Clearance of ceftazidime during continuous venovenous haemofiltration in critically ill patients

Ceftazidime dosing in obese patients: is it time for more?

INTRODUCTION

Ceftazidime is used for the treatment of many bacterial infections, including severe P. aeruginosa infections. Like other beta-lactams, inter-individual variability in ceftazidime pharmacokinetics has been described. Due to its related pathophysiological modifications, obesity might influence ceftazidime pharmacokinetics.

AREAS COVERED

The objective of this review is to assess the current state of knowledge about the impact of obesity on ceftazidime treatment. A literature search was conducted on PubMed-MEDLINE (2016-2021) to retrieve pharmacokinetic studies published in English, matching the terms 'ceftazidime' AND 'pharmacokinetics.'

EXPERT OPINION

The impact of obesity on pharmacokinetics is generally poorly known, mainly because obese patients are often excluded from clinical studies. However, the published literature clearly shows that obese patients have significantly lower ceftazidime concentrations. This could be explained by increased volume of distribution and clearance. This low exposure represents a major factor of therapeutic failure, potentially fatal for critically ill patients. While further studies would be useful to better assess the magnitude and understanding of this variability, the use of higher doses of ceftazidime is needed in obese patients. Moreover, therapeutic drug monitoring for dose adaptation is of major interest for these patients, as the efficacy of ceftazidime seems to be directly related to its plasma concentration.

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.

Size Matters: The Influence of Patient Size on Antibiotics Exposure Profiles in Critically Ill Patients on Continuous Renal Replacement Therapy

(1) Purpose of this study: To determine whether patient weight influences the probability of target attainment (PTA) over 72 h of initial therapy with beta-lactam (cefepime, ceftazidime, piperacillin/tazobactam) and carbapenem (imipenem, ertapenem, meropenem) antibiotics in the critical care setting. This is the first paper to address the question of whether patient size affects antibiotic PTA in the ICU. (2) Methods: We performed a post hoc analysis of Monte Carlo simulations conducted in virtual critically ill patients receiving antibiotics and continuous renal replacement therapy. The PTA was calculated for each antibiotic on the following pharmacodynamic (PD) targets: (a) were above the target organism’s minimum inhibitory concentration (≥%fT≥1×MIC), (b) were above four times the MIC (≥%fT≥4×MIC), and (c) were always above the MIC (≥100%fT≥MIC) for the first 72 h of antibiotic therapy. The PTA was analyzed in patient weight quartiles [Q1 (lightest)-Q4 (heaviest)]. Optimal doses were defined as the lowest dose achieving ≥90% PTA. (3) Results: The PTA for fT≥1×MIC led to similarly high rates regardless of weight quartiles. Yet, patient weight influenced the PTA for higher PD targets (100%fT≥MIC and fT≥4×MIC) with commonly used beta-lactams and carbapenems. Reaching the optimal PTA was more difficult with a PD target of 100%fT≥MIC compared to fT≥4×MIC. (4) Conclusions: The Monte Carlo simulations showed patients in lower weight quartiles tended to achieve higher antibiotic pharmacodynamic target attainment compared to heavier patients.

In vivo / in vitro Correlation of Pharmacokinetics of Gentamicin, Vancomycin, Teicoplanin and Doripenem in a Bovine Blood Hemodialysis Model

