Pharmacokinetic changes in critical illness

Pharmacokinetic assessment in patients receiving continuous RRT: perspectives from the Kidney Health Initiative

The effect of AKI and modern continuous RRT (CRRT) methods on drug disposition (pharmacokinetics) and response has been poorly studied. Pharmaceutical manufacturers have little incentive to perform pharmacokinetic studies in patients undergoing CRRT because such studies are neither recommended in existing US Food and Drug Administration (FDA) guidance documents nor required for new drug approval. Action is urgently needed to address the knowledge deficit. The Kidney Health Initiative has assembled a work group composed of clinicians and scientists representing academia, the FDA, and the pharmaceutical and dialysis industries with expertise related to pharmacokinetics, AKI, and/or CRRT. The work group critically evaluated key considerations in the assessment of pharmacokinetics and drug dosing in CRRT, practical constraints related to conducting pharmacokinetic studies in critically ill patients, and the generalizability of observations made in the context of specific CRRT prescriptions and specific patient populations in order to identify efficient study designs capable of addressing the knowledge deficit without impeding drug development. Considerations for the standardized assessment of pharmacokinetics and development of corresponding drug dosing recommendations in critically ill patients with AKI receiving CRRT are proposed.

Total Phenytoin concentration is not well correlated with active free drug in critically-ill head trauma patients

Objective:

Phenytoin is an antiepileptic drug used widely for prophylaxis and treatment of seizure after neurotrauma. Phenytoin has a complex pharmacokinetics and monitoring of its serum concentrations is recommended during treatment. Total phenytoin concentration is routinely measured for monitoring of therapy. In this study, we evaluated the correlation between phenytoin total and free concentrations in neurotrauma critically-ill patients to determine whether the phenytoin total concentration is a reliable predictor of free drug, which is responsible for the therapeutic effects.

Methods:

A total of 40 adult head trauma patients evaluated for free (unbound) and total serum phenytoin concentrations. Patients were divided into two groups. Group A consists of 20 unconscious patients with severe head injury under mechanical ventilation and Group B consists of 20 conscious self-ventilated patients. Correlation and agreement between total and free phenytoin plasma concentrations were analyzed.

Findings:

Pearson correlation analysis and Bland-Altman test showed weak to moderate correlation (r = 0.528) and poor agreement between free and total phenytoin concentrations in patients with severe trauma and higher Acute Physiology And Chronic Health Evaluation II (APACHE II) scores (Group A) and good correlation (r = 0.817) and moderate agreement in patients with mild to moderate trauma and lower APACHE II scores (Group B).

Conclusion:

Our results indicated that total phenytoin serum concentration is not a reliable therapeutic goal for drug monitoring in severely-ill head trauma patients even in the absence of hypoalbuminemia, renal and hepatic failure. It seems justifiable to measure free phenytoin concentration in all severely ill neurotrauma patients.

How severe is antibiotic pharmacokinetic variability in critically ill patients and what can be done about it?

The pharmacokinetics (PK) of antimicrobial agents administered to critically ill patients exhibit marked variability. This variability results from pathophysiological changes that occur in critically ill patients. Changes in volume of distribution, clearance, and tissue penetration all affect the drug concentrations at the site of infection. PK-pharmacodynamic indices (fCmax:MIC; AUC0-24:MIC; fT>MIC; fCmin:MIC) for both antimicrobial effect and suppression of emergence of resistance are described for many antimicrobial drugs. Changing the regimen by which antimicrobial drugs are delivered can help overcome the PK variability and optimise target attainment. This will deliver optimised antimicrobial chemotherapy to individual critically ill patients. Delivery of β-lactams antimicrobial agents by infusions, rather than bolus dosing, is effective at increasing the duration of the dosing interval that the drug concentration is above the MIC. Therapeutic drug monitoring, utilising population PK mathematical models with Bayesian estimation, can also be used to optimise regimens following measurement of plasma drug concentrations. Clinical trials are required to establish if patient outcomes can be improved by implementing these techniques.

Changes in individual drug-independent system parameters during virtual paediatric pharmacokinetic trials: introducing time-varying physiology into a paediatric PBPK model

Although both POPPK and physiologically based pharmacokinetic (PBPK) models can account for age and other covariates within a paediatric population, they generally do not account for real-time growth and maturation of the individuals through the time course of drug exposure; this may be significant in prolonged neonatal studies. The major objective of this study was to introduce age progression into a paediatric PBPK model, to allow for continuous updating of anatomical, physiological and biological processes in each individual subject over time. The Simcyp paediatric PBPK model simulator system parameters were reanalysed to assess the impact of re-defining the individual over the study period. A schedule for re-defining parameters within the Simcyp paediatric simulator, for each subject, over a prolonged study period, was devised to allow seamless prediction of pharmacokinetics (PK). The model was applied to predict concentration-time data from multiday studies on sildenafil and phenytoin performed in neonates. Among PBPK system parameters, CYP3A4 abundance was one of the fastest changing covariates and a 1-h re-sampling schedule was needed for babies below age 3.5 days in order to seamlessly predict PK (<5% change in abundance) with subject maturation. The re-sampling frequency decreased as age increased, reaching biweekly by 6 months of age. The PK of both sildenafil and phenytoin were predicted better at the end of a prolonged study period using the time varying vs fixed PBPK models. Paediatric PBPK models which account for time-varying system parameters during prolonged studies may provide more mechanistic PK predictions in neonates and infants.

