Population pharmacokinetic model-based dosing proposal for ampicillin prophylaxis in cardiac surgery patients with cardiopulmonary bypass

The aim of this study was to describe and quantify pharmacokinetics of ampicillin used prophylactically in cardiac surgery both with and without cardiopulmonary bypass (CPB) using population pharmacokinetic analysis in order to propose an optimal dosing strategy. Adult patients undergoing cardiac surgery and treated with prophylactic dose of 2 g ampicillin were enrolled to this prospective study. Blood samples were collected according to the study protocol and ampicillin plasma concentrations were measured using HPLC/UV system. A three-stage population pharmacokinetic model using nonlinear mixed-effects modelling approach was developed. Totally 273 blood samples obtained from 20 patients undergoing cardiac surgery with the use of the CPB and 20 patients without CPB use were analyzed. Two-comparmental model best fits ampicillin concentration-time data. Mean ± SD body weight-normalized ampicillin central and peripheral volume of distribution was 0.12 ± 0.02 L/kg and 0.15 ± 0.03 L/kg, respectively, while mean ± SD ampicillin clearance in typical patient with eGFR of 1.5 mL/s/1.73 m2 was 1.17 ± 0.05 L/h. The use of CPB did not significantly affect the pharmacokinetics of ampicillin. When administering 2 g of ampicillin before surgery, an additional dose should be administered to reach the PK/PD target of fT > MIC = 50% if the operation lasts longer than 430 min in patients with moderate to severe renal impairment, 320 min in patients with mild renal impairment, 220 min in patients with normal renal function status or 140 min in patients with an augmented renal clearance.

Model-Informed Clinical Practice - Determining an Appropriate Ampicillin-Sulbactam Redosing Regimen in Surgical Patients by Utilizing Population Pharmacokinetics and Target Attainment Analysis

In the current study, population pharmacokinetic (PK) of ampicillin-sulbactam was performed based on the clinical pharmacokinetics data collected from a prospective study conducted in 40 surgical patients undergoing prolonged surgery where antibiotic redosing was implemented. A population PK model was successfully developed to characterize the disposition of ampicillin and sulbactam. The final models were two-compartment models for both drugs, with creatinine clearance and heart failure affecting clearance and body surface area having an impact on the central volume of distribution of both ampicillin and sulbactam. Comprehensive Monte Carlo simulations were performed to evaluate the probability of target attainment (PTA) of 24 different redosing scenarios. Simulation results indicated that the ampicillin-sulbactam 2-h redosing scheme recommended by ASHP guidelines is likely too conservative given that 3-g dose (2-g ampicillin/1-g sulbactam) with 4-h redosing interval can reach the breakpoint of 2 mg/L for ampicillin in all populations even with the aggressive pharmacokinetic/pharmacodynamic (PK/PD) target of 100% fT > MIC. With the target 50% fT > MIC, all redosing schemes evaluated, including the 8-h redosing scenario, are predicted to be able to reach the breakpoint of 64 mg/L in all patients. According to our findings, redosing of ampicillin-sulbactam should be every 4 h instead of the currently recommended 2-h redosing schedule. Our PTA results should inform future updates to existing general antibiotic redosing guidelines; and, when used in combination with the availability of institution- and/or unit-specific ampicillin susceptibility patterns, our PTA results may be used to customize SSI prophylaxis redosing recommendations for ampicillin-sulbactam at individual hospitals.

Dose optimization of β-lactams antibiotics in pediatrics and adults: A systematic review

Background: β-lactams remain the cornerstone of the empirical therapy to treat various bacterial infections. This systematic review aimed to analyze the data describing the dosing regimen of β-lactams.

Methods: Systematic scientific and grey literature was performed in accordance with Preferred Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. The studies were retrieved and screened on the basis of pre-defined exclusion and inclusion criteria. The cohort studies, randomized controlled trials (RCT) and case reports that reported the dosing schedule of β-lactams are included in this study.

Results: A total of 52 studies met the inclusion criteria, of which 40 were cohort studies, 2 were case reports and 10 were RCTs. The majority of the studies (34/52) studied the pharmacokinetic (PK) parameters of a drug. A total of 20 studies proposed dosing schedule in pediatrics while 32 studies proposed dosing regimen among adults. Piperacillin (12/52) and Meropenem (11/52) were the most commonly used β-lactams used in hospitalized patients. As per available evidence, continuous infusion is considered as the most appropriate mode of administration to optimize the safety and efficacy of the treatment and improve the clinical outcomes.

Conclusion: Appropriate antibiotic therapy is challenging due to pathophysiological changes among different age groups. The optimization of pharmacokinetic/pharmacodynamic parameters is useful to support alternative dosing regimens such as an increase in dosing interval, continuous infusion, and increased bolus doses.

