Drug dosage in patients during continuous renal replacement therapy. Pharmacokinetic and therapeutic considerations

Fluconazole dosing in continuous veno-venous haemofiltration (CVVHF): need for a high daily dose of 800 mg

To cover intermediate sensitive Candida glabrata in ICU patients, fluconazole plasma peak levels at least in the range of 16-32 microg/ml appear necessary for treatment. Previous studies did not reach these fluconazole levels under continuous veno-venous haemofiltration (CVVHF) with dosages of 200-600 mg fluconzole daily. In the present study, nine patients simultaneously requiring CVVHF for treatment of acute oligoanuric renal failure and antimycotic therapy of Candida septicemia received fluconazole 800 mg/day. Fluconazole plasma levels were determined to evaluate whether this dosage is adequate to reach the advised fluconazole levels. Patients were dialysed on two consecutive days with an ultrafiltration rate (UF) of 1000 ml/h or 2000 ml/h, respectively, in a randomized order. The predilution was 800 ml/h and 1800 ml/h, respectively. The treatment was tolerated without adverse effects. All patients reached plasma fluconazole concentrations between 16 and 32 microg/ml, remaining in this range for a minimum of 1 up to 24 h with a mean of 9.6 h and a UF rate of 2000 ml/h, and 15.7 h with a UF rate of 1000 ml/h. So far, there are no in vivo data on the fluconazole plasma concentrations required for effective treatment. However, our data demonstrate, that at least the fluconazole concentrations desirable on the basis of in vitro susceptibility testing can be reached in critically ill patients on CVVHF in an ICU setting. However, in these patients, 800 mg fluconazole/day are necessary to achieve fungicidal drug concentrations.

Pharmacokinetics and pharmacodynamics of imipenem during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of imipenem were studied in adult intensive care unit (ICU) patients during continuous venovenous hemofiltration (CVVH; n=6 patients) or hemodiafiltration (CVVHDF; n=6 patients). Patients (mean+/-standard deviation age, 50.9+/-15.9 years; weight, 98.5+/-15.9 kg) received imipenem at 0.5 g every 8 to 12 h (total daily doses of 1 to 1.5 g/day) by intravenous infusion over 30 min. Pre- and postmembrane blood (plasma) and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, and 8 or 12 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CL(S)) and elimination half-life (t1/2) of imipenem were 145+/-18 ml/min and 2.7+/-1.3 h during CVVH versus 178+/-18 ml/min and 2.6+/-1.6 h during CVVHDF, respectively. Imipenem clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 25% and 32% of CL(S), respectively. The results of this study indicate that CVVH and CVVHDF contribute to imipenem clearance to a greater degree than previously reported. Imipenem doses of 1.0 g/day appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC up to 2 microg/ml) during CVVH or CVVHDF, but doses of 2.0 g/day or more may be required to adequately treat and prevent resistance in pathogens with higher MICs (MIC=4 to 8 microg/ml). Higher doses should only be used after consideration of potential central nervous system toxicities or other risks of therapy in these severely ill patients.

[Antimycotic drugs under continuous renal replacement therapy]

In critically ill patients with acute renal failure and continuous renal replacement therapy (CRRT), the elimination of antimycotic agents is influenced by many factors; these include not only the nature and dose of the renal replacement therapy but also the properties of the medicine. High protein binding, a high molecular weight and little or no renal elimination even in subjects with normal renal function suggest that a substance is not eliminated by CRRT. This is the case with amphotericin B, caspofungin, itraconazole and voriconazole, but not with fluconazole. In the case of fluconazole, an increase in dose than that used in patients with normal renal function may be required according to the nature and dose of CRRT, because the clearance of fluconazole can be substantially higher under CRRT than in subjects with normal renal function. Daily doses of 800 mg or more may be necessary. As a result of the diverse influences on elimination in patients receiving CRRT, the determination of fluconazole through concentrations cannot be dispensed with, in order to avoid underdosing and a failure of the antimycotic therapy.

FHD: an index to evaluate drug elimination by hemodialysis

BACKGROUND

In hemodialyzed patients, physicians have to (1) adjust drug dosage for a creatinine clearance lower than 10-15 ml/min and (2) know whether or not the drug will be removed by the dialysis session to decide whether it may be administered before or after the session on dialysis days. However, of several indices being used to evaluate drug removal by dialysis none is appropriate and we suggest a novel index named F(HD), which reflects the role of hemodialysis clearance of a drug in its overall clearance during the session.

METHODS

Pharmacokinetic simulations were performed to test the influence of dialysis on the pharmacokinetics of some drugs, whether F(HD) was considered or not, to determine when to administer the drug. F(HD) was then calculated for several drugs and its value compared with other indices. Five hemodialysis patients from our department for whom the time of drug administration was determined according to F(HD) were included in a small study and their drugs' trough concentrations were monitored.