Xenobiotic metabolism: the effect of acute kidney injury on non-renal drug clearance and hepatic drug metabolism

Acute kidney injury (AKI) is a common complication of critical illness, and evidence is emerging that suggests AKI disrupts the function of other organs. It is a recognized phenomenon that patients with chronic kidney disease (CKD) have reduced hepatic metabolism of drugs, via the cytochrome P450 (CYP) enzyme group, and drug dosing guidelines in AKI are often extrapolated from data obtained from patients with CKD. This approach, however, is flawed because several confounding factors exist in AKI. The data from animal studies investigating the effects of AKI on CYP activity are conflicting, although the results of the majority do suggest that AKI impairs hepatic CYP activity. More recently, human study data have also demonstrated decreased CYP activity associated with AKI, in particular the CYP3A subtypes. Furthermore, preliminary data suggest that patients expressing the functional allele variant CYP3A5*1 may be protected from the deleterious effects of AKI when compared with patients homozygous for the variant CYP3A5*3, which codes for a non-functional protein. In conclusion, there is a need to individualize drug prescribing, particularly for the more sick and vulnerable patients, but this needs to be explored in greater depth.

Relevance of Liver Failure for Anti-Infective Agents: From Pharmacokinetic Alterations to Dosage Adjustments

The liver is a complex organ with great ability to influence drug pharmacokinetics. Due to its wide array of function, its impairment has the potential to affect bioavailability, enterohepatic circulation, drug distribution, metabolism, clearance, and biliary elimination. These alterations differ widely depending on the cause of the liver failure, if it is acute or chronic in nature, the extent of impairment, and comorbid conditions. In addition, effects on liver functions do not occur in a proportional or predictable manner for escalating degrees of liver impairment. The ability of hepatic alterations to influence PK is also dependent on drug characteristics, such as administration route, chemical properties, protein binding, and extraction ratio, among others. This complexity makes it difficult to predict what these effects have on drugs. Unlike certain classes of agents, efficacy of anti-infectives is most often dependent on fulfilling pharmacokinetic/pharmacodynamic targets, such as C_max/MIC, AUC/MIC, T_>MIC, IC₅₀/EC₅₀, or T>EC₉₅. Loss of efficacy, or conversely, increased risk of toxicity may occur in certain circumstances of liver injury. Although important to consider these potential alterations and their effects on specific anti-infectives, many lack data to constitute specific dosing adjustments, making it important to monitor patients for effectiveness and toxicities of therapy.

Turpentine oil induced inflammation decreases absorption and increases distribution of phenacetin without altering its elimination process in rats

Plasma concentrations and pharmacokinetics of phenacetin, a CYP1A2 substrate were determined in normal and experimentally induced inflamed rats by turpentine oil to know the role of inflammation on the pharmacokinetics of phenacetin and formation of its active metabolite (paracetamol) by CYP1A2 in wistar albino rats, weighing about 200-250 g that were randomly divided into two groups consisting six in each group. Rats in group I (control) received phenacetin (150 mg kg(-1), PO) where as group II received phenacetin 12 h after induction of inflammation by turpentine oil (0.4 mL, i.m). Blood samples were collected from retro orbital plexus at pre-determined time intervals prior to and at 0.166, 0.33, 0.67, 1.5, 2, 4, 8 and 12 h post-administration of phenacetin. Plasma was separated and analyzed for phenacetin and its metabolite paracetamol by HPLC assay. Based on plasma concentrations of phenacetin and its metabolite paracetamol, the pharmacokinetic parameters were determined by compartmental methods. C(max) of phenacetin was significantly (p < 0.01) decreased to 19.50 ± 2.74 μg mL(-1) in inflamed conditions compared to 38.13 ± 2.20 μg mL(-1) obtained in normal rats. Except, for significant (p < 0.001) increase in volume of distribution at steady state (V(dss)) from 2.87 ± 0.37 to 8.03 ± 1.26 L kg(-1) and increased the rate of absorption with shorter absorption half-life (t(1/2ka)) for phenacetin in inflammation. None of the pharmacokinetic parameters of either phenacetin or its metabolite paracetamol were affected. It can be concluded that turpentine oil induced inflammation has no role on the activity of CYP1A2 in rats, as the plasma concentrations and pharmacokinetic parameters of paracetamol were found unaltered.

