Pharmacokinetics of cefepime during continuous renal replacement therapy in critically ill patients

Removal of common antimicrobial agents by sustained low-efficiency dialysis

Adequate dosing of antimicrobials is paramount for treating infections in critically ill patients undergoing kidney replacement therapy; however, little is known about antimicrobial removal by sustained low-efficiency dialysis (SLED). The objective was to quantify the removal of cefepime, daptomycin, meropenem, piperacillin-tazobactam, and vancomycin in patients undergoing SLED. Adult patients ≥18 years with acute kidney injury (AKI) or end-stage kidney disease receiving one of the select antimicrobials and requiring SLED were included. Blood and dialysate flow rates were maintained at 250 and 100 mL/min, respectively. Simultaneous arterial and venous blood samples for the analysis of antibiotic concentrations were collected hourly for 8 hours during SLED (on-SLED). Arterial samples were collected every 2 hours for up to 6 hours while not receiving SLED (off-SLED) for the calculation of SLED clearance, half-life (t1/2) on-SLED and off-SLED, and the fraction of removal by SLED (fD). Twenty-one patients completed the study: 52% male, mean age (±SD) 53 ± 13 years, and mean weight of 98 ± 30 kg. Eighty-six percent had AKI, and 4 patients were receiving cefepime, 3 daptomycin, 10 meropenem, 6 piperacillin-tazobactam, and 13 vancomycin. The average SLED time was 7.3 ± 1.1 hours, and the mean ultrafiltration rate was 95 ± 52 mL/hour (range 10-211). The t1/2 on-SLED was substantially lower than the off-SLED t1/2 for all antimicrobials, and the SLED fD varied between 44% and 77%. An 8-hour SLED session led to significant elimination of most antimicrobials evaluated. If SLED is performed, modification of the dosing regimen is warranted to avoid subtherapeutic concentrations.

Antibiotic dosing recommendations in critically ill patients receiving new innovative kidney replacement therapy

BACKGROUND

The Tablo Hemodialysis System is a new innovative kidney replacement therapy (KRT) providing a range of options for critically ill patients with acute kidney injury. The use of various effluent rate and treatment durations/frequencies may clear antibiotics differently than traditional KRT. This Monte Carlo Simulation (MCS) study was to develop antibiotic doses likely to attain therapeutic targets for various KRT combinations.

METHODS

Published body weights and pharmacokinetic parameter estimates were used to predict drug exposure for cefepime, ceftazidime, imipenem, meropenem and piperacillin/tazobactam in virtual critically ill patients receiving five KRT regimens. Standard free β-lactam plasma concentration time above minimum inhibitory concentration targets (40-60%fT> MIC and 40-60%fT> MICx4) were used as efficacy targets. MCS assessed the probability of target attainment (PTA) and likelihood of toxicity for various antibiotic dosing strategies. The smallest doses attaining PTA ≥ 90% during 1-week of therapy were considered optimal.

RESULTS

MCS determined β-lactam doses achieving ∼90% PTA in all KRT options. KRT characteristics influenced antibiotic dosing. Cefepime and piperacillin/tazobactam regimens designed for rigorous efficacy targets were likely to exceed toxicity thresholds.

CONCLUSION

The flexibility offered by new KRT systems can influence β-lactam antibiotic dosing, but doses can be devised to meet therapeutic targets. Further clinical validations are warranted.

Cefepime Dosing in a Critically Ill Neonate Receiving Continuous Renal Replacement Therapy With the Cardio-Renal Pediatric Dialysis Emergency Machine (CARPEDIEM)

We report on a former 27-week gestational age infant who was placed on the Cardio-Renal Pediatric Dialysis Emergency Machine (CARPEDIEM) at 4 months post-menstrual age while receiving cefepime treatment for an Enterobacter cloacae bacteremia and persistent peritonitis secondary to an infected peritoneal dialysis catheter. Using therapeutic drug monitoring while assessing the clearance of cefepime on continuous renal replacement therapy (CRRT), we were able to successfully treat this patient's infection while also minimizing the risk of side effects from this medication. Current literature supports dosing in adult patients on all modalities of CRRT with effluent flow rates of 20 to 25 mL/kg/hr; however, pharmacokinetic data on cefepime dosing in pediatric CRRT are scant. This case report describes the successful dosing strategy used for this patient while on various rates of continuous veno-venous hemodialysis with CARPEDIEM. Therapeutic drug monitoring of cefepime should be considered in critically ill pediatric patients on CARPEDIEM receiving CRRT.

Cefepime Extraction by Extracorporeal Life Support Circuits

Extracorporeal life support (ECLS) devices are lifesaving for critically ill patients with multi-organ dysfunction. Despite this, patients supported with ECLS are at high risk for ECLS-related complications, including nosocomial infections, and mortality rates are high in this patient population. The high mortality rates are suspected to be, in part, a result of significantly altered drug disposition by the ECLS circuit, resulting in suboptimal antimicrobial dosing. Cefepime is commonly used in critically ill patients with serious infections. Cefepime dosing is not routinely guided by therapeutic drug monitoring and treatment success is dependent upon the percentage of time of the dosing interval that the drug concentration remains above the minimum inhibitory concentration of the organism. This ex vivo study measured the extraction of cefepime by continuous renal replacement therapy (CRRT) and extracorporeal membrane oxygenation (ECMO) circuits. Cefepime was studied in four closed-loop CRRT circuit configurations and a single closed-loop ECMO circuit configuration. Circuits were primed with a physiologic human blood-plasma mixture and the drug was dosed to achieve therapeutic concentrations. Serial blood samples were collected over time and concentrations were quantified using validated assays. In ex vivo CRRT experiments, cefepime was rapidly cleared by dialysis, hemofiltration, and hemodiafiltration, with greater than 96% cefepime eliminated from the circuit by 2 hours. In the ECMO circuits, the mean recovery of cefepime was similar in both circuit and standard control. Mean (standard deviation) recovery of cefepime in the ECMO circuits (n = 6) was 39.2% (8.0) at 24 hours. Mean recovery in the standard control (n = 3) at 24 hours was 52.2% (1.5). Cefepime is rapidly cleared by dialysis, hemofiltration, and hemodiafiltration in the CRRT circuit but minimally adsorbed by either the CRRT or ECMO circuits. Dosing adjustments are needed for patients supported with CRRT.

Pharmacokinetics, Pharmacodynamics, and Dose Optimization of Cefiderocol during Continuous Renal Replacement Therapy

BACKGROUND

The need for continuous renal replacement therapy (CRRT) in critically ill patients with serious infections is associated with clinical failure, emergence of resistance, and excess mortality. These poor outcomes are attributable in large part to subtherapeutic antimicrobial exposure and failure to achieve target pharmacokinetic/pharmacodynamic (PK/PD) thresholds during CRRT. Cefiderocol is a novel siderophore cephalosporin with broad in vitro activity against resistant pathogens and is often used to treat critically ill patients, including those receiving CRRT, despite the lack of data to guide dosing in this population.

OBJECTIVE

The aim of this study was to evaluate the PK and PD of cefiderocol during in vitro and in vivo CRRT and provide optimal dosing recommendations.

METHODS

The PK and dialytic clearance of cefiderocol was evaluated via an established in vitro CRRT model across various modes, filter types, and effluent flow rates. These data were combined with in vivo PK data from nine patients receiving cefiderocol while receiving CRRT from phase III clinical trials. Optimal dosing regimens and their respective probability of target attainment (PTA) were assessed via an established population PK model with Bayesian estimation and 1000-subject Monte Carlo simulations at each effluent flow rate.

RESULTS

The overall mean sieving/saturation coefficient during in vitro CRRT was 0.90 across all modes, filter types, effluent flow rates, and points of replacement fluid dilution tested. Adsorption was negligible at 10.9%. Three-way analysis of variance (ANOVA) and multiple linear regression analyses demonstrated that effluent flow rate is the primary driver of clearance during CRRT and can be used to calculate optimal cefiderocol doses required to match the systemic exposure observed in patients with normal renal function. Bayesian estimation of these effluent flow rate-based optimal doses in nine patients receiving CRRT from the phase III clinical trials of cefiderocol revealed comparable mean (± standard deviation) area under the concentration-time curve values as patients with normal renal function (1709 ± 539 mg·h/L vs. 1494 ± 58.4 mg·h/L; p = 0.26). Monte Carlo simulations confirmed these doses achieved >90% PTA against minimum inhibitory concentrations ≤4 mg/L at effluent flow rates from 0.5 to 5 L/h.

