Following a search of the literature we identified 11 articles in which the authors claimed to have evaluated the efficacy of this intervention. Only four were suitable for review, but, owing to multiple methodological flaws and a lack of standardization, the results of these studies do not permit reliable conclusions regarding the efficacy of cycling. Further studies are therefore required in order to resolve this question. However, before such studies can be undertaken, there are a great many issues relating to cycling which must be addressed. For the time being, we advise against the routine implementation of this measure as a means of reducing antibiotic resistance rates.

Appropriate use of antimicrobial agents: challenges and strategies for improvement

The use of inadequate empirical antimicrobial therapy is common in intensive care unit patients and contributes to a number of poor outcomes. Selecting appropriate antimicrobial therapy is complicated by many factors, including the large number of agents available, the presence of resistant organisms, and the general desire among practitioners to use the most focused therapy available. An important aspect of appropriate antimicrobial use is prompt initiation of adequate empirical therapy, which has been shown to improve mortality rates in hospitalized patients with pneumonia and other serious infections. Other key strategies include streamlining antimicrobial therapy when a pathogen is identified and switching from intravenous to oral therapy when clinically indicated. In addition, antibiotic rotation (or cycling) has been evaluated in several trials as a means to minimize resistance. Promoting appropriate antimicrobial therapy ultimately will require a multidisciplinary, system-oriented, institution-specific approach because each intensive care unit has its own unique flora and antimicrobial resistance patterns.

Moving from recommendation to implementation and audit: part 2. Review of interventions and audit

There are multiple interventions available that may help to control the development and spread of resistance to antimicrobial agents in bacteria implicated in community-acquired respiratory tract infections. Unfortunately, very few studies have assessed the effectiveness of these interventions using objective end-points, such as reduction in resistance rates and improvement in clinical outcomes. Most interventions are centered on reducing inappropriate or unnecessary use of antibiotics; others focus on reducing disease burden and bacterial colonization. With regard to antibiotic use, efforts should be concentrated at both the prescriber and consumer levels. Interventions that target prescribers include: provision of educational materials; strategies and tools to improve diagnosis; implementation of practice guidelines; personalized interactive sessions with feedback on the practice profile; and use of delayed prescription and alternative prescribing strategies. Optimal results are usually obtained when these interventions are combined with consumer education. Regulatory interventions (e.g. licensing regulations and controlled access to drugs), restrictions in the use of agents for growth promotion in animals, and use of nonantimicrobial therapies (e.g. probiotics) may help further to reduce inappropriate antibiotic use and thereby decrease the selective pressure for development of resistance. Infection-control strategies, public health measures, vaccination programs, and new antibiotics all have a role in minimizing the spread of resistant organisms. Ideally, resistance-control programs should include predefined criteria for success and integral audit processes based on objective end-points (antibiotic use, resistance trends, and health outcomes). Standardization of data collection is imperative so that the relative merits of various interventions can be compared. Effective implementation and audit of interventions is often difficult in developing countries owing to poor health-care infrastructures, lack of resources, poor education/training, and minimal regulatory controls on the supply and quality of antimicrobials. Substantial support from governments and health-care organizations across the globe is required to initiate and sustain effective intervention programs to control antimicrobial resistance.

Combating bacterial resistance in otorhinolaryngology

Bacterial resistance appears to be an ever-increasing problem and is threatening to spiral out of control. The scare caused by the rapid spread of methicillin-resistant Staphylococcus aureus among hospitals in the UK is the most recent. Otorhinolaryngology is deeply involved in this problem, as one of the reasons often cited for increasing bacterial resistance is the use of antibiotics in suspected bacterial infections in ear, nose and throat by primary care physicians. This speciality is also involved in the development of guidelines for antimicrobial use by primary and secondary care. This review attempts to discuss the reason for the development of antimicrobial resistance especially in relation to otorhinolaryngology, what can be done to contain this menace and the surveillance system developed to monitor the trend in the development of bacterial resistance.

Epidemiology of bacterial resistance in gastro-intestinal pathogens in a tropical area

During 1999-2000 a total of 4131 faecal specimens were collected and analysed at the medical centre St. Camille at Ouagadougou. Eight hundred and twenty-six (8.0%) grew significant bacteria. Escherichia coli (35%), Salmonella spp. (15%) and Shigella spp. (10%) were most frequently isolated. A large number of E. coli strains were resistant to aminopenicillins (>90%) and cotrimoxazole (80%); for Yersinia spp the resistance was 80 and 25%, respectively. Norfloxacin was the most active antibiotic but was rarely used. The study showed that it is necessary to create antibiotic-resistance surveillance centres in developing countries so that therapy may be appropriate and the spread of antibiotic resistance to other developed countries via increased emigration may be reduced.