Pharmacokinetics of ertapenem in critically ill patients receiving continuous venovenous hemodialysis or hemodiafiltration

This study characterizes the pharmacokinetics of ertapenem, a carbapenem antibiotic, in critically ill adult subjects receiving continuous renal replacement therapy (CRRT). Eight critically ill patients with suspected/known Gram-negative infections receiving continuous venovenous hemodialysis (CVVHD) or continuous venovenous hemodiafiltration (CVVHDF) and ertapenem were enrolled. One gram of ertapenem was infused over 30 min. Predialyzer blood samples were drawn with the first dose of ertapenem from the hemodialysis tubing at time zero, 30 min, and 1, 2, 4, 8, 12, 18, and 24 h after the start of the ertapenem infusion. Effluent was collected at the same time points. Ertapenem total serum, unbound serum, and effluent concentrations from all eight subjects were used simultaneously to perform a population compartmental pharmacokinetic modeling procedure using NONMEM. Monte Carlo simulations were performed to evaluate the ability of several ertapenem dosing regimens (500 mg once daily, 750 mg once daily, 500 mg twice daily, and 1,000 mg once daily) to obtain effective unbound serum concentrations above 0.5, 1, and 2 μg/ml. For our simulated patients, all regimens produced unbound ertapenem concentrations above 2 μg/ml for 40% of the dosing interval for at least 96% of simulated patients. (This study has been registered at ClinicalTrials.gov under registration no. NCT00877370.).

Treatment of Chryseobacterium indologenes ventilator-associated pneumonia in a critically ill trauma patient

OBJECTIVE

To report a case of Chryseobacterium indologenes ventilator-associated pneumonia (VAP) in a critically ill trauma patient.

CASE SUMMARY

This report describes a 66-year-old critically ill trauma patient who developed VAP, which was caused by C indologenes. The patient was injured in a riding lawn mower accident that trapped him underwater in a pond. The patient required surgery for intra-abdominal injuries and was mechanically ventilated in the trauma intensive care unit. On hospital day 5, the patient developed signs and symptoms of VAP. A diagnosis of C indologenes VAP was confirmed based on a quantitative culture from a bronchoscopic bronchoalveolar lavage. The patient's infection was successfully treated with moxifloxacin for 2 days followed by cefepime for 7 days.

DISCUSSION

Formally known as Flavobacterium indologenes, C indologenes is a Gram-negative bacillus normally found in plants, soil, foodstuffs, and fresh and marine water sources. Recently, worldwide reports of C indologenes infections in humans have been increasing, though reports from the United States are still rare. Bacteremia and pneumonia are the most commonly reported infections, and most patients are immunocompromised. The current case differs from most previous reports because this patient was in the United States and did not have any traditional immunocompromised states (eg, transplant, cancer, HIV/AIDS, or corticosteroid use).

CONCLUSION

This case report demonstrates that C indologenes can cause VAP in a trauma ICU patient.

Pharmacokinetics of amphotericin B lipid complex in critically ill patients undergoing continuous venovenous haemodiafiltration

The objective of this study was to examine the effect of continuous venovenous haemodiafiltration (CVVHDF) on the pharmacokinetics of amphotericin B (AmB) in critically ill patients following administration of amphotericin B lipid complex (ABLC). Plasma and ultrafiltrate (UF) samples were collected from patients administered ABLC and either receiving or not receiving CVVHDF. Pharmacokinetic (PK) analysis was performed on eight profiles from patients receiving CVVHDF and six profiles from patients not receiving CVVHDF. For patients receiving CVVHDF, the following median PK data were calculated: area under the concentration-time curve (AUC) = 13.9 h·μg/mL, volume of distribution at steady state (V(ss)) = 1476L and drug clearance (CL) = 27.4 L/h; for patients not receiving CVVHDF, the corresponding median PK data were 11.5 h μg/mL, 2048 L and 43.7 L/h, respectively. The median half-lives calculated during the dosage interval (t(1/2int)) were 30.9 h and 32.5 h on and off CVVHDF, respectively, and the total range of t(1/2int) values was 15.6-180.4 h. Observed median peak concentrations on Day 1 were 0.563 μg/mL and 0.468 μg/mL in patients on and off CVVHDF, respectively. From AmB present in the UF, clearance via CVVHDF contributed<1% of total plasma clearance. The AmB concentration-time profiles for patients administered ABLC on and off CVVHDF were compared and no statistically significant differences in AUC, CL, t(1/2int) and V(ss) were observed. In conclusion, CVVHDF had no clinically significant effect on the pharmacokinetics of AmB following administration of ABLC.

