Antimicrobial Stewardship Practices in Outpatient Parenteral Antimicrobial Therapy Programs in the United States.

Background: Outpatient parenteral antimicrobial therapy (OPAT) regimens typically prioritize ease of antimicrobial administration, tolerability, safety, and accessibility over using the narrowest-spectrum antimicrobial. In light of this, OPAT providers often utilize different techniques to promote antimicrobial stewardship (AMS) in their OPAT programs. This study aims to characterize the AMS practices of OPAT programs across the United States that might meet The Joint Commission requirements for outpatient AMS metrics. Methods: This is a cross-sectional electronic survey of the Vizient AMS network. A total of 95 possible questions were designed to inquire about demographics, OPAT program structure, AMS initiatives, performance metrics, and resources. Results: Seventy-four survey responses were received, with 58 (78.4%) of the respondents indicating their institution offered OPAT services. Respondents reported having at least 1 AMS protocol and tracking at least 1 metric in 91% and 74% of OPAT programs, respectively. Only 40% of programs reported billing for OPAT-related services. Approximately 45% of respondents disagreed or strongly disagreed that their OPAT program had the resources needed to care for the population it serves. Respondents identified data analytics (69%), funding for expansion of services (67%), and pharmacists (62%) as resources of greatest need for their OPAT programs. Conclusions: This survey collectively describes the AMS practices currently employed by OPAT programs across the United States. The results provide specific examples of AMS initiatives, metrics, and resources that institutions may reference to advance the practices of their OPAT programs to meet The Joint Commission Outpatient Antimicrobial Stewardship standards.

Performance of ePlex® blood culture identification panels in clinical isolates and characterization of antimicrobial stewardship opportunities.

We assessed the performance of GenMark's ePlex® Blood Culture Identification (BCID) Panels for overall agreement of organism identification and resistance mechanism detection with standard microbiologic methods. This study included patients with a positive blood culture from May 2020 to January 2021. The primary outcomes were to assess concordance of ePlex® organism identification with standard identification methods and concordance of ePlex® genotypic resistance mechanism detection with standard phenotypic susceptibility testing. Secondary outcomes included panel specific performance and characterization of antimicrobial stewardship opportunities. The overall identification concordance rate in 1276 positive blood cultures was 98.1%. The overall concordance for the presence of resistance markers was 98.2% and concordance for the absence of resistance markers was 100%. A majority of ePlex® results (69.5%) represented opportunities for potential antimicrobial stewardship intervention. High concordance rates between the ePlex® BCID panels and standard identification and susceptibility methods enable utilization of results to guide rapid antimicrobial optimization.

Diagnostic testing and antibiotic utilization among inpatients evaluated for coronavirus disease 2019 (COVID-19) pneumonia.

We evaluated diagnostic test and antibiotic utilization among 252 patients from 11 US hospitals who were evaluated for coronavirus disease 2019 (COVID-19) pneumonia during the severe acute respiratory coronavirus virus 2 (SARS-CoV-2) omicron variant pandemic wave. In our cohort, antibiotic use remained high (62%) among SARS-CoV-2-positive patients and even higher among those who underwent procalcitonin testing (68%).

Association of vancomycin-induced acute kidney injury with trough versus AUC monitoring in patients receiving extended durations of therapy.

Objective: Vancomycin therapy is associated with an increased risk of acute kidney injury (AKI). Previous studies suggest that area under the curve (AUC) monitoring reduces the risk of AKI, but literature is lacking to support this in patients receiving longer durations of vancomycin therapy. Design: Retrospective cohort study. Method: Patients ≥18 years old, admitted between August 2015 and July 2017 or October 2017 and September 2019, and received at least 14 days of intravenous (IV) vancomycin therapy were included in the study. Our primary outcome was the incidence of AKI between trough monitoring and AUC monitoring groups using Kidney Disease Improving Global Outcomes criteria. Secondary outcomes included inpatient mortality, median inpatient length of stay, and median intensive care unit length of stay. Results: Overall, 582 patients were included in the study, with 318 patients included in the trough monitoring group and 264 included in the AUC monitoring group. The median duration of vancomycin therapy was 23 days (interquartile range, 16-39). Patients within the trough monitoring group had a higher incidence of AKI compared to the AUC monitoring group (45.6% vs 28.4%, p < 0.001). Furthermore, logistic regression analysis showed that AUC monitoring was associated with a 54% lower incidence of AKI (OR 0.46, 95% CI [0.31-0.69]). All-cause inpatient mortality was numerically higher in the trough monitoring group (12.9% vs 8.3%, p = 0.078). Conclusions: In patients who received at least 14 days of IV vancomycin therapy, AUC monitoring was associated with a lower incidence of AKI.

