Study of the comparative activity of piperacillin/tazobactam with currently available antibiotics against 8206 aerobic isolates

Description and validation of a spectrum score method to measure antimicrobial de-escalation in healthcare associated pneumonia from electronic medical records data

BACKGROUND

Comparison of antimicrobial de-escalation rates between healthcare settings is problematic. To objectively and electronically measure de-escalation a method based upon the spectrum of antimicrobial regimens administered (i.e., spectrum score) was developed.

METHODS

A Delphi process was used to develop applicable concepts. Spectrum scores were created for 27 antimicrobials based upon susceptibility for 19 organisms. National VA susceptibility data was used to estimate microbial spectrum. Susceptibility estimates were converted to ordinal scores, and values for organisms with multi-drug resistance potential were weighted more heavily. Organism scores were summed to create antibiotic-specific spectrum scores and extended mathematically to score multi-antimicrobial regimens. Vignettes were created from antimicrobial regimens administered to 300 patients hospitalized with pneumonia. Daily spectrum scores were calculated for each case. Hospitalization day 4 scores were subtracted from day 2 scores (i.e., spectrum score ∆). A positive spectrum score ∆ defined de-escalation. Experts ranked each pneumonia case on a 7-point Likert scale (Likert >4 indicated de-escalation). Spectrum score ∆s were compared to expert review. Findings were used to identify score deficiencies. Next, 40 pairs of cases were modified to include antimicrobial administration routes. Each pair contained almost similar regimens; however, one contained oral (PO) the other only intravenous (IV) antimicrobials on day 4 of therapy. Experts reviewed cases as described. Spectrum score ∆ credits to account for PO conversion were derived from the mean paired differences in Likert Score. De-escalation status was evaluated in 100 vignettes containing antimicrobial route by different experts and compared to the modified method.

RESULTS

Initial sensitivity and specificity of the spectrum score ∆ to detect expert classified de-escalation events was 86.3 and 96.0%, respectively. In paired cases, the mean (± SD) Likert score was 5.0 (1.5) and 4.6 (1.5) for PO and IV (P = 0.002), respectively. To improve de-escalation event detection, two credits were added to spectrum score ∆s based upon the percentage of antimicrobials administered PO on day 4. The final method, exhibited sensitivity and specificity to detect expert classified de-escalation events of 96.2 and 93.6%, respectively.

CONCLUSIONS

The final spectrum score method exhibited excellent agreement with expert judgments of de-escalation events in pneumonia.

Cross-Canada survey of resistance of 2747 aerobic blood culture isolates to piperacillin/tazobactam and other antibiotics

OBJECTIVE

To compare the activity of piperacillin/tazobactam with that of other broad parenteral antibiotics against aerobic and facultative anaerobic blood culture isolates in a Canada-wide survey.

DESIGN

Fifty-eight laboratories in nine provinces each contributed up to 50 consecutive clinically significant aerobic and facultative anaerobic isolates for susceptibility testing.

SETTING

Participating hospitals included both tertiary care and community hospitals.

MATERIALS AND METHODS

Testing was performed in five regional centres by using the same microbroth dilution method, and results were interpreted according to National Commitee for Clinical Laboratory Standards M7-A3 and M100-S5 guidelines.

RESULTS

Piperacillin/tazobactam and imipenem were both active against more than 99% of the 1616 strains of Enterobacteriaceae species tested. The minimum inhibitory concentration of 90% of isolates (MIC(90)) of all Enterobacteriaceae species was 2 mg/L for piperacillin/tazobactam compared with 64 mg/L for piperacillin alone. Seventeen per cent of strains of Enterobacteriaceae species were susceptible to piperacillin/tazobactam but resistant to piperacillin. Piperacillin/tazobactam was highly active against Pseudomonas aeruginosa, inhibiting 99.1% of strains. MIC(90) was 8 mg/L. Nine per cent of P aeruginosa strains were not susceptible to imipenem. Most of these strains had a MIC of 8 mg/L, which falls in the intermediate category. Ninety-seven per cent of P aeruginosa were susceptible to ciprofloxacin and 97.3% to tobramycin. Ninety-six per cent of strains of Actinobacter species were susceptible to piperacillin/tazobactam, whereas only 76% of strains were susceptible to piperacillin alone. Overall, piperacillin/tazobactam was the most active agent tested; 98% of all strains were susceptible, followed closely by imipenem, to which 97.8% of strains were susceptible.

CONCLUSIONS

Aerobic blood culture isolates from Canadian centres continue to be highly susceptible to a variety of antibiotics. The broad spectrum of activity of piperacillin/tazobactam suggests that this combination should be considered for empirical treatment of sepsis while awaiting results of cultures and susceptibility testing.

A review of antimicrobial resistance in Canada

Antimicrobial resistance is a global concern. Over the past 10 years, considerable efforts and resources have been expended to detect, monitor, and understand at the basic level the many different facets of emerging and increasing resistance. This review summarizes our current understanding of bacterial antimicrobial resistance issues in Canada with particular emphasis given to the Enterobacteriaceae, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus, Neisseria meningitidis, Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and Streptococcus pyogenes. In addition, future concerns and programs for ongoing surveillance are discussed.

In-vitro activity of cefepime and seven other antimicrobial agents against 1518 non-fermentative Gram-negative bacilli collected from 48 Canadian health care facilities. Canadian Afermenter Study Group

Non-fermentative bacilli are primarily nosocomial pathogens, and are also often resistant in vitro to a broad range of antimicrobial agents. In this large Canadian study, we collected 1466 clinical, non-repeat isolates of Pseudomonas aeruginosa, 21 of Acinetobacter spp. and 31 Stenotrophomas maltophilia. MICs of eight antibiotics were determined by the NCCLS microdilution method in a central laboratory. Tobramycin was the most active agent against P. aeruginosa (94.5% susceptible); amikacin and imipenem were the most active against Acetinobacter spp. (100%) and ceftazidime was the most active against S. maltophilia (40.6%). Against each group of isolates, cefepime was active against 87, 86.4 and 15.6%, respectively. This in-vitro study showed that cefepime may be a useful additional agent in the treatment of infections caused by P. aeruginosa and Acinetobacter spp., but not when S. maltophilia is considered pathogenic.

Canadian Pseudomonas aeruginosa susceptibility study from 48 medical centers: focus on ciprofloxacin

We tested 1503 clinical isolates of Pseudomonas aeruginosa, from 48 Canadian medical centers, against ciprofloxacin and 11 other antimicrobial agents to determine in vitro activity. The frequency of susceptibility was highest for carbenicillin and ticarcillin (91% each) followed by imipenem and ceftazadime (90% each). Overall susceptibility (< or = 1.0 mg/l) to ciprofloxacin was 84% while resistance (> or = 4.0 mg/l) was 12%. Ciprofloxacin resistant isolates were more common from urinary tract specimens than from specimens collected from the respiratory and/or skin and soft tissue. Isolates from cystic fibrosis patients were more resistant to all agents tested than isolates from non-cystic fibrosis patients.

Resistance issues and treatment implications: pneumococcus, Staphylococcus aureus, and gram-negative rods

During the last decade there has been an unexpectedly rapid evolution of antimicrobial resistance in the respiratory pathogens for community- and hospital-acquired pneumonia. In order to choose the most optimal therapy for their patients, it is essential that physicians be aware of the prevalence and mechanisms of resistance and their implications on the effectiveness of the various antimicrobials.