The effect of antibiotic rotation on colonization with antibiotic-resistant bacilli in a neonatal intensive care unit

OBJECTIVE

This study was designed to test whether rotation of antibiotics can reduce colonization with resistant Gram-negative bacilli in a neonatal intensive care unit (NICU).

METHODS

A monthly rotation of gentamicin, piperacillin-tazobactam, and ceftazidime was compared with unrestricted antibiotic use in side-by-side NICU populations (rotation team vs control team). Pharyngeal and rectal samples were obtained 3 times a week and tested for Gram-negative bacilli resistant to each of the rotation antibiotics. Pulsed-field gel electrophoresis analysis determined the numbers of genetically discordant resistant organisms on each team. The association between colonization with a resistant bacillus (the primary outcome) and team assignment was tested.

RESULTS

A total of 1062 infants were studied during a 1-year period. A total of 10.7% infants on the rotation team versus 7.7% on the control team were colonized with a resistant bacillus. No interteam differences were distinguishable when the numbers of genetically discordant resistant organisms were normalized to the total number of team admissions. The incidence of nosocomial infection and mortality also were similar across teams.

CONCLUSION

These data indicate that rotation of parenteral antibiotics according to the applied protocol has no detectable effect in decreasing the reservoir of resistant Gram-negative bacilli in a tertiary-care NICU.

Infection in the intensive care unit: prevention strategies

PURPOSE OF THE REVIEW

Nosocomial infections remain among the most common treatment complications, particularly in intensive care unit patients. In many countries antibiotic resistance is increasingly hampering treatment of these infections. Preventive strategies have therefore become more important and have been directed both against the development of specific infections and against the spread of antibiotic-resistant pathogens. The present review addresses recent data on the latter issue. In particular, we discuss the first approaches to use mathematical modelling as a tool to analyse and guide strategies to prevent infection, and the effects of antibiotic cycling.

RECENT FINDINGS

Several mathematical models to address the dynamics of pathogen transmission in hospital settings have been developed. One of the models may allow quantification of the effects of different strategies to prevent infection in intensive care units, and another may be used to determine the relative importance of different colonization routes, without the need for expensive genotyping methods. The results of the first prospective studies on antibiotic cycling are inconclusive, and again mathematical modelling may help to provide testable hypotheses for such interventions. Finally, recent studies have shown that alcohol-based hand rubs are better than hand washing with soap and water for most hand disinfection purposes.

SUMMARY

The first results of use of mathematical modelling to guide infection control strategies should be subjected to prospective, empirical testing in order to determine their clinical usefulness. More rigorously designed studies are needed to determine the benefits of antibiotic cycling strategies. Hands should be disinfected with alcohol-based hand rubs, which should be available at each bedside.

Pilot study of antibiotic cycling in a pediatric intensive care unit

OBJECTIVE

This pilot study was performed to determine the safety and size of effect of antibiotic cycling to reduce colonization and infection with antibiotic-resistant bacteria.

DESIGN

Open, observational study.

SETTING

The study was performed in a 16-bed pediatric medical-surgical intensive care unit.

PATIENTS

Critically ill children requiring antibiotic therapy.

INTERVENTIONS

Three antibiotic classes were systematically cycled for 3-month intervals over 18 months. Antibiotic regimens were used for all empirical therapy and continued if the bacterial isolate was susceptible.

MEASUREMENTS

The primary outcome was colonization with antibiotic-resistant bacteria, determined by surveillance cultures obtained twice monthly from all patients in the unit. Rates of antibiotic-resistant, nosocomial blood stream infections, and risks of colonization over calendar time in the intensive care unit were also evaluated.

MAIN RESULTS

The cycling of broad-spectrum, empirical antibiotics was safe and did not generate increased antibiotic resistance nor select for new organisms. Over the study period, the trend in prevalence of children colonized with antibiotic-resistant bacteria was from 29% to 24% (p =.41). The effect on prevalence of resistant blood stream infections was similar (p =.29). Changes in individual risks of colonization with resistant bacteria over calendar time were consistent with the ecologic effect in size and direction.

CONCLUSIONS

Results of this pilot intervention suggest that cycling antibiotics may be a safe and viable strategy to minimize the emergence of antibiotic resistance in intensive care units. A definitive study will require a randomized and controlled trial of only four pediatric intensive care units over an 18-month period.

Rotating antibiotics in the intensive care unit: feasible, apparently beneficial, but questions remain

Rotating antibiotics in the intensive care unit may result in less infections caused by resistant organisms and in even less mortality. The selection of super-resistant organisms associated with the rotation strategy cannot be excluded, however, and many practical issues will have to be addressed before antibiotic rotation can be routinely recommended.