CONCLUSION

The optimal dosing regimens developed from this work have been incorporated into the prescribing information for cefiderocol, making it the first and only antimicrobial with labeled dosing for CRRT. Future clinical studies are warranted to confirm the efficacy and safety of these regimens.

An optimal extended-infusion dosing of cefepime and ceftazidime in critically ill patients with continuous renal replacement therapy

PURPOSE

This study aimed to determine optimal extended-infusion dosing regimens for cefepime and ceftazidime in critically ill patients receiving continuous renal replacement therapy using Monte Carlo Simulations (MCS).

MATERIALS AND METHODS

Pharmacokinetic models were built using published pharmacokinetic/demographic data to predict drug disposition in 5000 virtual critically ill patients receiving continuous venovenous hemofiltration (CVVH) with the standard (20-30 mL/kg/h) and a higher (40 mL/kg/h) effluent rates. MCS was performed to assess the probability of target attainment (PTA) of four cefepime and ceftazidime doses administered over 4-h with the target of ≥60% fT > 4×MIC. The lowest dose attaining PTA ≥90% during the first 48-h was considered optimal. Additionally, risk of drug toxicity was assessed at 48-h using suggested neurotoxicity thresholds.

RESULTS

Cefepime 2 g loading dose (LD), then extended-infusion of 2 g q8hr was optimal in CVVH at 20 mL/kg/h and the same ceftazidime dose was optimal in CVVH at 20-30 mL/kg/h. Higher cefepime and ceftazidime doses were required to be optimal at higher effluent rates. This optimal dose particularly for cefepime likely increases neurotoxicity risk in most virtual patients with all CVVH settings.

CONCLUSIONS

Cefepime and ceftazidime 2 g LD, followed by extended-infusion 2 g q8hr may be optimal in CVVH with standard effluent rates.

Therapeutic Drug Monitoring of Antibiotic Drugs in Patients Receiving Continuous Renal Replacement Therapy or Intermittent Hemodialysis: A Critical Review

PURPOSE

Antibiotics are frequently used in patients receiving intermittent or continuous renal replacement therapy (RRT). Continuous renal replacement may alter the pharmacokinetics (PK) and the ability to achieve PK/pharmacodynamic (PD) targets. Therapeutic drug monitoring (TDM) could help evaluate drug exposure and guide antibiotic dosage adjustment. The present review describes recent TDM data on antibiotic exposure and PK/PD target attainment (TA) in patients receiving intermittent or continuous RRT, proposing practical guidelines for performing TDM.

METHODS

Studies on antibiotic TDM performed in patients receiving intermittent or continuous RRT published between 2000 and 2020 were searched and assessed. The authors focused on studies that reported data on PK/PD TA. TDM recommendations were based on clinically relevant PK/PD relationships and previously published guidelines.

RESULTS

In total, 2383 reports were retrieved. After excluding nonrelevant publications, 139 articles were selected. Overall, 107 studies reported PK/PD TA for 24 agents. Data were available for various intermittent and continuous RRT techniques. The study design, TDM practice, and definition of PK/PD targets were inconsistent across studies. Drug exposure and TA rates were highly variable. TDM seems to be necessary to control drug exposure in patients receiving intermittent and continuous RRT techniques, especially for antibiotics with narrow therapeutic margins and in critically ill patients. Practical recommendations can provide insights on relevant PK/PD targets, sampling, and timing of TDM for various antibiotic classes.

CONCLUSIONS

Highly variable antibiotic exposure and TA have been reported in patients receiving intermittent or continuous RRT. TDM for aminoglycosides, beta-lactams, glycopeptides, linezolid, and colistin is recommended in patients receiving RRT and suggested for daptomycin, fluoroquinolones, and tigecycline in critically ill patients on RRT.

Correlation of antimicrobial fraction unbound and sieving coefficient in critically ill patients on continuous renal replacement therapy: a systematic review

Background

Fraction unbound has been used as a surrogate for antimicrobial sieving coefficient (SC) to predict extracorporeal clearance in critically ill patients on continuous renal replacement therapy (CRRT), but this is based largely on expert opinion.

Objectives

To examine relationships between package insert-derived fraction unbound (Fu-P), study-specific fraction unbound (Fu-S), and SC in critically ill patients receiving CRRT.

Methods

English-language studies containing patient-specific in vivo pharmacokinetic parameters for antimicrobials in critically ill patients requiring CRRT were included. The primary outcome included correlations between Fu-S, Fu-P, and SC. Secondary outcomes included correlations across protein binding quartiles, serum albumin, and predicted in-hospital mortality, and identification of predictors for SC through multivariable analysis.

Results

Eighty-nine studies including 32 antimicrobials were included for analysis. SC was moderately correlated to Fu-S (R2 = 0.55, P < 0.001) and Fu-P (R2 = 0.41, P < 0.001). SC was best correlated to Fu-S in first (<69%) and fourth (>92%) quartiles of fraction unbound and above median albumin concentrations of 24.5 g/L (R2 = 0.71, P = 0.07). Conversely, correlation was weaker in patients with mortality estimates greater than the median of 55% (R2 = 0.06, P = 0.84). SC and Fu-P were also best correlated in the first quartile of antimicrobial fraction unbound (R2 = 0.66, P < 0.001). Increasing Fu-P, flow rate, membrane surface area, and serum albumin, and decreasing physiologic charge significantly predicted increasing SC.

Conclusions

Fu-S and Fu-P were both reasonably correlated to SC. Caution should be taken when using Fu-S to calculate extracorporeal clearance in antimicrobials with 69%–92% fraction unbound or with >55% estimated in-hospital patient mortality. Fu-P may serve as a rudimentary surrogate for SC when Fu-S is unavailable.

Population pharmacokinetics of cefepime in critically ill patients receiving extracorporeal membrane oxygenation (an ASAP ECMO study)

OBJECTIVES

This study aimed to describe the population pharmacokinetics (PK) of cefepime during extracorporeal membrane oxygenation (ECMO) and through dosing simulations, identify a maximally effective and safe dosing strategy.

METHODS

Serial cefepime plasma concentrations were measured in patients on ECMO, and data were analysed using a population PK approach with Pmetrics®. Dosing simulations were used to identify the optimal dosing strategy that achieved target trough concentrations (C_min) of 8-20 mg/L. Six patients were enrolled, of which one was receiving renal replacement therapy. Cefepime was best described in a two-compartment model, with total body weight and creatinine clearance (CrCL) as significant predictors of PK parameters. The mean clearance and central volume of distribution were 2.42 L/h and 15.09 L, respectively.

RESULTS

Based on simulations, patients with CrCL of 120 mL/min receiving 1 g 8-hourly dosing achieved a 40-44% probability of efficacy (C_min > 8 mg/L) and 1-6% toxicity (C_min > 20 mg/L). Patients with CrCL 30 mL/min and 65 mL/min receiving 1 g 12-hourly dosing achieved an 84-92% and 46-53% probability of efficacy and 8-44% and 1-8% probability of toxicity, respectively. Simulations demonstrated a lower probability of efficacy and higher probability of toxicity with decreasing patient weight.

CONCLUSION

This study reported reduced cefepime clearance in patients receiving ECMO, resulting in an increased risk of cefepime toxicity. To avoid drug accumulation, modified dosing regimens should be used in critically ill patients on ECMO. Clinicians should adopt therapeutic drug monitoring when treating less susceptible organisms and in patients with reduced renal clearance on ECMO.

Applying cefepime population pharmacokinetics on critically ill patients receiving continuous renal replacement therapy

Patients admitted to the intensive care unit (ICU) may need continuous renal replacement therapy (CRRT) due to acute kidney injury or worsening of underlying chronic kidney disease. This will affect their antimicrobial exposure and may have a significant impact on the treatment. We aim to develop a cefepime pharmacokinetic (PK) model in CRRT ICU patients and generate the posterior predictions for a group and assess their therapy outcomes. Adult patients, admitted to the ICU, received cefepime, and had its concentration measured while on CRRT were included from three different datasets. In two datasets, samples were collected from the predialyzer, postdialyzer ports, and effluent fluid at different times within the same dosing interval. The third dataset had only cefepime plasma concentration measured as part of clinical service. Patients' demographics, cefepime regimens and concentration, CRRT parameters, and therapy outcomes were recorded. NPAG was used for population PK and posterior predictions. A total of 125 patients were included. Cefepime was described by a five-compartment model, and the CRRT flow rates described the rates of cefepime transfer between compartments. The posterior predictions were generated for the third dataset and the median (range) fT_>MIC was 100% (27%-100%) and fT_>4×MIC was 64% (0%-100%). The mortality rate was 53%. There was no difference in target attainment in terms of clinical cure and 30-day mortality. This model can be used as a precision dosing tool in CRRT patients. Future studies may address other PK/PD targets in a larger population.

