Does Combination Therapy With Vancomycin and Piperacillin-Tazobactam Increase the Risk of Nephrotoxicity Versus Vancomycin Alone in Pediatric Patients?

Epidemiology of Vancomycin in Combination With Piperacillin/Tazobactam-Associated Acute Kidney Injury in Children: A Systematic Review and Meta-analysis

BACKGROUND

Several studies have shown that vancomycin combined with piperacillin/tazobactam (VPT) increased the risk of acute kidney injury (AKI) compared with other antibiotics in children. However, the epidemiology of VPT-associated AKI in children is unknown.

OBJECTIVE

To evaluate the incidence and risk factors of VPT-associated AKI in children.

DATA SOURCES

Literature databases of PubMed, Embase, Cochrane Library, China National Knowledge Infrastructure (CNKI), VIP Database, WanFang Database, and China Biology Medicine Disc were searched from inception to November 2023. References of included studies were also manually checked.

STUDY SELECTION AND DATA EXTRACTION

Two independent reviewers selected studies, extracted data, and quality assessment. Meta-analyses were performed to quantify the incidence and risk factors of VPT-associated AKI in children.

DATA SYNTHESIS

Sixteen cohort studies were identified. Overall, the incidence of VPT-associated AKI in children was 24.3% (95% CI: 17.9%-30.6%). The incidence of VPT-associated AKI in critically ill children (26.6%) was higher than that in noncritically ill children (10.9%). Moreover, higher serum vancomycin trough concentration (>15 mg/L), use of vasopressors, combination of nephrotoxins and intensive care unit admission were risk factors for VPT-associated AKI in children (P < 0.05).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Identifying high-risk groups and determining safer treatments is critical to reducing the incidence of VPT-associated AKI in children.

CONCLUSIONS

The incidence of VPT-associated AKI in children is high, especially in critically ill children. Medication regimens should be personalized based on the presence of individual risk factors. Moreover, renal function was regularly assessed throughout treatment with VPT.

Vancomycin-associated acute kidney injury epidemiology in children: a systematic review

INTRODUCTION

Vancomycin is a recognised cause of drug-induced acute kidney injury (AKI).

OBJECTIVE

The aim of this systematic review was to summarise the incidence of, and the risk factors for, vancomycin-associated AKI (v-AKI) in children.

DESIGN

A systematic search was performed in November 2020 on the search engines PubMed, Web of Science and Medline, using predefined search terms. The inclusion criteria were primary paediatric studies, intervention with vancomycin and studies that included AKI as an outcome. Study quality was assessed using the relevant Critical Appraisal Skills Programme checklist. The data are reported using descriptive statistics.

RESULTS

890 studies were identified and screened with 25 studies suitable for inclusion. A cohort of 12 730 patients with v-AKI were included and the incidence of v-AKI in children was found to be 11.8% (1.6%-27.2%). The median age of the cohort was 2.5 years (range 0-23) and 57% were male patients. Risk factors that increased the likelihood of v-AKI were concomitant use of nephrotoxic medications, increased trough concentrations and, to a lesser extent, increased dose, longer duration of treatment, impaired renal function and if the patient required paediatric intensive care.

CONCLUSIONS

The incidence of v-AKI in children is significant and methods to reduce this risk should be considered. Further prospective interventional studies to understand the mechanisms of nephrotoxicity from vancomycin are needed and targeting risk factors may make vancomycin administration safer.

Extended infusion of piperacillin-tazobactam versus intermittent infusion in critically ill egyptian patients: a cost-effectiveness study

Extended infusion of piperacillin/tazobactam over 4 h has been proposed as an alternate mode of administration to the 30-min intermittent infusion to optimize treatment effects in patients with gram-negative bacterial infections. The study aimed to evaluate the extended infusion regimen of piperacillin/tazobactam in standings of efficacy, safety, and cost to the intermittent one in the treatment of gram-negative bacterial infections. A prospective randomized comparative study was performed on 53 patients, 27 in the intermittent infusion group and 26 in the extended infusion group. The primary outcome was the mean number of days to clinical success and the percentage of patients who were clinically cured after treatment. The secondary outcomes included mortality, readmission within 30-days, and cost-effectiveness analysis based on the mean number of days to clinical success. The clinical success rate was comparable in the two groups. Days on extended infusion were significantly lower than intermittent infusion (5.7 vs 8.9 days, respectively, p = 0.0001) as well as days to clinical success (4.6 vs 8.5 days, respectively, p = 0.026). The extended infusion was superior to the intermittent infusion regarding cost-effectiveness ratio ($1835.41 and $1914.09/expected success, respectively). The more cost-effective regimen was the extended infusion. Both regimens had comparable clinical and microbiological outcomes.

