The OPTAMA programme: utilizing MYSTIC (2002) to predict critical pharmacodynamic target attainment against nosocomial pathogens in Europe

Use of Monte Carlo simulation to assess the pharmacodynamics of β-lactams against pseudomonas aeruginosa infections in children: A report from the OPTAMA program

BACKGROUND

Assessing the likelihood of achieving bactericidal pharmacodynamic exposures against Pseudomonas aeruginosa with intravenous antimicrobial regimens would provide insights into the selection of empiric therapy in the pediatric population.

OBJECTIVE

The objective of this study was to use pharmacodynamic modeling to determine the likelihood of various pediatric antibiotic regimens achieving bactericidal exposures against P aeruginosa in children.

METHODS

Minimum inhibitory concentrations (MICs) were determined for meropenem (20 and 40 mg/kg q8h), imipenem (15 and 25 mg/kg q6h), ceftazidime (50 mg/kg q8h), cefepime (50 mg/kg q8h), and piperacillin/tazobactam (75 mg/kg q6h) against P aeruginosa isolates from 2 pediatric institutions. A 5000-patient Monte Carlo simulation was performed to predict attainment of pharmacodynamic targets against P aeruginosa for each of these regimens in a population of 10-year-olds. Optimal regimens were defined as those that had a > or =90% likelihood of attaining target exposures.

RESULTS

At institution 1, high-dose imipenem, high-dose meropenem, and ceftazidime achieved bactericidal pharmacodynamic exposures (likelihood of target attainment: 94%, 92%, and 92%, respectively). No other regimen was associated with a high probability of attaining bactericidal exposure (low-dose imipenem, 87%; cefepime, 85%; low-dose meropenem, 84%; piperacillin/tazobactam, 60%). At institution 2, no regimen was associated with a high likelihood of attaining bactericidal exposure; the calculated probabilities were cefepime, 78%; ceftazidime, 65%; high-dose meropenem, 58%; high-dose imipenem, 57%; low-dose imipenem, 54%; low-dose meropenem, 47%; and piperacillin/tazobactam, 47%. A lack of agreement between attainment of bactericidal exposures and percent susceptibility was apparent for many of the regimens.

CONCLUSIONS

Few regimens demonstrated a high likelihood of achieving bactericidal exposures against P aeruginosa at these institutions. Importantly, percent susceptibility overestimated attainment of the bactericidal target for some regimens, suggesting that further study is necessary in pediatric patients. The findings of this study highlight differences in target attainment and MIC distributions between institutions, emphasizing the importance of using institution-specific data when selecting empiric antimicrobial therapy.

Comparison of beta-lactam regimens for the treatment of gram-negative pulmonary infections in the intensive care unit based on pharmacokinetics/pharmacodynamics

OBJECTIVES

This study utilized pharmacokinetics/pharmacodynamics to compare beta-lactam regimens for the empirical and definitive treatment of gram-negative pulmonary infections in the ICU.

METHODS

Susceptibility data were extracted from the 2002 Intensive Care Unit Surveillance System (ISS) and pharmacokinetic parameters were obtained from published human studies. Monte Carlo simulation was used to model the free percent time above the MIC (free %T > MIC) for 18 beta-lactam regimens against all gram-negative isolates, Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii. The cumulative fraction of response (CFR) was determined for bacteriostatic and bactericidal targets (free %T > MIC): penicillins (> or = 30/50%), cephalosporins/monobactams (> or = 40/70%) and carbapenems (> or = 20/40%).

RESULTS

The 2002 ISS database contained MICs for 2408 gram-negative isolates including 1430 Enterobacteriaceae, 799 P. aeruginosa, and 179 A. baumannii. Imipenem had the highest percentage susceptible for all gram-negatives, Enterobacteriaceae and A. baumannii, while piperacillin/tazobactam had the highest percentage susceptible for P. aeruginosa. For empirical therapy, imipenem 0.5 g every 6 h, cefepime 2 g every 8 h and ceftazidime 2 g every 8 h demonstrated the highest CFR. For definitive therapy, imipenem 0.5 g every 6 h, ertapenem 1 g daily and cefepime 2 g every 8 h, cefepime 1 g every 8 h and cefepime 1 g every 12 h had the highest bactericidal CFR against Enterobacteriaceae; ceftazidime 2 g every 8 h, cefepime 2 g every 8 h, piperacillin/tazobactam 3.375 g every 4 h, ceftazidime 1 g every 8 h and aztreonam 1 g every 8 h against P. aeruginosa; and imipenem 0.5 g every 6 h, ticarcillin/clavulanate 3.1 g every 4 h, ceftazidime 2 g every 8 h, cefepime 2 g every 8 h and ticarcillin/clavulanate 3.1 g every 6 h against A. baumannii.

CONCLUSIONS

Based on pharmacokinetics/pharmacodynamics, imipenem 0.5 g every 6 h, cefepime 2 g every 8 h and ceftazidime 2 g every 8 h should be the preferred beta-lactam regimens for the empirical treatment of gram-negative pulmonary infections in the ICU. The order of preference varied against Enterobacteriaceae, P. aeruginosa and A. baumannii.

Simulation of Antibiotic Pharmacodynamic Exposure for the Empiric Treatment of Nosocomial Bloodstream Infections: A Report from the OPTAMA Program

OBJECTIVE

We developed a model to predict the pharmacodynamic exposure of antibiotics against bacteria commonly implicated in nosocomial bloodstream infections to determine which dosage regimens would provide the greatest likelihood of obtaining a bactericidal effect.

METHODS

Pharmacodynamic exposures were simulated for 5000 subjects receiving standard doses of ceftazidime, cefepime, piperacillin/tazobactam, meropenem, imipenem, or ciprofloxacin. Exposures were indexed to the MICs of bacteria weighted by their prevalence in causing nosocomial bloodstream infections, derived from 2002 SENTRY data. Enterococci were excluded. MIC data were derived from the 2003 Meropenem Yearly Surveillance Test Information Collection resistance study. The probabilities of achieving bactericidal exposures (ie, target attainment) for each antibiotic regimen were compared. The effect of increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) on attainment of bactericidal targets was tested.

RESULTS

All dosage regimens except ciprofloxacin and ceftazidime 1 g q8h achieved >90% likelihood of bactericidal exposure. The rank order of target attainment was as follows: imipenem 500 mg q6h, 100.0%; imipenem 1 g q8h, 99.9%; cefepime 2 g q12h, 99.4%; meropenem 1 g q8h, 98.4%; cefepime 1 g q12h, 98.2%; piperacillin/tazobactam 3.375 g q6h, 97.9%; piperacillin/tazobactam 4.5 gq8h, 95.0%; ceftazidime 2 g q8h, 94.2%; ceftazidime 1 g q8h, 71.7%; ciprofloxacin 400 mg q8h, 63.3%; and ciprofloxacin 400 mg q12h,63.0%. Target attainments dropped to <90% for all agents when MRSA was modeled at > or =10% prevalence.

CONCLUSIONS

The results of this model analysis suggest that standard doses of the carbapenems, piperacillin/tazobactam, and cefepime, and higher doses of ceftazidime, may provide optimal likelihood of achieving bactericidal exposure against pathogens implicated in nosocomial bloodstream infections, excluding MRSA and enterococci. When MRSA rates are > or =10%, therapy with an antibiotic that has activity against this phenotype should be empirically initiated.