RESULTS

F(HD) emphasized that considering hemodialysis clearance alone may lead to false interpretations of the potential dialyzability of some drugs. In our patients, who received their treatment according to the 'F(HD) rule', monitoring of trough levels gave satisfactory results.

CONCLUSION

The use of the 'F(HD) rule' should be tested on a long-term administration basis to confirm our conclusion. F(HD )could be the index of choice to determine when to administer a drug, before or after the session, in hemodialysis patients.

Cardiovascular Drug Therapy in Elderly Patients

An increasing number of elderly patients are exposed to cardiovascular drugs for the treatment of acute and/or chronic conditions. This is a result of the progressive aging of the population, a common feature in most industrialised countries, and an improvement in primary and secondary cardiovascular prevention strategies with increased survival rates. Traditionally, most elderly patients receiving cardiovascular drugs had advanced cardiac, liver and kidney disease that significantly influenced drug pharmacokinetic and pharmacodynamic parameters. Currently, however, many patients without significant organ impairment receive cardiovascular therapy for primary or early secondary prevention (i.e. increased vascular risk, asymptomatic left ventricular dysfunction, poststroke phase, type 2 diabetes mellitus), highlighting the need for a better understanding of specific age-related pharmacokinetic and pharmacodynamic effects. A systematic review has been conducted on the specific effects of aging, in the absence of major co-morbidities, on the pharmacokinetic and pharmacodynamic properties of traditional and newer cardiovascular drugs. Currently, the evidence available is poor or nonexisting for several drugs and mainly derived from very small and underpowered studies, thus limiting data interpretation. In particular, there is very little information on patients >80 years of age, thus raising important concerns about the correct use of these drugs in this constantly growing population.

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.

Drug dosing during intermittent hemodialysis and continuous renal replacement therapy : special considerations in pediatric patients

Chronic renal failure is, fortunately, an unusual occurrence in children; however, many children with various underlying illnesses develop acute renal failure, and transiently require renal replacement therapy - peritoneal dialysis, intermittent hemodialysis (IHD), or continuous renal replacement therapy (CRRT). As children with acute and chronic renal failure often have multiple comorbid conditions requiring drug therapy, generalists, intensivists, nephrologists, and pharmacists need to be aware of the issues surrounding the management of drug therapy in pediatric patients undergoing renal replacement therapy. This article summarizes the pharmacokinetics and dosing of many drugs commonly prescribed for pediatric patients, and focuses on the management of drug therapy in pediatric patients undergoing IHD and CRRT in the intensive care unit setting. Peritoneal dialysis is not considered in this review. Finally, a summary table with recommended initial dosages for drugs commonly encountered in pediatric patients requiring IHD or CRRT is presented.

A New, Rapid, Fully Automated Method for Determination of Fluconazole in Serum by Column-Switching Liquid Chromatography

A sensitive and rapid HPLC assay for the determination of fluconazole in serum is described. HPLC-integrated sample preparation allows direct injection of serum samples without any pretreatment. The in-line extraction technique is carried out by automatically switching from the extraction column (Lichrospher ADS C8) to the analytic column (Nucleosil C18). After 6 minutes the matrix passes the extraction column, and the retained analyte is quantitatively transferred to the analytic column, where separation by isocratic HPLC is performed. The extraction eluent is sodium dihydrogen phosphate buffer, pH 5.0 (50 mM), and the analytic eluent is acetonitrile/sodium dihydrogen phosphate buffer, pH 5.0 (50 mM) (26.8/73.2, vol/vol). Fluconazole is detected according to its absorption maximum at 210 nm. The lower limit of quantification (LLOQ) is 0.65 microg/mL, the limit of detection (LOD) is 0.2 microg/mL, and the quantification range is 0.65-23.3 microg/mL. The assay was precise with a between-run coefficient of variation of < or = 5.59%. The within-run accuracy was 99.8% and 103.4%, and the between-run accuracy was 99.2% and 99.7%, respectively, for the concentrations 23.3 microg/mL and 1.3 microg/mL. The recovery was 78%. The described procedure allows sample cleanup and determination within 20 minutes, thereby facilitating drug monitoring in clinical routine. The method was applied successfully.

Higher renal replacement therapy dose delivery influences on drug therapy

Higher doses of renal replacement therapy have profound effects on pharmacotherapy, yet little research has been conducted in this area. High-volume renal replacement therapies influence both the pharmacokinetic and the pharmacodynamic profiles of all drugs administered to these critically ill patients. Intermittent high-dose "hybrid" hemodialysis therapies remove drugs to a much different degree than standard thrice-weekly hemodialysis, yet pharmacokinetic studies have not been performed in patients receiving these therapies. High-volume continuous renal replacement therapies offer dosing challenges not seen with standard low-dose therapies. This article describes the pharmacokinetic and pharmacodynamic issues presented by high-volume renal replacement therapies. Given the importance that pharmacotherapy has on optimal patient outcomes, a better understanding of the influence that high-volume renal replacement therapy has on drugs is essential if these high volume therapies are to be used successfully in the intensive care unit.

