Cefepime versus ceftazidime: considerations for empirical use in critically ill patients

Efficacy and safety of antibiotics targeting Gram-negative bacteria in nosocomial pneumonia: a systematic review and Bayesian network meta-analysis

BACKGROUND

Multiple randomized controlled studies have compared numerous antibiotic regimens, including new, recently commercialized antibiotics in the treatment of nosocomial pneumonia (NP). The objective of this Bayesian network meta-analysis (NMA) was to compare the efficacy and the safety of different antibiotic treatments for NP.

METHODS

We conducted a systematic search of PubMed, Medline, Web of Science, EMBASE and the Cochrane Library databases from 2000 through 2021. The study selection included studies comparing antibiotics targeting Gram-negative bacilli in the setting of NP. The primary endpoint was 28 day mortality. Secondary outcomes were clinical cure, microbiological cure and adverse events.

RESULTS

Sixteen studies encompassing 4993 patients were included in this analysis comparing 13 antibiotic regimens. The level of evidence for mortality comparisons ranged from very low to moderate. No significant difference in 28 day mortality was found among all beta-lactam regimens. Only the combination of meropenem plus aerosolized colistin was associated with a significant decrease of mortality compared to using intravenous colistin alone (OR = 0.43; 95% credible interval [0.17-0.94]), based on the results of the smallest trial included. The clinical failure rate of ceftazidime was higher than meropenem with (OR = 1.97; 95% CrI [1.19-3.45]) or without aerosolized colistin (OR = 1.40; 95% CrI [1.00-2.01]), imipemen/cilastatin/relebactam (OR = 1.74; 95% CrI [1.03-2.90]) and ceftazidime/avibactam (OR = 1.48; 95% CrI [1.02-2.20]). For microbiological cure, no substantial difference between regimens was found, but ceftolozane/tazobactam had the highest probability of being superior to comparators. In safety analyses, there was no significant difference between treatments for the occurrence of adverse events, but acute kidney failure was more common in patients receiving intravenous colistin.

CONCLUSIONS

This network meta-analysis suggests that most antibiotic regimens, including new combinations and cefiderocol, have similar efficacy and safety in treating susceptible Gram-negative bacilli in NP. Further studies are necessary for NP caused by multidrug-resistant bacteria. Registration PROSPERO CRD42021226603.

Efficacy of Continuous vs. Intermittent Administration of Cefepime in Adult ICU Patients with Gram-Negative Bacilli Bacteremia: A Randomized Double-Blind Clinical Study

INTRODUCTION

The objective of this study was to compare the continuous infusion of cefepime with the intermittent infusion in patients with sepsis caused by Gram-negative bacilli (GNB).

METHODS

Randomized 1:1 multicenter double-blinded placebo-controlled study with allocation concealment; multicenter study in the intensive care units of Colombia. Patients with sepsis, severe sepsis or septic shock, and GNB-suspected bacteremia. Cefepime was administered for 7 to 14 days over 30 m intermittently every 8 h over 24 h plus continuous saline solution (0.9%) (G1) or 3 g administered continuously plus saline solution every 8 h (0.9%) (G2). The percentage of clinical response at 3, 7, and 14 days, relapse at 28 days, and mortality at discharge were measured.

RESULTS

The recruitment was stopped at the suggestion of the Institutional Review Board (IRB) following an FDA alert about cefepime. Thirty-two patients were randomized; 25 received the intervention, and GNB bacteremia was confirmed in 16 (9 G1 and 7 G2). Favorable clinical response in days 3, 7, and 14 was 88.8%, 88.8%, and 77.8% (G1) and was similar for G2 (85.7%). There were no relapses or deaths in G2, while in G1, one relapse and two deaths were observed.

CONCLUSIONS

The results of this study support the use of cefepime for the treatment of Gram-negative infections in critically ill patients, but we could not demonstrate differences between continuous or intermittent administration because of the small sample size, given the early suspension of the study.

Comparison of Outcomes in Neonates Receiving Cefepime or Ceftazidime

OBJECTIVES

Cefepime and ceftazidime are alternatives to cefotaxime for management of Gram-negative infections in neonates. The objective was to evaluate neonatal outcomes when receiving cefepime or ceftazidime.