Cefepime Population Pharmacokinetics and Target Attainment in Critically Ill Patients on Continuous Renal Replacement Therapy

Sepsis causes half of acute kidney injuries in the intensive care unit (ICU). ICU patients may need continuous renal replacement therapy (CRRT), which will affect their antimicrobial exposure. We aimed to build a cefepime population pharmacokinetic (PK) model in CRRT ICU patients and perform simulations to assess target attainment. Patients who were ≥18 years old, were admitted to the ICU, and received cefepime 2 g every 8 h as a 4-h infusion while on CRRT were enrolled prospectively. Samples were collected from the predialyzer ports, postdialyzer ports, and effluent fluid at 1, 2, 3, 4, and 8 h after the first dose and at steady state. Age, sex, weight, urine output, and CRRT parameters were recorded. Pmetrics was used for population PK and simulations. The target exposure was 100% of the dosing interval during which the free beta-lactam concentration is above the MIC (fT _>MIC). Ten patients were included; their mean age was 53 years, and mean weight was 119 kg. Seventy percent were males. Cefepime was described by a five-compartment model. The downtime was applied to the CRRT flow rates, which were used to describe the rates of transfer between the compartments. At MICs of ≤8 mg/liter, intermittent infusion of 2 g cefepime every 8 h achieved good target attainment both early in therapy and at steady state. Only extended- and continuous-infusion regimens achieved good target attainment at MICs of 16 mg/liter. In conclusion, 2 g cefepime infused over 30 min followed by extended infusion of 2 g every 8 h achieved good target attainment at MICs of ≤16 mg/liter with different CRRT flow rates and may be considered in resistant bacterial infections.

Drug dosing considerations in continuous renal replacement therapy

Acute kidney injury (AKI) is a common complication in critically ill patients, which is associated with increased in-hospital mortality. Delivering effective antibiotics to treat patients with sepsis receiving continuous renal replacement therapy (RRT) is complicated by variability in pharmacokinetics, dialysis delivery, lack of primary literature, and therapeutic drug monitoring. Pharmacokinetic alterations include changes in absorption, distribution, protein binding (PB), metabolism, and renal elimination. Drug absorption may be significantly changed due to alterations in gastric pH, perfusion, gastrointestinal motility, and intestinal atrophy. Volume of distribution for hydrophilic drugs may be increased due to volume overload. Estimation of renal clearance is challenged by the effective delivery of RRT. Drug characteristics such as PB, volume of distribution, and molecular weight impact removal of the drug by RRT. The totality of these alterations leads to reduced exposure. Despite our best knowledge, therapeutic drug monitoring of patients receiving continuous RRT demonstrates wide variability in antimicrobial concentrations, highlighting the need for expanded monitoring of all drugs. This review article will focus on changes in drug pharmacokinetics in AKI and dosing considerations to attain antibiotic pharmacodynamic targets in critically ill patients receiving continuous RRT.

Antibiotic Exposure Profiles in Trials Comparing Intensity of Continuous Renal Replacement Therapy

OBJECTIVES

To determine whether the probability of target attainment over 72 hours of initial therapy with beta-lactam (cefepime, ceftazidime, piperacillin/tazobactam) and carbapenem (imipenem, meropenem) antibiotics were substantially influenced between intensive and less-intensive continuous renal replacement therapy groups in the Acute Renal Failure Trial Network trial and The RENAL Replacement Therapy Study trial.

DESIGN

The probability of target attainment was calculated using pharmacodynamic targets of percentage of time that free serum concentrations (fT): 1) were above the target organism's minimum inhibitory concentration (≥ fT > 1 × minimum inhibitory concentration); 2) were above four times the minimum inhibitory concentration (≥ % fT > 4 × minimum inhibitory concentration); and 3) were always above the minimum inhibitory concentration (≥ 100% fT > minimum inhibitory concentration) for the first 72 hours of antibiotic therapy. Demographic data and effluent rates from the Acute Renal Failure Trial Network and RENAL Replacement Therapy Study trials were used. Optimal doses were defined as the dose achieving greater than or equal to 90% probability of target attainment.

SETTING

Monte Carlo simulations using demographic data from Acute Renal Failure Trial Network and RENAL Replacement Therapy Study trials.

PATIENTS

Virtual critically ill patients requiring continuous renal replacement therapy.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The pharmacodynamic target of fT greater than 1 × minimum inhibitory concentration led to similarly high rates of predicted response with antibiotic doses often used in continuous renal replacement therapy. Achieving 100% fT greater than minimum inhibitory concentration is a more stringent benchmark compared with T greater than 4 × minimum inhibitory concentration with standard antibiotic dosing. The intensity of effluent flow rates (less intensive vs intensive) did not substantially influence the probability of target attainment of antibiotic dosing regimens regardless of pharmacodynamic target.

CONCLUSIONS

Antibiotic pharmacodynamic target attainment rates likely were not meaningfully different in the low- and high-intensity treatment arms of the Acute Renal Failure Trial Network and RENAL Replacement Therapy Study Investigators trials.

Pharmacokinetic and Pharmacodynamic Profiles of Cefiderocol, a Novel Siderophore Cephalosporin

Cefiderocol, a novel parenteral siderophore cephalosporin, exhibits potent in vitro activity and in vivo efficacy against most gram-negative bacteria, including carbapenem-resistant strains of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia. In phase 1 studies, cefiderocol demonstrated linear pharmacokinetics, primarily urinary excretion, an elimination half-life of 2-3 hours, and a protein binding of 58% in human plasma. Cefiderocol is a time-dependent cephalosporin; the probability of a target attainment at ≥75% of the dosing interval during which the free drug concentration exceeds the minimum inhibitory concentration (ƒT/MIC) for bacterial strains with an MIC of ≤4 μg/mL is likely to be achieved at the therapeutic dose of 2 g over 3-hour infusion every 8 hours in most patients. As expected, renal function markers were the most influential covariates for the pharmacokinetics of cefiderocol for patients with renal impairment or augmented renal clearance (ARC). Dose adjustment is recommended for patients with impaired renal function, and additionally, in ARC patients with creatinine clearance >120 mL/minute, a more frequent dosing regimen (ie, 2 g every 6 hours) was predicted to achieve the target fT > MIC. The single and multiple doses of cefiderocol tested were well tolerated in both healthy subjects and those with renal impairment. Furthermore, neither QT interval prolongation nor drug-drug interaction via organic anion transporters was demonstrated in healthy subjects. Cefiderocol is being investigated in phase 3 clinical studies for the treatment of infections caused by carbapenem-resistant bacteria.

Pharmacokinetics and Pharmacodynamics of Extended-Infusion Cefepime in Critically Ill Patients Receiving Continuous Renal Replacement Therapy: A Prospective, Open-Label Study

STUDY OBJECTIVE

To evaluate extended-infusion (EI) cefepime pharmacokinetics (PK) and pharmacodynamic target attainment in critically ill patients receiving continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodialysis (CVVHD).

DESIGN

Prospective, open-label, PK study.

SETTING

Intensive care units at a large, academic, tertiary-care medical center.

PATIENTS

Ten critically ill adults who were receiving cefepime 2 g intravenously every 8 hours as a 4-hour infusion while receiving CVVH (eight patients) or CVVHD (two patients).

INTERVENTION

Two sets of five serum cefepime concentrations were collected for each patient to assess pharmacokinetics before and during presumed steady state. Concurrent serum and CRRT effluent samples were collected at hours 1, 2, 3, 4, and 8 after the first cefepime dose and after either the fourth, fifth, or sixth (steady-state) cefepime doses.

MEASUREMENTS AND MAIN RESULTS

Reversed-phase high-performance liquid chromatography was used to determine free cefepime concentrations. PK analyses included CRRT clearance, half-life, and sieving coefficient or saturation coefficient. Cefepime peak (4 hrs) concentrations, trough (8 hrs) concentrations (C_min ), and minimum inhibitory concentration breakpoint of 8 µg/ml for the pathogen (MIC₈ ) were used to evaluate attainment of pharmacodynamic targets: 100% of the dosing interval that free drug remains above MIC₈ (100% fT > MIC₈ ), 100% fT > 4 × MIC₈ (optimal), percentage of time fT > 4 × MIC₈ (%fT > 4 × MIC₈ ) at steady state, and ratio of C_min to MIC₈ (fC_min /MIC₈ ). Total CRRT effluent flow rate was a mean ± SD of 30.1 ± 5.4 ml/kg/hr, CRRT clearance was 39.6 ± 9.9 ml/min, and half-life was 5.3 ± 1.7 hours. Sieving coefficient or saturation coefficient were 0.83 ± 0.13 and 0.69 ± 0.22, respectively. First and steady-state dose C_min were 23.4 ± 10.1 µg/ml and 45.2 ± 14.6 µg/ml, respectively. All patients achieved 100% fT > MIC₈ on first and steady-state doses. First and steady-state dose 100% fT > 4 × MIC₈ were achieved in 22% (2/9 patients) and 87.5% (7/8 patients) of patients, respectively. The mean %fT > 4 × MIC₈ at steady state was 97.5%. The fC_min /MIC₈ was 2.92 ± 1.26 for the first dose and 5.65 ± 1.83 at steady state.

