Use of Broad-Spectrum Antimicrobials for the Treatment of Pneumonia in Seriously Ill Patients: Maximizing Clinical Outcomes and Minimizing Selection of Resistant Organisms

When to include polymyxins in the empirical antibiotic regimen in critically ill patients with fever? A decision analysis approach

We sought to approach a practical question: Should polymyxins be used in the initial empirical antibiotic regimen in the intensive care unit (ICU) patient with fever that is thought to be due to infection? By retrieving data from the literature and the WHONET Greece, we formulated a mathematical model to estimate the probability (Ptotal) that a gram-negative bacterium susceptible only to polymyxins is isolated from an ICU patient. Ptotal = P1 * P2 * P3 * P4, where Ptotal = total probability; P1 = probability that fever is due to infection; P2 = probability that infection is due to gram-negative bacteria; P3 = probability that the gram-negative bacterium is Acinetobacter baumannii, Pseudomonas aeruginosa, or Klebsiella pneumoniae; and P4 = probability that A. baumannii, P. aeruginosa, or K. pneumoniae is susceptible only to polymyxins. Using the information from our data sources, we estimated that P1 (before physician input in differential diagnosis) = 0.5, P2 = 0.523, P3 = 0.79, and P4 = 0.567, thus Ptotal = P1 * P2 * P3 * P4 = 0.5 * 0.523 * 0.79 * 0.567 = 0.117 = 11.7%. Based on this information and combining it with data regarding the attributable mortality of inappropriate empirical antimicrobial treatment, 4 to 5 patients in every 100 ICU patients will die if physicians do not include polymyxins in the initial empirical regimen in the ICU setting for an episode of fever due to infection. Polymyxins should probably be included in the empirical antibiotic regimen in the ICU setting in hospitals, where the observed probability that a gram-negative bacterium (A. baumannii, P. aeruginosa, or K. pneumoniae) is polymyxin-only-susceptible is close to that (50%) used in our model (based on the individual hospital data).

Development and persistence of antimicrobial resistance in Pseudomonas aeruginosa: a longitudinal observation in mechanically ventilated patients

Intubated patients frequently become colonized by Pseudomonas aeruginosa, which is subsequently responsible for ventilator-associated pneumonia. This pathogen readily acquires resistance against available antimicrobials. Depending on the resistance mechanism selected for, resistance might either be lost or persist after removal of the selective pressure. We investigated the rapidity of selection, as well as the persistence, of antimicrobial resistance and determined the underlying mechanisms. We selected 109 prospectively collected P. aeruginosa tracheal isolates from two patients based on their prolonged intubation and colonization periods, during which they had received carbapenem, fluoroquinolone (FQ), or combined beta-lactam-aminoglycoside therapies. We determined antimicrobial resistance phenotypes by susceptibility testing and used quantitative real-time PCR to measure the expression of resistance determinants. Within 10 days after the initiation of therapy, all treatment regimens selected resistant isolates. Resistance to beta-lactam and FQ was correlated with ampC and mexC gene expression levels, respectively, whereas imipenem resistance was attributable to decreased oprD expression. Combined beta-lactam-aminoglycoside resistance was associated with the appearance of small-colony variants. Imipenem and FQ resistance persisted for prolonged times once the selecting antimicrobial treatment had been discontinued. In contrast, resistance to beta-lactams disappeared rapidly after removal of the selective pressure, to reappear promptly upon renewed exposure. Our results suggest that resistant P. aeruginosa is selected in less than 10 days independently of the antimicrobial class. Different resistance mechanisms lead to the loss or persistence of resistance after the removal of the selecting agent. Even if resistant isolates are not evident upon culture, they may persist in the lung and can be rapidly reselected.

Antibacterial dosage in intensive-care-unit patients based on pharmacokinetic/pharmacodynamic principles

PURPOSE OF REVIEW

Selection of the best antibiotic dosage regimen in intensive-care-unit patients is a critical factor for decreasing morbidity and mortality rates. The integration of pharmacokinetics and pharmacodynamics is essential to establishing an adequate therapy. Many studies on this issue have been published in recent years due to its relevance, some of which are commented upon in this review.

