Antibiotic Dosing in Critically Ill Adult Patients Receiving Continuous Renal Replacement Therapy

β-lactam antibiotic concentrations during continuous renal replacement therapy

Introduction

The use of standard doses of β-lactam antibiotics during continuous renal replacement therapy (CRRT) may result in inadequate serum concentrations. The aim of this study was to evaluate the adequacy of unadjusted drug regimens (i.e., similar to those used in patients with normal renal function) in patients treated with CRRT and the influence of CRRT intensity on drug clearance.

Methods

We reviewed data from 50 consecutive adult patients admitted to our Department of Intensive Care in whom routine therapeutic drug monitoring (TDM) of broad-spectrum β-lactam antibiotics (ceftazidime or cefepime, CEF; piperacillin/tazobactam; TZP; meropenem, MEM) was performed using unadjusted β-lactam antibiotics regimens (CEF = 2 g q8h; TZP = 4 g q6h; MEM = 1 g q8h). Serum drug concentrations were measured twice during the elimination phase by high-performance liquid chromatography (HPLC-UV). We considered therapy was adequate when serum drug concentrations were between 4 and 8 times the minimal inhibitory concentration (MIC) of Pseudomonas aeruginosa during optimal periods of time for each drug (≥70% for CEF; ≥ 50% for TZP; ≥ 40% for MEM). Therapy was considered as early (ET) or late (LT) phase if TDM was performed within 48 hours of antibiotic initiation or later on, respectively.

Results

We collected 73 serum samples from 50 patients (age 58 ± 13 years; Acute Physiology and Chronic Health Evaluation II (APACHE II) score on admission 21 (17–25)), 35 during ET and 38 during LT. Drug concentrations were above 4 times the MIC in 63 (90%), but above 8 times the MIC in 39 (53%) samples. The proportions of patients with adequate drug concentrations during ET and LT were quite similar. We found a weak but significant correlation between β-lactam antibiotics clearance and CRRT intensity.

Conclusions

In septic patients undergoing CRRT, doses of β-lactam antibiotics similar to those given to patients with normal renal function achieved drug levels above the target threshold in 90% of samples. Nevertheless, 53% of samples were associated with very high drug levels and daily drug regimens may need to be adapted accordingly.

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.

Impact of renal function on the pharmacokinetics and safety of ceftolozane-tazobactam

Ceftolozane-tazobactam is a novel antipseudomonal cephalosporin with a β-lactamase inhibitor. We investigated the pharmacokinetics (PK) and safety of ceftolozane-tazobactam in subjects with various degrees of renal function. In two phase I, open-label studies, a single dose of ceftolozane-tazobactam was administered as a 1-h intravenous infusion to 24 subjects with normal, mild, or moderate renal impairment (1,000/500 mg) and six subjects with severe renal impairment (500/250 mg). Six subjects with end-stage renal disease (ESRD) received two doses of ceftolozane-tazobactam (500/250 mg each), pre- and posthemodialysis (post-HD). PK parameters were determined by noncompartmental methods. Plasma exposure to ceftolozane-tazobactam increased as renal function declined with only slightly increased exposures in subjects with mild renal impairment; the median area under the concentration-time curve from time zero to infinity (AUC0-∞) for ceftolozane and tazobactam increased 1.4- and 1.2-fold, respectively. In subjects with moderate renal impairment, the AUC0-∞ increased 2.5- and 2.2-fold for ceftolozane and tazobactam, respectively. In subjects with severe renal impairment, the dose-normalized median AUC0-∞ for ceftolozane and tazobactam increased 4.4- and 3.8-fold, respectively. In ESRD subjects, ceftolozane and tazobactam concentrations declined rapidly following the start of HD, with approximately 66 and 56% reductions in overall exposure based on the AUC0-∞ before and after dialysis. Slight increases in exposure with mild renal impairment do not warrant a dose adjustment; however, subjects with moderate or severe renal impairment and those on HD require a decrease in the dose, a change in the frequency of administration, or both to achieve exposures within the established safety and efficacy margins of ceftolozane-tazobactam. Ceftolozane-tazobactam was well tolerated by all renal impairment groups.

Role of linezolid in the treatment of complicated skin and soft tissue infections

Staphylococcus aureus is the most common cause of complicated skin and soft tissue infections (cSSTIs). Antibiotic choices for these infections continue to evolve. History has seen penicillin progress to antistaphylococcal penicillins and cephalosporins, but these drugs are now giving way to drugs that are effective against methicillin-resistant S. aureus (MRSA). While vancomycin has been the gold standard to treat MRSA infections, newer therapeutic options have been developed over the last 5 years. These include quinupristin-dalfopristin, daptomycin, tigecycline and linezolid, which is the focus for this review. Linezolid is efficacious in the treatment of cSSTIs (including diabetic foot infections) caused by Gram-positive organisms (including MRSA), with a well-defined safety profile and straightforward dosing. It is also approved for nosocomial pneumonia, community-acquired pneumonia and uncomplicated skin and skin structure infections. Linezolid has an oral and parenteral formulation, which are equivalent. The oral formulation has the potential to offer economic benefits as compared with other therapies. Currently, there are only a few new antibiotics in development with MRSA activity. The proper use of all antibiotics, including these newer agents, is increasingly important if we are to slow the evolution of microbial resistance.