METHODS

This was a single center, retrospective analysis of neonates exposed to at least 24 hours of cefepime or ceftazidime between June 1, 2018, and June 1, 2021. The primary outcome was incidence of culture-positive, late-onset sepsis after initial exposure. Secondary outcomes included culture-negative, respiratory, urinary tract, and resistant infections; necrotizing enterocolitis; length of stay; age at discharge; mortality; and adverse effects.

RESULTS

A total of 105 neonates were included (cefepime, n = 50; ceftazidime, n = 55). Baseline characteristics were similar except more cumulative days of antibiotics (25.0 [IQR, 9.3-47.0] versus 9.0 [IQR, 4.0-23.5], p = 0.01), central line days (11.0 [IQR, 6.0-40.0] versus 6.5 [IQR, 0.0-11.5], p = 0.001), and ventilator days (13.0 [IQR, 2.3-48.0] versus 4.0 [IQR, 0.0-25.0], p = 0.02) were found in the cefepime group than in the ceftazidime group. There was no difference in culture-positive sepsis after the initial antibiotic course (8.0% versus 3.6%, p = 0.42). Statistical differences were seen in select secondary outcomes including treated respiratory infections (16.0% versus 1.8%, p = 0.01), length of stay greater than 30 days (72.0% versus 50.9%, p = 0.03), and mortality (26.0% versus 9.1%, p = 0.02). These differences were not observed in analyses adjusted for ventilator days.

CONCLUSIONS

This analysis found no difference in culture-positive sepsis in neonates exposed to cefepime versus ceftazidime. Moreover, there were no differences in secondary outcomes in adjusted analyses. Further research is needed to assess neonatal outcomes in a larger analysis.

Pharmacokinetics of YK-1169 in healthy subjects and pharmacokinetic/pharmacodynamic analysis by Monte Carlo simulation

OBJECTIVE

This study (NCT05588531) aimed to evaluate the safety and pharmacokinetics of cefepime-avibactam (YK-1169) in healthy Chinese subjects and explore the optimal regimen for treating carbapenem-resistant Klebsiella pneumoniae (CRKP) based on the pharmacokinetic/pharmacodynamic evaluation.

METHODS

YK-1169 single-ascending doses (0.5, 1.25, 2.5 or 3.75 g, 2-h infusion) and multiple doses (2.5 or 3.75 g every 8 h [q8h], 2-h infusion) given for 7 days were evaluated in pharmacokinetic studies. Subjects were randomized to receive cefepime (2 g), avibactam (0.5 g) or YK-1169 (2.5 g) to assess drug-drug interactions. The minimum inhibitory concentrations (MICs) of YK-1169 were determined by the broth microdilution method. Monte Carlo simulation was used to evaluate 10 different dose regimens.

RESULTS

Cefepime and avibactam both showed a linear pharmacokinetic profile. No accumulation was found after multiple doses. The cefepime Cmax,ss and AUC0-∞,ss were 9.20 and 16.0 μg/mL, 407.2 and 659.45 μg·h/mL in the 2.5 and 3.75 g multiple-dose groups, respectively. The avibactam Cmax,ss and AUC0-∞,ss were 0.545 and 0.837 μg/mL, 53.31 and 79.55 μg·h/mL in the 2.5 and 3.75 g multiple-dose groups, respectively. Cefepime and avibactam did not affect each other's pharmacokinetics. No serious adverse events occurred. All regimens achieved 90% probability of target attainment (PTA) goals when the MIC was ≤8 mg/L. The regimens of 2.5 (q8h, 2-h infusion), 3.75 (q8h, 2-, 3- and 4-h infusions) and 7.5 g (24-h continuous infusion) reached a 90% cumulative fraction of response.

CONCLUSION

YK-1169 had good antibacterial activity against CRKP and could be an option for CRKP infections. The regimen of 2.5 g q8h intravenously guttae (ivgtt) 2 h should be considered in future clinical trials.

Pharmacokinetics of Ceftazidime in Children and Adolescents with Obesity

PURPOSE

The aim of this study was to evaluate ceftazidime pharmacokinetics (PK) in a cohort that includes a predominate number of children and adolescents with obesity and assess the efficacy of competing dosing strategies.

METHODS

A population PK model was developed using opportunistically collected plasma samples. For each dosing strategy, model-based probability of target attainment (PTA) estimates were computed for study participants using empirical Bayes estimates. In addition, the effects of body size and renal function on PTA were evaluated using stochastic model simulations with virtually generated subjects.