Linezolid clearance during continuous venovenous hemodiafiltration: a case report

OBJECTIVE

To determine the linezolid clearance and serum concentrations in a critically ill man receiving continuous venovenous hemodiafiltration (CVVHDF).

METHODS

Intravenous linezolid 600 mg every 12 hours was administered to a critically ill, 85-year-old man with anuria who was receiving CVVHDF at a dialysate flow rate of 2000 ml/hour and a mean ultrafiltrate production rate of 775 ml/hour. Samples of blood and spent dialysate and ultrafiltrate were obtained at the time of linezolid peaks and troughs, and linezolid concentrations were determined.

RESULTS

The CVVHDF yielded a mean linezolid clearance of 36.5 ml/minute and an elimination half-life of 7.5 hours. The linezolid saturation coefficient ranged from 0.77-0.81. Administration of intravenous linezolid 600 mg every 12 hours yielded suitable serum trough concentrations.

CONCLUSION

Administration of intravenous linezolid 600 mg every 12 hours maintained therapeutic serum trough concentrations in this critically ill patient receiving CVVHDF.

Renal failure and renal replacement therapy

Continuous renal replacement therapy is an effective means for fluid and solute management in ARF/MOSF. Prospective studies have examined issues of anticoagulation, the impact of replacement/dialysis, the effects of bicarbonate-versus lactate-based solutions, and nutritional and medication clearance. Speculation and bias exists concerning when and for what indications CRRT should be initiated. Many clinicians, supported by data from Ronco and Goldstein, would contest that early institution is better if the risks (eg, access, anticoagulation) are minimal and the possible benefits are maximal. The authors, examining the issues as an intensivist and as a nephrologist, believe that early institution, aggressive replacement/dialysis, and use of citrate-based replacement fluids provide substantive advantages. With the advent of Ronco's recent data on sepsis managed with filtration and plasma absorption, the indication for use of CRRT in MOSF may become more evident regardless of the presence or absence of ARF.

[Use of midazolam in postoperative sedation of patients with multiple organ failure treated with hemodiafiltration. Clinical study and pharmacokinetics]

OBJECTIVES

Evaluate the risk of accumulation of midazolam and conjugated 1-hydroxy-midazolam in high-risk ICU patients treated by continuous veno-venous haemofiltration.

STUDY DESIGN

A prospective pharmocokinetic and clinical evaluation in 11 patients, with hepatic and renal failure.

METHODS

Midazolam and metabolites were dosed in plasma and ultratiltration liquid by chromatography. Sedation was assessed by a simplified Ramsay score (EDS) with 4 levels.

RESULTS

The mean duration of continuous infusion was 11 +/- 6 days. Peak plasma levels were over 150 ng ml-1 during the first 3 days, but normalized after that, only by drug adjustment based on scoring and clinical observation. There was no progressive accumulation of OH-midazolam, in spite of high levels (> 1000 ng ml-1). The Sieving coefficient (S) was 0.11 +/- 0.10 and 0.44 +/- 0.15 for midazolam and conjugated OH-midazolam respectively. A significant clearance (9.6 +/- 1.9 ml min-1) was observed for the conjugated products. T 1/2 beta was 11 h and was correlated with the mean time of recovery. A significant correlation was found between sedation score and both midazolam (r = 0.47) and OH-midazolam (r = 0.32).

CONCLUSION

OH-midazolam risk of accumulation and significant clearance by haemodiafiltration should be taken into account in the drug adjustment in patients treated by continuous veno-venous haemofiltration.

Pharmacokinetics of piperacillin-tazobactam in anuric intensive care patients during continuous venovenous hemodialysis

The pharmacokinetics of piperacillin-tazobactam were investigated in eight anuric intensive care patients treated by continuous venovenous hemodialysis (CVVHD). The elimination half-life of piperacillin was 4.3 +/- 1.2 h, and that of tazobactam was 5.6 +/- 1.3 h. The contribution of CVVHD to the overall elimination was relevant (>25%) for both drugs.

The application of population pharmacokinetic modeling to individualized antibiotic therapy

This paper describes applications of population pharmacokinetic modeling to the optimization of antibiotic dosing. Parametric and nonparametric pharmacokinetic modeling approaches are discussed. Population models can be important extensions of therapeutic drug monitoring (TDM) in infectious disease. The concept of population model-based individualized antimicrobial therapy is described. With the availability of population modeling for obtaining PK parameter estimates, the focus has shifted to quantifying the antimicrobial effect and linking kinetics to drug effects. Examples of integrated pharmacokinetic-pharmacodynamic (PK-PD) models to describe bacterial killing as a function of drug concentration are discussed. Application of PK-PD mathematical models that correlate with microbiological and clinical outcomes will provide us with a better rationale for the proper dose selection of anti-infective therapy in different patient populations.

