The effect of adsorption, filter material and point of dilution on antibiotic elimination by haemofiltration an in vitro study of levofloxacin

Elimination of cefotaxime using polysulfone and polyacrylonitrile-derived filters: An in vitro assessment

Continuous renal replacement therapy (CCRT) efficiently eliminates cefotaxime. To our knowledge, there are no previous in vitro studies dealing with the disposition of cefotaxime. We studied the elimination of cefotaxime by two filters in a model mimicking a session of CRRT using the NeckEpur^® technology. The ST150^®-polyacrylonitrile filter with the Prismaflex, Baxter-Gambro, and the AV1000^®-polysulfone filter with the Multifiltrate Pro, Fresenius, were studied. Continuous filtration used a flowrate of 1 L/h in post-dilution only. Simulated blood flowrate was set at 200 mL/min. Routes of elimination were assessed using the NeckEpur^® technology. Cefotaxime concentrations were measured using ultra high-performance liquid chromatography, and tandem mass spectrometry. Two sessions were performed using the ST^® filter and three using the AV^® filter. Stability of cefotaxime during 6 h was assessed in triplicate with a mean variation of concentrations of 2.4 ± 1.5% at the end of the study. The mean measured initial concentration in the central compartment (CC) for the five sessions was 52.4 mg/L. The mean amount eliminated from the CC at the end of the sessions using the ST150^®-polyacrylonitrile and the AV1000^®-polysulfone filters were 72% and 73%, respectively. The clearances of cefotaxime from the central compartment (CC) were 1.1 and 1.2 L/h, respectively. The mean sieving coefficient were 0.99 and 0.99, respectively. The mean percentages of the amount eliminated from the CC by filtration/adsorption were 87/13% and 92/8%, respectively. Both adsorption percentages were below 15%. We conclude neither the ST150^®-polyacrylonitrile nor the AV1000^®-polysulfone filters result in clinically significant adsorption of cefotaxime.

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.

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.

Pharmacokinetics and dialytic clearance of apixaban during in vitro continuous renal replacement therapy

Background

To evaluate the transmembrane clearance (CL_TM) of apixaban during modeled in vitro continuous renal replacement therapy (CRRT), assess protein binding and circuit adsorption, and provide initial dosing recommendations.

Methods

Apixaban was added to the CRRT circuit and serial pre-filter bovine blood samples were collected along with post-filter blood and effluent samples. All experiments were performed in duplicate using continuous veno-venous hemofiltration (CVVH) and hemodialysis (CVVHD) modes, with varying filter types, flow rates, and point of CVVH replacement fluid dilution. Concentrations of apixaban and urea were quantified via liquid chromatography-tandem mass spectrometry. Plasma pharmacokinetic parameters for apixaban were estimated via noncompartmental analysis. CL_TM was calculated via the estimated area under the curve (AUC) and by the product of the sieving/saturation coefficient (SC/SA) and flow rate. Two and three-way analysis of variance (ANOVA) models were built to assess the effects of mode, filter type, flow rate, and point of dilution on CL_TM by each method. Optimal doses were suggested by matching the AUC observed in vitro to the systemic exposure demonstrated in Phase 2/3 studies of apixaban. Linear regression was utilized to provide dosing estimations for flow rates from 0.5–5 L/h.

Results

Mean adsorption to the HF1400 and M150 filters differed significantly at 38 and 13%, respectively, while mean (± standard deviation, SD) percent protein binding was 70.81 ± 0.01%. Effect of CVVH point of dilution did not differ across filter types, although CL_TM was consistently significantly higher during CRRT with the HF1400 filter compared to the M150. The three-way ANOVA demonstrated improved fit when CL_TM values calculated by AUC were used (adjusted R² 0.87 vs. 0.52), and therefore, these values were used to generate optimal dosing recommendations. Linear regression revealed significant effects of filter type and flow rate on CL_TM by AUC, suggesting doses of 2.5–7.5 mg twice daily (BID) may be needed for flow rates ranging from 0.5–5 L/h, respectively.

Conclusion

For CRRT flow rates most commonly employed in clinical practice, the standard labeled 5 mg BID dose of apixaban is predicted to achieve target systemic exposure thresholds. The safety and efficacy of these proposed dosing regimens warrants further investigation in clinical studies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12882-021-02248-7.