The impact of coronavirus disease 2019 (COVID-19) on the antimicrobial stewardship pharmacist workforce: A multicenter survey.

Objective: The coronavirus disease 2019 (COVID-19) pandemic has required healthcare systems and hospitals to rapidly modify standard practice, including antimicrobial stewardship services. Our study examines the impact of COVID-19 on the antimicrobial stewardship pharmacist. Design: A survey was distributed nationally to all healthcare improvement company members. Participants: Pharmacist participants were mostly leaders of antimicrobial stewardship programs distributed evenly across the United States and representing urban, suburban, and rural health-system practice sites. Results: Participants reported relative increases in time spent completing tasks related to medication access and preauthorization (300%; P = .018) and administrative meeting time (34%; P = .067) during the COVID-19 pandemic compared to before the pandemic. Time spent rounding, making interventions, performing pharmacokinetic services, and medication reconciliation decreased. Conclusion: A shift away from clinical activities may negatively affect the utilization of antimicrobials.

Changing times: The impact of gram-negative breakpoint changes over the previous decade.

We assessed breakpoint changes of 13,101 Enterobacterales and Pseudomonas aeruginosa isolates from the past decade. All ß-lactams and fluoroquinolones demonstrated decreased susceptibilities following breakpoint changes. Enterobacter cloacae experienced the largest average decrease in susceptibility amongst the Enterobacterales at 5.3% and P. aeruginosa experienced an average decrease in susceptibility of 9.3%.

Acute Kidney Injury Associated with Area under the Curve versus Trough Monitoring of Vancomycin in Obese Patients.

Vancomycin is a first-line agent used in the treatment of methicillin-resistant Staphylococcus aureus; however, vancomycin is associated with acute kidney injury (AKI). Previous literature demonstrates decreased incidence of AKI using 24-h area under the concentration-time curve (AUC24) monitoring, but its safety is unknown in obese populations. Patients ≥18 years, with body mass indices (BMI) ≥30 kg/m2, admitted between August 2015 and July 2017 or October 2017 and September 2019, who received vancomycin for ≥72 h and had level(s) drawn within 96 h of initiation were included. The primary outcome was incidence of AKI. Secondary outcomes included inpatient mortality rate, median inpatient length of stay, median vancomycin trough concentration, and median vancomycin AUC24. AKI was identified using the highest serum creatinine value compared with the value immediately prior to vancomycin initiation based on Kidney Disease Improving Global Outcomes (KDIGO) criteria. Overall, 1,024 patients met inclusion criteria, with 142 out of 626 patients in the trough group and 65 out of 398 patients in the AUC24 group meeting criteria for AKI (22.7% versus 16.3%, P = 0.008). Logistic regression of the data to account for confounding factors maintained significance for the reduction in incidence of AKI with AUC24 monitoring compared to trough monitoring (P = 0.010). Monitoring of vancomycin with AUC24 was associated with a decreased risk of AKI when compared with trough monitoring in obese patients.

Appropriateness of antibiotic use in patients with and without altered mental status diagnosed with a urinary tract infection.

Objective: The objective of this study was to determine antibiotic appropriateness based on Loeb minimum criteria (LMC) in patients with and without altered mental status (AMS). Design: Retrospective, quasi-experimental study assessing pooled data from 3 periods pertaining to the implementation of a UTI management guideline. Setting: Academic medical center in Lexington, Kentucky. Patients: Adult patients aged ≥18 years with a collected urinalysis receiving antimicrobial therapy for a UTI indication. Methods: Appropriateness of UTI management was assessed in patients prior to an institutional UTI guideline, after guideline introduction and education, and after implementation of a prospective audit-and-feedback stewardship intervention from September to November 2017-2019. Patient data were pooled and compared between patients noted to have AMS versus those with classic UTI symptoms. Loeb minimum criteria were used to determine whether UTI diagnosis and treatment was warranted. Results: In total, 600 patients were included in the study. AMS was one of the most common indications for testing across the 3 periods (19%-30.5%). Among those with AMS, 25 patients (16.7%) met LMC, significantly less than the 151 points (33.6%) without AMS (P < .001). Conclusions: Patients with AMS are prescribed antibiotic therapy without symptoms indicative of UTI at a higher rate than those without AMS, according to LMC. Further antimicrobial stewardship efforts should focus on prescriber education and development of clearly defined criteria for patients with and without AMS.