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 of cefepime during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of cefepime were studied in 12 adult patients in intensive care units during continuous venovenous hemofiltration (CVVH) or continuous venovenous hemodiafiltration (CVVHDF) with a Multiflow60 AN69HF 0.60-m(2) polyacrylonitrile hollow-fiber membrane (Hospal Industrie, Meyzieu, France). Patients (mean age, 52.0 +/- 13.0 years [standard deviation]; mean weight, 96.7 +/- 18.4 kg) received 1 or 2 g of cefepime every 12 or 24 h (total daily doses of 1 to 4 g/day) by intravenous infusion over 15 to 30 min. Pre- and postmembrane blood (serum) samples and corresponding ultrafiltrate or dialysate samples were collected 1, 2, 4, 8, and 12 or 24 h (depending on dosing interval) after completion of the drug infusion. Drug concentrations were measured using validated high-performance liquid chromatography methods. Mean systemic clearance (CL(S)) and elimination half-life (t(1/2)) of cefepime were 35.9 +/- 6.0 ml/min and 12.9 +/- 2.6 h during CVVH versus 46.8 +/- 12.4 ml/min and 8.6 +/- 1.4 h during CVVHDF, respectively. Cefepime clearance was substantially increased during both CVVH and CVVHDF, with membrane clearance representing 40 and 59% of CL(S), respectively. The results of this study confirm that continuous renal replacement therapy contributes substantially to total CL(S) of cefepime and that CVVHDF appears to remove cefepime more efficiently than CVVH. Cefepime doses of 2 g/day (either 2 g once daily or 1 g twice daily) appear to achieve concentrations adequate to treat most common gram-negative pathogens (MIC <or= 8 microg/ml) during CVVH or CVVHDF.

Pharmacokinetics of levofloxacin and ciprofloxacin during continuous renal replacement therapy in critically ill patients

The pharmacokinetics of intravenously administered levofloxacin and ciprofloxacin were studied in intensive care unit patients during continuous venovenous hemofiltration (CVVH; four patients received levofloxacin, and five received ciprofloxacin) or hemodiafiltration (CVVHDF; six patients received levofloxacin, and five received ciprofloxacin). Levofloxacin clearance was substantially increased during both CVVH and CVVHDF, while ciprofloxacin clearance was affected less. The results of this study suggest that doses of levofloxacin of 250 mg/day and ciprofloxacin of 400 mg/day are sufficient to maintain effective drug concentrations in the plasma of patients undergoing CVVH or CVVHDF.

An appraisal of antiretroviral drugs in hemodialysis

BACKGROUND

Acquired immunodeficiency syndrome (AIDS)-related kidney disorders concern 30% of those patients and can lead to end-stage renal disease (ESRD; 6 to 10%). Therefore, the administration of antiretroviral drugs in human immunodeficiency virus (HIV) patients with nephropathy is not uncommon.

METHODS

The influence of ESRD on the different phases of the pharmacokinetic profile of drugs in general is examined in light of bioavailability, distribution, protein binding, metabolism, and elimination. Then, the pharmacokinetics of antiretroviral drugs in hemodialysis are detailed.

RESULTS

From these data, dosing recommendations are given for nucleoside reverse transcriptase inhibitors (NRTIs), non-NRTIs, and protease inhibitors (PIs).

CONCLUSION

Dosage adjustments are often necessary for patients with renal insufficiency. These adaptations have to be carefully performed to optimize drug exposure and reduce the risk of side effects.

Pharmacokinetics and dosing regimen of meropenem in critically ill patients receiving continuous venovenous hemofiltration

OBJECTIVE

To study the pharmacokinetics of meropenem in critically ill patients with acute renal failure receiving continuous venovenous hemofiltration (CWHF).

DESIGN

Prospective, open-labeled study.

SETTING

Medical intensive care unit of the University Medical Center Utrecht.

PATIENTS

Five critically ill patients receiving CWHF for acute renal failure treated with meropenem for documented or suspected bacterial infection.

INTERVENTION

All patients received meropenem (500 mg) administered intravenously every 12 hrs. Plasma samples and ultrafiltrate aliquots were collected during one dosing interval.

MEASUREMENTS AND RESULTS

Mean age and body weight of the patients studied were 46.6 yrs (range, 28-61 yrs) and 85.8 kg (range, 70-100 kg), respectively. The following pharmacokinetic variables for meropenem were obtained: mean peak plasma concentration was 24.5 +/- 7.2 mg/L, mean trough plasma concentration was 3.0 +/- 0.9 mg/L, mean terminal elimination half-life was 6.37 +/- 1.96 hrs, mean total plasma clearance was 4.57 +/- 0.89 L/hr, mean CWHF clearance was 1.03 +/- 0.42 L/hr, mean nonrenal clearance was 3.54 +/- 1.06 L/hr, and mean volume of distribution was 0.37 +/- 0.15 L/kg.