Adsorption of vancomycin, gentamycin, ciprofloxacin and tygecycline on the filters in continuous renal replacement therapy circuits: in full blood in vitro study

The aim of this study was to assess the in vitro adsorption of antibiotics: vancomycin, gentamicin, ciprofloxacin and tigecycline on both polyethyleneimine-treated polyacrylonitrile membrane of AN69ST filter and polysulfone membrane of AV1000 filter using porcine blood as a model close to in vivo conditions. The porcine blood with antibiotic dissolved in it was pumped into hemofiltration circuit (with AN69ST or AV1000 filter), ultrafiltration fluid was continuously returned to the reservoir containing blood with antibiotic. Blood samples to determine antibiotic concentrations were taken at minutes 0, 5, 15, 30, 45, 60, 90 and 120 from the pre- blood pump of the hemofiltration circuit. To assess possible spontaneous degradation of the drug in the solution there was an additional reservoir prepared for each antibiotic, containing blood with the drug, which was not connected to the circuit. In the case of vancomycin, ciprofloxacine and tigecycline, a statistically significant decrease in the drug concentration in the hemofiltration circuit in comparison to initial value as well as to the concentrations in the control blood was observed, both for polyacrylonitrile and plolysulfone membrane. In the case of gentamicin, significant adsorption was noted only on polyacrylonitrile membrane. Our studies demonstrated that in full blood adsorption of antibiotics may be big enough to be of clinical significance. In particular in the case of polyacrylonitrile membrane.

Diafiltration flowrate is a determinant of the extent of adsorption of amikacin in renal replacement therapy using the ST150®-AN69 filter: An in vitro study

Introduction:

In continuous renal replacement therapy, conduction and convection are controlled allowing prescribing dosage regimen improving survival. In contrast, adsorption is an uncontrolled property altering drug disposition. Whether adsorption depends on flowrates is unknown. We hypothesized an in vitro model may provide information in conditions mimicking continuous renal replacement therapy in humans.

Methods:

ST150®-AN69 filter and Prismaflex dialyzer, Baxter-Gambro were used. Simulated blood flowrate was set at 200 mL/min. The flowrates in the filtration (continuous filtration), dialysis (continuous dialysis), and diafiltration (continuous diafiltration) were 1500, 2500, and 4000 mL/h, respectively. Routes of elimination were assessed using NeckEpur® analysis.

Results:

The percentages of the total amount eliminated by continuous filtration, continuous dialysis, and continuous diafiltration were 82%, 86%, and 94%, respectively. Elimination by effluents and adsorption accounted for 42% ± 7% and 58% ± 5%, 57% ± 7% and 43% ± 6%, and 84% ± 6% and 16% ± 6% of amikacin elimination, respectively. There was a linear regression between flowrates and amikacin clearance: Y = 0.6 X ± 1.7 (R2 = 0.9782). Conversely, there was a linear inverse correlation between the magnitude of amikacin adsorption and flowrate: Y = –16.9 X ± 84.1 (R2 = 0.9976).

Conclusion:

Low flowrates resulted in predominant elimination by adsorption, accounting for 58% of the elimination of amikacin from the central compartment in the continuous filtration mode at 1500 mL/h of flowrate. Thereafter, the greater the flowrate, the lower the adsorption of amikacin in a linear manner. Flowrate is a major determinant of adsorption of amikacin. There was an about 17% decrease in the rate of adsorption per increase in the flowrate of 1 L/min.

Pharmacokinetics and Pharmacodynamics of Anti-infective Agents during Continuous Veno-venous Hemofiltration in Critically Ill Patients: Lessons Learned from an Ancillary Study of the IVOIRE Trial

Background

Hemofiltration rate, changes in blood and ultrafiltration flow, and discrepancies between the prescribed and administered doses strongly influence pharmacokinetics (PK) and pharmacodynamics (PD) of antimicrobial agents during continuous veno-venous hemofiltration (CVVH) in critically ill patients.

Methods

Ancillary data were from the prospective multicenter IVOIRE (hIgh VOlume in Intensive caRE) study. High volume (HV, 70 mL/kg/h) was at random compared with standard volume (SV, 35 mL/kg/h) CVVH in septic shock patients with acute kidney injury (AKI). PK/PD parameters for all antimicrobial agents used in each patient were studied during five days.

Results

Antimicrobial treatment met efficacy targets for both percentage of time above the minimal inhibitory concentration and inhibitory quotient. A significant correlation was observed between the ultrafiltration flow and total systemic clearance (Spearman test: P < 0.005) and between CVVH clearance and drug elimination half-life (Spearman test: P < 0.005). All agents were easily filtered. Mean sieving coefficient ranged from 38.7% to 96.7%. Mean elimination half-life of all agents was significantly shorter during HV-CVVH (from 1.29 to 28.54 h) than during SV-CVVH (from 1.51 to 33.85 h) (P < 0.05).

