Pharmacokinetics of Imipenem in Critically Ill Patients with Life-threatening Severe Infections During Support with Extracorporeal Membrane Oxygenation

Imipenem/relebactam pharmacokinetics in critically ill patients supported on extracorporeal membrane oxygenation

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is a life-saving modality but has the potential to alter the pharmacokinetics (PK) of antimicrobials. Imipenem/cilastatin/relebactam is an antibiotic with utility in treating certain multi-drug resistant Gram-negative infections. Herein, we describe the population pharmacokinetics of imipenem and relebactam in critically ill patients supported on ECMO.

METHODS

Patients with infection supported on ECMO received 4-6 doses of imipenem/cilastatin/relebactam per current prescribing information based on estimated creatinine clearance. Blood samples were collected following the final dose of the antibiotic. Concentrations were determined via LC-MS/MS. Population PK models were fit with and without covariates using Pmetrics. Monte Carlo simulations of 1000 patients assessed joint PTA of fAUC0-24/MIC ≥ 8 for relebactam, and ≥40% fT > MIC for imipenem for each approved dosing regimen.

RESULTS

Seven patients supported on ECMO were included in PK analyses. A two-compartment model with creatinine clearance as a covariate on clearance for both imipenem and relebactam fitted the data best. The mean ± standard deviation parameters were: CL0, 15.21 ± 6.52 L/h; Vc, 10.13 ± 2.26 L; K12, 2.45 ± 1.16 h-1 and K21, 1.76 ± 0.49 h-1 for imipenem, and 6.95 ± 1.34 L/h, 9.81 ± 2.69 L, 2.43 ± 1.13 h-1 and 1.52 ± 0.67 h-1 for relebactam. Simulating each approved dose of imipenem/cilastatin/relebactam according to creatinine clearance yielded PTAs of ≥90% up to an MIC of 2 mg/L.

CONCLUSIONS

Imipenem/cilastatin/relebactam dosed according to package insert in patients supported on ECMO is predicted to achieve exposures sufficient to treat susceptible Gram-negative isolates, including Pseudomonas aeruginosa.

Acinetobacter baumannii in the critically ill: complex infections get complicated

Acinetobacter baumannii is increasingly associated with various epidemics, representing a serious concern due to the broad level of antimicrobial resistance and clinical manifestations. During the last decades, A. baumannii has emerged as a major pathogen in vulnerable and critically ill patients. Bacteremia, pneumonia, urinary tract, and skin and soft tissue infections are the most common presentations of A. baumannii, with attributable mortality rates approaching 35%. Carbapenems have been considered the first choice to treat A. baumannii infections. However, due to the widespread prevalence of carbapenem-resistant A. baumannii (CRAB), colistin represents the main therapeutic option, while the role of the new siderophore cephalosporin cefiderocol still needs to be ascertained. Furthermore, high clinical failure rates have been reported for colistin monotherapy when used to treat CRAB infections. Thus, the most effective antibiotic combination remains disputed. In addition to its ability to develop antibiotic resistance, A. baumannii is also known to form biofilm on medical devices, including central venous catheters or endotracheal tubes. Thus, the worrisome spread of biofilm-producing strains in multidrug-resistant populations of A. baumannii poses a significant treatment challenge. This review provides an updated account of antimicrobial resistance patterns and biofilm-mediated tolerance in A. baumannii infections with a special focus on fragile and critically ill patients.

A personalised approach to antibiotic pharmacokinetics and pharmacodynamics in critically ill patients

Critically ill patients admitted to intensive care unit (ICU) with severe infections, or those who develop nosocomial infections, have poor outcomes with substantial morbidity and mortality. Such patients commonly have suboptimal antibiotic exposures at routinely used antibiotic doses related to an increased volume of distribution and altered clearance due to their underlying altered physiology. Furthermore, the use of extracorporeal devices such as renal replacement therapy and extracorporeal membrane oxygenation in these group of patients also has the potential to alter in vivo drug concentrations. Moreover, ICU patients are likely to be infected with less-susceptible pathogens. Therefore, one potential contributing cause to the poor outcomes observed in critically ill patients may be related to subtherapeutic antibiotic exposures. Newer concepts include the clinician considering optimised dosing based on a blood antibiotic exposure defined by pharmacokinetic modelling and therapeutic drug monitoring, combined with a knowledge of the antibiotic penetration into the site of infection, thereby achieving optimal bacterial killing. Such optimised dosing is likely to improve patient outcomes. The aim of this review is to highlight key aspects of antibiotic pharmacokinetics and pharmacodynamics (PK/PD) in critically ill patients and provide a PK/PD approach to tailor antibiotic dosing to the individual patient.

