Previous Article | Next Article ![]()
Antimicrobial Agents and Chemotherapy, May 2002, p. 1557-1560, Vol. 46, No. 5
0066-4804/02/$04.00+0 DOI: 10.1128/AAC.46.5.1557-1560.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Department of Clinical Pharmacology, Institute of Experimental and Clinical Pharmacology and Toxicology,1 Clinic for Internal Medicine,2 Clinic for Anesthesiology and Intensive Care Medicine,3 Clinic for Surgery, University of Rostock, D-18057 Rostock, Germany4
Received 16 January 2001/ Returned for modification 15 July 2001/ Accepted 25 January 2002
|
|
|---|
|
|
|---|
Eight critically ill patients were included in the investigation (Table 1). Inclusion criteria were an age of >18 years, acute renal failure treated by CVVHD, anuria (<100 ml of urine/day), and treatment with piperacillin-tazobactam. Patients with severe liver failure or cholestasis were excluded. The protocol of the study was approved by the local ethical committee, and informed consent was obtained from a first-degree relative. CVVHD was performed with an AN69 hollow-fiber dialyzer (Multiflow 60; Hospal, Nuremberg, Germany) under the following conditions: a blood flow rate of 150 ml/min, a dialysate flow rate of 1.5 liters/h, and an ultrafiltrate flow rate of 80 to 200 ml/h. Doses of piperacillin-tazobactam (4.5 g of Tazobac; Wyeth-Lederle) and dosing schedules were chosen empirically by the attending physicians (Table 2). Piperacillin-tazobactam was administered intravenously over 15 min. Corresponding predialyzer blood samples and dialyzer-outlet dialysate samples were taken before drug administration, at 10 and 30 min after infusion, and at 1, 2, 4, 6, 8, 12, 20, 22, and 24 h after infusion. Sampling was performed in the first dosage interval after the dialyzer membrane was changed. Blood samples were centrifuged immediately after they were taken, and plasma and dialysate samples were frozen at -80°C until analysis. The concentrations of piperacillin and tazobactam were determined by reversed-phase high-performance liquid chromatography with UV detection, with modification of the methods reported previously (13, 16). Plasma specimens were deproteinated, and dialysate was used without pretreatment. The presence of piperacillin was determined from the water layer extracted with dichloromethane; tazobactam samples were derivatized with 1,2,3-triazole and injected without extraction. The chromatographic conditions for piperacillin were as follows: a guarded Nucleosil C18 100-5/250 x 4 column, an eluent of methanol-KH2PO4 (1:1, vol/vol; 67 mM; pH 3), ambient temperature, a flow rate of 0.5 ml/min, a
of 214 nm, and a retention time of
20 min. The chromatographic conditions for tazobactam were as follows: a Superspher C18 100-5/250 x 4 column; an eluent of acetonitrile-Na2HPO4 (1:3, vol/vol; 1 mM), NaH2PO4 (1 mM), and tetrabutylammoniumbromide (5 mM) (pH 3); a temperature of 40°C; a flow rate of 0.5 ml/min; a
of 326 nm; and a retention time of
6 min. The assay was calibrated over a linear concentration range of 5 to 100 mg/liter and validated at 5, 10, and 100 mg/liter (19). In each matrix (plasma and dialysate), the limit of quantification for both substances was below 1 mg/liter; the intraday and interday coefficients of variation (n = 5) did not exceed 5 and 9% for piperacillin and 4 and 8% for tazobactam, respectively; accuracies were between 97 and 107%.