CONCLUSION

Extended-infusion cefepime dosing in critically ill patients receiving CRRT successfully attained 100% fT > MIC₈ in all patients and an appropriate fC_min /MIC₈ for both first and steady-state doses. All but one patient achieved 100% fT > 4 × MIC₈ at steady state. No significant differences were observed in PK properties between first and steady-state doses among or between patients. It may be reasonable to initiate an empiric or definitive regimen of EI cefepime in critically ill patients receiving concurrent CRRT who are at risk for resistant organisms. Further research is needed to identify the optimal dosing regimen of EI cefepime in this patient population.

Pharmacokinetic variability of beta-lactams in critically ill patients: A narrative review

The use of antibacterial drugs is very common in critically ill patients and beta-lactam agents are widely used in this context. Critically ill patients show several characteristics (e.g., sepsis, renal impairment or conversely augmented renal clearance, renal replacement therapy) that may alter beta-lactam pharmacokinetics (PK) in comparison with non-critically ill patients. This narrative literature review aims to identify recent studies quantifying the variability of beta-lactams volume of distribution and clearance and to determine its main determinants. Seventy studies published between 2000 and 2018 were retained. Data on volume of distribution and clearance variability were reported for 5 penicillins, 3 beta-lactamase inhibitors, 6 cephalosporins and 4 carbapenems. Data confirm specific changes in PK parameters and important variability of beta-lactam PK in critically ill patients. Renal function, body weight and use of renal replacement therapy are the principal factors influencing PK parameters described in this population. Few studies have directly compared beta-lactam PK in critically ill versus non-critically ill patients. Conclusions are also limited by small study size and sparse PK data in several studies. These results suggest approaches to assess this PK variability in clinical practice. Beta-lactam therapeutic drug monitoring seems to be the best way to deal with this issue.

Basic Principles of Antibiotics Dosing in Patients with Sepsis and Acute Kidney Damage Treated with Continuous Venovenous Hemodiafiltration

Sepsis is the leading cause of acute kidney damage in patients in intensive care units. Pathophysiological mechanisms of the development of acute kidney damage in patients with sepsis may be hemodynamic and non-hemodynamic. Patients with severe sepsis, septic shock and acute kidney damage are treated with continuous venovenous hemodiafiltration. Sepsis, acute kidney damage, and continuous venovenous hemodiafiltration have a significant effect on the pharmacokinetics and pharmacodynamics of antibiotics. The impact dose of antibiotics is increased due to the increased volume of distribution (increased administration of crystalloids, hypoalbuminemia, increased capillary permeability syndrome toproteins). The dose of antibiotic maintenance depends on renal, non-renal and extracorporeal clearance. In the early stage of sepsis, there is an increased renal clearance of antibiotics, caused by glomerular hyperfiltration, while in the late stage of sepsis, as the consequence of the development of acute renal damage, renal clearance of antibiotics is reduced. The extracorporeal clearance of antibiotics depends on the hydrosolubility and pharmacokinetic characteristics of the antibiotic, but also on the type of continuous dialysis modality, dialysis dose, membrane type, blood flow rate, dialysis flow rate, net filtration rate, and effluent flow rate. Early detection of sepsis and acute kidney damage, early target therapy, early administration of antibiotics at an appropriate dose, and early extracorporeal therapy for kidney replacement and removal of the inflammatory mediators can improve the outcome of patients with sepsis in intensive care units.

Myoclonic status epilepticus induced by cefepime overdose requiring haemodialysis

We report a case of cefepime neurotoxicity characterised by myoclonic status epilepticus with coma, in a context of acute renal failure and requiring one discontinuous conventional haemodialysis. Cefepime is a fourth-generation broad-spectrum cephalosporin mainly used to treat hospital-acquired Gram-negative infections. Acute neurotoxicity is an increasingly reported adverse effect which occurs predominantly in patients with renal impairment. Renal replacement therapy has been proposed to treat this condition.

Cefepime Pharmacokinetics in Critically Ill Pediatric Patients Receiving Continuous Renal Replacement Therapy

This retrospective study included pediatric intensive care unit patients receiving continuous veno-venous hemodiafiltration (CVVHDF) being treated with cefepime. The free drug concentration above one time the MIC (fT>1×MIC) and four times a presumed MIC (fT>4×MIC) of 8 μg/ml were calculated. Four patients received doses ranging from 48 to 64 mg/kg of body weight every 6 to 12 h. Three patients achieved 100% fT>1×MIC, with the fourth patient achieving 98% fT>1×MIC. Therapeutic drug monitoring should be considered for critically ill patients receiving cefepime on CVVHDF.

Pharmacokinetics-pharmacodynamics issues relevant for the clinical use of beta-lactam antibiotics in critically ill patients

Antimicrobials are among the most important and commonly prescribed drugs in the management of critically ill patients and beta-lactams are the most common antibiotic class used. Critically ill patient's pathophysiological factors lead to altered pharmacokinetics and pharmacodynamics of beta-lactams.A comprehensive bibliographic search in PubMed database of all English language articles published from January 2000 to December 2017 was performed, allowing the selection of articles addressing the pharmacokinetics or pharmacodynamics of beta-lactam antibiotics in critically ill patients.In critically ill patients, several factors may increase volume of distribution and enhance renal clearance, inducing high intra- and inter-patient variability in beta-lactam concentration and promoting the risk of antibiotic underdosing. The duration of infusion of beta-lactams has been shown to influence the fT > minimal inhibitory concentration and an improved beta-lactam pharmacodynamics profile may be obtained by longer exposure with more frequent dosing, extended infusions, or continuous infusions.The use of extracorporeal support techniques in the critically ill may further contribute to this problem and we recommend not reducing standard antibiotic dosage since no drug accumulation was found in the available literature and to maintain continuous or prolonged infusion, especially for the treatment of infections caused by multidrug-resistant bacteria.Prediction of outcome based on concentrations in plasma results in overestimation of antimicrobial activity at the site of infection, namely in cerebrospinal fluid and the lung. Therefore, although no studies have assessed clinical outcome, we recommend using higher than standard dosing, preferably with continuous or prolonged infusions, especially when treating less susceptible bacterial strains at these sites, as the pharmacodynamics profile may improve with no apparent increase in toxicity.A therapeutic drug monitoring-guided approach could be particularly useful in critically ill patients in whom achieving target concentrations is more difficult, such as obese patients, immunocompromised patients, those infected by highly resistant bacterial strains, patients with augmented renal clearance, and those undergoing extracorporeal support techniques.

Cefepime dosing regimens in critically ill patients receiving continuous renal replacement therapy: a Monte Carlo simulation study

Background

Cefepime can be removed by continuous renal replacement therapy (CRRT) due to its pharmacokinetics. The purpose of this study is to define the optimal cefepime dosing regimens for critically ill patients receiving CRRT using Monte Carlo simulations (MCS).

Methods

The CRRT models of cefepime disposition during 48 h with different effluent rates were developed using published pharmacokinetic parameters, patient demographic data, and CRRT settings. Pharmacodynamic target was the cumulative percentage of a 48-h period of at least 70% that free cefepime concentration exceeds the four times susceptible breakpoint of Pseudomonas aeruginosa (minimum inhibitory concentration, MIC of 8). All recommended dosing regimens from available clinical resources were evaluated for the probability of target attainment (PTA) using MCS to generate drug disposition in a group of 5000 virtual patients for each dose. The optimal doses were defined as achieving the PTA at least 90% of virtual patients with lowest daily doses and the acceptable risk of neurotoxicity.

Results

Optimal cefepime doses in critically ill patients receiving CRRT with Kidney Disease: Improving Global Outcomes (KDIGO) recommended effluent rates were a regimen of 2 g loading dose followed by 1.5–1.75 g every 8 h for Gram-negative infections with a neurotoxicity risk of < 17%. Cefepime dosing regimens from this study were considerably higher than the recommended doses from clinical resources.