Pharmacist Survey: Pharmacist Perception of Vancomycin Area Under the Curve Therapeutic Drug Monitoring.

BACKGROUND: Evidence suggests the standard vancomycin trough goal of 15 to 20 mg/L for serious Staphylococcus aureus infections is associated with acute kidney injury, whereas appropriate monitoring of 24-hour area under the curve (AUC) may decrease nephrotoxicity. As a result, institutions have transitioned to AUC monitoring, the predictive pharmacokinetic/pharmacodynamic parameter of vancomycin to improve safety outcomes. However, this method may require increased pharmacist time and effort. Pharmacist perception of the practice change is largely unknown and warrants investigation. METHODS: An electronic survey was disseminated via e-mail to pharmacists 5 months post-AUC implementation. Items of interest were focused on pharmacist perception, including quantity of patients monitored using AUC, justification of the practice change, differences in efficacy and safety, and changes in monitoring time requirements. RESULTS: The pharmacist survey was distributed to 196 pharmacists and 84 responded (43% response rate). Eighty-one pharmacists had monitored patients using AUC methods. Sixty-nine percent of these respondents perceived the change to result in increased or slightly increased patient safety, 27% described no difference, and 4% stated safety was decreased or slightly decreased. Forty-two percent perceived the transition to result in increased or slightly increased efficacy, while 48% noted no difference and 10% responded that efficacy was decreased or slightly decreased. Pharmacists stated the creation of an institutional calculator decreased the time required to calculate AUC. CONCLUSION: After the change to AUC monitoring, pharmacists perceived improvements in safety outcomes while efficacy was at least similar if not increased.

Focusing the Lens on the CAMERA Concepts: Early Combination ß-Lactam and Vancomycin Therapy in Methicillin-Resistant Staphylococcus aureus Bacteremia.

Methicillin-resistant Staphylococcus aureus (MRSA) has grown to become a major burden on health care systems. The cumulation of limited therapeutic options and worsened patient outcomes with persistent MRSA bacteremia has driven research in optimizing its initial management. The guidelines published by the Infectious Diseases Society of America currently recommend combination therapy for refractory MRSA bacteremia, but the utility of combining antibiotics from the start of therapy is under investigation. The alternative strategy of early use of ß-lactam antibiotics in combination with vancomycin upon initial MRSA bacteremia detection has shown promise. While this concept has gained international attention, providers should give this strategy serious consideration prior to implementation. The objective of this review is to examine retrospective and prospective evidence for early combination with vancomycin and ß-lactam antibiotics, as well as explore potential consequences of combination therapy.

Vancomycin Area Under the Curve Dosing and Monitoring at an Academic Medical Center: Transition Strategies and Lessons Learned.

Due to the inconsistent correlation of vancomycin trough concentrations with 24-hour area under the curve (AUC) and a desire to reduce rates of vancomycin-associated acute kidney injury, an institutional guideline was implemented by the Antimicrobial Stewardship Team in September 2017 to monitor vancomycin using AUC. Three stages were utilized to organize the process: preparation, implementation, and evaluation. The preparation stage was used to present literature to key stakeholders, and pharmacy meetings focused on the development of a dosing and monitoring guideline. Along with institution-wide education, the implementation stage included information technology development and support. The evaluation stage was comprised of quality improvement and clinical research. Future plans include dissemination of the results and analyses. Numerous lessons were learned due to barriers experienced during the process, but the transition was successful.

Fever Burden in Patients With Subarachnoid Hemorrhage and the Increased Use of Antibiotics.