CONCLUSION

In critically ill patients with acute renal failure, nonrenal clearance became the main elimination route. CWHF substantially contributed to the clearance of meropenem (23% of mean total plasma clearance). We recommend meropenem to be dosed at 500 mg intravenously every 12 hrs in patients receiving CWHF, according to our operational characteristics. This dosing regimen resulted in adequate trough plasma levels for susceptible microorganisms.

[Glycopeptides]

OBJECTIVES

To review pharmacology, pharmacokinetic and therapeutic use of glycopeptides in intensive care units.

DATA SOURCES

Extraction from Medline database of French and English articles on glycopeptides and search along with major review articles.

DATA SELECTION

The collected articles were reviewed and selected according to their quality and originality. The more recent data were selected.

DATA SYNTHESIS

Glycopeptides are bactericidal antibiotics which are only active against Gram positive species acting by inhibiting peptidoglycan synthesis. They had been in clinical use for almost 30 years without high-level resistance underlining. For ten years, there have been disturbing reports of first, resistance to vancomycin in enterococcal species and more recently in strains of Staphylococcus aureus by complex and large mechanisms of action. This new resistances may lead to a therapeutic impasse and a fatal issue for infected patients. The only response to this situation is the respect of prescription rules and the careful use of antibiotics.

CONCLUSION

Considering their spectrum, glycopeptides are an antibiotic family which importance is fundamental to treat infected patients of intensive care units. Staff members of intensive care units are responsible for their good use.

Renal replacement therapies

Slow continuous renal replacement therapy is more hemodynamically stabilizing and is replacing conventional hemodialysis as the therapy of choice for acute renal failure in the intensive care unit. This article presents practical information, including basic terminology, basic physiology, technical aspects, and indications for and application of this technique.

Pharmacokinetics of isepamicin during continuous venovenous hemodiafiltration

The objective of this study was to analyze the pharmacokinetics of isepamicin during continuous venovenous hemodiafiltration. Six patients received 15 mg of isepamicin per kg of body weight. The mean isepamicin concentration peak in serum was 62.88 +/- 18.20 mg/liter 0.5 h after the infusion. The elimination half-life was 7. 91 +/- 0.83 h. The mean total body clearance was 1.75 +/- 0.28 liters/h, and dialysate outlet (DO) clearance was 2.76 +/- 0.59 liters/h. The mean volume of distribution was 19.83 +/- 2.95 liters. The elimination half-life, DO clearance, and volume of distribution were almost constant. In this group of patients, the initial dosage of 15 mg/kg appeared to be adequate, but the dosage interval should be determined by monitoring residual isepamicin concentrations in plasma.

Polymyxin B sulfate and colistin: old antibiotics for emerging multiresistant gram-negative bacteria

BACKGROUND

Polymyxin B sulfate and colistin, also known as colistimethate, have not been used for many years because less toxic antimicrobials are available. Gram-negative bacteria that are resistant to the aminoglycosides, beta-lactams, and fluoroquinolones are becoming more common. These bacteria are often susceptible to the polymyxins.

OBJECTIVE

To present a review of the chemistry, antibacterial spectrum, dosing, pharmacokinetics, toxicity, and indications for polymyxin B sulfate and colistin.

DATA SOURCE

A MEDLINE search (1966-1998) of the English-language literature was performed to identify primary literature on the polymyxins. Older citations ( 1949-1965) were identified through the bibliographies of these articles.

STUDY SELECTION

All available reports of in vitro antibacterial activity, animal and clinical trials, and case reports were reviewed.

DATA SYNTHESIS

The polymyxins are amphipathic molecules that interact with lipopolysaccharide in the bacterial outer membrane. They have potent antiendotoxic properties and antibacterial activity against Pseudomonas aeruginosa and many of the Enterobacteriaceae. Polymyxin B and colistin are usually given at a dose of 1.5-2.5 and 5 mg/kg/d, respectively, in two divided doses. Dosing must be altered in renal failure since the kidney is the primary route of elimination. Distribution into pleural fluid, joints, and cerebrospinal fluid is poor. Toxic effects involve the kidney and central nervous system. The polymyxins are recommended for serious systemic infections caused by gram-negative bacteria that are resistant to other agents.

CONCLUSIONS

Polymyxin B sulfate and colistin have a role in the therapy of multidrug-resistant gram-negative bacterial infections.

