Comparison of ampicillin-sulbactam and imipenem-cilastatin for the treatment of acinetobacter ventilator-associated pneumonia

Antimicrobial resistance among gram-negative organisms in the intensive care unit

PURPOSE OF REVIEW

We review the hospital-acquired gram-negative organisms commonly encountered among patients in the intensive care unit and discuss pertinent surveillance data, resistance mechanisms and patterns, and optimal treatment regimens for these pathogens.

RECENT FINDINGS

There has been a notable increase in antibiotic resistance among gram-negative intensive care unit pathogens. Data from surveillance programs such as National Nosocomial Infections Surveillance System, Intensive Care Antimicrobial Resistance Epidemiology, and others have documented undesirable trends in antibiotic resistance, indicating decreasing efficacy of antibiotic classes such as third-generation cephalosporins, carbapenems, and fluoroquinolones, The increased prevalence of extended-spectrum beta-lactamases has contributed to the finding of multidrug resistance among bacteria such as Klebsiella and Escherichia coli. Furthermore, organisms such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia display intrinsic resistance to many antibiotics, making selection of optimal therapy difficult. Studies have correlated infection by these organisms with prior antibiotic exposure, and containment of the spread of infection can be achieved by careful antibiotic use and infection control practices.

SUMMARY

Antibiotic resistance continues to rise among hospital-acquired gram-negative pathogens. Optimal management of these infections requires knowledge of local epidemiology and practices to control their spread.

Tetracyclines for treating multidrug-resistant Acinetobacter baumannii ventilator-associated pneumonia

OBJECTIVE

To report the use of tetracyclines for the treatment of multidrug-resistant Acinetobacter baumannii ventilator-associated pneumonia (VAP).

DESIGN

Observational case series.

SETTING

. The Presley Regional Trauma Center located within the Regional Medical Center, Memphis, Tennessee, USA.

PATIENTS AND PARTICIPANTS

Seven critically ill trauma patients with VAP caused by A. baumannii isolates that were resistant to all antibiotics tested except for doxycycline or minocycline.

INTERVENTIONS

Patients were treated with IV doxycycline or minocycline for an average of 13.5 (range 9-20) days.

MEASUREMENTS AND RESULTS

Doxycycline or minocycline was successful in six of seven patients.

CONCLUSIONS

Doxycycline or minocycline may be effective for treating multidrug-resistant A. baumannii VAP.

Treatment of Acinetobacter spp infections

Acinetobacter spp. are predominantly nosocomial pathogens of growing importance. One of their important features is antimicrobial resistance that includes beta-lactams, aminoglycosides and quinolones. Imipenem, considered the most effective drug against Acinetobacter spp., is not universally active against clinical isolates and therapeutic options are necessary. In vitro studies demonstrate the activity of beta-lactamase inhibitors with direct antimicrobial activity, polymyxins, doxycycline and rifampin. Synergy of various combinations has been demonstrated in vitro. Experimental models of infection in mice and rabbits show the efficacy of rifampin and doxycycline. Colistin did not lead to good results in a mouse pneumonia model. There are no randomised, controlled studies on the treatment of Acinetobacter spp. infections. Retrospective comparative studies suggest that ampicillin-sulbactam may be comparable to imipenem in the treatment of pneumonia and bacteraemia. There are a few uncontrolled studies using ampicillin-sulbactam and one study with colistin with results that suggest that they may be acceptable options to treat multi-resistant infections.