BACKGROUND: Fever occurs in the majority of subarachnoid hemorrhage (SAH) patients. Nearly 50% of SAH patients have noninfectious fevers. Data are lacking describing the effects of fever burden in the SAH patient population. METHODS: This was a single-center, retrospective observational cohort study in patients more or equal to 18 years of age with a diagnosis of nontraumatic SAH admitted to an ICU between January 1, 2010 and September 1, 2015. Exclusion criteria were SAH secondary to trauma or admission for more than 48 hours. Temperature measurements, demographic data, and other pertinent information were collected from Day 0 to Day 13. Daily fever burden was calculated for each patient by calculating an area under the curve. RESULTS: A total of 194 subjects were included. The mean study period maximum temperature (Tmax) for all 194 patients was 40.8 ± 0.83°C. The mean overall fever burden for all 194 patients was 89.2 ± 99.59°C h more than 37°C. The overall fever burden peaked on day 5 and declined thereafter. Fever burden, Tmax, and length of stay in the hospital were all significantly associated with receipt of antibiotics. Only Tmax was associated with poor outcome. The 31 patients who had fever but no identified cause of infection received 1000 doses of antibiotics or 32.25 doses per patient. CONCLUSION: Fever is common in SAH patients and is associated with antibiotic use, infection, vasospasm, and poor outcome. Some SAH patients may receive antibiotics unnecessarily for noninfectious fever. Clinicians should consider using site-specific parameters related to infection rather than systemic symptoms such as fever to evaluate infection in SAH patients.

Amikacin target achievement in adult cystic fibrosis patients utilizing Monte Carlo simulation.

AIM: Pseudomonas aeruginosa (PsA) is a common pathogen in cystic fibrosis (CF). Management of an acute pulmonary exacerbation (APE) caused by PsA is dual anti-pseudomonal antibiotics, a beta-lactam plus aminoglycoside. Aminoglycoside dosing in CF differs from the general population due to altered pharmacokinetics. The primary objective of this study was to utilize pharmacokinetic data from adult CF patients that received amikacin to determine the probability of target attainment for APEs caused by PsA. METHODS: This was a single-center, non-randomized, retrospective cohort study of patients >18 years with CF that received intravenous amikacin between January 2010 and July 2016. Amikacin dose, frequency, and serum concentrations were used to calculate pharmacokinetic parameters assuming a one-compartment model. Monte Carlo simulation was conducted with MIC values from CF patients with a PsA positive sputum culture between January 2014 and September 2016 to predict concentration-time profiles for different doses of amikacin. RESULTS: This study included pharmacokinetic parameters for 14 amikacin courses administered to six unique patients. The average empiric dose of amikacin was 24.3 ± 14.6 mg/kg, achieving a peak:MIC ratio ≥8 at a rate of 37% (median 5.87; IQR 3.05-10.96). A dose of 45 mg/kg/day was needed to achieve target peak:MIC ratios 90% of the time for a PsA MIC of 8 mg/L. CONCLUSION: Our data suggests it may not be clinically feasible to utilize amikacin for PsA isolates with a MIC of 16 mg/L. Current guideline dosing recommendations of amikacin 30-35 mg/kg/day are only adequate for PsA with a MIC ≤4 mg/L.

Influence of ß-Lactam Infusion Strategy on Acute Kidney Injury.

Limited literature is available assessing nephrotoxicity with prolonged ß-lactam infusions. This study compared the incidence of acute kidney injury (AKI) associated with a prolonged ß-lactam infusion or an intermittent infusion. This was a retrospective, matched-cohort study at an academic medical center from July 2006 to September 2015. Adult patients who received piperacillin-tazobactam (TZP), cefepime (FEP), or meropenem (MEM) for at least 48 h were evaluated. Patients were excluded for preexisting renal dysfunction or pregnancy. The primary outcome was difference in incidence of AKI evaluated using the RIFLE (risk, injury, failure, loss, and end-stage) criteria. Patients in the intermittent group were matched 3:1 to patients in the prolonged-infusion group based on the following: ß-lactam agent, age, gender, Charlson comorbidity index, baseline creatinine clearance, hypotension, receipt of vancomycin, and treatment in an intensive care unit. A total of 2,390 patients were included in the matched analysis, with 1,700 receiving intermittent infusions and 690 receiving prolonged infusion. The incidence of AKI was similar in the prolonged-infusion group to that in the intermittent-infusion group (21.6% versus 18.6%; P = 0.1). After multivariate regression, prolonged infusion was not associated with increased odds of AKI (odds ratio [OR], 1.07; 95% confidence interval [95% CI], 0.83 to 1.39). Independent predictors of AKI included TZP therapy, concomitant nephrotoxins, hypotension, and heart failure. Although AKIs were numerically more common in patients receiving prolonged ß-lactam infusions than those receiving intermittent infusions, prolonged infusion was not an independent risk factor for AKI.

Nephrotoxicity in Patients with or without Cystic Fibrosis Treated with Polymyxin B Compared to Colistin.