Impact of ascorbic acid in reducing the incidence of vancomycin associated nephrotoxicity in critically ill patients: A preliminary randomized controlled trial

Background Antioxidants show nephroprotective effect against vancomycin associated nephrotoxicity (VAN) in animals. This study aimed to assess the ascorbic acid nephro-protective role against VAN clinically.

Methods Forty-one critically ill patients were randomly assigned to one of two groups: intervention group (vancomycin IV plus ascorbic acid, n=21) or control group (vancomycin IV only, n=20). Primary outcomes were the incidence of VAN and the absolute change in creatinine parameters, while mortality rate was the secondary outcome. Nephrotoxicity was defined as an increase in serum creatinine (S.cr) by at least 0.5 mg/dL or 50% of baseline for at least two successive measurements. This study is registered at Clinicaltrials.gov (NCT03921099), April 2019.

Results Mean absolute S.cr increase was significant when compared between both groups, P-value = 0.036, where S.cr increased by 0.05(0.12) and 0.34(0.55) mg/dL in the intervention and control groups, respectively. Mean absolute Cr.cl decline was significant when compared between both groups, P-value = 0.04, where Cr.cl was decreased by 5.9(17.8) and 22.3(30.4) ml/min in the intervention and control groups, respectively. Incidence of VAN was 1/21(4.7%) versus 5/20(25%) in the intervention and control groups, respectively (RR: 0.19; CI: 0.024–1.49; P-value = 0.093). Mortality was higher in the control group; however, it was not statistically significant, P-value = 0.141.

Conclusion Co-administration of ascorbic acid with vancomycin preserved renal function and reduced the absolute risk of VAN by 20.3%, however, the reduction in VAN incidence didn’t reach statistical significance level. Further large multicenter prospective trials are recommended.

Lowered Risk of Nephrotoxicity through Intervention against the Combined Use of Vancomycin and Tazobactam/Piperacillin: A Retrospective Cohort Study

The combined use of vancomycin (VCM) and tazobactam/piperacillin (TAZ/PIPC) is a major risk factor for nephrotoxicity. We sought to evaluate interventions against the combined use of VCM and TAZ/PIPC. This retrospective cohort study involved patients who considered the combined use of VCM and TAZ/PIPC as a treatment. Patients that had either or both antimicrobials replaced were assigned to the intervention group, whereas those who were continued on combination therapy were assigned to the comparison group. The primary endpoint was the incidence of acute kidney injury (AKI). The survival rate of patients on day 30 was evaluated as the secondary endpoint. The comparison and intervention groups were composed of 65 and 68 patients, respectively, and the incidence rates of AKI were 44.6% and 17.6%, respectively. Cox proportional hazard analysis identified the intervention as the only independent factor against AKI development, with a hazard ratio of 0.282 (95% confidence interval [CI], 0.141 to 0.565). For the incidence of AKI of grade greater than 1, the hazard ratio was 0.114 (95% CI, 0.025 to 0.497). The survival rates on day 30 in the comparison and intervention groups were 92.3% and 91.2%, respectively, with a relative risk of 0.988 (95% CI, 0.892 to 1.094). The trough VCM concentration was not associated with the incidence of AKI in patients receiving the combination therapy. This study demonstrated that intervention against the combined use of VCM and TAZ/PIPC can lower the risk of nephrotoxicity. IMPORTANCE The combined use of vancomycin (VCM) and tazobactam/piperacillin (TAZ/PIPC) is a major risk factor for nephrotoxicity. We retrospectively evaluated interventions against the combined use of VCM and TAZ/PIPC. Patients for whom either or both antimicrobials were replaced were assigned to the intervention group (65 patients), whereas those who were continued on combination therapy were assigned to the comparison group (68 patients). The primary endpoint was the incidence of acute kidney injury (AKI). The incidence rates of AKI in the intervention and comparison groups were 44.6% and 17.6%, respectively. Cox proportional hazard analysis identified intervention as the only independent factor against AKI development, with a hazard ratio of 0.282 (95% confidence interval [CI], 0.141 to 0.565). In conclusion, this study demonstrated that intervention against the combined use of VCM and TAZ/PIPC can lower the risk of nephrotoxicity.

