"CATCH" Study: Correct Antibiotic Therapy in Continuous Hemofiltration in the Critically Ill in Continuous Renal Replacement Therapy: A Prospective Observational Study

The proper posology of antibiotics in the critically ill in CRRT is difficult to assess. We therefore performed a prospective observational cohort study to make clear hints in this topic. Our results reveal a high Sieving Coefficient for all antibiotics, equal to or higher than those described in previous papers. CVVH clearance in relation to total body clearance was significant, (i.e., >than 25% for all classes). A strong correlation between the antibiotic concentrations obtained in plasma and ultrafiltrate was found both at the peak and in the valley, with the determination of two equations that allow a new method for calculating the amount of antibiotic lost in CVVH both for trough levels and peak. Based on the results of our study and considering the limitations we believe that we can extrapolate the following final considerations: (1) it is likely to carry out a loading dose for the main antibiotics (2) subsequent administrations must take into account the daily loss identified by the linear regression equation. This angular coefficient gives the idea that the average daily loss of given antibiotic is about 25%; this implies that on the basis of the linear regression equation that correlates ultrafiltered/plasma antibiotic concentration, the dosage should be increased by 25% every day, while still ensuring a daily plasma TDM of the drug.

Antibiotic Therapy in the Critically Ill with Acute Renal Failure and Renal Replacement Therapy: A Narrative Review

The outcome for critically ill patients is burdened by a double mortality rate and a longer hospital stay in the case of sepsis or septic shock. The adequate use of antibiotics may impact on the outcome since they may affect the pharmacokinetics (Pk) and pharmacodynamics (Pd) of antibiotics in such patients. Acute renal failure (ARF) occurs in about 50% of septic patients, and the consequent need for continuous renal replacement therapy (CRRT) makes the renal elimination rate of most antibiotics highly variable. Antibiotics doses should be reduced in patients experiencing ARF, in accordance with the glomerular filtration rate (GFR), whereas posology should be increased in the case of CRRT. Since different settings of CRRT may be used, identifying a standard dosage of antibiotics is very difficult, because there is a risk of both oversimplification and failing the therapeutic efficacy. Indeed, it has been seen that, in over 25% of cases, the antibiotic therapy does not reach the necessary concentration target mainly due to lack of the proper minimal inhibitory concentration (MIC) achievement. The aim of this narrative review is to clarify whether shared algorithms exist, allowing them to inform the daily practice in the proper antibiotics posology for critically ill patients undergoing CRRT.

Aminoglycoside Pharmacokinetics in Critically Ill Patients Undergoing Continuous Renal Replacement Therapy

BACKGROUND

There are few studies describing aminoglycoside pharmacokinetics during continuous renal replacement therapy (CRRT).

OBJECTIVE

To characterize the effect of CRRT on aminoglycoside clearance and volume of distribution (V_d).

METHODS

Retrospective observational pharmacokinetic study of adult critically ill oncologic patients who received a first dose of amikacin or tobramycin during CRRT between February 2012 and May 2017. Study outcomes included aminoglycoside clearance, V_d, and attainment of the target peak: MIC (minimum inhibitory concentration) ratio as a surrogate for dosing appropriateness.

RESULTS

In total, 80 patients were included, sustained low-efficiency dialysis (SLED), n = 49; continuous venovenous hemodialysis (CVVHD), n = 19; continuous venovenous hemofiltration (CVVH), n = 12. Fifty-one patients received amikacin at a median dose of 14.5 mg/kg per actual body weight and achieved a median peak level of 26.7 mg/L. Twenty-nine patients received tobramycin at a median dose of 6.5 mg/kg actual body weight and achieved a median peak level of 10.3 mg/L. The median aminoglycoside clearance was 63.1 mL/min and was similar between CRRT modality groups (P = 0.97). The median V_d was 0.47 L/kg and was different between the SLED and CVVH groups (P = 0.007). Attainment of target peak: MIC occurred in 29% in the total study population and 44% in the subgroup of 23 patients with isolates tested for aminoglycoside susceptibility.

CONCLUSION AND RELEVANCE

Critically ill oncology patients undergoing CRRT exhibited reduced clearance and expanded V_d that was not significantly different between CRRT modalities. Current dosing regimens led to low peak concentrations and poor attainment of pharmacokinetic targets.