Background: Elimination of a drug during renal replacement therapy is not only dependent on flow rates, molecular size and protein binding, but is often influenced by difficult to predict drug membrane interactions. In vitro models allow for extensive profiling of drug clearance using a wide array of hemofilters and flow rates. We present a bovine blood based in vitro pharmacokinetic model for intermittent renal replacement therapy. Methods: Four different drugs were analyzed: gentamicin, doripenem, vancomicin and teicoplanin. The investigated drug was added to a bovine blood reservoir connected to a hemodialysis circuit. In total seven hemofilter models were analyzed using commonly employed flow rates. Pre-filter, post-filter and dialysate samples were drawn, plasmaseparated and analyzed using turbidimetric assays or HPLC. Protein binding of doripenem and vancomycin was measured in bovine plasma and compared to previously published values for human plasma. Results: Clearance values were heavily impacted by choice of membrane material and surface as well as by dialysis parameters such as blood flow rate. Gentamicin clearance ranged from a minimum of 90.12 ml/min in a Baxter CAHP-170 diacetate hemofilter up to a maximum of 187.90 ml/min in a Fresenius medical company Fx80 polysulfone model (blood flow rate 400 ml/min, dialysate flow rate 800 ml/min). Clearance of Gentamicin vs Vancomicin over the F80s hemofilter model using the same flow rates was 137.62 mL vs 103.25 ml/min. Doripenem clearance with the Fx80 was 141.25 ml/min. Conclusion: Clearance values corresponded very well to previously published data from clinical pharmacokinetic trials. In conjunction with in silico pharmacometric models. This model will allow precise dosing recommendations without the need of large scale clinical trials.

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 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.

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.

Population pharmacokinetics and dosing simulations of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis

Objectives

To describe the population PKs of ceftazidime in critically ill patients receiving sustained low-efficiency dialysis (SLED).

Patients and methods

This study was performed in ICUs of a university hospital. We collected blood samples during three consecutive days of SLED sessions in patients receiving ceftazidime. Concentration versus time curves were analysed using a population PKs approach with Pmetrics ® . Monte Carlo simulation for the first 24 h including a 6 h SLED session was performed with the final model. The fractional target attainment against the MIC of Pseudomonas aeruginosa was executed using targets of 50 and 100% fT  >   MIC .

Results

In total, 211 blood samples of 16 critically ill patients under SLED were collected. SLED treatments were 299.3 (68.4) min in duration. A two-compartment linear population PK model was most appropriate. The mean (SD) CL of ceftazidime on SLED, and off SLED were 5.32 (3.2), 1.06 (1.0) L/h respectively. The PTA for 50% fT  >   MIC for a dose of 1 g intravenously every 8 h was 98%. Assuming a target of 100% fT  >   MIC a dose of 2 g every 12 h covers isolates with MIC ≤8 mg/L with a PTA of 96%.

Conclusion

In critically ill patients receiving SLED, ceftazidime 1 g every 8 h and ceftazidime 2 g every 12 h appear to be sufficient for achieving traditional (50% fT  >   MIC ) and aggressive PD targets (100% fT  >   MIC ) for susceptible isolates (MIC ≤8 mg/L), respectively.

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.

Pharmacokinetics and Dialytic Clearance of Ceftazidime-Avibactam in a Critically Ill Patient on Continuous Venovenous Hemofiltration

Ceftazidime-avibactam administered at 1.25 g every 8 h was used to treat multidrug-resistant Pseudomonas aeruginosa bacteremia in a critically ill patient on continuous venovenous hemofiltration (CVVH). Prefiltration plasma drug concentrations of ceftazidime and avibactam were measured at 0, 1, 2, 4, 6, and 8 h along with postfiltration and ultrafiltrate concentrations at h 2 and h 6. Plasma pharmacokinetic parameters of ceftazidime and avibactam, respectively, were as follows: maximum plasma concentration (C_max), 61.10 and 14.54 mg/liter; minimum plasma concentration (C_min), 31.96 and 8.45 mg/liter; half-life (t_1/2), 6.07 and 6.78 h; apparent volume of distribution at the steady state (V_ss), 27.23 and 30.81 liters; total clearance at the steady state (CL_ss), 2.87 and 2.95 liters/h; area under the concentration-time curve from 0 to 8 h (AUC_0-8), 347.87 and 85.69 mg · h/liter. Concentrations of ceftazidime in plasma exceeded the ceftazidime-avibactam MIC (6 mg/liter) throughout the 8-h dosing interval. Mean CVVH extraction ratios for ceftazidime and avibactam were 14.44% and 11.53%, respectively, and mean sieving coefficients were 0.96 and 0.93, respectively. The calculated mean clearance of ceftazidime by CVVH was 1.64 liters/h and for avibactam was 1.59 liters/h, representing 57.1% of the total clearance of ceftazidime and 54.3% of the total clearance of avibactam. Further data that include multiple patients and dialysis modes are needed to verify the optimal ceftazidime-avibactam dosing strategy during critical illness and CVVH.