Dosage adjustment of fluconazole during continuous renal replacement therapy (CAVH, CVVH, CAVHD, CVVHD)

Continuous arterio-venous haemofiltration (CAVH), continuous veno-venous haemofiltration (CVVH), continuous arterio-venous haemodialysis (CAVHD) and continuous veno-venous haemodialysis (CVVHD) are increasingly used in patients with acute renal failure (ARF). The elimination rate of fluconazole varies considerably depending on the procedure used. (In Germany, fluconazole is approved for the treatment of life-threatening fungal infections caused by Candida spp. and Cryptococcus neoformans at a dosage of up to 800 mg day-1.) The elimination rate of fluconazole by CVVHD depends on the combined dialysate/ultrafiltrate flow rate, but is much higher than achieved with CVVH and intermittent dialysis, with a fluconazole clearance in patients with CVVHD 2 l h-1 exceeding the values of healthy persons. To achieve therapeutic plasma levels during continuous renal replacement therapy, the same loading dose as in patients without renal failure should be administered, followed by a maintenance dose that is adjusted for anuric patients by multiplying by a factor that takes into account the extracorporeal elimination of the absorbed dose (CAVH, CVVH x 2.2, ultrafiltrate flow 0.5 l h-1; CAVHD, CVVHD x 3.8, combined dialysate/ultrafiltrate flow 1.5 l h-1). Despite the broad therapeutic margin of fluconazole, drug monitoring is recommended to achieve therapeutic drug levels in life-threatening indications because there have been only a few investigations of this, all involving relatively low dosages (up to 200 mg day-1).

[Pharmacokinetics and dosage of fluconazole in continuous hemofiltration (CAVH, CVVH) and hemodialysis (CAVHD, CVVHD)]

Continuous haemofiltration (CAVH, CVVH) and haemodialysis (CAVHD, CVVHD) are increasingly used in patients with acute renal failure (ARF). The elimination rates of fluconazole vary considerably among the different procedures. In CVVHD, the elimination rate is, depending on the combined dialysate/ultrafiltrate flow rate, the most marked compared to CVVH and intermittent dialysis with a fluconazole clearance exceeding the values of healthy persons in CVVHD 2 L/h. To achieve therapeutic plasma levels during continuous renal replacement therapy, the same loading dose as in patients without renal failure should be applied, followed by the adjusted maintenance dose for anuric patients multiplied by a factor taking the extracorporeal elimination of the absorbed dose into account (CAVH, CVVH: x 2.2, ultrafiltrate flow 0.5 L/h; CAVHD, CVVHD: x 3.8, combined dialysate/ultrafiltrate flow 1.5 L/h). Despite the broad therapeutic margin of fluconazole, drug monitoring is recommended with respect to the very limited number of investigations with relatively low dosages up to 200 mg/day and--which is of paramount importance--to achieve therapeutic drug levels in vital indications.

Use of in vitro models of haemofiltration and haemodiafiltration to estimate dosage regimens for critically ill patients prescribed cefpirome

BACKGROUND

The physico-chemical properties of cefpirome (low protein binding, high water solubility and low molecular weight) suggest that it may be lost readily from the extracorporeal circulation of intensive care unit patients during continuous renal replacement therapy.

METHOD

In order to make informed dosage recommendations for patients receiving artificial renal support, cefpirome loss from human blood has been quantified using in vitro models of continuous haemofiltration and haemodiafiltration. Cefpirome clearance was measured using three membrane types at varying ultrafiltrate (UFR) and dialysis flow rates (Qd).

RESULTS

During haemofiltration cefpirome was found to cross hollow fibre polyamide (PA) and polyacrylonitrile (PAN) membranes with equal efficiency. The mean sieving coefficients (S) of both PA and PAN membranes were consistently high (> 0.7) when two different ultrafiltration rates were used. Changing the ultrafiltration rate or membrane type had no significant effect on the sieving coefficient of cefpirome but did result in an increase in cefpirome filter clearance (Fcl). Using the haemodiafiltration model, cefpirome penetrated PAN membranes (flat plate AN69S) more efficiently than hollow fibre PA membranes (FH66D). In each case, increasing the dialysis flow rate reduced the S-value. However, although increasing Qd was associated with a greater Fcl of cefpirome when PAN membranes were employed, no such relationship was found for the PA hollow fibre membrane.

CONCLUSION

The information generated can be used to estimate a dosing regimen for intensive care patients prescribed cefpirome and receiving continuous renal replacement therapy.

Pharmacokinetics of meropenem in critically ill patients with acute renal failure treated by continuous hemodiafiltration

The pharmacokinetics of meropenem were studied in nine anuric critically ill patients treated by continuous venovenous hemodiafiltration. Peak levels after infusion of 1,000 mg over 30 min amounted to 103.2 +/- 45.9 microgram/ml, and trough levels at 12 h were 9.6 +/- 3.8 microgram/ml. A dosage of 1,000 mg of meropenem twice a day provides plasma drug levels covering intermediately susceptible microorganisms. Further reductions of the dosage might be appropriate for highly susceptible bacteria or when renal replacement therapies with lower clearances are applied.

Single dose pharmacokinetics of lamivudine in subjects with impaired renal function and the effect of haemodialysis

AIMS

The purpose of this study was to investigate the pharmacokinetics of a single oral dose of lamivudine administered to subjects with renal impairment and to determine whether lamivudine was dialysable in subjects with severe renal impairment undergoing haemodialysis.