Approaches for dosage individualisation in critically ill patients

INTRODUCTION

Pharmacokinetic variability in critically ill patients is the result of the overlapping of multiple pathophysiological and clinical factors. Unpredictable exposure from standard dosage regimens may influence the outcome of treatment. Therefore, strategies for dosage individualisation are recommended in this setting.

AREAS COVERED

The authors focus on several approaches for dosage individualisation that have been developed, ranging from the well-established therapeutic drug monitoring (TDM) up to the innovative application of pharmacogenomics criteria. Furthermore, the authors summarise the specific population pharmacokinetic models for different drugs developed for critically ill patients to improve the initial dosage selection and the Bayesian forecasting of serum concentrations. The authors also consider the use of Monte Carlo simulation for the selection of dosage strategies.

EXPERT OPINION

Pharmacokinetic/pharmacodynamics (PK/PD) modelling and dosage individualisation methods based on mathematical and statistical criteria will contribute in improving pharmacologic treatment in critically ill patients. Moreover, substantial effort will be necessary to integrate pharmacogenomics criteria into critical care practice. The lack of availability of target biomarkers for dosage adjustment emphasizes the value of TDM which allows a large part of treatment outcome variability to be controlled.

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.

0.5 mg/kg versus 1 mg/kg of intravenous omeprazole for the prophylaxis of gastrointestinal bleeding in critically ill children: a randomized study

OBJECTIVE

To compare the effect of 2 doses of intravenous omeprazole on gastric pH, gastrointestinal bleeding, and adverse effects in critically ill children.

STUDY DESIGN

We undertook a prospective randomized clinical trial in critically ill children at risk of gastrointestinal bleeding. The effect of 2 intravenous omeprazole regimens (0.5 or 1 mg/kg every 12 hours) on the gastric pH and incidence of gastrointestinal hemorrhage was compared. The efficacy criteria were a gastric pH >4 and the absence of clinically significant gastrointestinal bleeding.

RESULTS

Forty patients, 20 in each treatment group, were studied. Overall, the gastric pH was greater than 4 for 57.8% of the time, with no difference between the doses (P = .66). The percentage of time with a gastric pH > 4 increased during the study (47.8% between 0 and 24 hours vs 76% between 24 and 48 hours, P = .001); the greater dose showed a greater increase in the percentage of time with a pH > 4: between hours 24 and 48 of the study, the gastric pH was greater than 4 for 84.5% of the time with the 1 mg/kg dose and for 65.5% of the time with the 0.5 mg/kg dose (P = .036). Plasma omeprazole levels were greater with 1 mg/kg dose, but no correlation was found between omeprazole plasma levels and gastric pH. No toxic adverse effects were detected, and there was no clinically significant bleeding.

CONCLUSION

Neither of the 2 omeprazole regimens achieved adequate alkalinization of the gastric pH during the first 24 hours. Between 24 and 48 hours, the 1 mg/kg dose maintained the gastric pH greater than 4 for a greater percentage of the time.

Mesenteric blood flow, glucose absorption and blood pressure responses to small intestinal glucose in critically ill patients older than 65 years

PURPOSE

To compare nutrient-stimulated changes in superior mesenteric artery (SMA) blood flow, glucose absorption and glycaemia in individuals older than 65 years with, and without, critical illness.

METHODS

Following a 1-h 'observation' period (t (0)-t (60)), 0.9 % saline and glucose (1 kcal/ml) were infused directly into the small intestine at 2 ml/min between t (60)-t (120), and t (120)-t (180), respectively. SMA blood flow was measured using Doppler ultrasonography at t (60) (fasting), t (90) and t (150) and is presented as raw values and nutrient-stimulated increment from baseline (Δ). Glucose absorption was evaluated using serum 3-O-methylglucose (3-OMG) concentrations during, and for 1 h after, the glucose infusion (i.e. t (120)-t (180) and t (120)-t (240)). Mean arterial pressure was recorded between t (60)-t (240). Data are presented as median (25th, 75th percentile).

RESULTS

Eleven mechanically ventilated critically ill patients [age 75 (69, 79) years] and nine healthy volunteers [70 (68, 77) years] were studied. The magnitude of the nutrient-stimulated increase in SMA flow was markedly less in the critically ill when compared with healthy subjects [Δt (150): patients 115 (-138, 367) versus health 836 (618, 1,054) ml/min; P = 0.001]. In patients, glucose absorption was reduced during, and for 1 h after, the glucose infusion when compared with health [AUC(120-180): 4.571 (2.591, 6.551) versus 11.307 (8.447, 14.167) mmol/l min; P < 0.001 and AUC(120-240): 26.5 (17.7, 35.3) versus 40.6 (31.7, 49.4) mmol/l min; P = 0.031]. A close relationship between the nutrient-stimulated increment in SMA flow and glucose absorption was evident (3-OMG AUC(120-180) and ∆SMA flow at t (150): r (2) = 0.29; P < 0.05).

