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ICU Nephrology |










* Division of Nephrology, University Hospital Ulm, Ulm,
Division of Nephrology and
Department of Abdominal and Transplant Surgery, Hannover Medical School, Hannover, and
Pharmacy Department, University of Heidelberg, Heidelberg, Germany
Address correspondence to: Dr. Jan T. Kielstein, Department of Nephrology, Medical School Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany. Phone: +49-511-532-6319; Fax: +49-511-532-4005; E-mail: kielstein{at}yahoo.com
| Abstract |
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| Introduction |
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In intensive care unit (ICU) patients who have sepsis and multiple organ failure, extended daily dialysis (EDD) represents an important extracorporeal renal replacement therapy that is increasingly used in ICU throughout Europe, the United States, and Brazil (28). EDD could remove drugs to a much different degree compared with standard intermittent hemodialysis (IHD) three times a week or continuous renal replacement therapy (CRRT) (9). Nevertheless, only scarce data are available on the effect of this highly efficient renal replacement therapy on the elimination of frequently used drugs in critically ill patients with renal failure (1013). The aim of our study was to investigate the pharmacokinetics of moxifloxacin and levofloxacin in anuric critically ill patients who were undergoing EDD. Because there is no reliable standard approach, we applied various methods to estimate extracorporeal drug removal.
| Materials and Methods |
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EDD was performed using the GENIUS batch dialysis system (Fresenius Medical Care, Bad Homburg, Germany) with a polysulfone high-flux dialyzer (F60S, surface area 1.3 m2; Fresenius Medical Care) as described previously (14,15). The technical details of the system are explained elsewhere (16). In brief, sterile bicarbonate dialysate is filled into a 75-L tank and subsequently is circulated in a closed-loop circuit. During dialysis, fresh dialysate is taken from the top of the tank while the spent dialysate flows back to the bottom. Complete collection of spent dialysate in the same tank after the dialysis session permits estimation of the total amount of a substance that is removed, assuming that adsorption of the substance to the dialyzer system is negligible. The average dialysis time during the study was 481 ± 9 min, and mean blood and countercurrent dialysate flow was 161 ± 4 ml/min. Vascular access in all patients was achieved by a double-lumen catheter inserted either into the internal jugular or into the femoral vein.
Blood samples were drawn from the arterial line placed in the radial or femoral artery before as well as 0.5, 1, 2, 4, 6, and 8 h after administration of moxifloxacin or levofloxacin. In the case of levofloxacin, an additional blood sample was obtained 12 h after administration of the drug. Additional blood samples were drawn before and during dialysis at time points 2, 4, and 6 h; at the end of dialysis; and 0.5, 1, 3, and 8 h after the end of the EDD treatment. Extra blood samples were drawn before and after dialyzer (i.e., from the afferent "artery" and efferent "venous" dialyzer blood tubing) to calculate the dialyzer clearance from the pre- and postdialyzer concentration difference and the estimated plasma flow. In addition, total drug removal was estimated by measurement of drug concentration in the spent dialysate, because the GENIUS system permits easy access to the entire used dialysate (16).
Chemical Assays
Moxifloxacin plasma concentrations were determined by HPLC with fluorometric detection similar to a previously described method (17). Shortly, an internal standard was added to 100 µl of plasma or dialysate. After protein precipitation of the sample, liquid chromatography and fluorescence detection were performed using an HP 1090 instrument (Hewlett-Packard, Waldbronn, Germany), equipped with a fluorescence detector (HP 1046 A; excitation at 296 nm and emission at 504 nm for all analyses). The autosampler temperature was kept at 8°C using a Haake D 8 water bath. A Nucleosil 100 C18 (5-µm particle size, 200 x 2.0 mm ID) capillary column preceded by a guard column (20 x 2.0 mm ID) was used for separation. The column oven temperature was set to 50°C. The mobile phase consisted of an aqueous solution of 0.01 mol/L tetrabutyl ammonium sulfate and 0.05 M sodium dihydrogen phosphate. The flow rate was set at 1.1 ml/min for the separation. The limit of quantification was 10 µg/L. Quality control samples that were produced from blank plasma and dialysate that was spiked with known concentrations of the drug (0.03, 0.5, and 4.0 mg/L) were stored and analyzed together with the study samples. The linear working range of the analytical assay was between 0.025 (lower limit of quantification) and 5 mg/L (upper limit of quantification).