Incidence and Risk Factors for Acute Kidney Injury in Hospitalized Children Receiving Piperacillin-Tazobactam

OBJECTIVE

Drug-induced kidney injury contributes to morbidity and mortality in hospitalized children. Antibiotics such as TZP have been implicated in the development of acute kidney injury (AKI) in adults; however, data are limited in children. The purpose of this study was to determine the incidence of AKI in hospitalized children receiving TZP.

METHODS

This was a retrospective cohort study of hospitalized children between 2 months and 19 years of age who received TZP for at least 48 hours. Acute kidney injury was defined as a 50% increase from the initial serum creatinine (SCr) prior to TZP initiation. Serum creatinine values were adjusted for fluid balance using a validated approach. Severity of AKI was characterized using the Pediatric Risk, Injury, Failure, Loss, End-Stage Renal Disease (pRIFLE) criteria. Descriptive and inferential statistics were used to describe the incidence and risk factors of AKI, with an alpha = 0.05.

RESULTS

A total of 65 subjects were included. Twenty-five (38.5%) required PICU admission. The incidence of AKI was 7.7% (n = 5) using adjusted SCr (13.37 cases/1000 patient-days). According to pRIFLE, 6.15% (n = 4) subjects met criteria for Risk (n = 3) or Injury (n = 1), and none developed Failure, Loss, or End-Stage (10.70 cases/1000 patient-days for Risk and Injury categories). No risk factors were identified. Hospital length of stay was longer in subjects who experienced AKI compared with those who did not (p = 0.04).

CONCLUSIONS

The incidence of AKI in hospitalized children exposed to TZP was low. In those who did develop AKI, peak SCr occurred approximately 1 week after TZP initiation.

Risk factors for acute kidney injury in vancomycin and piperacillin/tazobactam combination therapy: A retrospective study

INTRODUCTION

Combined use of vancomycin (VCM) and piperacillin/tazobactam (PIPC/TAZ) has been reported to increase the incidence of acute kidney injury (AKI). However, the risk factors associated with AKI after VCM and PIPC/TAZ (VPT) administration have not yet been identified. Therefore, we retrospectively assessed patients treated with VPT to investigate the risk factors for AKI development.

METHODS

The study involved patients who were treated with VPT from January 1, 2016 to March 31, 2020. The patients were divided into the AKI or non-AKI group. The clinical characteristics of patients and antimicrobial therapy were compared between the groups. Their association with AKI risk was evaluated using multivariate logistic regression analysis.

RESULTS

In total, 182 patients were included, with 118 in the non-AKI group and 64 in the AKI group. Therefore, the incidence of AKI was 35.2 %. The initiation of VPT combination therapy on the same day and concomitant use of vasopressors were associated with an increased risk of AKI (odds ratio [OR] 2.55, 95 % confidential interval [CI] 1.20-5.44 and OR 3.22, 95 % CI 1.31-7.89, respectively).

CONCLUSION

Our findings suggest that the concomitant use of vasopressors and initiating VPT combination therapy on the same day are likely risk factors for AKI development.

Evaluating and Mitigating Risk of Acute Kidney Injury with the Combination of Vancomycin and Piperacillin-Tazobactam in Children

The antibiotic combination of vancomycin (VAN) and piperacillin-tazobactam (PTZ) has been associated with an increased risk of acute kidney injury (AKI) in both adult and pediatric patients. In this review, we highlight some of the limitations of existing pediatric studies evaluating the combination of VAN/PTZ, focusing on AKI risk in specific pediatric patient populations. We also review the variability in defining AKI in children and provide guidance to clinicians for use of prospective surveillance and stewardship in mitigating the risk of AKI in pediatric patients treated with combination of VAN/PTZ. Based on review of available pediatric studies, if the combination of VAN/PTZ is selected as an empirical antibiotic combination, it should be used in those at low risk for AKI and should be used with extreme caution in patients with additional nephrotoxic risks. Systems should be in place to monitor the use of VAN/PTZ and associated renal function in those receiving this antibiotic combination.