Impact of pharmacist antimicrobial dosing adjustments in septic patients on continuous renal replacement therapy in an intensive care unit

BACKGROUND

Correct dosing of antimicrobial drugs in septic patients receiving continuous renal replacement therapy (CRRT) is complex. This study aimed to evaluate the effects of dosing adjustments performed by pharmacists on the length of intensive care unit (ICU) stay, ICU cost, and antimicrobial adverse drug events (ADEs).

METHODS

A single-center, 2-phase (pre-/post-intervention) study was performed in an ICU of a university-affiliated hospital. Septic patients receiving CRRT in the post-intervention phase received a specialized antimicrobial dosing service from critical care pharmacists, whereas patients in the pre-intervention phase received routine medical care without involving pharmacists. The 2 phases were compared to evaluate the outcomes of pharmacist interventions.

RESULTS

Pharmacists made 183 antimicrobial dosing adjustment recommendations for septic patients receiving CRRT. Changes in CRRT-related variables (116, 63.4%) were the most common risk factors for dosing errors, and β-lactams (101, 55.2%) were the antimicrobials most commonly associated with dosing errors. Dosing adjustments were related to a reduced length of ICU stay from 10.7 ± 11.1 days to 7.7 ± 8.3 days (p = 0.037) in the intervention group, and to cost savings of $3525 (13,463 ± 12,045 vs. 9938 ± 8811, p = 0.038) per septic patient receiving CRRT in the ICU. Suspected antimicrobial adverse drug events in the intervention group were significantly fewer than in the pre-intervention group (19 events vs. 8 events, p = 0.048).

CONCLUSIONS

The involvement of pharmacists in antimicrobial dosing adjustments in septic patients receiving CRRT is associated with a reduced length of ICU stay, lower ICU costs, and fewer ADEs. Hospitals may consider employing clinical pharmacists in ICUs.

Ampicillin/sulbactam: its potential use in treating infections in critically ill patients

The purpose of this paper was to review the potential utility of ampicillin/sulbactam (SAM) as a therapy for serious infections in critically ill patients. Data for this review were identified by searches of PubMed and of the reference lists of the included articles. We found that SAM appears to have a number of characteristics that support its use in the treatment of serious infections in critically ill patients. SAM demonstrates extensive penetration into many infection sites, supporting its use in a wide range of infection types. Microbiologically, sulbactam has strong intrinsic antibiotic activity against multidrug-resistant (MDR) bacteria, including Acinetobacter baumannii, which supports its use for the treatment of infections mediated by this pathogen. Of some concern, there have been reports showing a decline in susceptibility of some bacteria to SAM. As such, use of lower doses (4/2g/day), particularly for MDR A. baumannii, has been linked with a 30% reduced success rate in critically ill patients. The therapeutic challenges for ensuring achievement of optimal dosing of SAM result partly from bacterial susceptibility but also from the pharmacokinetic (PK) alterations common to β-lactam agents in critical illness. These PK changes are likely to reduce the ability of standard dosing to achieve the concentrations observed in non-critically ill patients. Optimisation of therapy may be more likely with the use of higher doses, administration by 4h infusion or by combination therapy, particularly for the treatment of infections caused by MDR pathogens.

Population pharmacokinetics of piperacillin and tazobactam in critically ill patients undergoing continuous renal replacement therapy: application to pharmacokinetic/pharmacodynamic analysis

OBJECTIVES

To evaluate the pharmacokinetics of piperacillin/tazobactam in critically ill patients undergoing continuous renal replacement therapy (CRRT) and to assess the success of the therapy against susceptible bacteria.

PATIENTS AND METHODS

Sixteen patients undergoing CRRT with different degrees of renal function were included in the study. Blood and ultrafiltrate samples were drawn after administration of piperacillin/tazobactam (4/0.5 g) every 4, 6 or 8 h. The data were analysed by a population approach using NONMEM 7.2. The probability of target attainment (PTA) of maintaining free piperacillin levels above the MIC during the entire dosing interval was estimated by simulation of intermittent and continuous infusions.

RESULTS

The pharmacokinetics of piperacillin and tazobactam were best described by two-compartment models where the elimination of both drugs was conditioned by renal [dependent on creatinine clearance (CLCR)], non-renal and extracorporeal clearances. A 20 min infusion of piperacillin/tazobactam administered every 6 h provided high PTAs against MICs ≤ 32 mg/L in patients with severe renal failure. In patients with normal or moderate renal function PTAs ≥ 90% were only obtained up to MICs ≤ 8 mg/L with short infusions. However, simulating continuous infusion, higher probabilities of success were obtained against MICs of 32 and 16 mg/L when CLCR was 50 and 100 mL/min, respectively.

CONCLUSIONS

Population pharmacokinetic models have been developed and validated for piperacillin and tazobactam. Based on the pharmacokinetic/pharmacodynamic analysis, dosing recommendations are given considering the residual renal function of the patient and the MIC for the isolated bacteria.