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.

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.

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.

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.

Pharmacokinetics of piperacillin in critically ill patients receiving continuous venovenous haemofiltration: A randomised controlled trial of continuous infusion versus intermittent bolus administration

Here we describe the pharmacokinetics of piperacillin administered by continuous infusion (CI) versus intermittent bolus (IB) dosing in critically ill patients receiving continuous venovenous haemofiltration (CVVH) and compare the frequency of pharmacodynamic/pharmacokinetic (PK/PD) target attainment with each dosing strategy. This was a prospective pharmacokinetic trial in 16 critically ill patients with severe sepsis or septic shock undergoing CVVH and randomised to receive either CI or IB administration of a standard daily dose of piperacillin/tazobactam (11.25g/day on Day 1 followed by 9g/day). Serial blood samples were measured on two occasions. Piperacillin pharmacokinetics were calculated using a non-compartmental approach. Blood concentrations were compared with established PK/PD targets. On occasion 1 (Days 1-3 of therapy), IB administration resulted in significantly higher piperacillin peak concentrations (169 vs. 89mg/L; P=0.002), whereas significantly higher steady-state concentrations were observed in CI patients (83 vs. 57mg/L; P=0.04). Total clearance and clearance not mediated by CVVH were significantly higher with CI administration [median (interquartile range), 1.0 (0.7-1.1) and 0.8 (0.6-1.0)mL/kg/min; P=0.001 and 0.001, respectively]. The estimated unbound piperacillin concentrations were four times above the target susceptibility breakpoint (16mg/L) for the entire dosing interval (100%fT>4xMIC) in 87.5% of patients receiving CI administration (sampling occasion 1), compared with 62.5% of IB patients achieving the desired target (50%fT>4xMIC). Compared with IB dosing, and despite similar CVVH settings, CI administration of piperacillin results in a pharmacokinetic profile that may optimise outcomes for less susceptible pathogens.

Amikacin pharmacokinetics during continuous veno-venous hemodialysis

Introduction

Little is known about the pharmacokinetics of amikacin during continuous renal replacement therapy.

Methods

This prospective observational study included patients admitted to an academic medical center who received amikacin therapy while on continuous veno-venous hemodialysis (CVVHD) and had at least two serum sample concentrations measured after first-dose administration. First-order pharmacokinetic parameters, patient characteristics, and CVVHD parameters were recorded.

Results

Fifteen patients were included in the analysis. The median (interquartile range) dose of amikacin and dialysate flow rate, based on adjusted body weight, were 14.1 mg/kg (11.7–17.3 mg/kg) and 23.9 mL/kg/h (19.0–29.5 mL/kg/h), respectively. This corresponded with a median C_max of 28.5 μg/mL (20.9–39.0 μg/mL). There was a significant correlation between clearance and dialytic dose (for every 1 L/h increase in dialysate flow rate, clearance rate increased by 23.6 mL/min [95% confidence interval 1.7–45.4 mL/min; P = 0.037]).

Conclusion

The results of this study suggest that amikacin dose and interval should be individualized for each patient on CVVHD based on first-dose pharmacokinetic assessment.

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.

Antimicrobial dosing in acute renal replacement

Acute kidney injury (AKI) is a common problem in hospitalized patients and is associated with significant morbidity and mortality. Two large trials showed no benefit from increased doses of renal replacement therapy (RRT) despite previous clinical data suggesting that increased clearance from RRT has beneficial effects. Since infection is the leading cause of death in AKI, my group and others hypothesized that increased RRT antibiotic clearance might create a competing morbidity. The data from my group, as well as those of other groups, show that many patients are underdosed when routine "1 size fits all" antibiotic dosing is used in patients with AKI receiving continuous RRT (CRRT). Here, concepts of drug distribution and clearance in AKI are briefly discussed and then 1 antibiotic (piperacillin) is discussed in depth to illustrate the challenges in applying the medical literature to clinical practice. The fact that published data on drug dosing in AKI and dialysis reflect the evolution of practice patterns and often do not apply to present prescribing habits is also discussed. A more general approach to drug dosing facilitates situation-specific prescribing by the nephrologist and critical care specialist.