Nephrotoxicity from Vancomycin Combined with Piperacillin-Tazobactam: A Comprehensive Review

BACKGROUND

Recent studies have identified the combination of vancomycin with piperacillin-tazobactam (VPT) to be associated with increased nephrotoxicity. Multiple, large cohort studies have found this widely used combination to have a higher risk of nephrotoxicity than other regimens in a variety of populations.

SUMMARY

This review summarizes the epidemiology and clinical features of VPT-associated acute kidney injury (AKI). Potential mechanisms involved in the pathogenesis of this phenomenon are also discussed. Key Message: VPT-associated nephrotoxicity is a recently recognized clinical entity. Clinical strategies to minimize the risk of toxicity in this setting include antimicrobial stewardship, monitoring of kidney function, and emerging data supporting the potential role for novel biomarkers in predicting and managing AKI.

The association of acute kidney injury with the concomitant use of vancomycin and piperacillin/tazobactam in children: A systematic review and meta-analysis

Concomitant use of vancomycin plus piperacillin/tazobactam (TZP) has been associated with increased risk of acute kidney injury (AKI) in hospitalized adults. In this systematic review and meta-analysis, we searched PubMed and EMBASE for pediatric studies examining this hypothesis, with reference to vancomycin monotherapy or in combination with another beta-lactam antibiotic. Out of 1381 non-duplicate studies, 10 met our inclusion criteria. We performed a random effects meta-analysis, based on crude odds ratios, and we accounted for both quality of included studies and publication bias. In primary analysis, concomitant vancomycin and TZP use yielded a statistically significant association with the development of AKI. More specifically, children with AKI had higher odds to have been exposed to vancomycin plus TZP, in comparison with vancomycin monotherapy (OR 8.15; 95% CI: 3.49-18.99), or vancomycin plus any other beta-lactam antibiotic (OR 3.48; 95% CI: 2.71-4.46). Based on the results of the Newcastle Ottawa Scale quality assessment, a secondary analysis including only higher quality studies (6 out of 10 studies) yielded again higher odds of exposure to vancomycin plus TZP, compared to vancomycin plus another beta-lactam antibiotic (OR 3.76; 95% CI: 2.56-5.51). Notably, even after controlling for possible publication bias our results remained statistically significant (OR 3.09; 95% CI: 2.30-4.14). In conclusion, the concomitant use of vancomycin and TZP could be associated with AKI development and the clinical significance of this potential association needs to be studied further in the pediatric population.

Piperacillin/Tazobactam and Antibiotic-Associated Acute Kidney Injury in Critically Ill Children

BACKGROUND

There continues to be uncertainty about whether piperacillin/tazobactam (TZP) increases the risk of AKI in critically ill pediatric patients. We sought to compare rates of AKI among critically ill children treated with TZP or cefepime, an alternative frequently used in intensive care units, with and without vancomycin.

METHODS

We conducted a retrospective cohort study assessing the risk of AKI in pediatric intensive care unit patients after exposure to vancomycin, TZP, and cefepime, alone or in combination, within 48 hours of admission. The primary outcome was development of stage 2 or 3 AKI or an increase in AKI stage from 2 to 3 within the 6 days after the 48-hour exposure window. Secondary outcomes included lengths of stay, need for RRT, and mortality.

RESULTS

Of 5686 patients included, 494 (8.7%) developed stage 2 or 3 AKI. The adjusted odds of developing AKI after medication exposure were 1.56 for TZP (95% confidence interval [95% CI], 1.23 to 1.99), 1.13 for cefepime (95% CI, 0.79 to 1.64), and 0.86 for vancomycin (95% CI, 0.69 to 1.07). The adjusted odds of developing AKI for vancomycin plus TZP versus vancomycin plus cefepime was 1.38 (95% CI, 0.85 to 2.24).

CONCLUSIONS

Observational data in critically ill children show that TZP use is associated with increased odds of AKI. A weaker, nonsignificant association between vancomycin plus TZP and AKI compared with vancomycin plus cefepime, creates some uncertainty about the nature of the association between TZP and AKI. However, cefepime is an alternative not associated with AKI.