Ceftriaxone pharmacokinetic properties during continuous veno-veno haemofiltration using an in vitro adult, paediatric and neonatal model

During continuous venoveno haemofiltration (CVVH), extracorporeal drug clearance is dependant on blood flow, ultrafiltration rate, albumin binding, and the drug’s molecular weight and volume of distribution. Drug doses are adjusted assuming reduced drug clearance by the renal system and CVVH. High volume haemofiltration, pre-dilution and different filter membranes can greatly alter drug clearance. Consequently, assessing the adequacy of cephalosporin dosing during CVVH is complex; under- or overdosing may occur. We studied the pharmacokinetic properties of ceftriaxone during CVVH in vitro. Renaflow filters were used to model 6, 20 and 50 kg patients. Each circuit and reservoir was prepared with a known volume of Hartmann’s solution, human albumin solution 4.5% or blood. Pump speed and exchange rate were standardised for weight. Haemosol BO was used as the replacement fluid with 70% pre-dilution. Following paired sampling from the circuit and ultrafiltrate fluid, ceftriaxone was injected into the circuit. Paired samples were taken up to 720 minutes. Ceftraxione concentrations were determined using high performance liquid chromatography (HPLC). Maximum circuit concentrations (Cmax) at 2 minutes for albumin were 3.5, 2.65 and 4.85 mg/l, for blood were 4.5, 6.5 and 5.55 mg/l and for Hartmann’s were 1.65, 2.95 and 3.65 mg/l for 6kg, 20kg and 50kg models. The sieving coefficients (Sc) from blood (ratio of mean concentrations in the ultrafiltrate/circuits samples) were 0.31 and 0.51 with T1/2 (the half life) 62 and 20 minutes in the 6kg and the 20kg circuits, respectively. The data suggest in an in vitro model of ceftriaxone is rapidly cleared during CVVH. Albumin circuits had the lowest Sc and longest terminal T1/2, reflecting protein binding of the drug and suggest ceftriaxone clearance may be more rapid in hypoalbuminaemic patients. The Cmax was lower in the Hartmann circuits, possibly reflecting precipitation of the drug with calcium in this solution.

Compliance with Antibiotic Dosing Guidelines in Critically Ill Patients Receiving Renal Replacement Therapy

Background:

Compliance with antibiotic dosing guidelines and achievement of target serum concentrations in patients with infection who are on renal replacement therapy (RRT) is complex, essential for supportive care, and not well studied.

Objective:

To determine adherence rates to antibiotic dosing guidelines in the setting of RRT in the intensive care unit (ICU).

Methods:

We conducted a retrospective, single-center, cohort study evaluating antibiotic dosing in all patients in the ICU receiving RRT between July 2007 and June 2009. Appropriate dosing was determined by comparing dose administered with established guidelines. Dosing was denoted as accurate if adjustment occurred prior to the third administered dose or, if appropriate dosing is every 12 hours or more, within 24 hours. We compared rates according to modality of RRT (intermittent hemodialysis [IHD] vs continuous veno-venous hemodialysis [CVVHD]), indication for RRT (acute kidney injury [AKI] vs end-stage renal disease [ESRD]), and presence of a clinical pharmacist on rounds.

Results:

Adherence rates of 546 patients receiving RRT, with 1761 individual antibiotic prescriptions, were analyzed. Dosing errors were more common in the group receiving CVVHD than in the IHD group (58.1% vs 49.5%; p < 0.001). Frequency of dosing errors did not differ significantly between patients receiving RRT for AKI versus those with ESRD (55.4% vs 51.3%; p = 0.24) or in ICUs with or without a pharmacist on rounds (53.0% vs 54.6%; p = 0.67). Underdosing occurred less frequently with a clinical pharmacist on rounds (18.7% vs 31.3%; p < 0.001). However, in-hospital mortality was not significantly different in underdosed individuals compared with the rest of the cohort (52.3% vs 51.6%; p = 0.92).

Conclusions:

Antibiotic underdosing is common. Increased awareness of dose adjustment guidelines for CVVHD and having a clinical pharmacist on rounds may improve rates of underdosing.

Drug absorption, distribution, metabolism and excretion considerations in critically ill adults

INTRODUCTION

All critically ill patients require medication to treat organ dysfunction. However, the pharmacokinetics of drugs used to treat these patients is complex due to frequent alterations in drug absorption, distribution, metabolism, and excretion (ADME).

AREAS COVERED

This review examines pharmacokinetic aspects of drug administration for adult intensive care unit (ICU) patients. Specifically, the authors examine the ADME changes that occur and which should be considered by clinicians when delivering drug therapy to critically ill patients.

EXPERT OPINION

Dosage pharmacokinetics determined from single-dose or limited-duration administration studies in healthy volunteers may not apply to critically ill patients. Organ dysfunction among these patients may be due to pre-existing disease or the effects of a systemic or locoregional inflammatory response precipitated by their illness. Alterations in pharmacokinetics observed among the critically ill include altered bioavailability after enteral administration, increased volume of distribution and blood-brain barrier permeability and changes in P-glycoprotein and cytochrome P450 enzyme function. However, the effect of these changes on clinically important outcomes remains uncertain and poorly studied. Future investigations should examine not only pharmacokinetic changes among the critically ill, but also whether recognition of these changes and alterations in drug therapy directed as a consequence of their observation alters patient outcomes.

Vancomycin clearance in high-volume venovenous hemofiltration

OBJECTIVE

To report the pharmacokinetic and pharmacodynamic properties of vancomycin in 4 patients undergoing high-volume continuous venovenous hemofiltration (CVVH).