Considerations in control and treatment of nosocomial infections due to multidrug-resistant Acinetobacter baumannii

We sought to control infection due to multidrug-resistant Acinetobacter baumannii (MDR-Ab) by identifying isolates as clonally related, leading to enhanced infection-control measures, including cohorting, surveillance, contact precaution, initial therapy with ampicillin/sulbactam and local polymyxin B, and, more recently, therapy with synergistic antibiotic combinations. Class restriction of cephalosporins has been associated with a reduction in cephalosporins-cephamycin-carbapenem resistance among nosocomial Klebsiella isolates. This has been supplemented by restriction of carbapenem use after an initial 24-h period in an effort to reduce the selection of porin-deficient, carbapenem-resistant A. baumannii and Pseudomonas aeruginosa. Evidence is reviewed suggesting that eradication of MDR-Ab nosocomial colonization may prevent subsequent infection. Relatively few standard antibacterial drugs remain active against MDR-Ab. Published clinical results of therapy with these agents are reviewed, and in vitro evidence of synergy between them is presented that suggests that combination therapy should be studied for enhanced clinical activity.

Treatment of multidrug-resistant Acinetobacter baumannii ventilator-associated pneumonia (VAP) with intravenous colistin: a comparison with imipenem-susceptible VAP

We prospectively evaluated the efficacy and toxicity of intravenously administered colistin in 35 episodes of ventilator-associated pneumonia (VAP) due to multidrug-resistant Acinetobacter baumannii. Microbiological diagnosis was performed with use of quantitative culture. In 21 patients, the episodes were caused by a strain susceptible exclusively to colistin (the CO group) and were all treated with this antimicrobial intravenously. In 14 patients, the episodes were caused by strains that remained susceptible to imipenem and were treated with imipenem-cilastatin (the IM group). Acute Physiology and Chronic Health Evaluation II scores at the time of admission and Sequential Organ Failure Assessment scores at time of diagnosis were similar in both groups. VAP was considered clinically cured in 57% of cases in both groups. In-hospital mortality rates were 61.9% in the CO group and 64.2% in the IM group, and the VAP-related mortality rates were 38% and 35.7%, respectively. Four patients in the CO group and 6 in the IM group developed renal failure. Neurophysiological evaluation was performed during 12 episodes in the CO group, but it revealed no signs of neuromuscular blockade. Intravenous colistin appears to be a safe and effective alternative to imipenem for the management of VAP due to carbapenem-resistant strains of A. baumannii.

The threat from the pink corner

In terms of numbers of isolates, the greatest present resistance problems arise with gram-positive pathogens (which stain purple/black in Gram's method), especially methicillin-resistant Staphylococcus aureus (MRSA). But, is the MRSA problem--by its size--blinding us to something ultimately more dangerous: the slow emergence of gram-negative pathogens (which stain pink) with resistance to all reliable antibiotics? Although presently rare, 'pan-resistant' gram-negative bacteria--predominantly strains of Pseudomonas aeruginosa and Acinetobacter baumannii--have more comprehensive resistance than any gram-positive pathogen. They already pose treatment problems in compromised hospital patients, especially in specialist units, as well in particular groups, such as cystic fibrosis patents. Disturbingly, there is a near-total lack of developmental antibiotics active against gram-negative pathogens.

Severe nosocomial infections with imipenem-resistant Acinetobacter baumannii treated with ampicillin/sulbactam

Forty consecutive patients with nosomial infections caused by multidrug-resistant Acinetobacter baumannii were treated with intravenous ampicillin/sulbactam. The infections were primary bloodstream (32.5%), pneumonia (30%), urinary tract (15%), peritonitis (7.5%), surgical site (7.5%), meningitis (5%) and sinusitis (2.5%). Most were severe infections with underlying conditions (median APACHE II score: 14.5) and 72.5% occurred in the ICU. Twenty-seven (67.5%) were improved/cured, seven (17.5%) were failures and six (15%) were considered to have an indeterminate outcome because patients died within the first 48 h of treatment. Two cases of meningitis were treated and did not respond. The median daily dose of ampicillin/sulbactam was 6 g/3 g and six patients received 12 g/6 g. No adverse effects were observed. This study indicates that ampicillin/sulbactam may be a good and safe therapeutic option to treat severe nosocomial infections caused by multi-drug resistant A. baumannii.