Incidence of Nephrotoxicity Among Pediatric Patients Receiving Vancomycin With Either Piperacillin-Tazobactam or Cefepime: A Cohort Study

BACKGROUND

Recent studies in adults have found an incidence of acute kidney injury (AKI) in patients treated with a combination of vancomycin and piperacillin-tazobactam (TZP) that is greater than that expected with either medication alone. The purpose of this study was to determine whether combination therapy with vancomycin and TZP is associated with an incidence of AKI in pediatric patients higher than that in those on combination therapy with vancomycin and cefepime.

METHODS

We performed a retrospective single-center matched-cohort study of pediatric patients who received vancomycin in combination with TZP or cefepime between January 2015 and June 2016. The patients were matched according to chronic disease, age, sex, and number of concomitant nephrotoxic medications at the time of combination antibiotic therapy. The primary outcome was incidence of AKI. Secondary outcomes included differences between groups in time to AKI, resolution of AKI, and effect of vancomycin trough levels on the incidence of nephrotoxicity. Conditional logistic regression was used to compare categorical and continuous variables between treatment groups. Conditional Poisson regression was used to assess the association between AKI and treatment groups. Stratified log-rank tests and Cox proportional hazards models with shared frailty were used to compare the times to AKI according to treatment group.

RESULTS

Two hundred twenty-eight matched patients were included. AKI developed in 9 (7.9%) of 114 and 33 (28.9%) of 114 patients in the cefepime and TZP groups, respectively (P < .001). Type of combination therapy remained a significant predictor for AKI in multivariate conditional Poisson analysis in which adjustments were made for age, sex, use of concomitant nephrotoxins, and vancomycin dose (relative risk, 2.5 [95% confidence interval, 1.1-5.8]; P = .03). AKI developed almost 3 times sooner in the TZP group than in the cefepime group (hazard ratio, 2.9 [95% confidence interval, 1.3-6.1]; P = .006). Sensitivity analyses in which adjustment was made for antibiotic indication in addition to the aforementioned variables and excluding those with gastrointestinal infection revealed similar results.

CONCLUSION

Among hospitalized children at our institution, combination therapy with vancomycin and TZP was associated with an incidence of AKI higher than that associated with vancomycin and cefepime.

Incidence of Acute Kidney Injury in Critically Ill Patients Receiving Vancomycin with Concomitant Piperacillin-Tazobactam, Cefepime, or Meropenem

Critically ill patients are frequently treated with empirical antibiotic therapy, including vancomycin and β-lactams. Recent evidence suggests an increased risk of acute kidney injury (AKI) in patients who received a combination of vancomycin and piperacillin-tazobactam (VPT) compared with patients who received vancomycin alone or vancomycin in combination with cefepime (VC) or meropenem (VM), but most studies were conducted predominately in the non-critically ill population. A retrospective cohort study that included 2,492 patients was conducted in the intensive care units of a large university hospital with the primary outcome being the development of any AKI. The rates of any AKI, as defined by the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines, were 39.3% for VPT patients, 24.2% for VC patients, and 23.5% for VM patients (P < 0.0001 for both comparisons). Similarly, the incidences of stage 2 and stage 3 AKI were also significantly higher for VPT patients than for the patients in the other groups. The rates of stage 2 and stage 3 AKI, respectively, were 15% and 6.6% for VPT patients, 5.8% and 1.8% for VC patients, and 6.6% and 1.3% for VM patients (P < 0.0001 for both comparisons). In multivariate analysis, the use of vancomycin in combination with piperacillin-tazobactam was found to be an independent predictor of AKI (odds ratio [OR], 2.161; 95% confidence interval [CI], 1.620 to 2.883). In conclusion, critically ill patients receiving the combination of VPT had the highest incidence of AKI compared to critically ill patients receiving either VC or VM.

Acute Kidney Injury in Pediatric Treated with Vancomycin and Piperacillin-Tazobactam in Tertiary Care Hospital

Background

Vancomycin and piperacillin-tazobactam (PTZ) are commonly used as empirical therapy for patients with health care associated infections. Vancomycin has been recognized as a nephrotoxic agent and in a few cases in the literature PTZ has been associated with interstitial nephritis nevertheless; the combination of these agents has routinely been used for many years. However, there have been some observational studies that showed high rates of acute kidney injury (AKI) in patients receiving vancomycin and PTZ concomitant treatment compared to patients receiving vancomycin alone. The incidence of AKI in adult patients receiving vancomycin and PTZ concomitant treatment was reported in these studies to be relatively high. Similar studies in pediatric patients are lacking.