CASE SUMMARY

Data from 4 patients prescribed high-volume CVVH for acute renal failure treated with vancomycin were analyzed. Vancomycin plasma concentrations were measured 4 and 24 hours after the end of a 1-hour vancomycin infusion. The mean therapy fluid rate on initiation of vancomycin was 56.2 mL/kg/h (range 48.0-65.5). The mean loading dose of vancomycin was 18.3 mg/kg (range 14.7-19.7). Median vancomycin concentration 4 hours after the dose was 18.1 mg/L (range 13.1-30.0). At 24 hours after the dose, only 1 patient had a detectable vancomycin concentration (5.2 mg/L).

DISCUSSION

There was a large variability in the clearance of vancomycin in this patient population. Current strategies for dosing vancomycin may lead to subtherapeutic trough concentrations. Vancomycin dosing in this patient population should be based on a detailed assessment of the CVVH prescription, vancomycin concentrations, and clinical needs and response.

CONCLUSIONS

An initial vancomycin dose of 20-25 mg/kg with frequent monitoring and adjustment is recommended for patients receiving high-volume CVVH.

Antimicrobial dosing in acute renal replacement

Acute kidney injury (AKI) is a common problem in hospitalized patients and is associated with significant morbidity and mortality. Two large trials showed no benefit from increased doses of renal replacement therapy (RRT) despite previous clinical data suggesting that increased clearance from RRT has beneficial effects. Since infection is the leading cause of death in AKI, my group and others hypothesized that increased RRT antibiotic clearance might create a competing morbidity. The data from my group, as well as those of other groups, show that many patients are underdosed when routine "1 size fits all" antibiotic dosing is used in patients with AKI receiving continuous RRT (CRRT). Here, concepts of drug distribution and clearance in AKI are briefly discussed and then 1 antibiotic (piperacillin) is discussed in depth to illustrate the challenges in applying the medical literature to clinical practice. The fact that published data on drug dosing in AKI and dialysis reflect the evolution of practice patterns and often do not apply to present prescribing habits is also discussed. A more general approach to drug dosing facilitates situation-specific prescribing by the nephrologist and critical care specialist.

Effect of continuous venovenous hemofiltration dose on achievement of adequate vancomycin trough concentrations

The vancomycin dose necessary for the achievement of target serum trough concentrations during continuous venovenous hemofiltration (CVVH) remains to be elucidated. This was a retrospective cohort study of critically ill adults at a tertiary medical center on concurrent CVVH and vancomycin between 2006 and 2010 with a steady-state vancomycin trough concentration. The 87 included patients were grouped according to low (≤30 ml/kg/h; n = 10) or high (>30 ml/kg/h; n = 77) CVVH hemofiltration rate (HFR) for analysis. Vancomycin goal trough achievement occurred in only 32 (37%) patients. The primary endpoint of trough attainment significantly differed between HFR subgroups: 90% versus 30% in low- and high-HFR individuals, respectively (P < 0.001). Patients with subtherapeutic trough concentrations had a median (interquartile range) HFR of 40 ml/kg/h (range, 37 to 47 ml/kg/h) compared to 36 ml/kg/h (range, 30 to 39 ml/kg/h) in those who achieved the trough goal. Irrespective of goal trough, an inverse correlation existed between HFR and serum vancomycin concentration (r = -0.423; P < 0.001). In the subgroup of 14 methicillin-resistant Staphylococcus aureus (MRSA) patients, trough achievement was similar to the aggregate cohort (36%). Mortality at 28 days was unrelated to trough achievement in both the overall sample (P = 0.516) and in culture-positive MRSA patients (P = 0.396). Critically ill patients undergoing CVVH therapy may experience clinically significant reductions in goal vancomycin troughs. The results of the present study justify prospective evaluations in this population to determine the optimal vancomycin dosing strategy for attainment of goal trough concentrations.

Evaluation of antibiotic prescribing patterns in patients receiving sustained low-efficiency dialysis: opportunities for pharmacists

OBJECTIVES

Sustained low-efficiency dialysis (SLED) is a 'hybrid' form of continuous renal replacement therapy; however, there is very limited information on drug disposition during this procedure. Individuals requiring SLED are often critically ill and require antibiotics. The study aim was to evaluate antibiotic orders for patients requiring SLED compared to literature-based recommendations. We also evaluated whether doses were administered as prescribed and assessed clinical and microbiologic cure.

METHODS

A retrospective review was performed over a 2-year period for patients who received concurrent SLED and antibiotic therapy. Demographic data, prescribed antibiotic dosing regimens and doses delivered as prescribed were determined for 10 antibiotics: cefepime (C), daptomycin (Da), doripenem (D), gentamicin (G), imipenem-cilastatin (I), linezolid (L), meropenem (M), piperacillin-tazobactam (P), tobramycin (T) and vancomycin (V). Dosing regimens were compared to recommendations from the literature where available. The incidence of clinical and microbiologic cure was also evaluated.

RESULTS

A total of 87 patients met inclusion criteria: mean age 54 ± 14 years, 60% male, 58% white. Prescribed doses were evidence-based for 37% of Da, 97% of L, 15% of M and 7% of V orders. The majority of discrepancies were due to under-dosing. There were 129 (11%) antibiotic doses missed. Of the 13 patients who met criteria for assessment of clinical and microbiologic cure, 10 achieved a microbiologic cure and none reached clinical cure.

CONCLUSIONS

Prescribed antibiotic dosing regimens varied substantially and under-dosing was common. There is a need to further define appropriate dosing regimens for antibiotics administered during SLED and determine how pharmacists may help to ensure appropriate therapy.