Once-daily amikacin dosing in burn patients treated with continuous venovenous hemofiltration

Amikacin clearance can be increased in burn injury, which is often complicated by renal insufficiency. Little is known about the impact of renal replacement therapies, such as continuous venovenous hemofiltration (CVVH), on amikacin pharmacokinetics. We retrospectively examined the clinical pharmacokinetics, bacteriology, and clinical outcomes of 60 burn patients given 15 mg/kg of body weight of amikacin in single daily doses. Twelve were treated with concurrent CVVH therapy, and 48 were not. The pharmacodynamic target of ≥10 for the maximum concentration of drug in serum divided by the MIC (C(max)/MIC) was achieved in only 8.5% of patients, with a small reduction of C(max) in patients receiving CVVH and no difference in amikacin clearance. Mortality and burn size were greater in patients who received CVVH. Overall, 172 Gram-negative isolates were recovered from the blood cultures of 39 patients, with amikacin MIC data available for 82 isolates from 24 patients. A 10,000-patient Monte Carlo simulation was conducted incorporating pharmacokinetic and MIC data from these patients. The cumulative fraction of response (CFR) was similar in CVVH and non-CVVH patients. The CFR rates were not significantly improved by a theoretical 20 mg/kg amikacin dose. Overall, CVVH did not appear to have a major impact on amikacin serum concentrations. The low pharmacodynamic target attainment appears to be primarily due to higher amikacin MICs rather than more rapid clearance of amikacin related to CVVH therapy.

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.

Systemic tobramycin concentrations during selective decontamination of the digestive tract in intensive care unit patients on continuous venovenous hemofiltration

Objective

To study whether selective decontamination of the digestive tract (SDD) results in detectable serum tobramycin concentrations in intensive care unit (ICU) patients with acute renal failure treated with continuous venovenous hemofiltration (CVVH).

Design and setting

Prospective, observational, single-center study in a mixed medical–surgical ICU.

Patients

Adult ICU patients receiving SDD for at least 3 days and being treated with CVVH because of acute renal failure.

Measurements and results

Tobramycin serum concentrations were measured at the 3rd day after start of CVVH and every 3 days thereafter. Detectable serum concentrations of tobramycin were found in 12 (63%) of 19 patients and in 15 (58%) of the 26 samples. With a toxic tobramycin concentration defined as more than 2.0 mg/l, we found one patient with a toxic concentration of 3.0 mg/l. In three other patients tobramycin concentrations of ≥ 1.0 mg/l were found.

Conclusions

In patients with acute renal failure treated with CVVH, administration of SDD with tobramycin can lead to detectable and potentially toxic serum tobramycin concentrations.

Adsorption of amikacin, a significant mechanism of elimination by hemofiltration

We used an in vitro model of continuous venovenous hemofiltration (CVVH) to characterize amikacin adsorption by polyacrylonitrile (PAN) and polyamide filters. A blood-crystalloid mixture dosed with amikacin was pumped from a reservoir through a hemofiltration circuit and back to the reservoir. All ultrafiltrate was also returned to the reservoir. The level of adsorption was calculated from the fall in the amikacin concentration. The dose and the initial concentration of amikacin were varied, as were the pH, the type of hemofilter, and the hemofilter surface area. The reversibility of adsorption and the effect of repeated dosing were also studied. The level of adsorption by 0.6-m2 PAN filters was significantly greater than that by 0.6-m2 polyamide filters. Adsorption was increased by increasing the dose of amikacin even when the initial concentration was unchanged. It was unaffected by the pH (pH 6.8 or 7.4) or the hemofilter surface area (0.6 m2 or 0.9 m2). Repeated doses of amikacin resulted in further adsorption. In a saturation experiment, the maximum adsorptive capacity of 0.6-m2 PAN hemofilters was at least 546.9 mg (range, 427.6 to 577.5 mg). The adsorption of amikacin by hemofilters is irreversible and was associated with the dose and the hemofilter material but not the hemofilter surface area. Close monitoring of peak amikacin levels should be considered for patients receiving CVVH with PAN hemofilters.