Conclusions

This study confirms that CVVH influences the PK/PD behavior of most antimicrobial agents. Antimicrobial elimination was directly correlated with convection rate. Current antimicrobial dose recommendations will expose patients to underdosing and increase the risk for treatment failure and development of resistance. Dose recommendations are proposed for some major antibiotic and antifungal treatments in patients receiving at least 25 mL/kg/h CVVH.

Comparison of adsorption of selected antibiotics on the filters in continuous renal replacement therapy circuits: in vitro studies

The aim of this study was to assess the adsorption of selected antibiotics: vancomycin, gentamicin, ciprofloxacine and tigecycline in an experimental continuous veno-venous hemofiltration circuit with the use of both polyethyleneimine-treated polyacrylonitrile (PAN) and the polysulfone (PS) filter membranes. The crystalloid fluid dosed with one of antibiotic was pumped from a reservoir through a hemofiltration circuit (with PAN or PS membrane) and back to reservoir. All ultrafiltrate was also returned to the reservoir. During the procedures samples were collected from the post-hemofilter port at 5, 15, 30, 45, 60, 90, and 120 min. To determine spontaneous degradation of the antimicrobials, an additional bag with each study drug was prepared, which was not attached to the hemofiltration circuit. The samples from these bags were used as controls. In the case of vancomycin, gentamycin and tigecycline there was a statistically significant decrease in the drug concentration in the hemofiltration circuit in comparison to the control for PAN membrane (P < 0.05, P < 0.001, P < 0.001, respectively). In the case of ciprofloxacine adsorption was reversible and the drug concentrations increase to achieve the initial level for both membranes. Our studies indicated that a large portion of the administered dose of antibiotics may be adsorbed on a PAN membrane. In the case of gentamicin and tigecycline this amount is sufficiently big (over 90% of the administered dose) to be of clinical importance. In turn, adsorption on PS membranes is clearly lower (up to 10%) and may be clinically unimportant.

Therapeutic drug monitoring-guided continuous infusion of piperacillin/tazobactam significantly improves pharmacokinetic target attainment in critically ill patients: a retrospective analysis of four years of clinical experience

PURPOSE

Standard dosing and intermittent bolus application (IB) are important risk factors for pharmacokinetic (PK) target non-attainment during empirical treatment with β-lactams in critically ill patients, particularly in those with sepsis and septic shock. We assessed the effect of therapeutic drug monitoring-guided (TDM), continuous infusion (CI) and individual dosing of piperacillin/tazobactam (PIP) on PK-target attainment in critically ill patients.

METHODS

This is a retrospective, single-center analysis of a database including 484 patients [933 serum concentrations (SC)] with severe infections, sepsis and septic shock who received TDM-guided CI of PIP in the intensive care unit (ICU) of an academic teaching hospital. The PK-target was defined as a PIP SC between 33 and 64 mg/L [fT > 2-4 times the epidemiological cutoff value (ECOFF) of Pseudomonas aeruginosa (PSA)].

RESULTS

PK-target attainment with standard dosing (initial dose) was observed in 166 patients (34.3%), whereas only 49 patients (10.1%) demonstrated target non-attainment. The minimum PK-target of ≥ 33 mg/L was overall realized in 89.9% (n = 435/484) of patients after the first PIP dose including 146 patients (30.2%) with potentially harmful SCs ≥ 100 mg/L. Subsequent TDM-guided dose adjustments significantly enhanced PK-target attainment to 280 patients (62.4%) and significantly reduced the fraction of potentially overdosed (≥ 100 mg/L) patients to 4.5% (n = 20/449). Renal replacement therapy (RRT) resulted in a relevant reduction of PIP clearance (CL_PIP): no RRT CL_PIP 6.8/6.3 L/h (median/IQR) [SCs n = 752, patients n = 405], continuous veno-venous hemodialysis (CVVHD) CL_PIP 4.3/2.6 L/h [SCs n = 160, n = 71 patients], intermittent hemodialysis (iHD) CL_PIP 2.6/2.3 L/h [SCs n = 21, n = 8 patients]). A body mass index (BMI) of > 40 kg/m² significantly increased CL_PIP 9.6/7.7 L/h [SC n = 43, n = 18 patients] in these patients. Age was significantly associated with supratherapeutic PIP concentrations (p < 0.0005), whereas high CrCL led to non-target attainment (p < 0.0005). Patients with target attainment (33-64 mg/L) within the first 24 h exhibited the lowest hospital mortality rates (13.9% [n = 23/166], p < 0.005). Those with target non-attainment demonstrated higher mortality rates (≤ 32 mg/L; 20.8% [n = 10/49] ≥ 64 mg/L; 29.4% [n = 79/269]).