Clinical update on linezolid in the treatment of Gram-positive bacterial infections

Gram-positive pathogens are a significant cause of morbidity and mortality in both community and health care settings. Glycopeptides have traditionally been the antibiotics of choice for multiresistant Gram-positive pathogens but there are problems with their use, including the emergence of glycopeptide-resistant strains, tissue penetration, and achieving and monitoring adequate serum levels. Newer antibiotics such as linezolid, a synthetic oxazolidinone, are available for the treatment of resistant Gram-positive bacteria. Linezolid is active against a wide range of Gram-positive bacteria and has been generally available for the treatment of Gram-positive infections since 2000. There are potential problems with linezolid use, including its bacteriostatic action and the relatively high incidence of reported adverse effects, particularly with long-term use. Long-term use may also be complicated by the development of resistance. However, linezolid has been shown to be clinically useful in the treatment of several serious infections where traditionally bacteriocidal agents have been required and many of its adverse effects are reversible on cessation. It has also been shown to be a cost-effective treatment option in several studies, with its high oral bioavailability allowing an early change from intravenous to oral formulations with consequent earlier patient discharge and lower inpatient costs.

Introduction to drug pharmacokinetics in the critically ill patient

Despite regular use of drugs for critically ill patients, overall data are limited regarding the impact of critical illness on pharmacokinetics (PK). Designing safe and effective drug regimens for patients with critical illness requires an understanding of PK. This article reviews general principles of PK, including absorption, distribution, metabolism, and elimination, and how critical illness can influence these parameters. In the area of drug absorption, we discuss the impact of vasopressor use, delayed gastric emptying and feeding tubes, and nutrient interactions. On the topic of drug distribution, we review fluid resuscitation, alterations in plasma protein binding, and tissue perfusion. With drug metabolism, we discuss hepatic enzyme activity, protein binding, and hepatic blood flow. Finally, we review drug elimination in the critically ill patient and discuss the impact of augmented renal clearance and acute kidney injury on drug therapies. In each section, we highlight select literature reviewing the PK impact of these conditions on a drug PK profile and, where appropriate, provide general suggestions for clinicians on how to modify drug regimens to manage PK challenges.

Presence and accuracy of drug dosage recommendations for continuous renal replacement therapy in tertiary drug information references

BACKGROUND

Clinicians commonly rely on tertiary drug information references to guide drug dosages for patients who are receiving continuous renal replacement therapy (CRRT). It is unknown whether the dosage recommendations in these frequently used references reflect the most current evidence.

OBJECTIVE

To determine the presence and accuracy of drug dosage recommendations for patients undergoing CRRT in 4 drug information references.

METHODS

Medications commonly prescribed during CRRT were identified from an institutional medication inventory database, and evidence-based dosage recommendations for this setting were developed from the primary and secondary literature. The American Hospital Formulary System-Drug Information (AHFS-DI), Micromedex 2.0 (specifically the DRUGDEX and Martindale databases), and the 5th edition of Drug Prescribing in Renal Failure (DPRF5) were assessed for the presence of drug dosage recommendations in the CRRT setting. The dosage recommendations in these tertiary references were compared with the recommendations derived from the primary and secondary literature to determine concordance.

RESULTS

Evidence-based drug dosage recommendations were developed for 33 medications administered in patients undergoing CRRT. The AHFS-DI provided no dosage recommendations specific to CRRT, whereas the DPRF5 provided recommendations for 27 (82%) of the medications and the Micromedex 2.0 application for 20 (61%) (13 [39%] in the DRUGDEX database and 16 [48%] in the Martindale database, with 9 medications covered by both). The dosage recommendations were in concordance with evidence-based recommendations for 12 (92%) of the 13 medications in the DRUGDEX database, 26 (96%) of the 27 in the DPRF5, and all 16 (100%) of those in the Martindale database.

CONCLUSIONS

One prominent tertiary drug information resource provided no drug dosage recommendations for patients undergoing CRRT. However, 2 of the databases in an Internet-based medical information application and the latest edition of a renal specialty drug information resource provided recommendations for a majority of the medications investigated. Most dosage recommendations were similar to those derived from the primary and secondary literature. The most recent edition of the DPRF is the preferred source of information when prescribing dosage regimens for patients receiving CRRT.

Low cefepime concentrations during high blood and dialysate flow continuous venovenous hemodialysis

Dosing of cefepime during high blood flow (Qb; 300 ml/min), high dialysate flow (Qd; 3 liter/h) continuous venovenous hemodialysis (CVVHD) is undefined. Six patients on CVVHD had serum and effluent cefepime concentrations measured at 0.5, 1, 2, 6, and 12 h after dosing. Three patients had cefepime concentrations less than the MIC for Pseudomonas aeruginosa. A dose of 2,000 mg every 12 h or 1,000 mg every 8 h may increase time at a therapeutic concentration.

Pharmacokinetics and pharmacodynamics of piperacillin-tazobactam in 42 patients treated with concomitant CRRT

BACKGROUND AND OBJECTIVES

Current recommendations for piperacillin-tazobactam dosing in patients receiving continuous renal replacement therapy originate from studies with relatively few patients and lower continuous renal replacement therapy doses than commonly used today. This study measured the pharmacokinetic and pharmacodynamic characteristics of piperacillin-tazobactam in patients treated with continuous renal replacement therapy using contemporary equipment and prescriptions.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A multicenter prospective observational study in the intensive care units of two academic medical centers was performed, enrolling patients with AKI or ESRD receiving piperacillin-tazobactam while being treated with continuous renal replacement therapy. Pregnant women, children, and patients with end stage liver disease were excluded from enrollment. Plasma and continuous renal replacement therapy effluent samples were analyzed for piperacillin and tazobactam levels using HPLC. Pharmacokinetic and pharmacodynamic parameters were calculated using standard equations. Multivariate analyses were used to examine the association of patient and continuous renal replacement therapy characteristics with piperacillin pharmacokinetic parameters.