RESULTS

Twenty-nine participants, 24 of whom were obese, contributed data towards the analysis. The median (range) age, body weight, and body mass index of participants were 12.2 years (2.3-20.6), 59.2 kg (8.4-121), and 25.2 kg/m2 (13.8-42.9), respectively. Administration of 50 mg/kg intravenously (IV) every 8 hours (q8h; max 6 g/day) or 40 mg/kg IV q6h (max 6 g/day) resulted in PTA values of ≥ 90% (minimum inhibitory concentration 8 mg/L) for the subset of obese participants with estimated glomerular filtration rates (GFR) ≥ ~ 80 mL/min/1.73 m2. However, for both regimens, stochastic model simulations denoted lower PTA values (< 90%) with increasing body weight for virtual subjects with GFR ≥ 120 mL/min/1.73 m2. Alternatively, permitting for a maximum daily dose of 8 g/day using a 40 mg/kg IV q6h regimen provided PTA values that were near or above target (90%) for virtual subjects between 10 to 120 kg with GFR ≥ 80 mL/min/1.73 m2.

CONCLUSION

Our analysis suggests administration of 40 mg/kg IV q6h (max 8 g/day) maximizes PTA in children and adolescents with obesity and GFR ≥ 80 mL/min/1.73 m2.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: NCT01431326.

Pharmacokinetic evaluation of cefquinome in febrile goats following intravenous administration

Pharmacokinetics of cefquinome was studied in febrile female goats following its intravenous (IV) administration at the dose rate of 2 mg/kg body weight. The fever was induced by administration of Escherichia coli lipopolysaccharide (lμg/kg body weight). Cefquinome concentration in plasma of goats was estimated using HPLC. The drug was detected upto 24 h in febrile goats. The disposition kinetics of the drug was described by twocompartment open model. PK-PD indices; AUC24h/MIC, Cmax/MIC, T>MIC were calculated by integrating in-vivo PK data with earlier generated MIC data against Pasteurella (P.) multocida. A favourable PK and PK-PD indices suggested that the dose of 2 mg/kg/24 h of cefquinome would be effective clinically to treat goats affected with P. multocida infections.

A Meta-Analysis of the Prevalence of Class 1 Integron and Correlation with Antibiotic Resistance in Pseudomonas aeruginosa Recovered from Iranian Burn Patients

The role of integrons has been highlighted in antibiotic resistance among Pseudomonas aeruginosa isolates. Therefore, we here reviewed the prevalence of class 1 integrons and their correlations with antibiotic resistance of P. aeruginosa isolated from Iranian burn patients. This review was conducted according to the guidelines of Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA). Cross-sectional and cohort studies published from January 1, 2000 until December 31, 2018 were enrolled. Meta-analysis was performed by Comprehensive Meta-Analysis (CMA) software using the random effects model, Cochran's Q, and I2 tests. Publication bias was estimated by Funnel plot and Egger's linear regression test. Nine out of 819 studies met the eligibility criteria. The overall combined prevalence of class 1 integrons in P. aeruginosa isolates was 69% (95% confidence interval [CI]: 50.5-83%). The highest combined resistance was reported against Cloxacillin (87.7%), followed by Carbenicillin (79.1%) and Ceftriaxone (77.3%). The combined prevalence of multidrug-resistant (MDR) isolates was 79.3% (95% CI: 31.1-97%). Also, a significant correlation was noted between the presence of class 1 integrons and antibiotic resistance in 55.5% of the included studies (P < .05). The results showed high prevalence of class 1 integrons, antibiotic resistance, and MDR strains in P. aeruginosa isolated from Iranian burn patients. Also, most of the included studies showed a significant correlation between the presence of class 1 integrons and antibiotic resistance.

Evaluating the best empirical antibiotic therapy in patients with acute-on-chronic liver failure and spontaneous bacterial peritonitis

BACKGROUND/AIMS

Spontaneous bacterial peritonitis (SBP) is a life-threatening complication of advanced cirrhosis. By studying the susceptibility of isolated organisms and analyzing empirical antibiotic therapy combined with clinical outcomes, we aimed to find an improved empirical antibiotic therapy by considering the individual acute-on-chronic liver failure (ACLF) grade for patients with or without sepsis.