METHODS

Twenty-nine subjects were enrolled, nine with normal renal function (creatinine clearance (CL(CR)) 82-117 ml min(-1)), eight with moderately impaired renal function (CL(CR) 25-49 ml min(-1)), six with severe impairment (CL(CR) 13-19 ml min(-1)) and six with severe impairment who were also receiving haemodialysis. After an overnight fast, nondialysis subjects received a single oral dose of lamivudine. Subjects on haemodialysis were given two doses on separate occasions (intra and interdialysis). Blood was obtained before lamivudine administration and at regular intervals to 48 h post dose. Timed urine collections were performed for subjects able to produce urine. Pharmacokinetic parameters were calculated by using standard non compartmental techniques.

RESULTS

Decreasing renal function was associated with reduced lamivudine clearance in a proportional and apparently linear relationship. Lamivudine was well dialysed with an extraction ratio in the order of 50%. However, because lamivudine has a large volume of distribution (approximately 100 1), a haemodialysis session of 4 h did not affect overall exposure to a clinically significant degree in most subjects.

CONCLUSIONS

Impaired renal function does require lamivudine dose modification according to the degree of impairment, but no further modification of dose is required for subjects undergoing regular haemodialysis.

Removal of piperacillin in critically ill patients undergoing continuous venovenous hemofiltration

OBJECTIVE

Continuous hemofiltration is now widely used in the intensive care unit. Our study aimed to assess the removal of piperacillin under continuous hemofiltration and to define a suitable dosage regimen of administration.

DESIGN

Prospective study of blood and ultrafiltrate concentrations of piperacillin to assess the pharmacokinetics of the antibiotic.

SETTING

The medical intensive care unit of a teaching hospital.

PATIENTS

Ten patients were included in the study. Six patients were receiving their first dose of piperacillin (group 1) and four had already been treated for 2 to 6 days (group 2). The mean Simplified Acute Physiology II score was 74 +/- 6 (SEM), and the number of organ failures was 3.6 +/- 0.3 (range 3 to 5). Renal failure was related to septic shock in seven patients and to cardiogenic shock in three patients. Seven patients were anuric. Hepatic dysfunction was present in four of the ten patients.

INTERVENTIONS

Patients were treated with continuous venovenous hemofiltration using a hollow polysulfone capillary fiber. Piperacillin (4 g) was injected intravenously over 20 mins. Arterial blood and ultrafiltrate were sampled immediately before the injection and then every hour until 8 hrs after injection time. Piperacillin concentrations were assayed using high performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

In group 1, the mean serum peak concentration of piperacillin was in the normal range (125 +/- 21 mg/L), but trough values were higher (48 +/- 8 mg/L) than in normal subjects. In group 2, trough values before the injection were increased in all patients (188 +/- 71 mg/L). At T1, blood peak concentration reached 470 +/- 127 mg/L. A small amount of piperacillin was retrieved from the ultrafiltrate. The elimination half-life was 5.1 +/- 1.4 and 4.8 +/- 1.4 hrs in groups 1 and 2, respectively.

CONCLUSIONS

Piperacillin was not removed to a significant extent during continuous hemofiltration. Further, in the intensive care unit, patients in shock with multiple organ failure such as liver failure might behave differently from patients with stable end-stage renal disease. A 4-g dose of piperacillin twice a day is recommended in such patients.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

Pharmacokinetics of imipenem-cilastatin in critically ill patients undergoing continuous venovenous hemofiltration

The pharmacokinetics of imipenem-cilastatin were investigated in 12 critically ill patients with acute renal failure (ARF) managed by continuous veno-venous hemofiltration (CVVH) while receiving a fixed combination of 500 mg of imipenem-cilastatin intravenously three or four times daily. No adverse drug reactions were observed. Plasma and hemofiltrate samples were taken at specified times during one dosing interval, and the concentrations of imipenem and cilastatin were determined by high-performance liquid chromatography. Pharmacokinetic variables were calculated by a first-order, two-compartment pharmacokinetic model for both substances. Total clearances of imipenem and cilastatin (mean +/- standard deviations) were 122.2 +/- 28.6 and 29.2 +/- 13.7 ml/min, respectively, with hemofiltration clearances of 22.9 +/- 2.5 and 16.1 +/- 3.1 ml/min, respectively, and nonrenal, nonhemofiltration clearances of 90.8 +/- 26.3 and 13.2 +/- 13.9 ml/min, respectively. Mean imipenem dosage requirements were approximately 2,000 mg/24 h (2,111.8 +/- 493.4 mg/24 h). They were calculated in order to achieve an average steady-state concentration of 12 mg/liter to ensure that concentrations in plasma exceeded the MICs at which 90% of intermediately resistent bacteria are inhibited (8 mg/liter) during the majority of the dosing interval. By contrast, the recommended dosage for patients with end-stage renal failure (ESRF) and infections caused by intermediately resistant bacteria is 1,000 mg/24 h. This remarkable difference may be due (i) to differences in the nonrenal clearance of imipenem between patients with ARF and ESRF and (ii) to the additional clearance by the hemofilter. Since the total clearance of cilastatin was low, marked accumulation occurred, and this was particularly pronounced in patients with additional liver dysfunction. Thus, in patients with ARF managed by CVVH, rather high imipenem doses are required, and these inevitably result in a marked accumulation of cilastatin. The doses of imipenem recommended for patients with ESRF, however, will lead to underdosing and inadequate antibiotic therapy.