RESULTS

Forty-two of fifty-five subjects enrolled had complete sampling. Volume of distribution (median=0.38 L/kg, intraquartile range=0.20 L/kg) and elimination rate constants (median=0.104 h(-1), intraquartile range=0.052 h(-1)) were highly variable, and clinical parameters could explain only a small fraction of the large variability in pharmacokinetic parameters. Probability of target attainment for piperacillin was 83% for total drug but only 77% when the unbound fraction was considered.

CONCLUSIONS

There is significant patient to patient variability in pharmacokinetic/pharmacodynamic parameters in patients receiving continuous renal replacement therapy. Many patients did not achieve pharmacodynamic targets, suggesting that therapeutic drug monitoring might optimize therapy.

[Antibiotic dose adjustment in the treatment of MRSA infections in patients with acute renal failure undergoing continuous renal replacement therapies]

Acute renal failure is frequent in critically ill patients. In those patients who need renal replacement therapy, continuous techniques are an alternative to intermittent haemodialysis. Critically ill patients often have an infection, which can lead to sepsis and renal failure. An early and adequate antibiotic treatment at correct dosage is extremely important. Methicillin resistant Staphylococcus aureus (MRSA) is a frequent nosocomial pathogen that causes a high rate of morbidity and mortality in critically ill patients. Many antibiotics are easily removed by continuous renal replacement therapies (CRRT) leading to a high risk of under dosing and therapeutic failure or resistance breakthrough. The objective of this review is to assess the clinical evidence on the pharmacokinetics and dosage recommendations of the main antibiotic groups used in MRSA treatment in patients treated with CRRT.

Appropriate antibiotic dosage levels in the treatment of severe sepsis and septic shock

Antibiotic treatment of critically ill patients remains a significant challenge. Optimal antibacterial strategy should achieve therapeutic drug concentration in the blood as well as the infected site. Achieving therapeutic drug concentrations is particularly difficult when infections are caused by some pathogens, such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) and Gram-negative rods, because of their low susceptibility to antimicrobials. In sepsis, pharmacokinetics (PKs) of antibiotics are profoundly altered and may result in inadequate drug concentrations, even when recommended regimens are used, which potentially contribute to increased mortality and spread of resistance. The wide inter-individual PK variability observed in septic patients strongly limits the a priori prediction of the optimal dose that should be administered. Higher than standard dosages are necessary for the drugs, such as β-lactams, aminoglycosides, and glycopeptides, that are commonly used as first-line therapy in these patients to maximize their antibacterial activity. However, the benefit of reaching adequate drug concentrations on clinical outcome needs to be further determined.

Population pharmacokinetics of fluconazole in critically ill patients receiving continuous venovenous hemodiafiltration: using Monte Carlo simulations to predict doses for specified pharmacodynamic targets

Fluconazole is a widely used antifungal agent that is extensively reabsorbed in patients with normal renal function. However, its reabsorption can be compromised in patients with acute kidney injury, thereby leading to altered fluconazole clearance and total systemic exposure. Here, we explore the pharmacokinetics of fluconazole in 10 critically ill anuric patients receiving continuous venovenous hemodiafiltration (CVVHDF). We performed Monte Carlo simulations to optimize dosing to appropriate pharmacodynamic endpoints for this population. Pharmacokinetic profiles of initial and steady-state doses of 200 mg intravenous fluconazole twice daily were obtained from plasma and CVVHDF effluent. Nonlinear mixed-effects modeling (NONMEM) was used for data analysis and to perform Monte Carlo simulations. For each dosing regimen, the free drug area under the concentration-time curve (fAUC)/MIC ratio was calculated. The percentage of patients achieving an AUC/MIC ratio greater than 25 was then compared for a range of MIC values. A two-compartment model adequately described the disposition of fluconazole in plasma. The estimate for total fluconazole clearance was 2.67 liters/h and was notably 2.3 times faster than previously reported in healthy volunteers. Of this, fluconazole clearance by the CVVHDF route (CL(CVVHDF)) represented 62% of its total systemic clearance. Furthermore, the predicted efficiency of CL(CVVHDF) decreased to 36.8% when filters were in use >48 h. Monte Carlo simulations demonstrated that a dose of 400 mg twice daily maximizes empirical treatment against fungal organisms with MIC up to 16 mg/liter. This is the first study we are aware of that uses Monte Carlo simulations to inform dosing requirements in patients where tubular reabsorption of fluconazole is probably nonexistent.