METHODS

Clinical outcomes of 182 patients were assessed retrospectively with multivariable regression analysis. Each of the 223 isolates was individually evaluated regarding susceptibility results and intrinsic resistances.

RESULTS

Piperacillin/tazobactam had the highest antimicrobial susceptibility among monotherapies/fixed combinations, which was significantly lower than combination therapies such as meropenem-linezolid (75.3% vs. 98.5%, P < 0.001). The sensitivity of pathogens to empirical antibiotic therapy correlated with significantly lower inpatient mortality (18.9% vs. 37.0%, P = 0.018), shorter inpatient stay (16.3 ± 10.2 vs. 26.4 ± 21.0 days, P = 0.053) and shorter intensive care treatment (2.1 ± 4.5 vs. 7.9 ± 15.4 days, P = 0.016). The largest difference of mortality was observed in patients with ACLF grade 3 (54.5% vs. 73.1% [sensitive vs. non-sensitive]).

CONCLUSION

All SBP patients benefited from efficient empirical antibiotic therapy, regarding the reduced inpatient mortality and complications. For SBP patients with ACLF grade 3 without sepsis, the combination therapy with meropenem-linezolid may be suitable considering the susceptibility results and the concentration in the peritoneal cavity.

Comparison of efficiency of intravitreal ceftazidime and intravitreal cefepime in the treatment of experimental Pseudomonas aeruginosa endophthalmitis

In this study, we evaluated the efficiency of cefepime in the treatment of experimental Pseudomonas aeruginosa endophthalmitis. We compared the findings with the standard dose of ceftazidime (1 mg/0.1 ml). Thirty-six New-Zealand White rabbits were divided into 6 equal groups and were treated with different methods (Group 1 = sham, Group 2 = 0.5 mg/0.1 ml cefepime, Group 3 = 1 mg/0.1 ml cefepime, Group 4 = 2 mg/0.1 ml cefepime, Group 5 = 1 mg/0.1 ml ceftazidime, Group 6 = control). The eyes of rabbits in each group were examined clinically on 1^st, 3^rd, and 6^th day of the experiment. At 6^th day, 0.1 ml vitreous humor aspirates were obtained and plated for quantification on the blood agar and the results were expressed as colony-forming unit/ml. Subsequently, the eyeballs were enucleated and the histopathological evaluation was performed. Our findings denoted beneficial effects of cefepime in treatment groups (especially, in Groups 3 and 4). Intravitreal cefepime may be an alternative drug in the treatment of P. aeruginosa endophthalmitis.

Ceftazidime for respiratory infections

INTRODUCTION

Ceftazidime is a third-generation cephalosporin that has activity against Gram-negative bacilli, including Pseudomonas aeruginosa. The increasing prevalence of antimicrobial resistance and the limited number of antimicrobial agents in development have necessitated a review of the current status of treatments involving ceftazidime.

AREAS COVERED

This review focuses on studies examining the in vitro antibacterial activity of ceftazidime against recent clinical isolates and recent randomized controlled trials studying the clinical efficacy of ceftazidime, and discusses strategies for the optimal use of ceftazidime for treating respiratory tract infections, mainly hospital-acquired pneumonia (HAP).

EXPERT OPINION

Although ceftazidime remains an important option for HAP treatment, its role as an effective antimicrobial agent has been compromised by the sharp increase in resistance rates over the last decade, especially in P. aeruginosa and Acinetobacter baumannii. To maintain or improve the clinical use of ceftazidime in patients with severe HAP, it will be essential to gain a thorough understanding of local resistance patterns, reserve ceftazidime use when pathogens are susceptible to other third-generation cephalosporins, optimize ceftazidime therapy using prolonged or continuous infusion, determine the effectiveness of the combination of ceftazidime with inhibitors of broad-spectrum β-lactamases and role of combination therapy for P. aeruginosa infections, and judiciously use antimicrobial agents through individualization of antimicrobial therapy for HAP.

Piperacillin/tazobactam versus cefozopran for the empirical treatment of pediatric cancer patients with febrile neutropenia

BACKGROUND

The aim of this study was to evaluate the efficacy and safety of piperacillin/tazobactam (PIP/TAZO) and cefozopran (CZOP) monotherapy in pediatric cancer patients with febrile neutropenia (FN).