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).

Meropenem and continuous renal replacement therapy: in vitro permeability of 2 continuous renal replacement therapy membranes and influence of patient renal function on the pharmacokinetics in critically ill patients

The pharmacokinetics of meropenem were characterized in 20 patients with different degrees of renal function who underwent continuous renal replacement therapy. Previously, no differences were detected in vitro in the removal of meropenem by continuous venovenous hemofiltration or continuous venovenous hemodialysis or when AN69 or polysulfone membranes were compared. In patients, no significant differences in the sieving coefficient or the saturation coefficient with the renal function were found, and the mean sieving coefficient/saturation coefficient value (0.80 +/- 0.12) was similar to the unbound fraction (0.79 +/- 0.08). An increase in total clearance and a decrease in elimination half-life were observed to the extent that the patient's creatinine clearance was higher. Likewise, the contribution of continuous renal replacement therapy to total clearance diminished in patients with less renal impairment. The results suggest that the renal function of the patient may influence meropenem pharmacokinetics during continuous renal replacement therapy. The lower trough plasma levels observed in nonrenal patients would not lead to adequate time during which serum drug concentrations are above the minimum inhibitory concentration values in many infections.

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.

Vancomycin pharmacokinetics in critically ill patients receiving continuous venovenous haemodiafiltration

AIMS

To investigate the pharmacokinetics of vancomycin in critically ill patients on continuous venovenous haemodiafiltration (CVVHDF), a continuous renal replacement therapy (CRRT) and to see if routine measures approximate vancomycin clearance.

METHODS

Pharmacokinetic profiles (15) of initial and steady-state doses of 750 mg twice daily intravenous vancomycin were obtained from blood and ultrafiltrate samples from 10 critically ill patients in the intensive care unit, with acute renal failure on CVVHDF (1 l h(-1) dialysate plus 2 l h(-1) filtration solution; 3 l h(-1) effluent; extracorporeal blood flow 200 ml min(-1)).

RESULTS

CVVHDF clearance of vancomycin was 1.8 +/- 0.4 l h(-1) (30 +/- 6.7 ml min(-1)). This was 1.3-7.2 times that reported previously for vancomycin using other forms of CRRT. Total vancomycin body clearance was 2.5 +/- 0.7 l h(-1) (41.7 +/- 11.7 ml min(-1)). The clearance of vancomycin by CVVHDF was 76 +/- 16.5% of the total body clearance. CVVHDF removed approximately half the vancomycin dose during the 12-h period (A(CVVHDF) = 413 mg). The fraction eliminated by all routes was 60%. The sieving coefficient for vancomycin was 0.7 +/- 0.1 and for urea was 0.8 +/- 0.06.

CONCLUSIONS

Vancomycin is cleared effectively by CVVHDF. Clearance was faster than other forms of CRRT, therefore doses need to be relatively high. Urea clearance slightly overestimates vancomycin clearance. The administered doses of 750 mg every 12 h were too high and accumulation occurred, as only approximately 60% of a dose was cleared over this period. The maintenance dose required to achieve a target average steady-state plasma concentration of 15 mg l(-1) can be calculated as 450 mg every 12 h.

Influence of renal replacement therapy on pharmacokinetics in critically ill patients

Critical illness has a great impact on many pharmacokinetic parameters. An increased volume of distribution often results in drug underdosing, whereas organ impairment may lead to drug accumulation and overdosing. Renal replacement therapy (RRT) in critically ill patients with renal failure may significantly increase drug clearance, requiring drug-dosing adjustments. Drugs significantly eliminated by the kidney are likely to experience substantial removal during RRT, and a supplemental dose--corresponding to the amount of drug removed by RRT--should be administered. Mechanisms of drug removal during RRT are reviewed together with methods for measuring or estimating RRT drug clearances. Approaches for drug-dosing adjustments are suggested and, at the end, the pharmacological principles for antibiotic prescription in the critically ill are discussed.