Proposal of a pharmacokinetically optimized dosage regimen of antibiotics in patients receiving continuous hemodiafiltration

The aim of the study was to quantitatively predict the clearance of three antibiotics, amikacin, vancomycin, and teicoplanin, during continuous hemodiafiltration (CHDF) and to propose their optimal dosage in patients receiving CHDF. For this goal, in vitro CHDF experiments with a polyacrylonitrile (PAN) membrane were first performed using these antibiotics, and then the clearances were compared with in vivo CHDF situations determined in 16 critically ill patients. The in vitro CHDF clearances were described as the product of the outflow rate of a drain (Q(outflow)) and the drug unbound fraction in artificial plasma, indicating that drug adsorption to the PAN membrane has minor effect on drug clearance in our settings. The observed in vivo clearances also agreed very well with the predicted values, with a product of Q(outflow) and plasma unbound fraction, when residual creatinine clearance (CL(CR)) was taken into account (within a range of 0.67- to 1.5-fold for 15 of 16 patients). Based on these results, a nomogram of the optimized dosages of amikacin, vancomycin, and teicoplanin was proposed, and it was evident that Q(outflow) and residual CL(CR) are major determinants of the dosage and dosing interval for these antibiotics. Although the applicability needs to be confirmed with another type of membrane or higher Q(outflow), our nomogram can help determine the dosage setting in critically ill patients receiving CHDF.

Pharmacokinetics of sulfobutylether-β-cyclodextrin (SBECD) in subjects on hemodialysis

BACKGROUND

The disposition of sulfobutylether-β-cyclodextrin (SBECD), the solubilizing excipient in intravenous (i.v.) voriconazole, was assessed in seven male subjects with end-stage renal disease on hemodialysis and six subjects with normal renal function.

METHODS

All subjects received twice-daily i.v. voriconazole at the standard voriconazole dose [6 mg/kg (96 mg/kg SBECD) every 12 h (Q12h) on Day 1 followed by 3 mg/kg (48 mg/kg SBECD) Q12h on Days 2-4, with a single i.v. dose on the morning of Day 5]. Subjects were sampled at selected pre-dose trough times, at selected times after infusions and intensively on Day 3 (non-dialysis) and Day 4 (dialysis with high-flux membranes). Compartmental analyses were performed by NONMEM.

RESULTS

SBECD disposition was characterized by a two-compartment model. In renal failure, mean central (V(1)) and peripheral compartment volumes (V(2)) were 9.9 and 6.5 L, respectively. In normal subjects, V(1) and V(2) were 9.6 and 5.2 L, respectively; SBECD clearance (CL) was 130 mL/min. CL in renal failure off-dialysis was 2.6 and 48 mL/min during dialysis; mean half-life decreased from 79 to 5 h during dialysis (normal subjects: 2.1 h).

CONCLUSION

Hemodialysis can significantly reduce levels of SBECD in subjects with end-stage renal disease.

Once-daily amikacin dosing in burn patients treated with continuous venovenous hemofiltration

Amikacin clearance can be increased in burn injury, which is often complicated by renal insufficiency. Little is known about the impact of renal replacement therapies, such as continuous venovenous hemofiltration (CVVH), on amikacin pharmacokinetics. We retrospectively examined the clinical pharmacokinetics, bacteriology, and clinical outcomes of 60 burn patients given 15 mg/kg of body weight of amikacin in single daily doses. Twelve were treated with concurrent CVVH therapy, and 48 were not. The pharmacodynamic target of ≥10 for the maximum concentration of drug in serum divided by the MIC (C(max)/MIC) was achieved in only 8.5% of patients, with a small reduction of C(max) in patients receiving CVVH and no difference in amikacin clearance. Mortality and burn size were greater in patients who received CVVH. Overall, 172 Gram-negative isolates were recovered from the blood cultures of 39 patients, with amikacin MIC data available for 82 isolates from 24 patients. A 10,000-patient Monte Carlo simulation was conducted incorporating pharmacokinetic and MIC data from these patients. The cumulative fraction of response (CFR) was similar in CVVH and non-CVVH patients. The CFR rates were not significantly improved by a theoretical 20 mg/kg amikacin dose. Overall, CVVH did not appear to have a major impact on amikacin serum concentrations. The low pharmacodynamic target attainment appears to be primarily due to higher amikacin MICs rather than more rapid clearance of amikacin related to CVVH therapy.

Appropriate antibiotic dosing in severe sepsis and acute renal failure: factors to consider

Severe sepsis and septic shock cause considerable morbidity and mortality. Early appropriate empiric broad-spectrum antibiotics and advanced resuscitation therapy are the cornerstones of treatment for these conditions. In prescribing an antibiotic regimen in septic patients with acute renal failure treated with continuous renal replacement therapy, several factors should be considered: pharmacokinetics, weight, residual renal function, hepatic function, mode of renal replacement therapy (membrane and surface area, sieving coefficient, effluent and dialysate rate, and blood flow rate), severity of illness, microorganism, minimum inhibitory concentration, and others. Studies that determine the serum antibiotic concentrations are very useful in establishing the correct dosage in critical patients.

A review of daptomycin for injection (Cubicin) in the treatment of complicated skin and skin structure infections

Daptomycin is a novel bactericidal antibiotic with excellent activity against gram-positive organisms. It is a large cyclic lipopeptide with a unique mechanism of action. Daptomycin is given once a day and is renally cleared, requiring dose adjustment in patients with impaired renal function. Unfortunately, there have been case reports of resistant gram-positive organisms. Daptomycin is generally well tolerated, though myopathy has been reported. 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors should be stopped in patients on daptomycin. Daptomycin shows promise in experimental models of endocarditis, meningitis, ventriculitis, and peritonitis, and is currently approved for use in skin and soft-tissue infections. Daptomycin is a welcome newcomer to the gram-positive antimicrobial arsenal.