RECENT FINDINGS

Several studies have shown that it is feasible to theoretically forecast pharmacodynamic outcomes and select the most adequate antibiotic therapy with Monte Carlo simulations. Moreover, new strategies such as the use of continuous or extended intravenous beta-lactam infusions may considerably improve therapeutic efficacy.

SUMMARY

Future studies are needed in patients to assess the influence of selecting antibiotic therapy based on the impact of pharmacokinetic/pharmacodynamic on mortality, morbidity, cost, etc. It would be of special interest to evaluate this impact on patients with infections caused by multiresistant pathogens, whose mortality rates are even higher. Moreover, although studies such as this would not be easy, mainly due to the large number of patients required to obtain statistically significant results, they should be strongly encouraged because of the possible clinical and economic benefits.

De-escalation in lower respiratory tract infections

PURPOSE OF REVIEW

The present article reviews recent data on the de-escalation of empirical antibiotic treatment on pneumonia, with special attention to newer strategies aimed at increasing adequacy and minimizing resistance emergence risks in ventilator-associated pneumonia.

RECENT FINDINGS

A de-escalation strategy is feasible in a large proportion of patients with pneumonia, and at least two reports have associated de-escalation with a significantly better survival. Combined with other strategies, such as using biomarkers (e.g. C-reactive protein or procalcitonin), antibiotic heterogeneity, adherence to local microbiological flora, objective clinical criteria of non-response and of clinical ventilator-associated pneumonia resolution, they contribute to rationalizing and individualizing antimicrobial therapy.

SUMMARY

A patient-based approach with prompt adequate empirical therapy, using broad-spectrum antibiotics based on reliable local microbiological data with streamlining as soon as microbiological data become available, allow outcomes to be improved and the emergence of resistance to be minimized.

The relationship between antimicrobial resistance and patient outcomes: mortality, length of hospital stay, and health care costs

There is an association between the development of antimicrobial resistance in Staphylococcus aureus, enterococci, and gram-negative bacilli and increases in mortality, morbidity, length of hospitalization, and cost of health care. For many patients, inadequate or delayed therapy and severe underlying disease are primarily responsible for the adverse outcomes of infections caused by antimicrobial-resistant organisms. Patients with infections due to antimicrobial-resistant organisms have higher costs (approximately 6,000-30,000 dollars) than do patients with infections due to antimicrobial-susceptible organisms; the difference in cost is even greater when patients infected with antimicrobial-resistant organisms are compared with patients without infection. Strategies to prevent nosocomial emergence and spread of antimicrobial-resistant organisms are essential.

Controlling multiple-drug-resistant organisms at the hospital level

Nosocomial infections due to multiple-drug-resistant (MDR) organisms are associated with poor patient outcomes and increased healthcare cost. The natural history of an MDR nosocomial infection can be characterised in four steps. First is the introduction of MDR organisms into the patient's normal flora as a consequence of inappropriate infection control practices. Second is the selection of MDR organisms due, in part, to inappropriate antibiotic therapy. Third is the development of an MDR infection due, in part, to inappropriate invasive techniques. The fourth step occurs when the patient has developed poor clinical outcomes due, in part, to inappropriate antibiotic therapy. At the local hospital level, a multidisciplinary MDR control programme should be developed with the goals to optimise local surveillance of MDR organisms, improve local infection-control practices, and control local antimicrobial use. Without achieving these three goals, hospitals will not be able to control the spread of MDR organisms.

Antimicrobial resistance: factors and outcomes

Antimicrobial resistance in the ICU is characterized by increasing overall resistance rates among gram-negative and gram-positive pathogens and increased frequency of multidrug-resistant organisms. In addition to basic principles of appropriate drug selection for empiric and definitive therapy, other specific strategies that may decrease problems of resistance through improved use of antimicrobials include appropriate application of pharmacokinetic and pharmacodynamic principles to antimicrobial use, aggressive dosing of antimicrobials, use of broad-spectrum and combination antimicrobial therapy for initial treatment, decreased duration of antimicrobial therapy, hospital formulary-based antimicrobial restrictions, use of antimicrobial protocols and guidelines, programs for restriction of target antimicrobials, scheduled antimicrobial rotation, and use of antimicrobial management programs. Combinations of various approaches may offer the best potential for effectively intervening in and reducing the spread of resistant pathogens in critically ill patients.