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.

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.

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.

[Pharmacokinetic and pharmacodynamic aspects in antibiotic treatment]

Severe sepsis and septic shock have a high mortality and, therefore require fast and effective antibiotic treatment with low toxicity. Because of sepsis-induced pathophysiological changes, pharmacokinetics of antimicrobial agents can be altered. Particularly water-soluble drugs display an enhanced volume of distribution during early sepsis. Therefore high loading doses are necessary. Renal clearance can also be increased at this time. Later on, organ damage frequently occurs resulting in delayed drug elimination which requires further dose adjustment. The different classes of antibiotics differ in their relevant pharmacokinetic-pharmacodynamic target parameters. Thus, the efficacy of an antimicrobial agent can depend on its concentration, on the exposure time, and on the total exposure as expressed by the area under the time-concentration curve. During treatment with time-dependent antibiotics (e.g. β-lactams), their concentration should be maintained above the minimal inhibitory concentration (MIC) warranting more frequent administration or continuous infusion. For concentration dependent agents (e.g. aminoglycosides), the single dose is pivotal, whereas the dosage interval can be extended. Drug-drug interactions involving antibiotics are mainly caused by inhibition of their metabolism, particularly of cytochrome P 450 iso-enzymes, or by additive toxic effects. They can result in severe complications such as renal failure or ventricular arrhythmias. Conversely, enzyme induction may lead to subtherapeutic drug levels. When continuous renal replacement therapy is required, the dosage of antibiotics has to be adapted according to the results of respective pharmacokinetic studies.

Single-dose pharmacokinetics of cidofovir in continuous venovenous hemofiltration

Dosage recommendations for cidofovir are available for renally competent as well as impaired patients; however, there are no data for patients undergoing continuous renal replacement therapy. We determined the single-dose concentration-versus-time profile of cidofovir in a critically ill patient undergoing continuous venovenous hemofiltration (CVVH). One dose of 450 mg cidofovir (5 mg/kg) was administered intravenously due to a proven cytomegalovirus (CMV) infection and failure of first-line antiviral therapy. Additionally, 2 g of probenecid was administered orally 3 h prior to and 1 g was administered 2 h as well as 8 h after completion of the infusion. The concentrations of cidofovir in serum and ultrafiltrate were assessed by high-performance liquid chromatography. The peak serum concentration measured at 60 min postinfusion was 28.01 mg/liter at the arterial port. The trough serum level was 19.33 mg/liter at the arterial port after 24 h. The value of the area under the concentration-versus-time curve from 0 to 24 h was 543.8 mg·h/liter. The total body clearance was 2.46 ml/h/kg, and the elimination half-life time was 53.32 h. The sieving coefficient was 0.138±0.022. Total removal of the drug was 30.99% after 24 h. Because of these data, which give us a rough idea of the concentration profile of cidofovir in patients undergoing CVVH, a toxic accumulation of the drug following repeated doses may be expected. Further trials have to be done to determine the right dosage of cidofovir in patients undergoing CVVH to avoid toxic accumulation of the drug.

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.

[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.

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.

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.

Antimicrobial dosing strategies in critically ill patients with acute kidney injury and high-dose continuous veno-venous hemofiltration

PURPOSE OF REVIEW

Delivery of appropriate antimicrobial therapy is a great challenge during continuous veno-venous hemofiltration (CVVH), particularly if the recommended higher doses are applied. The present contribution discusses the principles of drug dosing during CVVH and compares the various proposed dosing strategies.

