Antimicrobial Doses in Continuous Renal Replacement Therapy: A Comparison of Dosing Strategies

Purpose. Drug dose recommendations are not well defined in patients undergoing continuous renal replacement therapy (CRRT) due to limited published data. Several guidelines and pharmacokinetic equations have been proposed as tools for CRRT drug dosing. Dose recommendations derived from these methods have yet to be compared or prospectively evaluated. Methods. A literature search of PubMed, Micromedex, and Embase was conducted for 40 drugs commonly used in the ICU to gather pharmacokinetic data acquired from patients with acute and chronic kidney disease as well as healthy volunteers. These data and that obtained from drug package inserts were gathered for use in three published CRRT drug dosing equations. Doses calculated for a model patient using each method were compared to doses suggested in a commonly used dosing text. Results. Full pharmacokinetic data was available for 18, 31, and 40 agents using acute kidney injury, end stage renal disease, and normal patient data, respectively. On average, calculated doses differed by 30% or more from the doses recommended by the renal dosing text for >50% of the medications. Conclusion. Wide variability in dose recommendations for patients undergoing CRRT exists when these equations are used. Alternate, validated dosing methods need to be developed for this at-risk patient population.

[Drugs dosing in intensive care unit during continuous renal replacement therapy]

Drug dosing in the intensive care unit can be challenging. Acute kidney injury (AKI) is a common complication of sepsis and a part of multiple organ dysfunction syndrome. Continuous renal replacement therapy (CRRT) is increasingly used as dialysis therapy in this critically ill population. Available data demonstrate that sepsis, AKI and different modalities of CRRT can profoundly change drugs pharmacokinetic. The severity of these changes depends on molecules characteristics (volume of distribution, plasma protein binding, molecular weight, plasma half-life, plasma clearance), patient itself (volemia, residual renal function, tissue perfusion, hepatic dysfunction) and modality of CRRT (diffusion, convection, adsorption). There are no available recommendations to adapt drug dosing in a given critically ill patient with a given modality of CRRT. It is necessary to fully understand the different methods of CRRT and drug pharmacokinetic to prescribe the appropriate dose and to avoid under or potentially toxic overdosing. Monitoring the plasma level of drug - when available - can establish a relation between the blood concentration and its effect; thus, facilitating drug dosing.

The hemophagocytic syndrome: titrating continuous hemofiltration to the degree of lactic acidosis

In 3 cases of severe multiple organ failure due to hemophagocytic lymphohistiocytosis (HLH) in children, the authors demonstrate the utility of continuous hemofiltration in attenuating the consequences of excess cytokine activity, with therapy titrated to the degree of lactic acidosis. HLH was diagnosed in 3 encephalopathic children with multiple organ failure, elevated ferritin (49,396-237,582 pmol/L; or 21,983-105,733 ng/mL), elevated serum triglyceride, and depressed cell lines. One had a known malignancy, one had EBV-associated lymphoproliferative disease, and one was previously healthy. Continuous hemofiltration was initiated, with the ultrafiltrate production rate and countercurrent dialysate flow titrated to metabolic acidosis as reflected by the serum lactate (maximum 3.5 mmol/L or 31.6 mg/dL). Hemofiltration was titrated upward until lactic acidosis resolved, through clearance of lactate or interruption of excess cytokine-driven activity; maximum prescription was 2000 mL/h ultrafiltrate production plus 2500 mL/h dialysate flow. Stability was achieved with hemofiltration, then substantial resolution occurred with treatment according to the HLH-94 protocol (dexamethasone, cyclosporin, VP-16, intrathecal methotrexate). One child succumbed to candidiasis. Another made a full recovery. A third succumbed to his primary malignancy. HLH should be suspected in unexplained or unresolving multiple organ failure. Titration of hemofiltration based on measurable parameters of cellular metabolism (e.g., lactate, base deficit) may stabilize the child with metabolic acidosis long enough to allow proper diagnosis and institution of definitive therapy. Hemofiltration is not a panacea but rather a stabilizing mechanism, with poorly understood effects on interstitial water and solute flux, that facilitates recovery over weeks, not days.

Pharmacokinetics of levofloxacin during continuous venovenous hemodiafiltration and continuous venovenous hemofiltration in critically ill patients

STUDY OBJECTIVE

To assess the pharmacokinetics of levofloxacin during continuous venovenous hemodiafiltration (CVVHDF) and continuous venovenous hemofiltration (CVVH).

DESIGN

Nonrandomized pharmacokinetic evaluation.

SETTING

University surgical intensive care unit.

PATIENTS

Six critically ill patients.

INTERVENTION

Five patients received levofloxacin 500 mg/day and one patient received levofloxacin 125 mg/day All patients received continuous renal replacement therapy: CVVHDF on day 1 and CVVH on day 2, using an acrylonitrile hollow-fiber 0.9-m2 filter, constant blood flow rate of 90 ml/minute, substitution flow rate of 1 L/hour predilution, and dialysate flow rate of 1 L/hour (CVVHDF).

MEASUREMENTS AND MAIN RESULTS

Serum, ultrafiltrate, and dialysate concentrations of levofloxacin were determined by high-performance liquid chromatography. Extracorporeal clearance was 26.05 +/- 4.66 ml/hour during CVVHDF and 15.71 +/- 2.73 ml/hour during CVVH (p<0.05). Elimination half-life was 28.08 +/- 4.5 hours and 45.9 +/- 17.7 hours, and distribution volume was 1.51 +/- 0.52 L/kg and 1.42 +/- 0.42 L/kg for CVVHDF and CVVH, respectively. Saturation was 0.76 +/- 0.13 for CVVHDF versus a sieving coefficient of 0.77 +/- 0.16 for CVVH.

CONCLUSION

Marked extracorporeal elimination of levofloxacin occurs, requiring a dosage adjustment that can be calculated from the characteristics of CVVH and CVVHDF.

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.