Extended-spectrum beta-lactamases in the 21st century: characterization, epidemiology, and detection of this important resistance threat

Beta-lactamases continue to be the leading cause of resistance to beta-lactam antibiotics among gram-negative bacteria. In recent years there has been an increased incidence and prevalence of extended-spectrum beta-lactamases (ESBLs), enzymes that hydrolyze and cause resistance to oxyimino-cephalosporins and aztreonam. The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel, unrelated beta-lactamases. Several different methods for the detection of ESBLs in clinical isolates have been suggested. While each of the tests has merit, none of the tests is able to detect all of the ESBLs encountered. ESBLs have become widespread throughout the world and are now found in a significant percentage of Escherichia coli and Klebsiella pneumoniae strains in certain countries. They have also been found in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Strains expressing these beta-lactamases will present a host of therapeutic challenges as we head into the 21st century.

Antimicrobial cycling: the future or a fad?

OBJECTIVE

To assess the current evidence of the value of cycling of antimicrobials to control the emergence of resistance or to reverse existing resistance to antimicrobials.

DATA SOURCES

Articles were obtained through a MEDLiNE search of the English-language literature from 1966 to January 2000. Additionally, references from retrieved publications were reviewed to identify further articles.

STUDY SELECTION AND DATA EXTRACTION

All investigations of switching between or cycling among antimicrobials were evaluated. Studies switching between or cycling among specific drugs or classes of drugs within institutional settings were included in this review.

DATA SYNTHESIS

Studies involving cycling among different aminoglycosides suggest that, although temporary decreases in resistance can be documented, resistance usually rebounds rapidly on completion of the cycle and return to the original agent. Switching between classes of antimicrobials has produced inconsistent results and has been shown to replace resistance to one agent with resistance to another. Mathematical models using both in vitro and clinical data have suggested that, due to residual resistance in the population, cycling among drug classes is unlikely to yield long-term reductions in antimicrobial resistance, especially if a high level of antimicrobial resistance exists.

CONCLUSIONS

Cycling among different antimicrobials to reverse resistance trends is currently not supported by published literature. Cycling to prevent the emergence of resistance may ultimately be more useful; however, no studies have evaluated this concept. Well-designed prospective studies are needed to evaluate the potential clinical value of antimicrobialcycling.

Detection of multiresistant ceftazidime-susceptible Klebsiella pneumoniae isolates lacking TEM-26 after class restriction of cephalosporins

A multitude of extended spectrum beta-lactamases (ESBLs) have evolved in response to the use of late generation cephalosporins. In those hospitals where Klebsiella pneumoniae and other bacteria possessing these enzymes flourish, many interventions have been applied to reduce this trend. We instituted a policy of class restriction of cephalosporins in our hospital in 1996 that led to a 44% reduction in ceftazidime-resistant K. pneumoniae hospital-wide and an 87% decrease in the surgical intensive care unit. Another interesting outcome of this strategy was the identification of multiresistant K. pneumoniae, which was now susceptible to ceftazidime. Characterization of these novel isolates demonstrated that the TEM-26 enzyme, which was responsible for ceftazidime resistance in our earlier described outbreak, was lacking in most of the isolates examined. Among the remaining ceftazidime-resistant K. pneumoniae, TEM-26 was also absent, and new enzymes that hydrolyze ceftazidime were detected. Loss of ceftazidime-hydrolyzing beta-lactamases was observed after in vitro passage of ceftazidime-resistant K. pneumoniae on antibiotic-free media. These findings suggest that class restriction of cephalosporins may increase susceptibility among extended-spectrum beta-lactamase-producing pathogens.

Intensive care unit antimicrobial resistance and the role of the pharmacist

Over the past 20 yrs, pharmacists have successfully integrated their services and expertise to gain acceptance as full members of pediatric, surgical, medical, and intensive care unit (ICU) patient care teams. The pharmacists' training in pharmacology, pharmacokinetics, pharmacodynamics, and pharmacoeconomics complements the expertise of other members of the patient care team. Generally, a strong background in infectious diseases and critical care also provides a focal point for clinical pharmacy service intervention. Although practitioners often focus on issues exclusively related to their specific hospital or ICU, the issues surrounding antibiotic resistance are more global and societal in nature. Medical, surgical, and pharmaceutical practices inside the hospital and ICU extend their influence into the community. Customs and practices of daily living in our society coupled with use of agents capable of altering microbial flora impact our hospital and ICU when patients from the community are admitted. The misuse of antibiotics and the lack of effective infection control programs are often identified as key components in the perpetuation of these phenomena. The focus for the pharmacist and the ICU team must be on the optimization of antibiotic use and infection control guidelines. This review will address the many issues that surround the appropriate use of antibiotics and what role the pharmacist can play in ensuring the optimal use of infection control measures in the ICU and hospital.