Pharmacokinetics of ciprofloxacin in patients with acute renal failure undergoing continuous venovenous haemofiltration: influence of concomitant liver cirrhosis

To determine an adequate dosage of ciprofloxacin in critically ill medical patients on continuous venovenous haemofiltration, we studied the pharmacokinetics of ciprofloxacin in eight critically ill medical patients with renal failure treated with continuous venovenous haemofiltration using polysulfone membranes. Three of those patients also presented with severe liver dysfunction. For comparison, three patients with approximately normal renal function and two patients with impaired renal function were included. During haemofiltration, plasma concentrations of ciprofloxacin were variable. In all critically ill patients ciprofloxacin elimination was significantly slowed; the mean half-life was similarly prolonged to about 14 h in patients on haemofiltration and those with approximately normal renal function. In critically ill patients with impaired renal function not on haemofiltration, the mean half-life was longest. Ciprofloxacin clearance by haemofiltration was a quarter of the total clearance. Although a unique dose recommendation can hardly be made because of the high variability of pharmacokinetics during haemofiltration, a daily dose of 800 mg (400 mg b.i.d.) in average can be regarded as appropriated for reaching a target plasma concentration of 2 to 3 micrograms/mL (mean concentration). Because the half-life of ciprofloxacin was further prolonged by the presence of liver cirrhosis, the dose should be reduced to 600 mg in patients on haemofiltration with concomitant severe liver dysfunction.

Pharmacokinetics and drug dosing adjustments during continuous venovenous hemofiltration or hemodiafiltration in critically ill patients

Continuous renal replacement therapy (CRRT) in critically ill patients with renal failure may significantly increase drug clearance, requiring drug dosing adjustments. Drugs significantly eliminated by the kidney often undergo substantial removal during CRRT, and a supplemental dose corresponding to the amount of drug removed by CRRT should be administered. Clearance by CRRT can either be measured or estimated. The high-flux membranes used in CRRT make no filtration barrier to most drugs, and the filtrate concentration can be estimated by the unbound fraction of the drug in plasma. When adding dialysis to filtration, this approach overestimates drug clearance, and a correcting factor should be used. A method for estimating drug clearance as a function of creatinine clearance is also suggested, but it has the same limitations in overestimating drug clearance when dialysis is combined with filtration. For non-toxic drugs, doses can safely be increased 30% above actual estimates to ensure adequate dosing. For drugs with a narrow therapeutical margin, monitoring plasma concentrations are mandatory. When appropriate, the use of a readily available reference for drug dosing is recommended.

Determinants of ceftazidime clearance by continuous venovenous hemofiltration and continuous venovenous hemodialysis

Although several dosage adjustment regimens have been proposed, there is little quantitative information to guide the initiation of ceftazidime therapy in patients who are receiving continuous renal replacement therapy. To determine the clearance of ceftazidime by continuous venovenous hemofiltration (CVVH) and continuous venovenous hemodialysis (CVVHD), we performed controlled clearance studies with stable hemodialysis patients with three hemofilters: a 0.6-m(2) acrylonitrile copolymer (AN69; Hospal) filter, a 2.1-m(2) polymethylmethacrylate filter (PMMA; Toray) filter and a 0.65-m(2) polysulfone (PS; Fresenius) filter. Subjects received 1,000 mg of ceftazidime intravenously prior to the start of a clearance study. The concentration of ceftazidime in multiple plasma and dialysate or ultrafiltrate samples was determined by high-performance liquid chromatography. The diffusional clearances (CI(diffusion)) and sieving coefficients of ceftazidime were compared by a mixed-model repeated-measures analysis of variance with filter and blood, dialysate inflow, or ultrafiltration rate as the main effect and the patient as a random effect. The fraction of ceftazidime bound to plasma proteins was 17%+/-7% (range, 10 to 25%). The clearances of ceftazidime, urea, and creatinine by CVVHD were essentially constant at blood flow rates of 75 to 250 ml/min for all three filters. Significant linear relationships (P<0.0001) were observed between CI(diffusion) of ceftazidime and clearance of urea for all three filters: AN69 (slope = 0.83), PMMA (slope = 0.89), and PS (slope = 1.03). Ceftazidime clearance was membrane independent during CVVH and CVVHD. CVVH and CVVHD can significantly augment the clearance of ceftazidime. Dosing strategies for initiation of ceftazidime therapy in patients receiving CVVH and CVVHD are proposed.