RECENT FINDINGS

The basic principles underlying removal of antibiotics during CVVH and the published dosing strategies are reviewed. The key factor to consider is the fractional CVVH clearance (FrCVVH). Critical illness and acute kidney injury, however, may dramatically affect the pharmacokinetic properties of a drug and thus FrCVVH. Five dosing strategies have been proposed on the basis of either available references, total creatinine clearance, the reduction in total body clearance, the maintenance dose multiplication factor, or therapeutic drug monitoring. Dose predictions according to the various strategies show reasonable approximations for some but not all antibiotics.

SUMMARY

The delivery of appropriate antimicrobial therapy during CVVH leaves us with uncertainty and presents a great challenge. To ensure efficacy and prevent toxicity, therapeutic drug monitoring is highly recommended. In the absence of therapeutic drug monitoring, adequate concentrations can only be inferred from clinical response. For nontoxic antibiotics overdosing is preferred to underdosing because the danger of underdosing is far greater than that of overdosing.

Dosing of antimicrobial agents in critically-ill patients with acute kindey injury and continuous venvenous haemofiltration

OBJECTIVE

To summarize the general guidelines for drug dosing in critically-ill patients with acute kidney injury and continuous venovenous haemofiltration (CVVH), and to discuss whether the predicted dose adjustment is an as reliable estimate than one based on observed data, considering the recent literature.

METHODS

Literature search was done in PubMed database for human studies.

CONCLUSIONS

In critically-ill patients receiving CVVH, dosing of antibiotics based on the predicted clearances yield rough estimates. Because of interpatient variability observed in the clearance of many antibiotics, monitoring of plasma concentration is highly recommended whenever possible, and especially for those antibiotics that are eliminated predominantly by the kidney, and that have a low therapeutic threshold such as aminoglycosides and glycopeptides, or in patients requiring protracted treatment. However, for many antibiotics, monitoring of blood concentrations is not routinely available and adequate concentrations can only be inferred from clinical response. Therefore, it is important to realize that among many other causes, failure to respond within the first few days of antibiotic treatment may be due to inadequate dosing.

In vitro AN69 and Polysulphone Membrane Permeability to Ceftazidime and in vivo Pharmacokinetics during Continuous Renal Replacement Therapies

BACKGROUND

Ceftazidime is a third-generation cephalosporin almost entirely eliminated by glomerular filtration and dose reductions are essential in patients with renal impairment. The physicochemical and pharmacokinetic properties of ceftazidime make it susceptible to be eliminated by continuous renal replacement therapies (CRRT), but there is little clinical information to guide the correct administration in patients undergoing these techniques.

METHODS

In vitro procedures were carried out in three different fluids, using AN69 or polysulphone membranes. Four patients entered the in vivo study. Two patients received 1,000 mg every 6 h and the other two 2,000 mg every 6 h. Concentrations of ceftazidime were measured by high-performance liquid chromatography.

RESULTS

No differences were detected in thesieving coefficients (Sc) or saturation coefficients (Sa)between membranes during continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodiafiltration (CVVHD). Sc-Sa values were close to 1 when Ringer's lactate was used as ceftazidime vehicle, but were lower in plasma samples (p < 0.05). In patients, the Sc-Sa was 0.93 +/- 0.06 and correlated well with the unbound fraction (0.86 +/- 0.08). The contribution of CRRT to ceftazidime clearance was higher in anuric patients than in nonanuric patients.

CONCLUSIONS

No differences were shown in vitro in the Sc obtained with both membranes during CVVH or the Sa obtained during CVVHD. The contribution of clearance by CRRT to total clearance is clearly dependent on the renal function. The administration of ceftazidime every 6 h could be associated with unnecessarily high trough levels which increase the risk of drug nephrotoxicity. Nonanuric patients undergoing CRRT need higher ceftazidime doses to reach adequate plasma concentrations against pathogens isolated in the critically ill.

Continuous infusion of ceftazidime in critically ill patients undergoing continuous venovenous haemodiafiltration: pharmacokinetic evaluation and dose recommendation

Introduction

In seriously infected patients with acute renal failure and who require continuous renal replacement therapy, data on continuous infusion of ceftazidime are lacking. Here we analyzed the pharmacokinetics of ceftazidime administered by continuous infusion in critically ill patients during continuous venovenous haemodiafiltration (CVVHDF) in order to identify the optimal dosage in this setting.