CONCLUSIONS

In critically ill patients aged >65 years, stimulation of SMA flow by small intestinal glucose infusion may be attenuated, which could account for the reduction in glucose absorption.

Sedation for critically ill or injured adults in the intensive care unit: a shifting paradigm

As most critically ill or injured patients will require some degree of sedation, the goal of this paper was to comprehensively review the literature associated with use of sedative agents in the intensive care unit (ICU). The first and selected latter portions of this article present a narrative overview of the shifting paradigm in ICU sedation practices, indications for uninterrupted or prolonged ICU sedation, and the pharmacology of sedative agents. In the second portion, we conducted a structured, although not entirely systematic, review of the available evidence associated with use of alternative sedative agents in critically ill or injured adults. Data sources for this review were derived by searching OVID MEDLINE and PubMed from their first available date until May 2012 for relevant randomized controlled trials (RCTs), systematic reviews and/or meta-analyses and economic evaluations. Advances in the technology of mechanical ventilation have permitted clinicians to limit the use of sedation among the critically ill through daily sedative interruptions or other means. These practices have been reported to result in improved mortality, a decreased length of ICU and hospital stay and a lower risk of drug-associated delirium. However, in some cases, prolonged or uninterrupted sedation may still be indicated, such as when patients develop intracranial hypertension following traumatic brain injury. The pharmacokinetics of sedative agents have clinical importance and may be altered by critical illness or injury, co-morbid conditions and/or drug-drug interactions. Although use of validated sedation scales to monitor depth of sedation is likely to reduce adverse events, they have no utility for patients receiving neuromuscular receptor blocking agents. Depth of sedation monitoring devices such as the Bispectral Index (BIS©) also have limitations. Among existing RCTs, no sedative agent has been reported to improve the risk of mortality among the critically ill or injured. Moreover, although propofol may be associated with a shorter time to tracheal extubation and recovery from sedation than midazolam, the risk of hypertriglyceridaemia and hypotension is higher with propofol. Despite dexmedetomidine being linked with a lower risk of drug-associated delirium than alternative sedative agents, this drug increases risk of bradycardia and hypotension. Among adults with severe traumatic brain injury, there are insufficient data to suggest that any single sedative agent decreases the risk of subsequent poor neurological outcomes or mortality. The lack of examination of confounders, including the type of healthcare system in which the investigation was conducted, is a major limitation of existing pharmacoeconomic analyses, which likely limits generalizability of their results.

Increased sedation requirements in patients receiving extracorporeal membrane oxygenation for respiratory and cardiorespiratory failure

Critically ill patients receiving extracorporeal membrane oxygenation (ECMO) are often noted to have increased sedation requirements. However, data related to sedation in this complex group of patients is limited. The aim of our study was to characterise the sedation requirements in adult patients receiving ECMO for cardiorespiratory failure. A retrospective chart review was performed to collect sedation data for 30 consecutive patients who received venovenous or venoarterial ECMO between April 2009 and March 2011. To test for a difference in doses over time we used a regression model. The dose of midazolam received on ECMO support increased by an average of 18 mg per day (95% confidence interval 8, 29 mg, P=0.001), while the dose of morphine increased by 29 mg per day (95% confidence interval 4, 53 mg, P=0.021) The venovenous group received a daily midazolam dose that was 157 mg higher than the venoarterial group (95% confidence interval 53, 261 mg, P=0.005). We did not observe any significant increase in fentanyl doses over time (95% confidence interval 1269, 4337 µg, P=0.94). There is a significant increase in dose requirement for morphine and midazolam during ECMO. Patients on venovenous ECMO received higher sedative doses as compared to patients on venoarterial ECMO. Future research should focus on mechanisms behind these changes and also identify drugs that are most suitable for sedation during ECMO.

Treatment of methicillin-resistant Staphylococcus aureus ventilator-associated pneumonia with high-dose vancomycin or linezolid

BACKGROUND

The purpose of this study was to determine the clinical cure rate of high-dose vancomycin for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) ventilator-associated pneumonia (VAP) in critically ill trauma patients. Recent trials suggest that a traditional dose of 1 g q12 hours results in unacceptable cure rates for MRSA VAP. Thus, more aggressive vancomycin dosing has the potential to improve efficacy. Based on pharmacokinetic principles, the goal initial dose at the study center has been 20 mg/kg q12 hours or q8 hours since the 1990s.

METHODS

All patients admitted to the trauma intensive care unit from 1997 to 2008 diagnosed with MRSA VAP were retrospectively reviewed. Diagnosis required bacterial growth ≥ 100,000 colony forming units/mL from a bronchoscopic bronchoalveolar lavage, new or changing infiltrate, plus at least two of the following: fever, leukocytosis or leukopenia, or purulent sputum.