PROCEDURE

A total of 119 febrile episodes in 49 neutropenic pediatric cancer patients (20 females and 29 males) with a median age of 6.8 years (range, 0.3-18.4 years) received randomized treatment either with PIP/TAZO 125 mg/kg every 8 hr or CZOP 25 mg/kg every 6 hr. Clinical response was determined at completion of therapy. Durations of fever and neutropenia, the need for modification of the therapy, and mortality rates were compared between the two groups.

RESULTS

The frequency of success without modification of treatment was not significantly different between PIP/TAZO (59.6%) and CZOP (53.2%). Durations of fever and antibiotic therapy did not differ between the treatment groups, and no major side effects were observed in either group.

CONCLUSIONS

PIP/TAZO and CZOP monotherapy were both effective and safe for the initial empirical treatment of pediatric cancer patients with FN.

Cefepime-resistant Pseudomonas aeruginosa

Resistance to extended-spectrum cephalosporins complicates treatment of Pseudomonas aeruginosa infections. To elucidate risk factors for cefepime-resistant P. aeruginosa and determine its association with patient death, we conducted a case-control study in Philadelphia, Pennsylvania. Among 2,529 patients hospitalized during 2001-2006, a total of 213 (8.4%) had cefepime-resistant P. aeruginosa infection. Independent risk factors were prior use of an extended-spectrum cephalosphorin (p<0.001), prior use of an extended-spectrum penicillin (p = 0.005), prior use of a quinolone (p<0.001), and transfer from an outside facility (p = 0.01). Among those hospitalized at least 30 days, mortality rates were higher for those with cefepime-resistant than with cefepime-susceptible P. aeruginosa infection (20.2% vs. 13.2%, p = 0.007). Cefepime-resistant P. aeruginosa was an independent risk factor for death only for patients for whom it could be isolated from blood (p = 0.001). Strategies to counter its emergence should focus on optimizing use of antipseudomonal drugs.

Dissemination of cefotaxime-M-producing Escherichia coli isolates in poultry farms, but not swine farms, in China

The objective of this study was to investigate the distribution of extended spectrum β-lactamase (ESBL)-producing Escherichia coli isolates in swine and poultry farms in China. Rectal or cloaca swabs of swine and chicken were collected from four province-level regions of China, and E. coli isolates were recovered and tested for antimicrobial susceptibility. The isolates producing ESBLs were further characterized by pulsed-field gel electrophoresis (PFGE) and sequence analysis of genes encoding β -lactamases and class I integrons. In total, 156 and 224 E. coli isolates were recovered from rectal swabs of four swine farms and cloaca swabs of six chicken farms, respectively. Prevalence of resistant isolates was higher in chicken than in swine. Fifty-six isolates producing ESBLs were identified from chicken samples, but no ESBL-producing isolates were identified from swine samples. Of 56 ESBL-producing isolates, 54 isolates contained cefotaxime (CTX)-M type β-lactamases, including bla(CTX-M-14) (n = 24), bla(CTX-M-65) (n = 13), bla(CTX-M-55) (n = 10), bla(CTX-M-24) (n = 3), bla(CTX-M-3) (n = 2), bla(CTX-M-15) (n = 1), and bla(CTX-M-64) (n = 1). Among 54 E. coli isolates containing bla(CTX-M), 11 PFGE clusters and 42 PFGE patterns were identified. More importantly, more than three-fourth of the ESBL-producing isolates in chicken were also resistant to ciprofloxacin. Our data demonstrated that chicken had become an important reservoir of bla(CTX-M) in China. Detailed molecular comparison of plasmids and genomes of isolates from various sources will help to better define the transmission dynamics of bla(CTX-M) between humans and food-producing animals.

A prospective, randomized study comparing cefozopran with piperacillin-tazobactam plus ceftazidime as empirical therapy for febrile neutropenia in children with hematological disorders

BACKGROUND

The aim of this randomized study was to evaluate the efficacy of cefozopran monotherapy and piperacillin-tazobactam plus ceftazidime (PIPC/TAZ + CAZ) combination therapy in pediatric neutropenic patients.