Levofloxacin plasma concentrations also were determined by HPLC with fluorometric detection as described previously (18). Briefly, serum samples that were spiked with the internal standard ciprofloxacin (Bayer Pharmaceuticals, Leverkusen, Germany) were prepared by protein precipitation using a precipitation reagent that consisted of water, methanol, perchloric acid 70%, and orthophosphoric acid (500:500:10:1 vol/vol/vol/vol). After centrifugation (7826 x g, 10 min, 10°C) 20 µl of the supernatant was applied to the analytical column (Waters Symmetry column C18 5 µm, 150 x 4.6 mm; Eschborn, Germany). The mobile phase consisted of water, methanol, triethylamine, and orthophosphoric acid (750:250:4:2.5 vol/vol/vol/vol). All analyses were performed at room temperature. The fluorescence detector (Perkin Elmer, Überlingen, Germany) was set at excitation and emission wavelengths of 295 and 490 nm, respectively. At a flow rate of 1.5 ml/min, the retention times of levofloxacin and ciprofloxacin were 4.3 min and 6.0 min, respectively.
The calibration curve was linear over the usable concentration range from 0.1 to 40 mg/L. The intra- and interday coefficients of variation were determined using 1, 4, and 8 mg/L levofloxacin and were <5%. Limit of quantification was determined as 0.01 mg/L, and the limit of detection was 0.001 mg/L.
Pharmacokinetic Calculations
Pharmacokinetic parameters of moxifloxacin and levofloxacin on and off EDD were estimated by noncompartmental methods. The half-life on (T
on) and off (T
off) EDD was estimated from the concentration decline during and after EDD. The drug clearance without EDD was calculated as CLoff = D/AUCoff (dose/area under the curve [AUC]). In the case of a first dose, the AUCoff was extrapolated from the beginning of EDD to infinity using T
off. In the case of steady-state conditions after multiple doses (two patients in the levofloxacin group had received levofloxacin over 9 d before the study), the AUCoff was extrapolated to the end of the individually applied dosage interval disregarding EDD. The apparent volume of distribution was estimated as Vd = CLoff x T
off/ln(2).
Because there is no standard approach, we applied five methods to estimate drug removal by hemodialysis. In method 1, the dialysis clearance was calculated from the area under the curve during EDD (AUCEDD), the drug concentration (Cdial), and amount of dialysate (Vdial) as CLdial = Cdial x Vdial/AUCEDD. In method 2, the dialysis clearance was estimated from concentrations before (Cin) and directly after (Cout) the dialysis membrane as CLdial = (Flin x Cin Flout x Cout)/Cin, where the plasma flow in (Flin) and out (Flout) of the dialyzer was estimated using the blood flow, hematocrit, and ultrafiltration rate. In method 3, the fraction of drug removed by one EDD was calculated as fractD = 1 exp(CLdial x TEDD/Vd), where TEDD is the time on EDD and CLdial as derived by method 1 was applied. In method 4, the removed fraction was derived from the half-life on and off EDD as fractD = (1 exp[ln(2) x TEDD/T
on] x (T
off T
on)/T
off. In method 5, the removed fraction was estimated using the AUC as fractD = (AUCwithoutEDD AUCwithEDD)/AUCwithoutEDD, as described previously (19). It should be noted that the dialysis clearance is an estimate of the extracorporeal clearance by the dialysis system. The total drug clearance during dialysis could be estimated by adding CLoff and CLdial. All pharmacokinetic calculations were performed with the help of the software WinNonlin Professional 4.0.1 (Pharsight Corp., Mountain View, CA) and Excel 2000 (Microsoft Corp., Seattle, WA).
| Results |
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The levofloxacin clearance off dialysis was 3.07 L/h (range 2.96 to 3.17 L/h), resulting in a half-life of 34.5 h (range 21.2 to 47.7 h). Because the dialysis procedure itself added a clearance of 2.93 to 3.12 L/h, the half-life of levofloxacin during dialysis was reduced to 10.3 h (range 10.0 to 10.6 h).
These data are summarized and compared with the results reported for IHD and CRRT in the literature in Tables 3 (moxifloxacin) and 4 (levofloxacin). No adverse effects were attributable to the use of moxifloxacin and levofloxacin in our patients.
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| Discussion |
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Rationale for Using Different Methods to Calculate Dialysis Clearance
We applied several methods to estimate the drug clearance by hemodialysis and the fraction of drug removed by hemodialysis because each method has its limitations. Dialysate-based methods (methods 1 and 3) depend on the stability of the drug in the dialysate and the adsorbence of the drug by the dialysis membrane. Methods that use plasma concentrations before and after the dialysis membrane (method 2) provide information on the drug clearance at a given time, but drug clearance can decrease during hemodialysis. In contrast, methods that use only plasma concentrations from the patient (methods 4 and 5) depend on the terminal half-life of the drug. The estimation of this terminal half-life can be difficult when the drug distribution is not complete before the start of hemodialysis, when there is a concentration rebound after hemodialysis, and when the observation period is limited by the clinical necessity to administer the next dose.