CONCLUSION

TDM-guided CI of PIP is safe in critically ill patients and improves PK-target attainment. Exposure to defined PK-targets impacts patient mortality while lower and higher than intended SCs may influence the outcome of critically ill patients. Renal function and renal replacement therapy are main determinants of PK-target attainment. These results are only valid for CI of PIP and not for prolonged or intermittent bolus administration of PIP.

A Guide to Understanding Antimicrobial Drug Dosing in Critically Ill Patients on Renal Replacement Therapy

A careful management of antimicrobials is essential in the critically ill with acute kidney injury, especially if renal replacement therapy is required. Acute kidney injury may lead per se to clinically significant modifications of drugs' pharmacokinetic parameters, and the need for renal replacement therapy represents a further variable that should be considered to avoid inappropriate antimicrobial therapy. The most important pharmacokinetic parameters, useful to determine the significance of extracorporeal removal of a given drug, are molecular weight, protein binding, and distribution volume. In many cases, the extracorporeal removal of antimicrobials can be relevant, with a consistent risk of underdosing-related treatment failure and/or potential onset of bacterial resistance. It should also be taken into account that renal replacement therapies are often not standardized in critically ill patients, and their impact on plasma drug concentrations may substantially vary in relation to membrane characteristics, treatment modality, and delivered dialysis dose. Thus, in this clinical scenario, the knowledge of the pharmacokinetic and pharmacodynamic properties of different antimicrobial classes is crucial to tailor maintenance dose and/or time interval according to clinical needs. Finally, especially for antimicrobials known for a tight therapeutic range, therapeutic drug monitoring is strongly suggested to guide dosing adjustment in complex clinical settings, such as septic patients with acute kidney injury undergoing renal replacement therapy.

Amino Acid Loss during Continuous Venovenous Hemofiltration in Critically Ill Patients

BACKGROUND/OBJECTIVES

During continuous venovenous hemofiltration (CVVH), there is unwanted loss of amino acids (AA) in the ultrafiltrate (UF). Solutes may also be removed by adsorption to the filter membrane. The aim was to quantify the total loss of AA via the CVVH circuit using a high-flux polysulfone membrane and to differentiate between the loss by ultrafiltration and adsorption.

METHODS

Prospective observational study in ten critically ill patients, receiving predilution CVVH with a new filter, blood flow 180 mL/min, and predilution flow 2,400 mL/h. Arterial blood, postfilter blood, and UF samples were taken at baseline, and 1, 8, and 24-h after CVVH initiation, to determine AA concentrations and hematocrit. Mass transfer calculations were used to determine AA loss in the filter and by UF, and the difference between these 2.

RESULTS

The median AA loss in the filter was 10.4 g/day, the median AA loss by UF was 13.4 g/day, and the median difference was -2.9 g/day (IQR -5.9 to -1.4 g/day). For the individual AA, the difference ranged from -1 g/day to +0.4 g/day, suggesting that some AA were consumed or adsorbed and others were generated. AA losses did not significantly change over the 24-h study period.

CONCLUSION

During CVVH with a modern polysulfone membrane, the estimated AA loss was 13.4 g/day, which corresponds to a loss of about 11.2 g of protein per day. Adsorption did not play a major role. However, individual AA behaved differently, suggesting complex interactions and processes at the filter membrane or peripheral AA production.

Ex Vivo Characterization of Effects of Renal Replacement Therapy Modalities and Settings on Pharmacokinetics of Meropenem and Vaborbactam

The combination product meropenem-vaborbactam, with activity against KPC-producing carbapenem-resistant Enterobacteriaceae, is likely to be used during renal replacement therapy. The aim of this work was to describe the extracorporeal removal (adsorption and clearance) of meropenem-vaborbactam during continuous venovenous hemofiltration (CVVH).