|
View this table: [in a new window] |
TABLE 1. Clinical characteristics of patients participating in the study
|
|
View this table: [in a new window] |
TABLE 2. Pharmacokinetic parameters of piperacillin and tazobactama for eight anuric patients treated by CVVHD
|
Pharmacokinetic parameters of piperacillin and tazobactam are presented in Table 2. No drug-related adverse effects were observed. Under the conditions chosen for the performance of CVVHD in this investigation, saturation coefficients of 0.87 ± 0.21 for piperacillin and 0.64 ± 0.19 for tazobactam were determined. Only solutes that are not bound to plasma proteins can cross the dialyzer membrane. Therefore, these results agree with predictions that were based on the plasma protein binding level of 20 to 30% reported to occur in healthy individuals (15). For intensive care patients undergoing continuous arteriovenous hemodialysis (CAVHD), a saturation coefficient of 0.7 ± 0.21 (standard deviation) for piperacillin was determined (7). CLtotal varied among the patients investigated and ranged from 26 to 220 ml/min (median, 47 ml/min) for piperacillin and from 22 to 59 ml/min (median, 29.5 ml/min) for tazobactam. This variability might be due in part to differences in V. The patient with the highest CL of piperacillin (220 ml/min) had very low peak plasma concentrations and therefore the highest V. Since piperacillin is hydrophilic and distributes extracellularly (15), this might be an indication of fluid overload in this patient. The estimated values of CLtotal and the variability determined in this investigation are comparable with values reported for intensive care patients undergoing CAVHD or CVVH (7, 21) and renal-failure patients with creatinine CL values of <20 ml/min/1.73 m2 (4). CL via extracorporeal detoxication systems should be considered relevant for dosing if it exceeds more than 25% of CLtotal (17). In this study, the CLCVVHD of piperacillin was 37% (median, with a range of 13 to 100%) and the CLCVVHD of tazobactam was 38% (median, with a range of 32 to 92%) of CLtotal. Therefore, a relevant contribution of CVVHD to the overall elimination of both drugs has to be taken into account. For drug dosage design, V and t1/2ß in particular have to be considered. V may change during renal insufficiency due to fluid overload, since piperacillin and tazobactam are hydrophilic drugs (10, 15), and it may also vary among the individual patients. As predicted, the estimated V's for the patients investigated are greater than those of healthy subjects (1, 14). The t1/2ßs of both drugs were determined to be fourfold greater than those of healthy subjects (1, 4, 14) and twofold greater than those of subjects with creatinine CL values of <20 ml/min/1.73 m2 (4). On the other hand, the t1/2ßs obtained in this investigation are in accordance with the estimated values for CVVH and CAVHD patients (7, 21). As observed for patients with different degrees of renal impairment (2, 3, 15) and for patients undergoing CVVH (21), the t1/2ß of tazobactam was greater than that of piperacillin, indicating that a relative accumulation of tazobactam may occur. Since in vitro investigations suggest that the antibacterial activity of piperacillin and tazobactam in combination is more dependent on the pharmacokinetics of the inhibitor (tazobactam) and that the antibacterial activity of the combination appeared to be lost when the amount of inhibitor fell below a certain concentration (11), an increase in the elimination of tazobactam over the elimination of piperacillin would require additional doses of tazobactam to the fixed, commercially available combination to retain pharmacodynamic efficacy. With a relative accumulation of tazobactam, as observed in this investigation as well as in cases of renal failure (4, 15), a fixed combination can be used as long as tazobactam does not accumulate to toxic levels. Both piperacillin and tazobactam are considered drugs of low toxicity (18); thus, underestimation of the dosage needs of the critically ill patients is of concern. For each patient, simulations of different dosage regimens (multiple-dose) have been performed by using the individual patient pharmacokinetic data in order to evaluate whether this may help to guide dosage. Simulations of 4,000 mg of piperacillin and 500 mg of tazobactam administered every 12 h and 2,000 mg of piperacillin and 250 mg of tazobactam administered every 8 h resulted in times above MIC of >50% for piperacillin with susceptible (MIC of piperacillin = 16 mg/liter; time above MIC, 48 to 100%) and intermediate susceptible (MIC = 32 mg/liter; time above MIC, 17 to 100%) pathogens in seven of eight patients, while the time above 4 mg/liter for tazobactam was 100% for all patients. The patient with the highest V seemed to fail this dosage regimen and seems to require a higher dosage. Patients with residual renal function and patients that receive continuous renal replacement therapy with higher dialysate flow rates or higher additional hemofiltrate flow rates might have higher (extracorporeal) CL of piperacillin-tazobactam, resulting in higher dosage needs. If available, drug monitoring should be used to individualize treatment with piperacillin-tazobactam for critically ill patients undergoing continuous renal replacement therapy.
We thank K. Kroesche for her skillful technical assistance. Furthermore, we thank the intensive care unit staff for their support.
|
|
|---|
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Copyright © 2009 by the American Society for Microbiology. For an alternate route to Journals.ASM.org, visit: http://intl-journals.asm.org | More Info»