Antimicrobial management measures to limit resistance: A process-based conceptual framework

To curb the trend toward increasingly resistant microorganisms, we must at least ensure that antibiotics are used in accordance with the best available scientific evidence. Here we review the control and streamlining measures aimed at optimizing the use of antibiotics, placing an emphasis on their demonstrated effectiveness in the intensive care unit environment. Because of their wide variety, the measures have been organized along the process of choosing, dosing, delivering, and then adjusting the initial antibiotics according to the culture results. By clarifying the range of options available, this process-based conceptual framework assists in best adapting a creative mixture of control measures to a particular healthcare system. The framework also facilitates the overview of a proposed multidisciplinary antibiotic management program, thereby helping to secure the administrative and local provider support necessary for its implementation and continued improvement.

Is there a role for antibiotic cycling in the intensive care unit?

Antibiotic resistance of bacterial pathogens has emerged as one of the most important issues facing critical care practitioners. Resistance of many commonly encountered bacterial species is increasing and has been associated with greater administration of inadequate antimicrobial therapy to patients within intensive care units. This has resulted in greater patient morbidity, higher mortality rates, and increased healthcare costs. Methods to reduce antimicrobial resistance have focused on increasing adherence to infection control practices and improving antibiotic utilization. Antibiotic cycling is a strategy to reduce antimicrobial resistance by withdrawing an antibiotic or antibiotic class from use and subsequently reintroducing it at a later point in time. The main goal of cycling is to allow resistance rates for specific antibiotics to decrease, or at least remain stable, when their use is periodically eliminated from the intensive care unit.

Antimicrobial use and bacterial resistance

The current epidemic of bacterial resistance is attributed, in part, to the overuse of antibiotics. Recent studies have documented increases in resistance with over-use of particular antibiotics and improvements in susceptibility when antibiotic use is controlled. The most effective means of improving use of antibiotics is unknown. Comprehensive management programs directed by multi-disciplinary teams, computer-assisted decision-making, and antibiotic cycling have been beneficial in controlling antibiotic use, decreasing costs without impacting patient outcomes, and possibly decreasing resistance.

The impact of changing pathogens of serious infections in hospitalized patients

New epidemiological patterns are being observed for multidrug-resistant nosocomial organisms. Current problems include the appearance of resistance determinants in organisms that are virulent enough to cause infection in patients with normal host defenses. In addition, multidrug-resistant organisms are spreading from health care to community settings, and organisms from the community are spreading to health care settings. The appearance and spread of resistance can be examined both at a molecular level and on a larger scale involving several pathways. Potential pathways within institutions include the following: introduction of new strains from outside sources (e.g., patients or health care workers from other institutions); exchange of resistance determinants via genetic mutation or transfer of genetic material; emergence or selection of resistant strains following exposure to antimicrobials; and clonal dissemination. Strategies such as multidisciplinary management of infections, appropriate infection control measures, and surveillance of resistance patterns are necessary to address the problem of resistance.

A pilot study of antibiotic cycling in a hematology-oncology unit

OBJECTIVE

To determine the safety and treatment efficacy of cycling antibiotic regimens for prophylaxis or treatment of patients with profound neutropenia.

DESIGN

A prospective, nonrandomized, observational trial.

SETTING

A 20-bed adult hematology-oncology inpatient unit at a university referral hospital.

PATIENTS

Hospitalized adult patients with chemotherapy- or radiation-induced neutropenia (absolute neutrophil count less than 500 cells/mm3).

INTERVENTION

Between July 1994 and January 1996, 295 hospitalized patients were evaluated on an intent-to-treat basis for the cycling protocol. Of these, 271 were eligible and assigned to one of four antibiotic regimens being used at the time of enrollment: (1) ceftazidime+vancomycin; (2) imipenem; (3) aztreonam+cefazolin; (4) ciprofloxacin+clindamycin. Data on infection rates and types, and antibiotic resistance patterns, toxicity, and effectiveness were collected.

RESULTS

Twenty-four patients were excluded. Of the 271 evaluable patients, 123 (42%) were able to complete treatment on the assigned regimen. Of the 148 patients (50%) unable to do so, the reasons for failure included persistent fever (79%), breakthrough bacteremia (14%), and drug toxicity (7%). The antibiotic susceptibility profiles over the study period showed no increase in resistance. However, there was a marked increase in enterococcal infections.

CONCLUSIONS

Our data show no significant increase in side effects or decrease in efficacy while cycling antibiotics among neutropenic patients and thus support further study of its role.