When the various estimates for a drug are consistent with each other, the confidence in the estimate is increased. When there are differences between estimates, more insight into the pharmacokinetics of a drug is gained by explanation of these differences.
Moxifloxacin
Moxifloxacin (molecular weight 437.9 Da) undergoes mainly hepatic metabolism and fecal excretion. Its total clearance is approximately 12 L/h, and its half-life is approximately 12 h in healthy subjects. Only 20% of the drug is excreted unchanged by the kidney (20). Plasma protein binding of moxifloxacin is approximately 54% (21). Renal dysfunction has little effect on the pharmacokinetics of moxifloxacin. In renal failure, the moxifloxacin clearance is reduced by only approximately 20%. Therefore, a dose adjustment is not necessary. However, because moxifloxacin does not only undergo glomerular filtration but also tubular reabsorption, drug clearance by EDD, lacking tubular reabsorption, could be higher compared with normal renal function (22).
In our experiments, one third of moxifloxacin (with regard to the amount of drug present in the body at the beginning of EDD) was removed by one EDD in addition to the nonrenal drug clearance. This is indicated by the difference between the half-lives on and off EDD, the dialysis clearance (method 2), and fraction eliminated by dialysis (methods 4 and 5). In contrast to this finding, only a low amount of moxifloxacin was recovered from the dialysate; consequently, calculations that are based on this amount (methods 1 and 3) lead to low values that underestimate drug removal. Reasons for erroneously low dialysate measurements include adsorption of the drug by the dialyzer membrane and instability of the drug in the dialysate fluid.
Our results suggest that moxifloxacin pharmacokinetics in critically ill patients who have ARF and undergo EDD are similar to those from healthy subjects and patients without renal impairment. These data are in agreement with data that were obtained in critically ill patients who were undergoing continuous venovenous hemodiafiltration, in whom Fuhrmann et al. (23) showed that no dosage adaptation was required. Because moxifloxacin primarily undergoes hepatic metabolism and fecal excretion, severe liver impairment, which was present in six of the 10 patients, could have influenced the pharmacokinetic measurements. Whereas no dosage adjustment is necessary in patients with mild or moderate hepatic impairment, the pharmacokinetics of moxifloxacin in patients with severe hepatic impairment (Child-Pugh class C) has to our knowledge not been studied adequately. On the basis of theoretical reasoning, hepatic impairment should decrease hepatic clearance but also could decrease plasma protein binding of moxifloxacin and thereby increase its dialysance. We did not see, however, a distinct difference in pharmacokinetics between patients with and without severe liver impairment. Hence, in anuric critically ill patients, with and without liver impairment, who are undergoing EDD, we recommend a standard dosage of moxifloxacin (400 mg intravenously) administered once daily after the dialysis.
Levofloxacin
Levofloxacin (molecular weight 370 Da), an enantiomer of ofloxacin, is excreted primarily (80 to 86%) unchanged via the kidneys (24). Plasma protein binding of levofloxacin ranges between 24 and 38% (25). Its clearance is approximately 9 L/h, and its half-life is approximately 7 h in healthy subjects. In renal failure, levofloxacin clearance is reduced by approximately 75%, and the half-life is prolonged to 35 h. Therefore, dose adjustments are required in individuals with impaired renal function. Patients who were treated with EDD had a shorter half-life than those who were treated with IHD (26). The half-life during the treatment was similar to the one shown for patients who were on CRRT (27).
In our study, 20 to 30% of levofloxacin was removed by one EDD. This is in agreement with previous estimates in IHD (26). The fractional elimination by the renal replacement therapy itself is comparable to the data that were obtained in IHD (26) but significantly lower than for patients on CRRT (27). We could detect a median of 91 mg of levofloxacin in the total collected dialysate after an 8-h extended dialysis, which is in agreement with the estimated dialysis clearances. Because levofloxacin primarily is excreted renally, liver impairment, which was present in one patient, is unlikely to have influenced the pharmacokinetic parameters. Although a final recommendation of a dosing regime on the basis of our data cannot be provided, a dose adjustment still has to be used, despite using this highly efficient method of renal replacement therapy. With regard to the dialysis clearance, levofloxacin should be administered after EDD.
| Conclusion |
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| Acknowledgments |
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We thank Dr. U. Thuss (Department of Pharmacokinetics, BAYER AG) for the measurement of moxifloxacin.
| Footnotes |
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D.C. and C.H.-L contributed equally to this work.
Received May 27, 2006. Accepted August 21, 2006.
| References |
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