PROCEDURE

A total of 51 patients with 138 episodes of febrile neutropenia received antibiotic therapy. Of these episodes, 95 were considered eligible for the study. The episodes were treated randomly with either piperacillin-tazobactam (125 mg/kg/day) plus ceftazidime (100 mg/kg/day) or with cefozopran (100 mg/kg/day). Success was defined as resolution of fever and clinical signs of infection within 120 hr following initiation of antibiotic therapy. Duration of neutropenia did not differ statistically between the two groups, and resolution of fever in all cases without complication was seen before recovery from severe neutropenia.

RESULTS

The overall success rate was 61%. There was no statistically significant difference between the two groups: 53% for PIPC/TAZ + CAZ versus 69% for cefozopran (P = 0.122). Blood cultures were positive in eight episodes (8.4%), but there were not deaths as a result of infection.

CONCLUSION

Both cefozopran and PIPC/TAZ + CAZ combination therapy are safe and well tolerated in pediatric neutropenic patients. Our results show that cefozopran is a good candidate for monotherapy for neutropenic fever.

The safety of cefepime in the treatment of infection

BACKGROUND

Cefepime is a fourth-generation cephalosporin usually reserved for treating severe nosocomial pneumonia, as well as empirical treatment of febrile neutropenia, uncomplicated and complicated urinary tract infections, uncomplicated skin and skin structure infections, and complicated intra-abdominal infections.

OBJECTIVE

Since reports of neurotoxic effects and of an all-cause mortality higher with cefepime than with comparators have created some concerns regarding its safety, this paper reviews data available in the PubMed database up to December 2007 on cefepime safety.

METHODS

Literature data from PubMed obtained by combining cefepime and safety, or cefepime and clinical trials, were examined.

RESULTS/CONCLUSIONS

Caution in the use of cefepime should be adopted until new evidence on cefepime safety is available.

Pharmacokinetics/pharmacodynamics of antibacterials in the Intensive Care Unit: setting appropriate dosing regimens

Patients admitted to Intensive Care Units (ICUs) are at very high risk of developing severe nosocomial infections. Consequently, antimicrobials are among the most important and commonly prescribed drugs in the management of these patients. Critically ill patients in ICUs include representatives of all age groups with a range of organ dysfunction related to severe acute illness that may complicate long-term illness. The range of organ dysfunction, together with drug interactions and other therapeutic interventions (e.g. haemodynamically active drugs and continuous renal replacement therapies), may strongly impact on antimicrobial pharmacokinetics in critically ill patients. In the last decade, it has become apparent that the intrinsic pharmacokinetic (PK) and pharmacodynamic (PD) properties are the major determinants of in vivo efficacy of antimicrobial agents. PK/PD parameters are essential in facilitating the translation of microbiological activity into clinical situations, ensuring a successful outcome. In this review, we analyse the typical patterns of antimicrobial activity and the corresponding PK/PD parameters, with a special focus on a PK/PD dosing approach of the antimicrobial agent classes commonly utilised in the ICU setting.

Continuous infusion of beta-lactam antibiotics in severe infections: a review of its role

Continuous infusion of beta-lactam antibiotics has been widely promoted to optimise their time-dependent activity. Increasing evidence is emerging suggesting potential benefits in patient populations with altered pathophysiology, such as seriously ill patients. From a pharmacokinetic viewpoint, much information supports higher trough concentrations of beta-lactam antibiotics when administered by continuous infusion. This advantage of continuous infusion translates into a superior ability to achieve pharmacodynamic targets, particularly when the minimum inhibitory concentration (MIC) of the pathogen is >or=4 mg/L. One drawback of continuous infusion may be limited physicochemical stability. This issue exists particularly for carbapenem antibiotics whereby prolonged infusions (i.e. >3h) can be used to improve the time above the MIC compared with conventional bolus dosing. Few studies have examined clinical outcomes of bolus and continuous dosing of beta-lactam antibiotics in seriously ill patients. No statistically significant differences have been shown for: mortality; time to normalisation of leukocytosis or pyrexia; or duration of mechanical ventilation, intensive care unit stay or hospital stay. Some evidence suggests improved clinical cure and resolution of illness with continuous infusion in seriously ill patients. Pharmacoeconomic advantages of continuous infusion of beta-lactam antibiotics are well characterised. Available data suggest that seriously ill patients with severe infections requiring significant antibiotic courses (>or=4 days) may be the subgroup that will achieve better outcomes with continuous infusion.