Nephrotoxicity is the primary adverse effect of the polymyxins. The relative rates of toxicity of polymyxin B and colistin have not been fully elucidated, especially in patients with cystic fibrosis (CF). A retrospective cohort study of adults treated with polymyxin B or colistin for at least 48 h was conducted. The primary endpoint was the incidence of kidney injury assessed by RIFLE (i.e., risk, injury, failure, loss, end-stage renal disease) criteria. Risk factors for kidney injury were evaluated using multivariate Cox regression. A total of 414 patients were evaluated, 220 of whom had CF. In patients without CF, there was no difference in kidney injury with polymyxin B and colistin (42.9% versus 50.3%, P = 0.46). Loop diuretic exposure was a risk factor for kidney injury (adjusted hazard ratio [aHR], 1.82; 95% confidence interval [CI], 1.16 to 2.83) in this population. In patients with CF, polymyxin B and colistin were associated with similar rates of kidney injury (34.5% versus 29.8%, P = 0.77). Diabetes (aHR, 2.68; 95% CI, 1.01 to 7.11), loop diuretics (aHR, 3.02; 95% CI, 1.36 to 6.73), and progressive care unit admission (aHR, 8.21; 95% CI, 2.55 to 26.46) were risk factors for kidney injury, while higher baseline serum creatinine levels (per 1 mg/dl) were protective (aHR, 0.08; 95% CI, 0.01 to 0.48). Total unadjusted kidney injury in polymyxin-treated patients was less frequent in those who had CF (30.5% versus 48.5%, P < 0.001). Polymyxin B and colistin are associated with a high incidence of kidney injury; cystic fibrosis may be protective against polymyxin nephrotoxicity, but further investigation is needed to confirm this conjecture.

Acute kidney injury in patients treated with vancomycin and piperacillin-tazobactam: A retrospective cohort analysis.

BACKGROUND: Empiric antimicrobial therapy often consists of the combination of gram-positive coverage with vancomycin (VAN) and gram-negative coverage, specifically an antipseudomonal beta-lactam such as piperacillin-tazobactam (PTZ). Nephrotoxicity is commonly associated with VAN therapy; however, recent reports show higher nephrotoxicity rates among patients treated with the combination of VAN and PTZ. OBJECTIVE: This study evaluated the effect of the VAN/PTZ combination on acute kidney injury (AKI) compared to VAN and PTZ monotherapies. DESIGN, SETTING, AND PATIENTS: This is a retrospective cohort analysis of adult patients without renal disease receiving VAN, PTZ, or the combination from September 1, 2010 through August 31, 2014 at an academic medical center. MEASUREMENTS: The primary outcome was AKI incidence as defined by the Risk, Injury, Failure, Loss, End-stage (RIFLE) criteria. METHODS: Continuous and categorical variables were assessed with appropriate tests. Univariate and multivariate logistic regressions were performed to assess for associations between variables and AKI incidence. Subanalyses based on severity of illness were performed. RESULTS: Overall, 11,650 patients were analyzed, with 1647 (14.1%) developing AKI. AKI was significantly more frequent in the VAN/PTZ group (21%) compared to either monotherapy group (VAN 8.3%, PTZ 7.8%, P ⟨ 0.001 for both). Combination therapy was independently associated with higher AKI odds compared to monotherapy with either agent (adjusted odds ratio [aOR], 2.03; 95% confidence interval [CI], 1.74-2.39; aOR, 2.31; 95% CI, 1.97-2.71, for VAN and PTZ, respectively). Receipt of concomitant nephrotoxic drugs was independently associated with increased AKI rates, as were increased duration of therapy, hospital length of stay, increasing severity of illness, and increasing baseline renal function. CONCLUSIONS: In this study of more than 10,000 patients, VAN combined with PTZ was associated with twice the odds of AKI development compared to either agent as monotherapy. This demonstrates the need for judicious use of combination empiric therapy. Journal of Hospital Medicine 2017;12:77-82.

Increasing Incidence of Multidrug Resistance Among Cystic Fibrosis Respiratory Bacterial Isolates.