Method

Seven critically ill patients were prospectively enrolled in the study. CVVHDF was performed using a 0.6 m² AN69 high-flux membrane and with blood, dialysate and ultrafiltration flow rates of 150 ml/min, 1 l/hour and 1.5 l/hour, respectively. Based on a predicted haemodiafiltration clearance of 32.5 ml/min, all patients received a 2 g loading dose of ceftazidime, followed by a 3 g/day continuous infusion for 72 hours. Serum samples were collected at 0, 3, 15 and 30 minutes and at 1, 2, 4, 6, 8, 12, 24, 36, 48 and 72 hours; dialysate/ultrafiltrate samples were taken at 2, 8, 12, 24, 36 and 48 hours. Ceftazidime concentrations in serum and dialysate/ultrafiltrate were measured using high-performance liquid chromatography.

Results

The mean (± standard deviation) elimination half-life, volume of distribution, area under the concentration-time curve from time 0 to 72 hours, and total clearance of ceftazidime were 4 ± 1 hours, 19 ± 6 l, 2514 ± 212 mg/h per l, and 62 ± 5 ml/min, respectively. The mean serum ceftazidime steady-state concentration was 33.5 mg/l (range 28.8–36.3 mg/l). CVVHDF effectively removed continuously infused ceftazidime, with a sieving coefficient and haemodiafiltration clearance of 0.81 ± 0.11 and 33.6 ± 4 mg/l, respectively.

Conclusion

We conclude that a dosing regimen of 3 g/day ceftazidime, by continuous infusion, following a 2 g loading dose, results in serum concentrations more than four times the minimum inhibitory concentration for all susceptible pathogens, and we recommend this regimen in critically ill patients undergoing CVVHDF.

Discrepancies between observed and predicted continuous venovenous hemofiltration removal of antimicrobial agents in critically ill patients and the effects on dosing

OBJECTIVE

Drug dosing during continuous venovenous hemofiltration (CVVH) is based partly upon the CVVH clearance (Cl(CVVH)) of the drug. Cl(CVVH) is the product of the sieving coefficient (SC) and ultrafiltration rate (Q(uf)). Although it has been suggested that the SC can be replaced by the fraction of a drug not bound to protein (F(up)), the F(up) values as reported in the literature may not reflect the protein binding in critically ill patients with renal failure. We compared the observed Cl(CVVH) (SC x Q(uf)) with the estimated Cl(CVVH) (estimated F(UP) x Q(uf)) and determined the effect on the maintenance dose multiplication factor (MDMF).

DESIGN AND SETTING

Clinical study in a mixed ICU in a university hospital.

PATIENTS

45 oligoanuric patients on CVVH (2 l/h).

INTERVENTIONS

Timed blood and ultrafiltrate samples.

MEASUREMENTS AND RESULTS

Amoxicillin, ceftazidime, ciprofloxacin, fluconazole, metronidazole, and vancomycin were easily filtered (mean SC > 0.7) but not flucloxacillin (mean SC 0.3). Predicted and observed Cl(CVVH) corresponded only for fluconazole and metronidazole. The difference between observed and predicted MDMF was small for all drugs, with the exception of ceftazidime (mean 0.25, 95% CI -0.96 to 1.48) and vancomycin (0.05, -1.34 to 1.45). However, this difference was clinically relevant only for vancomycin, because of its narrow therapeutic index.

CONCLUSIONS

Dosing based on predicted CVVH removal provides an as reliable estimate than that based on observed CVVH removal except for those antibiotics that have both a narrow therapeutic index and a predominantly renal clearance (e.g., vancomycin).