Pharmacokinetics of cefepime during continuous venovenous hemodiafiltration

The objective of this study was to analyze the pharmacokinetics of cefepime, in six patients with acute renal failure related to septic shock, during continuous venovenous hemodiafiltration (CVVHD) (Hemospal AN 69S hemofilter; Hospal, Lyon, France). Six patients, mean age 65 +/- 4 years (range, 61 to 69), were included and each received 2 g of cefepime by intravenous infusion over a 30-min period every 12 h. Prefilter serum, dialysate outlet (DO), and ultrafiltrate samples were collected 0.47, 0.50, 0.57, 1, 3, 5, 7, and 12 h after the beginning of infusion. The time design of samples was optimized in accordance with the theory of D optimality. The cefepime concentrations were measured by high-performance liquid chromatography. The pharmacokinetics computation was carried out using P-PHARM software. Mean serum concentration peaks were 53 +/- 21.9 mg/liter (range, 13.0 to 68.9) one-half hour after the infusion. The mean elimination half-life was 8.11 +/- 2.22 h (range, 4.76 to 10.84). DO clearance was 66.57 +/- 30.14 ml/min (range, 38.66 to 119.87). The mean volume of distribution was 0.71 +/- 0.37 liters/kg of body weight. CVVHD was effective for cefepime elimination. In these subjects, the elimination half-life and DO clearance were almost constant. The results of this study suggested that a 2-g twice-daily infusion (usual dosage) was required for an effective concentration in this group of patients.

Antibiotic dosing in renal failure

The Dosing in Renopathy by Easy-To-Use Multipliers (DREM) System is a simple method for dose adjustments of anti-infectives in renal insufficiency. The simple 2-step method involves: (1) estimating creatinine clearance (CLcr) from age, sex, and serum creatinine, and (2) calculating the adjusted dose or dosing interval with the use of multipliers. By multiplying the normal dose or dosing interval with the dose (CLcr/100) or interval (100'CLcr) multiplier, the adjusted dose or dosing interval is obtained, respectively. Dose estimates with this method are reasonably accurate and compare favorably with previously published methods of correction.

Combined acute respiratory and renal failure: management by continuous hemodiafiltration

OBJECTIVES

To study the impact of continuous hemodiafiltration (CHD) on the morbidity and mortality of acute combined respiratory and renal failure in critically ill patients.

DESIGN

Prospective clinical study.

SETTING

Intensive Care Unit of a tertiary institution.

PATIENTS

One-hundred fifteen critically ill patients with combined acute respiratory and renal failure.

INTERVENTIONS

Treatment of all patients with either continuous arteriovenous hemodiafiltration (CAVHD) or continuous venovenous hemodiafiltration (CVVHD).

MEASUREMENTS

Assessment of illness severity, measurement of plasma urea, serum creatinine, electrolytes and arterial blood gases prior to and during treatment. Duration of oliguria, ICU stay, hospital stay, and final outcome.

RESULTS

One hundred fifteen critically ill patients with combined respiratory and renal failure (mean APACHE II score, 28.1; mean number of failing organs, 4.1) were studied. Thirty-five were treated with CAVHD and 80 with CVVHD for a mean treatment duration of 13.1 days per patient (range 2-47). Blood urea concentration fell from a mean of 29.4 mmol/l to a mean of 19.1 mmol/l (P < 0.001) and the serum creatinine concentration fell from a mean of 520 mumol/l to a mean of 374 mumol/l after 24 h of therapy (P < 0.001). The A-a gradient fell from a mean of 301 mmHg to a mean of 242 mmHg (P < 0.05). Despite the high degree of illness severity and the need for vasoactive drug infusion in 105 patients (91.3%), survival to hospital discharge was achieved in 33 patients (28.7%). For patients who required > 72 h of combined mechanical ventilation, survival was 22% (22 of 100 patients). Complications of continuous hemodiafiltration were few and all related to arterial vascular access.

CONCLUSIONS

In critically ill patients with combined acute respiratory and renal failure, continuous hemodiafiltration controlled azotemia without hypotension and with early improvement in gas exchange. PATIENTS treated with this approach achieved promising survival rates. Our findings support the view that CHD is safe and effective and that it offers important advantages over intermittent hemodialysis. It may be the dialytic therapy of choice in critically ill patients with combined acute respiratory and renal failure.