Conclusion

All recommended dosing regimens for patients receiving CRRT from available clinical resources failed to achieve the PTA target. The optimal dosing regimens were suggested based on CRRT modalities, MIC values, and different effluent rates. Clinical validation is warranted.

A Monte Carlo Simulation Approach for Beta-Lactam Dosing in Critically Ill Patients Receiving Prolonged Intermittent Renal Replacement Therapy

Cefepime, ceftazidime, and piperacillin/tazobactam are commonly used beta-lactam antibiotics in the critical care setting. For critically ill patients receiving prolonged intermittent renal replacement therapy (PIRRT), limited pharmacokinetic data are available to inform clinicians on the dosing of these agents. Monte Carlo simulations (MCS) can be used to guide drug dosing when pharmacokinetic trials are not feasible. For each antibiotic, MCS using previously published pharmacokinetic data derived from critically ill patients was used to evaluate multiple dosing regimens in 4 different prolonged intermittent renal replacement therapy effluent rates and prolonged intermittent renal replacement therapy duration combinations (4 L/h × 10 hours or 5 L/h × 8 hours in hemodialysis and hemofiltration modes). Antibiotic regimens were also modeled depending on whether drugs were administered during or well before prolonged intermittent renal replacement therapy therapy commenced. The probability of target attainment (PTA) was calculated using each antibiotic's pharmacodynamic target during the first 48 hours of therapy. Optimal doses were defined as the smallest daily dose achieving ≥90% probability of target attainment in all prolonged intermittent renal replacement therapy effluent and duration combinations. Cefepime 1 g every 6 hours following a 2 g loading dose, ceftazidime 2 g every 12 hours, and piperacillin/tazobactam 4.5 g every 6 hours attained the desired pharmacodynamic target in ≥90% of modeled prolonged intermittent renal replacement therapy patients. Alternatively, if an every 6-hours cefepime regimen is not desired, the cefepime 2 g pre-prolonged intermittent renal replacement therapy and 3 g post-prolonged intermittent renal replacement therapy regimen also met targets. For ceftazidime, 1 g every 6 hours or 3 g continuous infusion following a 2 g loading dose also met targets. These recommended doses provide simple regimens that are likely to achieve the pharmacodynamics target while yielding the least overall drug exposure, which should result in lower toxicity rates. These findings should be validated in the clinical setting.

Antibiotic Dosing in Continuous Renal Replacement Therapy

Appropriate antibiotic dosing is critical to improve outcomes in critically ill patients with sepsis. The addition of continuous renal replacement therapy makes achieving appropriate antibiotic dosing more difficult. The lack of continuous renal replacement therapy standardization results in treatment variability between patients and may influence whether appropriate antibiotic exposure is achieved. The aim of this study was to determine if continuous renal replacement therapy effluent flow rate impacts attaining appropriate antibiotic concentrations when conventional continuous renal replacement therapy antibiotic doses were used. This study used Monte Carlo simulations to evaluate the effect of effluent flow rate variance on pharmacodynamic target attainment for cefepime, ceftazidime, levofloxacin, meropenem, piperacillin, and tazobactam. Published demographic and pharmacokinetic parameters for each antibiotic were used to develop a pharmacokinetic model. Monte Carlo simulations of 5000 patients were evaluated for each antibiotic dosing regimen at the extremes of Kidney Disease: Improving Global Outcomes guidelines recommended effluent flow rates (20 and 35 mL/kg/h). The probability of target attainment was calculated using antibiotic-specific pharmacodynamic targets assessed over the first 72 hours of therapy. Most conventional published antibiotic dosing recommendations, except for levofloxacin, reach acceptable probability of target attainment rates when effluent rates of 20 or 35 mL/kg/h are used.

Optimizing β-lactams treatment in critically-ill patients using pharmacokinetics/pharmacodynamics targets: are first conventional doses effective?

INTRODUCTION

The pharmacokinetic/pharmacodynamic index determining β-lactam activity is the percentage of the dosing interval (%T) during which their free serum concentration remains above a critical threshold over the minimum inhibitory concentration (MIC). Regrettably, neither the value of %T nor that of the threshold are clearly defined for critically-ill patients. Areas covered: We review and assess the targets proposed for β-lactams in critical illness by screening the literature since 1997. Depending on the study intention (clinical cure vs. suppression of resistance), targets proposed range from 20%T > 1xMIC to 100%T > 5xMIC. Assessment and comparative analysis of their respective clinical efficacy suggest that a value of 100%T > 4xMIC may be needed. Simulation studies, however, show that this target will not be reached at first dose for the majority of critically-ill patients if using the most commonly recommended doses. Expert commentary: Considering that critically-ill patients are highly vulnerable and likely to experience antibiotic underexposure, and because effective initial treatment is a key determinant of clinical outcome, we support the use of a target of 100%T > 4xMIC, which could not only maximize efficacy but also minimize emergence of resistance. Clinical and microbiological studies are needed to test for the feasibility and effectiveness of reaching such a demanding target.

The Effects of Continuous Renal Replacement on Anti-infective Therapy in the Critically Ill

Acute renal failure represents a frequent, severe complication in critically ill patients leading to a direct increase in mortality and resource utilization. Today, continuous renal replacement therapy (CRRT) has replaced traditional hemodialysis, providing more precise fluid and metabolic control and decreased hemodynamic instability. There are a limited number of studies conducted for the ideal dosing of individual anti-infective agents for patients receiving CRRT. However, knowledge of the basic principles of CRRT, in conjunction with pharmacokinetics and pharmacodynamics of anti-infectives, allows sound dosing recommendations to be formulated to ensure maximal killing effects with minimal risk of toxicity in patients receiving CRRT.

Ceftolozane-Tazobactam Pharmacokinetics in a Critically Ill Patient on Continuous Venovenous Hemofiltration

Extended-infusion ceftolozane-tazobactam treatment at 1.5 g every 8 h was used to treat multidrug-resistant Pseudomonas aeruginosa in a critically ill patient on continuous venovenous hemofiltration. Serum drug concentrations were measured at 1, 4, 5, 6, and 8 h after the start of infusion. Prefilter levels of ceftolozane produced a maximum concentration of drug (Cmax) of 38.57 μg/ml, concentration at the end of the dosing interval (Cmin) of 31.63 μg/ml, time to Cmax (Tmax) of 4 h, area under the concentration-time curve from 0 to 8 h (AUC0-8) of 284.38 μg · h/ml, and a half-life (t1/2) of 30.7 h. The concentrations were eight times the susceptibility breakpoint for the entire dosing interval.

Severe cefepime-induced status epilepticus treated with haemofiltration

Neurotoxicity caused by cefepime may occur predominantly in patients with impaired renal function. A case of a cefepime-induced non-convulsive status epilepticus (NCSE) is presented. A 65-year-old woman suffered a severe NCSE due to cefepime in the presence of acute renal failure, requiring coma induction with sodium thiopental. A serious interaction between valproic acid (VPA) and meropenem was also produced after changing cefepime to meropenem. Continuous veno-venous haemofiltration was employed to improve cefepime clearance, and the patient progressively regained her previous mental condition. In conclusion, the cefepime dose must be adjusted according to renal function in order to avoid toxicity in patients with renal failure. Electroencephalogram should be considered in cases of acute confusional state in patients receiving cefepime, to achieve early detection of NCSE. Continuous renal replacement therapy may be successfully employed in severe cases in order to accelerate cefepime removal. Likewise, meropenem should not be used concomitantly with VPA.

Population pharmacokinetics and dosing simulations of cefepime in septic shock patients receiving continuous renal replacement therapy

The aim of this study was to describe the population pharmacokinetics of cefepime in septic shock patients requiring continuous renal replacement therapy and to determine whether current or alternative dosing regimens can achieve PK/PD targets. In this observational PK study, 62 samples from 13 patients were analysed using non-linear mixed-effects modelling. Different dosing regimens were evaluated using Monte Carlo simulations with ultrafiltration flow rates (UFRs) of 1000, 1500 and 2000 mL/h. The probability of target attainment was calculated against a conservative (60% T(>MIC)) and a higher PK/PD target (100% T(>MIC)) against an MIC of 8 mg/L, the clinical susceptibility breakpoint for Pseudomonas aeruginosa. A one-compartment model with between-subject variability (BSV) on clearance and volume of distribution (V(d)) described the data adequately. UFR was supported as a covariate on both parameters. Typical values for clearance and V(d) were 4.4L/h (BSV 37%) and 40.9L (BSV 20%), respectively. Dosing simulations showed failure to achieve both a conservative and a higher PK/PD target using a dose of 1g q12h for patients treated with a high UFR (≥1500 mL/h). The dose of 2g q8h or 1g q6h leads to optimal target attainment for high UFR. One gram q8h is optimal for low UFR (≤1000 mL/h). We found important variability in PK parameters. Dosing simulations show that a dose of 2g q8h or 1g q6h is needed to ensure rapid achievement of adequate levels if the UFR is ≥1500 mL/h and 1g q8h for low UFR (≤1000 mL/h).