RESULTS

Overall, 125 patients with 141 episodes of MRSA VAP were identified. Mean age was 47 years ± 21 years, median Injury Severity Score was 29 (22-43), 70% of patients were male, and the mean length of intensive care unit stay was 38 days ± 35 days. The mean initial vancomycin dose was 18.1 mg/kg/dose with a mean duration of therapy of 11 days. Clinical success was achieved in 88% (125 of 131) of episodes, with microbiological success in 89% (66 of 74) of episodes with a follow-up bronchoscopic bronchoalveolar lavage. Overall mortality was 20% (25 of 125), with death due to VAP in 12 of 25 deaths. Mean initial vancomycin trough concentrations were 10.6 mg/L in the clinical success group and 13.3 mg/L in the clinical failure group (p = not significant).

CONCLUSIONS

High-dose vancomycin provided an acceptable cure rate for MRSA VAP in critically ill trauma patients.

LEVEL OF EVIDENCE

Therapeutic study, level III.

Medications prescribed and occurrence of falls in general medicine inpatients

BACKGROUND

Although falls are multifactorial, medications are a key risk factor that may be modifiable. Falls were among the most common occurrences entered into a risk identification system at the authors' hospital.

OBJECTIVES

To identify whether general medicine inpatients who had experienced a fall were taking any medications known to be associated with falls.

METHODS

The literature was reviewed to develop a list of high-risk medications that have been associated with falls. In a retrospective quality-improvement database-based study, information from the risk identification system was merged with data from the pharmacy dispensing system for general medicine inpatients who had experienced a fall. The primary end point was the percentage of patients with a documented fall who had a prescription for a high-risk medication. The number of such medications that had been prescribed for patients who fell was also calculated.

RESULTS

Eighty-one unique medications were found to be associated with falls. During the study period (April 1, 2008, to March 31, 2009), 151 patients experienced a fall. Of those, 144 (95.4%) were taking at least one high-risk medication. The mean number of high-risk medications per patient who experienced a fall was 2.2. Of all documented falls, a new high-risk medication had been started within 7 days before the fall for 74 (49.0%) and within 24 h before the fall for 17 (11.3%). The most commonly prescribed drugs during all time periods (i.e., within 24 h or 7 days before the fall or since the patient's admission) were lorazepam and zopiclone. The pharmacy database did not track administration of medications, so it is possible that some of the drugs prescribed were not actually taken by the patient.

CONCLUSION

Almost all inpatients who experienced a fall during the hospital stay had a prescription for at least one medication associated with a high risk for falls. Lorazepam and zopiclone were the drugs most commonly associated with falls in this hospital, and their use should be reviewed.

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.

Pharmacokinetic changes in patients receiving extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) is a form of prolonged cardiopulmonary bypass used to temporarily sustain cardiac and/or respiratory function in critically ill patients. Extracorporeal membrane oxygenation further complicates the management of critically ill patients who already have profound physiologic derangements with consequent altered pharmacokinetics. The purpose of this study is to identify and critically review the published literature describing pharmacokinetics in the presence of ECMO. This review revealed a dearth of data describing pharmacokinetics during ECMO in critically ill adults, with most of the available data originating in neonates. Of concern, the present data indicate substantial variability and a lack of predictability in drug behavior in the presence of ECMO. The most common mechanisms by which ECMO affects pharmacokinetics are sequestration in the circuit, increased volume of distribution, and decreased drug elimination. While lipophilic drugs and highly protein-bound drugs (eg, voriconazole and fentanyl) are significantly sequestered in the circuit, hydrophilic drugs (eg, β-lactam antibiotics, glycopeptides) are significantly affected by hemodilution and other pathophysiologic changes that occur during ECMO. Although the published literature is insufficient to make any meaningful recommendations for adjusting therapy for drug dosing, this review systematically describes the available data enabling clinicians to make conclusions based on available data. Furthermore, this review serves to highlight the need for well-designed and conducted clinical and laboratory-based studies to provide the data from which robust dosing guidance can be developed to improve clinical outcomes in this most unwell cohort of patients.

[Clinically relevant pharmacokinetic drug interactions in the intensive care unit: an overview]

Critically ill patients in the intensive care unit (ICU) are predisposed to pharmacokinetic drug interactions because of the complexity of the drug regimens received in the intensive care setting. Drugs may affect the absorption, distribution, metabolism and/or elimination of an object drug and consequently alter the intended pharmacologic response and potentially lead to an adverse event. The paper presents an overview of pharmacokinetic drug-drug interactions which can occur with commonly used drugs in the ICU and outlines the underlying types and mechanisms.