Negative pressure wound therapy for patients with mediastinitis: A meta-analysis

To evaluate clinical effects between conditional treatment and negative pressure wound therapy for mediastinal infection. Multiple databases were searched to identify relevant studies, and the articles that eventually satisfied the criteria were included. All the meta-analyses were conducted with the Review Manager 5.2. To estimate the quality of each article, risk of bias table was performed. Finally, nine studies including 648 patients met the eligibility criteria. The negative pressure wound therapy (NPWT) group and the control group included 353 and 295 patients, respectively. The meta-analysis showed no significant difference in operative time (RR = -6.13, 95%CI [-50.00, 37.74], P = .78; P for heterogeneity <.000001, I2 = 100%). The length of hospital stay (MD = -3.07, 95%CI [-4.38, -1.77], P < .00001; P for heterogeneity = .99, I2 = 0%), re-infection (RR = 0.18, 100%CI [0.08, 0.40], P < .00001; P for heterogeneity = 0.48, I2 = 0%), and mortality were significantly different between the two groups (RR = 0.27, 95%CI [0.12, 0.63], P of overall effect = .002). NPWT is a better therapy than conventional treatment for mediastinitis.

In vivo synergism of ampicillin, gentamicin, ceftaroline and ceftriaxone against Enterococcus faecalis assessed in the Galleria mellonella infection model

BACKGROUND

The unfavourable safety profile of aminoglycosides and the synergistic effects observed in vitro have prompted the development of novel dual β-lactam therapies, e.g. ampicillin/ceftriaxone or ampicillin/ceftaroline, for the treatment of Enterococcus faecalis endocarditis.

OBJECTIVES

For comparison with in vitro chequerboard assay results, a partial chequerboard setup of ampicillin/gentamicin, ampicillin/ceftriaxone and ampicillin/ceftaroline against E. faecalis was established in the Galleria mellonella larval infection model.

METHODS

Discrimination of synergistic and additive interactions was based on the evaluation of larval survival, bacterial quantity in the haemolymph and a pathology score index (internal to the workgroup). Single and multiple dosing schemes based on the half-life of ampicillin were applied. Pharmacokinetic data of the antibiotics in the larvae were determined via agar plate diffusion assays.

RESULTS

Ampicillin and ceftriaxone exhibited strain-specific synergistic interactions in the larvae under both dosing regimens, while the other two combinations showed additive effects. Ampicillin/ceftaroline was inferior to ampicillin/ ceftriaxone. Not all synergistic effects observed in vitro could be replicated in the larvae.

CONCLUSIONS

Our results suggest superior efficacy of ampicillin/ceftriaxone for the treatment of high-inoculum enterococcal infections, for at least some strains, but question the benefit of the current standard of adding the nephrotoxic gentamicin compared with the safer ceftriaxone. This is the first study to develop a scheme for differentiation between additive and synergistic effects in larvae and apply a multiple-antibiotic dosing scheme based on the pharmacokinetics of ampicillin. The model allows the analysis of synergistic effects of antimicrobials in an in vivo setting, but the clinical correlation warrants further study.

Dosing antibiotic prophylaxis during cardiopulmonary bypass-a higher level of complexity? A structured review

In highly invasive procedures such as open heart surgery, the risk of post-operative infection is particularly high due to exposure of the surgical field to multiple foreign devices. Adequate antibiotic prophylaxis is an essential intervention to minimise post-operative morbidity and mortality. However, there is a lack of clear understanding on the adequacy of traditional prophylactic dosing regimens, which are rarely supported by data. The aim of this structured review is to describe the relevant pharmacokinetic/pharmacodynamic (PK/PD) considerations for optimal antibiotic prophylaxis for major cardiac surgery including cardiopulmonary bypass (CPB). A structured review of the relevant published literature was performed and 45 relevant studies describing antibiotic pharmacokinetics in patients receiving extracorporeal CPB as part of major cardiac surgery were identified. Some of the studies suggested marked PK alterations in the peri-operative period with increases in volume of distribution (V_d) by up to 58% and altered drug clearances of up to 20%. Mechanisms proposed as causing the PK changes included haemodilution, hypothermia, retention of the antibiotic within the extracorporeal circuit, altered physiology related to a systemic inflammatory response, and maldistribution of blood flow. Of note, some studies reported no or minimal impact of the CPB procedure on antibiotic pharmacokinetics. Given the inconsistent data, ongoing research should focus on clarifying the influence of CPB procedure and related clinical covariates on the pharmacokinetics of different antibiotics during cardiac surgery. Traditional prophylactic dosing regimens may need to be re-assessed to ensure sufficient drug exposures that will minimise the risk of surgical site infections.