How can we ensure effective antibiotic dosing in critically ill patients receiving different types of renal replacement therapy?

Determining appropriate antibiotic dosing for critically ill patients receiving renal replacement therapy (RRT) is complex. Worldwide unstandardized and heterogeneous prescribing of RRT as well as altered patient physiology and pathogen susceptibility all cause drug disposition to be much different to that seen in non-critically ill patients. Significant changes to pharmacokinetic parameters, including volume of distribution and clearance, could be expected, in particular, for antibiotics that are hydrophilic with low plasma protein binding and that are usually primarily eliminated by the renal system. Antibiotic clearance is likely to be significantly increased when higher RRT intensities are used. The combined effect of these factors that alter antibiotic disposition is that non-standard dosing strategies should be considered to achieve therapeutic exposure. In particular, an aggressive early approach to dosing should be considered and this may include administration of a 'loading dose', to rapidly achieve therapeutic concentrations and maximally reduce the inoculum of the pathogen. This approach is particularly important given the pharmacokinetic changes in the critically ill as well as the increased likelihood of less susceptible pathogens. Dose individualization that applies knowledge of the RRT and patient factors causing altered pharmacokinetics remains the key approach for ensuring effective antibiotic therapy for these patients. Where possible, therapeutic drug monitoring should also be used to ensure more accurate therapy. A lack of pharmacokinetic data for antibiotics during the prolonged intermittent RRT and intermittent hemodialysis currently limits evidence-based antibiotic dose recommendations for these patients.

The challenges of multiple organ dysfunction syndrome and extra-corporeal circuits for drug delivery in critically ill patients

The multiple organ dysfunction syndrome (MODS) is characterized by more than one organ system failing, especially during critical illness. MODS is the leading cause of morbidity and mortality in current ICU practice; moreover, multiple organ dysfunction, especially liver and kidneys, may significantly affect the pharmacokinetics (PKs) of different drugs that are currently administered in critically ill patients. These PK alterations may either result in insufficient drug concentrations to achieve the desired effects or in blood and tissue accumulation, with the development of serious adverse events. The use of extra-corporeal circuits, such as extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT), may further contribute to PKs changes in this patients' population. In this review, we have described the main PK changes occurring in all these conditions and how drug concentrations may potentially be affected. The lack of prospective studies on large cohorts of patients makes impossible any specific recommendation on drug regimen adjustment in ICU patients. Nevertheless, the clinicians should be aware of these abnormalities in order to better understand some unexpected therapeutic issues occurring in such patients.

β-lactam antibiotic concentrations during continuous renal replacement therapy

Introduction

The use of standard doses of β-lactam antibiotics during continuous renal replacement therapy (CRRT) may result in inadequate serum concentrations. The aim of this study was to evaluate the adequacy of unadjusted drug regimens (i.e., similar to those used in patients with normal renal function) in patients treated with CRRT and the influence of CRRT intensity on drug clearance.

Methods

We reviewed data from 50 consecutive adult patients admitted to our Department of Intensive Care in whom routine therapeutic drug monitoring (TDM) of broad-spectrum β-lactam antibiotics (ceftazidime or cefepime, CEF; piperacillin/tazobactam; TZP; meropenem, MEM) was performed using unadjusted β-lactam antibiotics regimens (CEF = 2 g q8h; TZP = 4 g q6h; MEM = 1 g q8h). Serum drug concentrations were measured twice during the elimination phase by high-performance liquid chromatography (HPLC-UV). We considered therapy was adequate when serum drug concentrations were between 4 and 8 times the minimal inhibitory concentration (MIC) of Pseudomonas aeruginosa during optimal periods of time for each drug (≥70% for CEF; ≥ 50% for TZP; ≥ 40% for MEM). Therapy was considered as early (ET) or late (LT) phase if TDM was performed within 48 hours of antibiotic initiation or later on, respectively.

Results

We collected 73 serum samples from 50 patients (age 58 ± 13 years; Acute Physiology and Chronic Health Evaluation II (APACHE II) score on admission 21 (17–25)), 35 during ET and 38 during LT. Drug concentrations were above 4 times the MIC in 63 (90%), but above 8 times the MIC in 39 (53%) samples. The proportions of patients with adequate drug concentrations during ET and LT were quite similar. We found a weak but significant correlation between β-lactam antibiotics clearance and CRRT intensity.

Conclusions

In septic patients undergoing CRRT, doses of β-lactam antibiotics similar to those given to patients with normal renal function achieved drug levels above the target threshold in 90% of samples. Nevertheless, 53% of samples were associated with very high drug levels and daily drug regimens may need to be adapted accordingly.

Simultaneous determination of seven β-lactam antibiotics in human plasma for therapeutic drug monitoring and pharmacokinetic studies

There is strong evidence in literature supporting the benefit of monitoring plasma concentrations of β-lactam antibiotics in the critically ill to ensure appropriateness of dosing. The objective of this work was to develop a method for the simultaneous determination of total concentrations piperacillin, benzylpenicillin, flucloxacillin, meropenem, ertapenem, cephazolin and ceftazidime in human plasma. Sample preparation involved protein precipitation with acetonitrile containing 0.1% formic acid and subsequent dilution of supernatant with 0.1% formic acid in water. Chromatographic separation was achieved on a reversed phase column (C18, 2.6 μm, 2.1 × 50 mm) via gradient elution using water and acetonitrile, each containing 0.1% formic acid, as mobile phase. Tandem mass spectrometry (MSMS) analysis was performed, after electrospray ionization in the positive mode, with multiple reaction monitoring (MRM). The method is accurate with the inter-day and intra-day accuracies of quality control samples (QCs) ranging from 95 to 107% and 95 to 108%, respectively. It is also precise with intra-day and inter-day coefficient of variations ranging from 4 to 12% and 5 to 14%, respectively. The lower limit of quantification was 0.1 μg/mL for each antibiotic except flucloxacillin (0.25 μg/mL). Recovery was greater than 96% for all analytes except for ertapenem (78%). Coefficients of variation for the matrix effect were less than 10% over the six batches of plasma. Analytes were stable over three freeze-thaw cycles, and for reasonable hours on the bench top as well as post-preparation. This novel liquid chromatography tandem mass spectrometry method proved accurate, precise and applicable for therapeutic drug monitoring and pharmacokinetic studies of the selected β-lactam antibiotics.

Compliance with Antibiotic Dosing Guidelines in Critically Ill Patients Receiving Renal Replacement Therapy

Background:

Compliance with antibiotic dosing guidelines and achievement of target serum concentrations in patients with infection who are on renal replacement therapy (RRT) is complex, essential for supportive care, and not well studied.

Objective:

To determine adherence rates to antibiotic dosing guidelines in the setting of RRT in the intensive care unit (ICU).

Methods:

We conducted a retrospective, single-center, cohort study evaluating antibiotic dosing in all patients in the ICU receiving RRT between July 2007 and June 2009. Appropriate dosing was determined by comparing dose administered with established guidelines. Dosing was denoted as accurate if adjustment occurred prior to the third administered dose or, if appropriate dosing is every 12 hours or more, within 24 hours. We compared rates according to modality of RRT (intermittent hemodialysis [IHD] vs continuous veno-venous hemodialysis [CVVHD]), indication for RRT (acute kidney injury [AKI] vs end-stage renal disease [ESRD]), and presence of a clinical pharmacist on rounds.

Results:

Adherence rates of 546 patients receiving RRT, with 1761 individual antibiotic prescriptions, were analyzed. Dosing errors were more common in the group receiving CVVHD than in the IHD group (58.1% vs 49.5%; p < 0.001). Frequency of dosing errors did not differ significantly between patients receiving RRT for AKI versus those with ESRD (55.4% vs 51.3%; p = 0.24) or in ICUs with or without a pharmacist on rounds (53.0% vs 54.6%; p = 0.67). Underdosing occurred less frequently with a clinical pharmacist on rounds (18.7% vs 31.3%; p < 0.001). However, in-hospital mortality was not significantly different in underdosed individuals compared with the rest of the cohort (52.3% vs 51.6%; p = 0.92).