Infectious diseases in the critically ill patients

Infection is common in the critically ill and often results due to the severity of the patient's illness. Recent data suggest 51% of intensive care unit (ICU) patients are infected, and 71% receive antimicrobial therapy. Bacterial infection is the primary concern, although some fungal infections are opportunistic. Infection more than doubles the ICU mortality rate, and the costs associated with infection may be as high as 40% of total ICU expenditures. There are many contemporary antimicrobial resistance concerns that the critical care clinician must consider in managing the pharmacotherapy of infection. Methicillin resistance in Staphylococcus aureus, vancomycin resistance in Enterococci, beta-lactamase resistance in Enterobacteriaceae, multidrug resistance in Pseudomonas aeruginosa and Acinetobacter species, fluoroquinolone resistance in Escherichia coli, and fungal resistance are among the most common issues ICU clinician's must face in managing infection. Critical illness causes changes in pharmacokinetics that influence drug and dosing considerations. Absorption, distribution, metabolism, and excretion may all be affected by the various disease states that define critical illness. Several specific diseases are discussed, including ventilator-associated pneumonia, various fungal infections, gastrointestinal infections due to Clostridium difficile, urinary tract infections, and bloodstream infections. Within each disease section, discussion includes causes and prevention strategies, microbiology, evidence-based guidelines, and important caveats.

Population pharmacokinetics of fluconazole after administration of fosfluconazole and fluconazole in critically ill patients

WHAT IS KNOWN AND OBJECTIVE

Fluconazole is an antifungal agent that is commonly used to treat patients with serious systemic fungal infections in intensive care units. Fosfluconazole is a phosphate prodrug of fluconazole, which was developed to reduce the volume of fluid required to administer fluconazole by intravenous injection. The objective of this study was to characterize the pharmacokinetics of the antifungal fluconazole after the intravenous administration of the prodrug fosfluconazole or fluconazole in critically ill patients with serious systemic fungal infections, by population pharmacokinetic analysis using the nonmem software package.

METHODS

Clinical biochemical data including serum fluconazole levels were obtained from 57 patients treated in the intensive care unit along with two naïve pooled patients gleaned from previous reports. The pharmacokinetic model of fluconazole was estimated using a one-compartment model. The probability that the area under the concentration-time curve is higher than 800 μg h/mL was determined by simulation.

RESULTS

It was assumed that all the administered fosfluconazole was converted to fluconazole with an estimated fosfluconazole-fluconazole conversion rate constant of 2·05/h. The significant covariates for clearance for fluconazole (CL) and volume of distribution for fluconazole (Vd) were resulted in creatinine clearance (CLcr) and body weight (BW), respectively, in the final pharmacokinetic model equations: CL (L/h) = 0·799 × [CLcr (mL/min)/92·7](0·685) and Vd (L) = 48·1 × [BW (kg)/65](1·40) , where the interpatient variabilities in CL and Vd and the intrapatient variability were 44·8%, 79·7% and 19·8%, respectively. On the basis of the results of the Monte Carlo simulation, the probabilities of target attainment were 60%, 26% and 11% for 400 mg/day administration as fluconazole equivalent at CLcr values of 40, 70 and 100 mL/min, respectively.

WHAT IS NEW AND CONCLUSION

The present population pharmacokinetic analysis strongly indicates that fosfluconazole (and fluconazole) dosage should be optimized in terms of CLcr in critically ill patients.

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.

Case Report: Persistent Elevation in Creatine Phosphokinase Associated with High-Dose Daptomycin Therapy

Objective

To report a persistent elevation in creatine phosphokinase (CPK) associated with high-dose daptomycin therapy that did not resolve following discontinuation of daptomycin.

Summary

A 34-year-old male with HIV/AIDS and stage IV Burkitt lymphoma was admitted for pain management. The patient's initial hospital course was complicated by left brachial deep vein thrombosis (DVT), Clostridium difficile colitis, and pancytopenia. The patient later developed severe sepsis and septic shock secondary to methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), Candida albicans, and Escherichia coli infection. High-dose daptomycin (12 mg/kg) was initiated to treat MRSA and VRE bacteremia. The patient's baseline CPK was 118 U/L, which increased to 327 U/L following 2 days of therapy. The patient's CPK continued to increase to 1648 U/L on day 10 of daptomycin, thereby necessitating a discontinuation of daptomycin and the initiation of linezolid. Six days after discontinuation of therapy, the patient's CPK remained elevated at 1940 U/L.

Discussion

A Naranjo scale score of 6 was calculated, indicating that daptomycin was the probable cause for the increase in CPK. Although daptomycin is known to cause elevations in CPK, there are limited published data describing this adverse event with high-dose daptomycin therapy.

Conclusion

High-dose daptomycin is becoming more frequently used in clinical practice, so clinicians should monitor for and report any adverse events associated with this dosing strategy.