Pseudomonas aeruginosa and Staphylococcus aureus are common pathogens in cystic fibrosis (CF) patients with increasing multidrug resistance (MDR). This study characterized antimicrobial susceptibility trends among organisms isolated from the respiratory tract of CF patients. Microbiological culture and sensitivity results for all CF patients were collected from January 2010 through December 2014. Minimum inhibitory concentrations were obtained using Phoenix® and Etest® methods. Clinical and Laboratory Standards Institute guidelines were used to remove duplicate isolates and develop antimicrobial susceptibility reports. MDR was defined as resistance to one agent in three or more antibiotic classes or oxacillin resistance in S. aureus. Overall, 542 bacterial isolates from 376 cultures were analyzed for trends. P. aeruginosa (41%), S. aureus (40%), and Stenotrophomonas maltophilia (8%) were the most commonly isolated organisms. Multidrug-resistant organism isolation increased from 39% to 49% (r = 0.76, p = 0.13), while representing 47.6% of all isolates. Multidrug-resistant P. aeruginosa incidence increased each year from 26% to 43% (r = 0.89, p = 0.046), while P. aeruginosa isolation decreased from 47% to 38% over the study period (r = -0.93, p = 0.02). MRSA accounted for 62.6% of all S. aureus isolated, while overall multidrug-resistant S. aureus incidence was 73.1% in all cultures. MDR among common pathogens in CF continues to increase. Empiric therapy for CF exacerbations should be targeted to previous antimicrobial susceptibility, and P. aeruginosa and S. aureus should be empirically covered.

Nephrotoxicity during Vancomycin Therapy in Combination with Piperacillin-Tazobactam or Cefepime.

Recent reports have demonstrated that vancomycin (VAN) may lead to an increase in the incidence of acute kidney injury (AKI) when it is combined with antipseudomonal beta-lactams. This study compared the incidence of AKI associated with VAN plus piperacillin-tazobactam (TZP) or cefepime (FEP). This was a retrospective, matched cohort study that was conducted at an academic medical center between September 2010 and September 2014 and that included adult patients without severe chronic or structural kidney disease, dialysis, pregnancy, cystic fibrosis, or a hospital transfer receiving TZP-VAN or FEP-VAN for at least 48 h. The primary outcome was the difference in the AKI incidence between the TZP-VAN and FEP-VAN groups, evaluated using the risk, injury, failure, loss of kidney function, and end-stage kidney disease (RIFLE) criteria. Patients in the two groups were matched on the basis of age, sex, severity of illness, baseline creatinine clearance, hypotension, number of nephrotoxicity risk factors, and intravenous contrast exposure. In total, 4,193 patients met all inclusion criteria (3,605 received TZP-VAN and 588 received FEP-VAN). The unadjusted AKI incidence was 21.4% in patients receiving TZP-VAN, whereas it was 12.6% in patients receiving FEP-VAN (P < 0.001). After the patients were matched, 1,633 patients receiving TZP-VAN and 578 patients receiving FEP-VAN were evaluated. The AKI incidence remained higher in patients receiving TZP-VAN than in those receiving FEP-VAN (21.4% versus 12.5%, P < 0.0001). This trend remained true for all classifications of the RIFLE criteria. After controlling for remaining confounders, TZP-VAN therapy was associated with 2.18 times the odds of AKI than FEP-VAN therapy (95% confidence interval, 1.64 to 2.94 times) in logistic regression. AKI was significantly more common in patients receiving vancomycin in combination with piperacillin-tazobactam than in those receiving vancomycin in combination with cefepime. This finding reinforces the need for the judicious use of combination empirical antimicrobial therapy.

Optimizing beta-lactam pharmacodynamics against Pseudomonas aeruginosa in adult cystic fibrosis patients.

BACKGROUND: Patients with cystic fibrosis (CF) exhibit increased clearance of beta-lactams. The purpose of this study was to predict the probability of beta-lactam target attainment (PTA) against Pseudomonas aeruginosa in adult CF patients based on local microbiological data. METHODS: CF-specific pharmacokinetic parameters were obtained from published data for aztreonam, cefepime, ceftazidime, meropenem and piperacillin-tazobactam. Pharmacodynamic modeling was used to determine the PTA for bolus, prolonged infusion, and continuous infusion regimens. RESULTS: Prolonged infusion of meropenem 2g every 8h performed the best among all regimens tested, with a PTA of 83%. The PTA was increased with both prolonged and continuous infusion; however, no regimen reached the target PTA of >90% against P. aeruginosa in CF patients at our institution. CONCLUSIONS: Prolonged and continuous infusion provided higher PTA than bolus for all regimens. Further investigation of novel regimens in CF patients is needed.