The combination product meropenem-vaborbactam, with activity against KPC-producing carbapenem-resistant Enterobacteriaceae, is likely to be used during renal replacement therapy. The aim of this work was to describe the extracorporeal removal (adsorption and clearance) of meropenem-vaborbactam during continuous venovenous hemofiltration (CVVH). An ex vivo model was used to examine the effects of a matrix of operational settings. Vaborbactam did not adsorb to AN69 (acrylonitrile and sodium methallylsulfonate copolymer) ST100 (surface area, 1 m²) hemofilter; the mean (±standard deviation [SD]) meropenem adsorption was 9% (±1%). The sieving coefficients (mean ± SD) with AN69 ST100 and ST150 (surface area, 1.5 m²) filters ranged from 0.97 ± 0.16 to 1.14 ± 0.12 and from 1.13 ± 0.01 to 1.53 ± 0.28, respectively, for meropenem and from 0.64 ± 0.39 to 0.90 ± 0.14 and 0.78 ± 0.18 to 1.04 ± 0.28, respectively, for vaborbactam. At identical settings, vaborbactam sieving coefficients were 25% to 30% lower than for meropenem. Points of dilution, blood flow rates, or effluent flow rates did not affect sieving coefficients for either drug. However, doubling the effluent flow rate resulted in >50 to 100% increases in filter clearance for both drugs. Postfilter dilution resulted in 40 to 80% increases in filter clearance at a high effluent flow rate (4,000 ml/h), compared with ∼15% increases at a low effluent flow rate (1,000 ml/h) for both drugs. For all combinations of setting and filters tested, vaborbactam clearance was lower than that of meropenem by ∼20 to 40%. Overall, meropenem-vaborbactam is efficiently cleared in CVVH mode.

Ex vivo Ceftolozane/Tazobactam Clearance during Continuous Renal Replacement Therapy

BACKGROUND/AIMS

To determine ceftolozane/tazobactam transmembrane clearances (CLTM) in continuous hemofiltration (CHF) and continuous hemodialysis (CHD) and to determine optimal ceftolozane/tazobactam dosing regimens for patients receiving continuous renal replacement therapy (CRRT).

METHOD

Validated, ex vivo CHF and CHD bovine blood models using polysulfone (HF1400) and AN69 (Multiflow 150-M) hemofilters were used to evaluate adsorption and CLTM at different effluent flow rates. Monte Carlo simulations (MCS) using pharmacokinetic parameters from published studies and CLTM from this study were used to generate ceftolozane/tazobactam dosing for patients receiving CRRT.

RESULTS

CHF and CHD CLTM did not differ at equivalent effluent rates. CLTM approximated effluent flow rates. No adsorption of ceftolozane/tazobactam occurred for either hemofilter. Effluent flow was the most important determinant of MCS-derived doses.

CONCLUSION

CRRT clearances of ceftolozane/tazobactam depended on effluent flow rates but not hemofilter types. MCS-derived ceftolozane/tazobactam doses of 750 (500/250)-1,500 (1,000/500) mg every 8 h met pharmacodynamic targets for virtual patients receiving CRRT at contemporary effluent rates.

Can we use an ex vivo continuous hemofiltration model to describe the adsorption and elimination of meropenem and piperacillin?

OBJECTIVES

To determine the adsorption and elimination characteristics of meropenem and piperacillin during simulated continuous renal replacement therapy (CRRT), and to compare the observed data from this ex vivo study with previous data from clinical studies.

METHOD

This was an experimental study utilizing a modified CRRT circuit and polysulfone membrane (1.2 m2), circulated with a blood-crystalloid mixture. Adsorption onto the CRRT circuit was tested over a 4-h period, and clearance was assessed separately using variable continuous hemofiltration settings.

RESULTS

A rapid 9% reduction in circulating meropenem and piperacillin concentrations was observed at approximately 0.5 and 1.0 h for each antibiotic, respectively. The post-dilution setting was associated with a significantly higher sieving coefficient (Sc) and filter clearance (CLfilter) (mean ± SD) (Sc 1.14 ± 0.10 versus 1.06 ± 0.04; CLfilter 19.05 ± 1.63 versus 17.59 ± 0.62 ml/min, P values < 0.05) for meropenem. No significant differences were observed for piperacillin pharmacokinetics. Clinically comparable Sc data were observed between data obtained from the ex vivo study and data from previous clinical studies, for both antibiotics.

CONCLUSIONS

Meropenem and piperacillin appear to be rapidly adsorbed into the CRRT circuit, and the delivery site of fluid replacement significantly influences meropenem pharmacokinetics. However, these findings are likely to be clinically insignificant and not affect dosing requirements. This ex vivo method could be a surrogate for future clinical pharmacokinetic studies of CRRT. Further research is required to explore the applicability of the ex vivo method to further characterize antibiotic pharmacokinetics during CRRT.