Method

We conducted a single center retrospective chart review of 248 pediatric patients receiving one of the following treatments: vancomycin alone 36 patients, vancomycin/PTZ 62 patients, vancomycin/ceftazidime 99 patients, and vancomycin/ceftriaxone 51 patients.

Result

Our results showed a low incidence of AKI in patients on vancomycin/PTZ concomitant treatment where overall incidence was only (4.8%) three cases and only one of them (2.0%) in a patient receiving the vancomycin/ceftriaxone concomitant treatment. No cases of AKI present in patients receiving vancomycin with ceftazidime or vancomycin alone. There were no statistically significant differences between the four treatment groups in terms of AKI incidence, vancomycin trough, and use of nephrotoxins.

Conclusion

Overall, the incidence of AKI was low in our study sample with no statistically significant increased risk when PTZ was used in combination with vancomycin in a pediatric population. However, further investigation with an equal larger sample size is needed to confirm our findings.

Association of Acute Kidney Injury With Concomitant Vancomycin and Piperacillin/Tazobactam Treatment Among Hospitalized Children

IMPORTANCE

β-Lactam antibiotics are often coadministered with intravenous (IV) vancomycin hydrochloride for children with suspected serious infections. For adults, the combination of IV vancomycin plus piperacillin sodium/tazobactam sodium is associated with a higher risk of acute kidney injury (AKI) compared with vancomycin plus 1 other β-lactam antibiotic. However, few studies have evaluated the safety of this combination for children.

OBJECTIVE

To assess the risk of AKI in children during concomitant therapy with vancomycin and 1 antipseudomonal β-lactam antibiotic throughout the first week of hospitalization.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study focused on children hospitalized for 3 or more days who received IV vancomycin plus 1 other antipseudomonal β-lactam combination therapy at 1 of 6 large children's hospitals from January 1, 2007, through December 31, 2012. The study used the Pediatric Health Information System Plus database, which contains administrative and laboratory data from 6 pediatric hospitals in the United States. Patients with underlying kidney disease or abnormal serum creatinine levels on hospital days 0 to 2 were among those excluded. Patients 6 months to 18 years of age who were admitted through the emergency department of the hospital were included. Data were collected from July 2015 to March 2016. Data analysis took place from April 2016 through July 2017. (Exact dates are not available because the data collection and analysis processes were iterative.).

MAIN OUTCOMES AND MEASURES

The primary outcome was AKI on hospital days 3 to 7 and within 2 days of receiving combination therapy. Acute kidney injury was defined using KDIGO criteria and was based on changes in serum creatinine level from hospital days 0 to 2 through hospital days 3 to 7. Multiple logistic regression was performed using a discrete-time failure model to test the association between AKI and receipt of IV vancomycin plus piperacillin/tazobactam or vancomycin plus 1 other antipseudomonal β-lactam antibiotic.

RESULTS

A total of 1915 hospitalized children who received combination therapy were identified. Of the 1915 patients, a total of 866 (45.2%) were female and 1049 (54.8%) were male, 1049 (54.8%) were identified as white in race/ethnicity, and the median (interquartile range) age was 5.6 (2.1-12.7) years. Among the cohort who received IV vancomycin plus 1 other antipseudomonal β-lactam antibiotic, 157 patients (8.2%) had antibiotic-associated AKI. This number included 117 of 1009 patients (11.7%) who received IV vancomycin plus piperacillin/tazobactam combination therapy. After adjustment for age, intensive care unit level of care, receipt of nephrotoxins, and hospital, IV vancomycin plus piperacillin/tazobactam combination therapy was associated with higher odds of AKI each hospital day compared with vancomycin plus 1 other antipseudomonal β-lactam antibiotic combination (adjusted odds ratio, 3.40; 95% CI, 2.26-5.14).

CONCLUSIONS AND RELEVANCE

Coadministration of IV vancomycin and piperacillin/tazobactam may increase the risk of AKI in hospitalized children. Pediatricians must be cognizant of the potential added risk of this combination therapy when making empirical antibiotic choices.