Antibiotic Dosing in Critically Ill Adult Patients Receiving Continuous Renal Replacement Therapy

Continuous renal replacement therapy (CRRT) is now commonly used as a means of support for critically ill patients with renal failure. No recent comprehensive guidelines exist that provide antibiotic dosing recommendations for adult patients receiving CRRT. Doses used in intermittent hemodialysis cannot be directly applied to these patients, and antibiotic pharmacokinetics are different than those in patients with normal renal function. We reviewed the literature for studies involving the following antibiotics frequently used to treat critically ill adult patients receiving CRRT: vancomycin, linezolid, daptomycin, meropenem, imipenem-cilastatin, nafcillin, ampicillin-sulbactam, piperacillin-tazobactam, ticarcillin-clavulanic acid, cefazolin, cefotaxime, ceftriaxone, ceftazidime, cefepime, aztreonam, ciprofloxacin, levofloxacin, moxifloxacin, clindamycin, colistin, amikacin, gentamicin, tobramycin, fluconazole, itraconazole, voriconazole, amphotericin B (deoxycholate and lipid formulations), and acyclovir. We used these data, as well as clinical experience, to make recommendations for antibiotic dosing in critically ill patients receiving CRRT.

Determination of ceftazidime and cefepime in plasma and dialysate-ultrafiltrate from patients undergoing continuous veno-venous hemodiafiltration by HPLC

We have developed and validated a new, rapid and reproducible HPLC method for the determination of cefepime and ceftazidime in plasma and dialysate-ultrafiltrate samples obtained from intensive care unit (ICU) patients undergoing continuous veno-venous hemodiafiltration (CVVHDF). The method for plasma samples involved protein precipitation with acetonitrile, followed by washing with dichloromethane to remove apolar lipophilic compounds. Dialysate-ultrafiltrate samples did not require any preparation. Separation was performed on a muBondapak C18 (30 cm x 3.9 mm x 10 microm) with UV detection. The mobile phase contained acetate buffer: ACN and was delivered at 2 ml/min. The coefficients of determination of the calibration curves were always > or = 0.998 and R.S.D.% of the response factors <10%. The intra and inter-assay precision and accuracy of the quality controls (QC) and limit of quantification (LOQ) were satisfactory in all cases. Plasma and dialysate-ultrafiltrate samples were stable at -20 and -80 degrees C for 2 months and also after three freeze/thaw cycles. Dialysate-ultrafiltrate samples were stable in the chromatographic rack for 24h at room temperature, but we recommend storing processed plasma samples at 4 degrees C until the analysis. The described method has proved to be useful to give accurate measurements of ceftazidime and cefepime in samples obtained from patients undergoing CVVHDF.

Multiple-dose pharmacokinetics of linezolid during continuous venovenous haemofiltration

OBJECTIVES

Linezolid is a new antibacterial agent with a broad spectrum of activity against Gram-positive pathogens including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus spp., and penicillin-resistant Streptococcus pneumoniae. The aim of this prospective, single-centre, open-label, two-arm study was to investigate the pharmacokinetics of linezolid during continuous venovenous haemofiltration (CVVH) in critically ill patients and to derive a dosage recommendation.

PATIENTS AND METHODS

Twenty anuric ICU patients undergoing CVVH (mean age and body weight 60.7 +/- 10.9 years and 86.0 +/- 18.0 kg) were included. All patients received linezolid 600 mg intravenously every 12 h. CVVH was performed using highly permeable polysulphone membranes (PSHF 1200, Baxter, Germany and AV 400, Fresenius, Germany). Mean blood flow rate and ultrafiltration rate were 186 +/- 15 and 40 +/- 8 mL/min, respectively. Post-dilution was performed.

RESULTS

The pharmacokinetics of linezolid in critically ill patients with acute renal failure undergoing CVVH were comparable to healthy subjects and patients without renal impairment. The elimination half-life, total clearance and haemofiltration clearance were 4.3 +/- 1.7 h, 9.3 +/- 3.5 L/h and 1.9 +/- 0.8 L/h, respectively.

CONCLUSIONS

Our results showed that linezolid was highly removable by CVVH. These data suggest that a schedule of 600 mg linezolid at least twice daily may also be an appropriate dosing for patients with severe Gram-positive infections undergoing CVVH with both types of membranes.