Trimethoprim and sulfamethoxazole transmembrane clearance during modeled continuous renal replacement therapy

BACKGROUND/AIMS

There is limited data regarding trimethoprim (TMP)/sulfamethoxazole (SMX) continuous renal replacement therapy (CRRT) dosing. We aimed to estimate TMP/SMX transmembrane clearance (CLtm) during continuous hemofiltration (CH) and continuous hemodialysis (CD) to guide dosing.

METHODS

Using an in vitro model, TMP/SMX sieving coefficients (SC) and saturation coefficients (SA) were determined with high-flux polyarylethersulfone and polyacrylonitrile-sodium methallyl sulfonate copolymer hemodiafilters at ultrafiltration/dialysate rates of 1, 2, 3, and 6 l/h. TMP/SMX CLtm was calculated using measured SC and SA. TMP/SMX CRRT doses were modeled using CLtm and published TMP/SMX pharmacokinetic parameters.

RESULTS

TMP SC/SA during CH/CD were significantly higher than SMX SC/SA. During modeling, TMP 10 mg/kg/day and its corresponding SMX dose, 50 mg/kg/day, resulted in steady state TMP/SMX peak concentrations associated with efficacy against Pneumocystis jirovecii.

CONCLUSIONS

CRRT resulted in greater TMP CLtm than SMX. TMP 10 mg/kg/day divided q12h may be an appropriate initial dose to consider in patients undergoing CRRT.

Treatment with echinocandins during continuous renal replacement therapy

Echinocandins are indicated as first-line treatment for invasive candidiasis in moderate to severe illness. As sepsis is the main cause of acute kidney injury, the combination of echinocandin treatment and continuous renal replacement therapy (CRRT) is common. Optimizing antibiotic dosage in critically ill patients receiving CRRT is challenging. The pharmacokinetics of echinocandins have been studied under various clinical conditions; however, data for CRRT patients are scarce. Classically, drugs like echinocandins with high protein binding and predominantly non-renal elimination are not removed by CRRT, indicating that no dosage adjustment is required. However, recent studies report different proportions of echinocandins lost by filter adsorption. Nevertheless, the clinical significance of these findings remains unclear.

Longitudinal hemodiafilter performance in modeled continuous renal replacement therapy

BACKGROUND/AIMS

With advanced anticoagulation, many institutions operate continuous renal replacement therapy (CRRT) circuits longer than manufacturers' recommendations. This extended use may change hemodiafilter performance and clearance properties. However, hemodiafilter performance over time has not been assessed. We investigated solute clearance over time in modeled CRRT.

METHODS

In vitro continuous hemofiltration (CH) and continuous hemodialysis (CD) were operated for 48 h using AN69 polyacrylonitrile, cellulose triacetate, F70 polysulfone, and Optiflux F160NR polysulfone hemodiafilters with citrated bovine blood. Urea, creatinine, gentamicin, vancomycin, and albumin clearances were assessed in CH (ultrafiltration rates = 1 and 3 l/h). Clearances of urea, creatinine, gentamicin, and albumin, were assessed in CD with dialysate flow rate of 2 l/h.

RESULTS

Solute CH clearances were significantly higher at 3 l/h. Only creatinine and gentamicin clearances were affected by time. Creatinine CD clearance significantly declined at 48 h for all hemodiafilters, especially polysulfone hemodiafilters.

CONCLUSIONS

CRRT duration affects solute transmembrane clearance. Clinicians should consider hemodiafilter age when assessing hemodialysis dose or drug clearance.

Antibiotic dosing in critically ill patients with acute kidney injury

A common cause of acute kidney injury (AKI) is sepsis, which makes appropriate dosing of antibiotics in these patients essential. Drug dosing in critically ill patients with AKI, however, can be complicated. Critical illness and AKI can both substantially alter pharmacokinetic parameters as compared with healthy individuals or patients with end-stage renal disease. Furthermore, drug pharmacokinetic parameters are highly variable within the critically ill population. The volume of distribution of hydrophilic agents can increase as a result of fluid overload and decreased binding of the drug to serum proteins, and antibiotic loading doses must be adjusted upwards to account for these changes. Although renal elimination of drugs is decreased in patients with AKI, residual renal function in conjunction with renal replacement therapies (RRTs) result in enhanced drug clearance, and maintenance doses must reflect this situation. Antibiotic dosing decisions should be individualized to take into account patient-related, RRT-related, and drug-related factors. Efforts must also be made to optimize the attainment of antibiotic pharmacodynamic goals in this population.

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.