Recommended β-lactam regimens are inadequate in septic patients treated with continuous renal replacement therapy

Introduction

Sepsis is responsible for important alterations in the pharmacokinetics of antibiotics. Continuous renal replacement therapy (CRRT), which is commonly used in septic patients, may further contribute to pharmacokinetic changes. Current recommendations for antibiotic doses during CRRT combine data obtained from heterogeneous patient populations in which different CRRT devices and techniques have been used. We studied whether these recommendations met optimal pharmacokinetic criteria for broad-spectrum antibiotic levels in septic shock patients undergoing CRRT.

Methods

This open, prospective study enrolled consecutive patients treated with CRRT and receiving either meropenem (MEM), piperacillin-tazobactam (TZP), cefepime (FEP) or ceftazidime (CAZ). Serum concentrations of these antibiotics were determined by high-performance liquid chromatography from samples taken before (t = 0) and 1, 2, 5, and 6 or 12 hours (depending on the β-lactam regimen) after the administration of each antibiotic. Series of measurements were separated into those taken during the early phase (< 48 hours from the first dose) of therapy and those taken later (> 48 hours).

Results

A total of 69 series of serum samples were obtained in 53 patients (MEM, n = 17; TZP, n = 16; FEP, n = 8; CAZ, n = 12). Serum concentrations remained above four times the minimal inhibitory concentration for Pseudomonas spp. for the recommended time in 81% of patients treated with MEM, in 71% with TZP, in 53% with CAZ and in 0% with FEP. Accumulation after 48 hours of treatment was significant only for MEM.

Conclusions

In septic patients receiving CRRT, recommended doses of β-lactams for Pseudomonas aeruginosa are adequate for MEM but not for TZP, FEP and CAZ; for these latter drugs, higher doses and/or extended infusions should be used to optimise serum concentrations.

Resurgence of colistin: a review of resistance, toxicity, pharmacodynamics, and dosing

Colistin is a polymyxin antibiotic that was discovered in the late 1940s for the treatment of gram-negative infections. After several years of clinical use, its popularity diminished because of reports of significant nephrotoxicity and neurotoxicity. Recently, the antibiotic has resurfaced as a last-line treatment option for multidrug-resistant organisms such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. The need for antibiotics with coverage of these gram-negative pathogens is critical because of their high morbidity and mortality, making colistin a very important treatment option. Unfortunately, however, resistance to colistin has been documented among all three of these organisms in case reports. Although the exact mechanism causing colistin resistance has not been defined, it is hypothesized that the PmrA-PmrB and PhoP-PhoQ genetic regulatory systems may play a role. Colistin dosages must be optimized, as colistin is a last-line treatment option; in addition, suboptimal doses have been linked to the development of resistance. The lack of pharmacokinetic and pharmacodynamic studies and no universal harmonization of dose units, however, have made it difficult to derive optimal dosing regimens and specific dosing guidelines for colistin. In critically ill patients who may have multiorgan failure, renal insufficiency may alter colistin pharmacokinetics. Therefore, dosage alterations in this patient population are imperative to achieve maximal efficacy and minimal toxicity. With regard to colistin toxicity, most studies show that nephrotoxicity is reversible and less frequent than once thought, and neurotoxicity is rare. Further research is needed to fully understand the impact that the two regulatory systems have on resistance, as well as the dosages of colistin needed to inhibit and overcome these developing patterns.

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.

Epidemiology and patient outcome after medical emergency team calls triggered by atrial fibrillation

INTRODUCTION

Atrial fibrillation (AF) in hospitalized patients may lead to activation of the medical emergency team (MET). We sought to assess the baseline characteristics and outcomes of the patients presenting AF as a cause of MET call activation.

METHODS

Using a prospectively constructed MET database, we retrospectively reviewed all patients with AF as a trigger for MET activation between August 2005 and April 2010. Demographics, principal diagnostic and outcome of these patients were compared with those of a control group of patients matched for age, sex and ward of origin, randomly selected from the database.

RESULTS

We studied 5431 MET calls of which 557 (10.3%), in 458 patients were triggered by AF. Mean age for AF patients was 74.8 years, 230 (50.2%) were female and 271 (59.1%) were in a surgical ward. 92 (20.1%) AF patients died in hospital compared with 131 (28.6%) in the control group. Among the 336 patients without limitations of medical therapy (LOMT), 46 (13.7%) died in hospital. In total, 46 (13.7%) patients were transferred to a higher level care ward while 290 (86.3%) remained on the ward. Only 2 (4.3%) of these patients died compared with 44 (15.2%) among those who remained in the general ward (p=0.03).

CONCLUSIONS

In our hospital, AF triggers one tenth of MET activations and mortality associated with it is high even when issues of LOMT are excluded. The decreased mortality among patients admitted to a higher level ward suggests that some of these deaths may be avoidable.

Extracorporeal removal of drugs and toxins

Renal replacement therapies (RRT) are increasingly used for the treatment of acute and chronic kidney diseases as well as intoxications and accidental drug overdoses. These therapies offer a mechanism for the removal of toxic substances from the patient's blood and supplement the standard detoxification protocols. If instituted early, RRT can have a significant effect on the course of the toxicity; however, this process is not selective for the removal of only harmful products and can also result in the clearance of medications intended for therapeutic use.