Conclusions:

Antibiotic underdosing is common. Increased awareness of dose adjustment guidelines for CVVHD and having a clinical pharmacist on rounds may improve rates of underdosing.

Influence of Renal Function on the Pharmacokinetics of Piperacillin/Tazobactam in Intensive Care Unit Patients During Continuous Venovenous Hemofiltration

The pharmacokinetics of piperacillin/tazobactam (4 g/0.5 g every 6 or 8 hours, by 20-minute intravenous infusion) were studied in 14 patients with acute renal failure who underwent continuous venovenous hemofiltration with AN69 membranes. Patients were grouped according to severity (CL(CR) < or =10 mL/min, 10 < CL(CR) < or =50 mL/min, and CL(CR) > 50 mL/min). A noncompartmental analysis was performed. The sieving coefficient (0.78 +/- 0.28) was similar to the unbound fraction (0.65 +/- 0.24) for tazobactam, but it was significantly different (0.34 +/- 0.25) from the unbound fraction (0.78 +/- 0.14) for piperacillin. Extracorporeal clearance was 37.0% +/- 28.8%, 12.7% +/- 12.6%, and 2.8% +/- 3.2% for piperacillin in each group and 62.5% +/- 44.9%, 35.4% +/- 17.0%, and 13.1% +/- 8.0% for tazobactam. No patients presented tazobactam accumulation. In patients with CL(CR) < 50 mL/min, t(%)ss >MIC90 values were 100% for a panel of 19 pathogens, but in those with CL(CR) > 50 mL/min, t(%)ss >MIC90 indexes were 55.5% and 16.6% for pathogens with MIC90 values of 32 and 64. The extracorporeal clearance of piperacillin/tazobactam is clinically significant in patients with CL(CR) > 50 mL/min, in which the risk of underdosing and clinical failure is important and extra doses are required.

Cefepime

Cefepime (Maxipime), Maxcef, Cepimax, Cepimex, Axepim, a parenteral fourth-generation cephalosporin, is active against many organisms causative in pneumonia. Cefepime has in vitro activity against Gram-positive organisms including Staphylococcus aureus and penicillin-sensitive, -intermediate and -resistant Streptococcus pneumoniae similar to that of cefotaxime and ceftriaxone. Cefepime also has good activity against Gram-negative organisms, including Pseudomonas aeruginosa, similar to that of ceftazidime. Importantly, cefepime is stable against many of the common plasmid- and chromosome-mediated beta-lactamases and is a poor inducer of AmpC beta-lactamases. As a result, it retains activity against Enterobacteriaceae that are resistant to third-generation cephalosporins, such as derepressed mutants of Enterobacter spp. Cefepime may be hydrolyzed by the extended-spectrum beta-lactamases produced by some members of the Enterobacteriaceae, but to a lesser extent than the third-generation cephalosporins. Monotherapy with cefepime 1 or 2g, usually administered intravenously twice daily, was as effective for clinical and bacteriological response as ceftazidime, ceftriaxone or cefotaxime monotherapy (1 or 2g two or three times daily) in a number of randomized, clinical trials in hospitalized adult, or less commonly, pediatric, patients with generally moderate to severe community-acquired or nosocomial pneumonia. More limited data indicated that monotherapy with cefepime 2g three times daily was also as effective in treating patients with nosocomial pneumonia as imipenem/cilostatin 0.5g four times daily, and when combined with amikacin, cefepime was as effective as ceftazidime plus amikacin. Patients with pneumonia who failed to respond to previous antibacterial therapy with penicillins or other cephalosporins responded to treatment with cefepime. Cefepime is generally well tolerated, with a tolerability profile similar to those of other parenteral cephalosporins. In clinical trials, the majority of adverse events experienced by cefepime recipients were mild to moderate and reversible. The most common adverse events with a causal relationship to cefepime reported in clinical trials included rash and diarrhea. Other, less common, adverse events included pruritus, urticaria, nausea, vomiting oral candidiasis, colitis, headache, fever, erythema and vaginitis.

CONCLUSION

Cefepime is an established and generally well tolerated parenteral drug with a broad spectrum of antibacterial activity which, when administered twice daily, provides coverage of most of the pathogens that may be causative in pneumonia. In randomized clinical trials in hospitalized patients with generally moderate to severe community-acquired or nosocomial pneumonia, cefepime monotherapy exhibited good clinical and bacteriological efficacy. Cefepime may become a preferred antibacterial agent for infections caused by Enterobacter spp. With prudent use in order to prevent the emergence of resistant organisms, cefepime will continue to be a suitable option for the empiric treatment of pneumonia.

Does Beta-lactam Pharmacokinetic Variability in Critically Ill Patients Justify Therapeutic Drug Monitoring? A Systematic Review

The pharmacokinetics of beta-lactam antibiotics in intensive care patients may be profoundly altered due to the dynamic, unpredictable pathophysiological changes that occur in critical illness. For many drugs, significant increases in the volume of distribution and/or variability in drug clearance are common. When “standard” beta-lactam doses are used, such pharmacokinetic changes can result in subtherapeutic plasma concentrations, treatment failure, and the development of antibiotic resistance. Emerging data support the use of beta-lactam therapeutic drug monitoring (TDM) and individualized dosing to ensure the achievement of pharmacodynamic targets associated with rapid bacterial killing and optimal clinical outcomes. The purpose of this work was to describe the pharmacokinetic variability of beta-lactams in the critically ill and to discuss the potential utility of TDM to optimize antibiotic therapy through a structured literature review of all relevant publications between 1946 and October 2011. Only a few studies have reported the utility of TDM as a tool to improve beta-lactam dosing in critically ill patients. Moreover, there is little agreement between studies on the pharmacodynamic targets required to optimize antibiotic therapy. The impact of TDM on important clinical outcomes also remains to be established. Whereas TDM may be theoretically rational, clinical studies to assess utility in the clinical setting are urgently required.

Presence and accuracy of drug dosage recommendations for continuous renal replacement therapy in tertiary drug information references

BACKGROUND

Clinicians commonly rely on tertiary drug information references to guide drug dosages for patients who are receiving continuous renal replacement therapy (CRRT). It is unknown whether the dosage recommendations in these frequently used references reflect the most current evidence.

OBJECTIVE

To determine the presence and accuracy of drug dosage recommendations for patients undergoing CRRT in 4 drug information references.

METHODS

Medications commonly prescribed during CRRT were identified from an institutional medication inventory database, and evidence-based dosage recommendations for this setting were developed from the primary and secondary literature. The American Hospital Formulary System-Drug Information (AHFS-DI), Micromedex 2.0 (specifically the DRUGDEX and Martindale databases), and the 5th edition of Drug Prescribing in Renal Failure (DPRF5) were assessed for the presence of drug dosage recommendations in the CRRT setting. The dosage recommendations in these tertiary references were compared with the recommendations derived from the primary and secondary literature to determine concordance.

RESULTS

Evidence-based drug dosage recommendations were developed for 33 medications administered in patients undergoing CRRT. The AHFS-DI provided no dosage recommendations specific to CRRT, whereas the DPRF5 provided recommendations for 27 (82%) of the medications and the Micromedex 2.0 application for 20 (61%) (13 [39%] in the DRUGDEX database and 16 [48%] in the Martindale database, with 9 medications covered by both). The dosage recommendations were in concordance with evidence-based recommendations for 12 (92%) of the 13 medications in the DRUGDEX database, 26 (96%) of the 27 in the DPRF5, and all 16 (100%) of those in the Martindale database.

CONCLUSIONS

One prominent tertiary drug information resource provided no drug dosage recommendations for patients undergoing CRRT. However, 2 of the databases in an Internet-based medical information application and the latest edition of a renal specialty drug information resource provided recommendations for a majority of the medications investigated. Most dosage recommendations were similar to those derived from the primary and secondary literature. The most recent edition of the DPRF is the preferred source of information when prescribing dosage regimens for patients receiving CRRT.

[Dosage of antipseudomonal antibiotics in patients with acute kidney injury subjected to continuous renal replacement therapies]

Critically ill patients are often affected by infections produced by Pseudomonas, which can be a cause of sepsis and renal failure. Early and adequate antibiotic treatment at correct dosage levels is crucial. Acute kidney injury is also frequent in critically ill patients. In those patients who require renal replacement therapy, continuous techniques are gaining relevance as filtering alternatives to intermittent hemodialysis. It must be taken into account that many antibiotics are largely cleared by continuous renal replacement therapies (CRRT). The aim of this review is to assess the clinical evidence on the pharmacokinetics and dosage recommendations of the main antibiotic groups used to treat Pseudomonas spp. infections in critically ill patients subjected to CRRT.