Pharmacokinetics of Commonly Used Antimicrobials in Critically Ill Adults During Extracorporeal Membrane Oxygenation: A Systematic Review

PURPOSE

Adequate dosing of antimicrobials is critical to properly treat infections and limit development of resistance and adverse effects. Limited guidance exists for antimicrobial dosing adjustments in patients requiring extracorporporeal membrane oxygenation (ECMO) therapy. A systematic review was conducted to delineate the pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobials in critically ill adult patients requiring ECMO.

METHODS

Medline, EMBASE, Global Health, and All EBM Reviews databases were searched. Grey literature was examined. All studies reporting PK/PD parameters of antimicrobials in critically ill adults treated with ECMO were included, except for case reports and congress abstracts. Ex vivo studies were included. Two independent reviewers applied the inclusion and exclusion criteria. Reviewers were then paired to independently abstract data and evaluate methodological quality of studies using the ROBINS-I tool and the compliance with ClinPK guidelines. Patients' and studies' characteristics, key PK/PD findings, details of ECMO circuits and co-treatments were summarized qualitatively. Dosing recommendations were formulated based on data from controlled studies.

RESULTS

Thirty-two clinical studies were included; most were observational and uncontrolled. Fourteen ex vivo studies were analysed. Information on patient characteristics and co-treatments was often missing. The effect of ECMO on PK/PD parameters of antimicrobials varied depending on the studied drugs. Few dosing recommendations could be formulated given the lack of good quality data.

CONCLUSION

Limited data exist on the PK/PD of antimicrobials during ECMO therapy. Rigorously designed and well powered populational PK studies are required to establish empiric dosing guidelines for antimicrobials in patients requiring ECMO support.

PROSPERO REGISTRATION NUMBER

CRD42018099992 (Registered: July 24th 2018).

[Effect of extracorporeal membrane oxygenation on pharmacokinetics of antimicrobial drugs: recent progress and recommendations]

Extracorporeal membrane oxygenation (ECMO) is an effective means to provide life support for patients with severe respiratory or heart failure. Existing studies have shown that ECMO may affect the metabolic process of some drugs by drug adsorption, increasing the apparent distribution volume and changing the clearance rate of the drugs. This review summarizes the recent progress in the studies of the effect of ECMO on the pharmacokinetics of antibacterial and antifungal drugs. For the antibacterial drugs, it is recommended that the dose of teicoplanin, imipenem, and linezolid should be increased during ECMO support, while the dose of azithromycin, ciprofloxacin, and tigecycline should not be modified for the time being. Currently studies on pharmacokinetic changes of antifungal drugs during ECMO support remain limited. Voriconazole can be absorbed substantially by ECMO due to its high lipophilicity, and higher doses are therefore recommended. The dose of micafungin also needs to be increased in children undergoing ECMO. However, current evidence concerning the dose of caspofungin and fluconazole are limited, and it is not clear whether the routine dose should be adjusted during ECMO support.

The role of antibiotic pharmacokinetic studies performed post-licensing

Post-licensing pharmacometric studies can provide a better understanding of the pharmacokinetic (PK) alterations in special patient populations and may lead to better clinical outcomes. Some patient populations exhibit markedly different pathophysiology to general ward patients or healthy individuals. This may be developmental (paediatric patients), a manifestation of an underlying disease pathology (patients with obesity or haematological malignancies) or due to medical interventions (critically ill patients receiving extracorporeal therapies). This paper outlines the factors that affect the PK of special patient populations and describes some novel methods of antimicrobial administration that may increase antimicrobial concentrations at the site of infection and improve treatment of severe infection.