[Study of factors affecting drug extraction during continuous hemofiltration and hemodiafiltration, and the contribution of extraction to systemic clearance]

The aim of this study was to elucidate the factors affecting dialysis clearance and the need for additional doses of drugs during and after continuous hemofiltration (CHF) and hemodiafiltration (CHDF). We performed a literature search of MEDLINE using the terms hemofiltration OR hemodiafiltration AND pharmacokinetics to obtain the clearances of CHF and CHDF in a clinical setting. The relationships between molecular weight, the unbound fraction (fuB), ultrafiltration flow rate (UFR) and dialysis flow rate were analyzed. The need for additional doses of certain drugs was also discussed based on the ratio of dialysis and systemic clearances. The clearance of CHF for 32 reported drugs was significantly correlated with the product of fuB×UFR (r=0.841, p<0.001), and furthermore the plots obtained lay on a line of y=x. The clearance of CHDF also showed good correlation with the product of fuB×UFR (r=0.795, p<0.001), but the plots were higher than the line for y=x, suggesting that additional clearance by dialysis was not negligible. The elimination by both forms of dialysis for drugs excreted mainly via the kidneys, and with a higher fuB, was considerable. The extent of drug clearance by both CHF and CHDF is determined mainly by fuB and UFR. The ratio of dialysis clearance to systemic clearance should be estimated to determine the contribution of CHF and CHDF.

Quality of pharmacokinetic studies in critically ill patients receiving continuous renal replacement therapy

Continuous renal replacement therapy (CRRT) is the preferred renal replacement therapy modality in the critically ill. We aimed to reveal the literature on the pharmacokinetic studies in critically ill patients receiving CRRT with special reference to quality assessment of these studies and the CRRT dose. We conducted a systematic review by searching the MEDLINE, EMBASE, and the Cochrane databases to December 2009 and bibliographies of relevant review articles. We included original studies reporting from critically ill adult subjects receiving CRRT because of acute kidney injury with a special emphasis on drug pharmacokinetics. We used the minimum reporting criteria for CRRT studies by Acute Dialysis Quality Initiative (ADQI) and, second, the Downs and Black checklist to assess the quality of the studies. We calculated the CRRT dose per study. We included pharmacokinetic parameters, residual renal function, and recommendations on drug dosing. Of 182 publications, 95 were considered relevant and 49 met the inclusion criteria. The median [interquartile range (IQR)] number of reported criteria by ADQI was 7.0 (5.0-8.0) of 12. The median (IQR) Downs and Black quality score was 15 (14-16) of 32. None of the publications reported CRRT dose directly. The median (IQR) weighted CRRT dose was 23.7 (18.8-27.9) ml/kg/h. More attention should be paid both to standardizing the CRRT dose and reporting of the CRRT parameters in pharmacokinetic studies. The general quality of the studies during CRRT in the critically ill was only moderate and would be greatly improved by reports in concordant with the ADQI recommendations.

Low cefepime concentrations during high blood and dialysate flow continuous venovenous hemodialysis

Dosing of cefepime during high blood flow (Qb; 300 ml/min), high dialysate flow (Qd; 3 liter/h) continuous venovenous hemodialysis (CVVHD) is undefined. Six patients on CVVHD had serum and effluent cefepime concentrations measured at 0.5, 1, 2, 6, and 12 h after dosing. Three patients had cefepime concentrations less than the MIC for Pseudomonas aeruginosa. A dose of 2,000 mg every 12 h or 1,000 mg every 8 h may increase time at a therapeutic concentration.

Neurotoxic effects associated with antibiotic use: management considerations

The clinical manifestations of antibiotic-induced neurotoxic effects, the underlying mechanisms and management strategies have been reviewed. PubMed and OVID searches (January 1960-June 2010) were conducted using search terms such as antibiotics, side effects, neurotoxicity and encephalopathy which yielded approximately 300 articles. All relevant case reports, case series, letters and retrospective reviews describing neurotoxic effects and those discussing mechanisms of neurotoxicity were included. Antibiotic-induced neurotoxic side effects can have a myriad of neurologic presentations. Patients with prior central nervous system (CNS) disease, renal insufficiency and advanced age may be particularly vulnerable. Treatment consists of discontinuation of the offending agent, use of antiepileptic drugs in the case of seizures or status epilepticus and haemodialysis in certain cases. The risk of CNS toxicity may be reduced via dosage adjustments in high risk populations. Awareness of the potential neurotoxic clinical manifestations of various antibiotics and high degree of vigilance in critically ill patients is essential in identifying a potentially serious, though reversible complications of antibiotic therapy particularly with the advent of newer antimicrobial agents.

Recommended β-lactam regimens are inadequate in septic patients treated with continuous renal replacement therapy

Introduction

Sepsis is responsible for important alterations in the pharmacokinetics of antibiotics. Continuous renal replacement therapy (CRRT), which is commonly used in septic patients, may further contribute to pharmacokinetic changes. Current recommendations for antibiotic doses during CRRT combine data obtained from heterogeneous patient populations in which different CRRT devices and techniques have been used. We studied whether these recommendations met optimal pharmacokinetic criteria for broad-spectrum antibiotic levels in septic shock patients undergoing CRRT.

Methods

This open, prospective study enrolled consecutive patients treated with CRRT and receiving either meropenem (MEM), piperacillin-tazobactam (TZP), cefepime (FEP) or ceftazidime (CAZ). Serum concentrations of these antibiotics were determined by high-performance liquid chromatography from samples taken before (t = 0) and 1, 2, 5, and 6 or 12 hours (depending on the β-lactam regimen) after the administration of each antibiotic. Series of measurements were separated into those taken during the early phase (< 48 hours from the first dose) of therapy and those taken later (> 48 hours).

Results

A total of 69 series of serum samples were obtained in 53 patients (MEM, n = 17; TZP, n = 16; FEP, n = 8; CAZ, n = 12). Serum concentrations remained above four times the minimal inhibitory concentration for Pseudomonas spp. for the recommended time in 81% of patients treated with MEM, in 71% with TZP, in 53% with CAZ and in 0% with FEP. Accumulation after 48 hours of treatment was significant only for MEM.

Conclusions

In septic patients receiving CRRT, recommended doses of β-lactams for Pseudomonas aeruginosa are adequate for MEM but not for TZP, FEP and CAZ; for these latter drugs, higher doses and/or extended infusions should be used to optimise serum concentrations.

Continuous-infusion beta-lactam antibiotics during continuous venovenous hemofiltration for the treatment of resistant gram-negative bacteria

OBJECTIVE

To describe the rationale, principles, and dosage calculations for continuous-infusion beta-lactam antibiotics to treat multidrug-resistant bacteria in patients undergoing continuous venovenous hemofiltration (CVVH).

DATA SOURCES

A MEDLINE search (1968-November 2008) of the English-language literature was performed using the terms continuous infusion and Pseudomonas or Acinetobacter; hemofiltration or CVVH or hemodiafiltration or CVVHDF or continuous renal replacement therapy or pharmacokinetics; and terms describing different beta-lactam antibiotics.

STUDY SELECTION AND DATA EXTRACTION

In vitro, in vivo, and human studies were evaluated that used continuous-infusion beta-lactam antibiotics to treat Pseudomonas aeruginosa and Acinetobacter baumannii infections. Studies were reviewed that described the pharmacokinetics of beta-lactam antibiotics during CVVH as well as other modalities of continuous renal replacement therapy.

DATA SYNTHESIS

Continuous infusion of beta-lactam antibiotics, maintaining drug concentrations 4-5 times higher than the minimum inhibitory concentration, is a promising approach for managing infections caused by P. aeruginosa and A. baumannii. Safe yet effective continuous infusion therapy is made difficult by the occurrence of acute renal failure and the need for renal replacement therapy. Case series and pharmacokinetic properties indicate that several beta-lactam antimicrobials that have been studied for continuous infusion, such as cefepime, ceftazidime, piperacillin, ticarcillin, clavulanic acid, and tazobactam, are significantly cleared by hemofiltration. Methodology and formulas are provided that allow practitioners to calculate dosage regimens and reach target drug concentrations for continuous beta-lactam antibiotic infusions during CVVH based on a literature review, pharmacokinetic principles, and our experience at the National Institutes of Health Clinical Center.

CONCLUSIONS

Continuous infusion of beta-lactam antibiotics may be a useful treatment strategy for multidrug-resistant gram-negative infections in the intensive care unit. Well-established pharmacokinetic and pharmacodynamic principles can be used to safely reach and maintain steady-state target concentrations of beta-lactam antibiotics in critical illness complicated by acute renal failure requiring CVVH.