Imipenem Population Pharmacokinetics: Therapeutic Drug Monitoring Data Collected in Critically Ill Patients with or without Extracorporeal Membrane Oxygenation

Carbapenem pharmacokinetic (PK) profiles are significantly different in critically ill patients because of the drastic variability of the patients' physiological parameters. Published population PK studies have mainly focused on specific diseases, and the majority of these studies had small sample sizes. The aim of this study was to develop a population PK model of imipenem in critically ill patients that estimated the influence of various clinical and biological covariates and the use of extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT). A two-compartment population PK model with creatinine clearance (CL_CR), body weight (WT), and ECMO as fixed effects was developed using the nonlinear mixed-effects model (NONMEM). A Monte Carlo simulation was performed to evaluate various dosing schemes and different levels of covariates based on the pharmacokinetic/pharmacodynamic index (ƒ%T>MIC) for the range of clinically relevant MICs. The results showed that there may be insufficient drug use in the clinical routine drug dose regimen, and 750 mg every 6 h (q6h) could achieve a higher treatment success rate. The blood concentrations of imipenem in ECMO patients were lower than those in non-ECMO patients; therefore, dosages may need to be increased. The dosage may need adjustment for patients with a CL_CR of ≤70 ml/min, but the dose should be lowered carefully to avoid the insufficient drug exposure. Dose adjustment is not necessary for patients with WT ranging from 50 to 80 kg. Due to the large variation in PK profile of imipenem in critically ill patients, therapeutic drug monitoring (TDM) should be carried out to optimize drug regimens.

Dose Optimization of Cefpirome Based on Population Pharmacokinetics and Target Attainment during Extracorporeal Membrane Oxygenation

To obtain the optimal dosage regimen in patients receiving extracorporeal membrane oxygenation (ECMO), we developed a population pharmacokinetics model for cefpirome and performed pharmacodynamic analyses. This prospective study included 15 patients treated with cefpirome during ECMO. Blood samples were collected during ECMO (ECMO-ON) and after ECMO (ECMO-OFF) at predose and 0.5 to 1, 2 to 3, 4 to 6, 8 to 10, and 12 h after cefpirome administration. The population pharmacokinetic model was developed using nonlinear mixed effects modeling and stepwise covariate modeling. Monte Carlo simulation was used to assess the probability of target attainment (PTA) and cumulative fraction of response (CFR) according to the MIC distribution. Cefpirome pharmacokinetics were best described by a two-compartment model. Covariate analysis indicated that serum creatinine concentration (SCr) was negatively correlated with clearance, and the presence of ECMO increased clearance and the central volume of distribution. The simulations showed that patients with low SCr during ECMO-ON had lower PTA than patients with high SCr during ECMO-OFF; so, a higher dosage of cefpirome was required. Cefpirome of 2 g every 8 h for intravenous bolus injection or 2 g every 12 h for extended infusion over 4 h was recommended with normal kidney function receiving ECMO. We established a population pharmacokinetic model for cefpirome in patients with ECMO, and appropriate cefpirome dosage regimens were recommended. The impact of ECMO could be due to the change in patient status on consideration of the small population and uncertainty in covariate relationships. Dose optimization of cefpirome may improve treatment success and survival in patients receiving ECMO. (This study has been registered at ClinicalTrials.gov under identifier NCT02581280.).

Antibiotic dosing during extracorporeal membrane oxygenation: does the system matter?

PURPOSE OF REVIEW

The aims of this review are to discuss the impact of extracorporeal membrane oxygenation (ECMO) on antibiotic pharmacokinetics and how this phenomenon may influence antibiotic dosing requirements in critically ill adult ECMO patients.

RECENT FINDINGS

The body of literature describing antibiotic pharmacokinetic and dosing requirements during ECMO support in critically adult patients is currently scarce. However, significant development has recently been made in this research area and more clinical pharmacokinetic data have emerged to inform antibiotic dosing in these patients. Essentially, these clinical data highlight several important points that clinicians need to consider when dosing antibiotics in critically ill adult patients receiving ECMO: physicochemical properties of antibiotics can influence the degree of drug loss/sequestration in the ECMO circuit; earlier pharmacokinetic data, which were largely derived from the neonatal and paediatric population, are certainly useful but cannot be extrapolated to the critically ill adult population; modern ECMO circuitry has minimal adsorption and impact on the pharmacokinetics of most antibiotics; and pharmacokinetic changes in ECMO patients are more reflective of critical illness rather than the ECMO therapy itself.

SUMMARY

An advanced understanding of the pharmacokinetic alterations in critically ill patients receiving ECMO is essential to provide optimal antibiotic dosing in these complex patients pending robust dosing guidelines. Antibiotic dosing in this patient population should generally align with the recommended dosing strategies for critically ill patients not on ECMO support. Performing therapeutic drug monitoring (TDM) to guide antibiotic dosing in this patient population appears useful.