Lacosamide in the treatment of acute recurrent seizures and periodic epileptiform patterns in critically ill patients

We investigated the safety, tolerability, and effectiveness of lacosamide (LCM) in patients with acute recurrent seizures or with periodic epileptiform activity captured during continuous EEG monitoring. A total of 17 patients received LCM; 12 patients received LCM as a second or third antiepileptic drug (AED), one patient as a fourth AED, and one patient as a fifth AED. No additional AEDs were introduced after LCM in 15 patients. Twelve patients responded to LCM with improvement in the seizures or periodic epileptiform activity. Two patients required further AED management or burst suppression. No adverse effects, including symptomatic bradycardia and allergic reactions, were seen for intravenous infusion dosages up to 300 mg. Eleven patients were eventually discharged on LCM. LCM is an important new AED in the add-on treatment of acute recurrent seizures and periodic epileptiform activity in critically ill patients.

Interação medicamentosa: conhecimento de enfermeiros das unidades de terapia intensiva

OBJETIVO: Avaliar o conhecimento das interações medicamentosas (IM)de enfermeiros que atuam em unidades de terapia intensiva de adultos, de três hospitais públicos de Goiás. MÉTODOS: Estudo descritivo, transversal. População 64 e amostra, 51 enfermeiros. Construiu-se um instrumento de coleta de dados, utilizando informações da base de dados MICROMEDEX®. RESULTADOS: Sobre o conhecimento de IM e manejo clínico, houve uma relação de acertos e erros de, aproximadamente, 50% dos enfermeiros. As duplas de medicamentos que os enfermeiros mais acertaram foram relativas a medicamentos com ação sedativa e analgésica e as que apresentaram mais erros, foram as de ação anti-infecciosa e anti-hipertensiva. CONCLUSÃO: É necessário sensibilizar autoridades e profissionais sobre a importância das IM na UTI e implementar ações para a segurança dos pacientes na terapêutica medicamentosa.

Drug dosing considerations for the critically ill patient with liver disease

Hepatic dysfunction in the critically ill patient presents a unique challenge to clinicians when designing pharmacotherapeutic treatment plans. Overall, the literature regarding drug dosing in critically ill patients with hepatic dysfunction is incomplete and current tools available to bedside clinicians have limitations. Despite these challenges, rational drug regimens can be implemented by critical care nurses who consider the potential impact of hepatic dysfunction on drug pharmacokinetics. This information can be applied clinically and careful monitoring plans can be implemented to assess a drug for efficacy and safety. This article reviews the pharmacokinetic changes that can occur in hepatic failure, identifies practical ways to quantify the severity of dysfunction, and discusses general drug dosing strategies in this patient population.

Diazepam as a component of goal-directed sedation in critically ill trauma patients

PURPOSE

Limited information addressing the safety and efficacy of diazepam in the intensive care unit, particularly in trauma patients, is available. The purpose of this study is to evaluate the safety and efficacy of diazepam when used in routine clinical practice as a component of a goal-directed sedation regimen in critically ill trauma patients.

MATERIAL AND METHODS

This is a prospective observational evaluation of adult trauma patients admitted to an intensive care unit with orders for as-needed midazolam or lorazepam followed by scheduled diazepam. Medication administration and Sedation-Agitation Scale scores were recorded.

RESULTS

Twenty-four patients were evaluated. The most common diazepam dosage was 10 mg every 6 hours, and individual doses ranged from 5 to 30 mg. Sedation-Agitation Scale scores were recorded a median of 20 times per day (interquartile range, 15-24), and the majority (68%) were in the target range. No diazepam-related adverse events were observed.

CONCLUSIONS

Based on this limited sample, the use of diazepam as a component of goal-directed therapy appears safe and effective in providing adequate sedation in critically ill trauma patients using an average dosage of 40 mg/d.

Bioavailability of fondaparinux to critically ill patients

INTRODUCTION

Venous thromboembolism is a common problem in the intensive care unit (ICU). To decrease its incidence, prophylactic pharmacologic interventions are part of the ICU routine. However, common ICU conditions may impair the bioavailability of subcutaneously administered agents. The present study evaluates the bioavailability of prophylactic subcutaneous fondaparinux to critically ill patients.

PURPOSE

The purpose of the study was to evaluate vasopressor effect on the bioavailability of subcutaneously administered fondaparinux.

MATERIALS AND METHODS

A 2-center, prospective, observational study was performed. Forty patients were enrolled and divided into 2 groups depending on their vasopressor requirements. All subjects were critically ill patients admitted to a medical ICU for an anticipated stay of more than 72 hours.

INTERVENTIONS

All patients received subcutaneous fondaparinux 2.5 mg/d, and serum anti-Xa factor was serially assessed during the first 100 hours of medical ICU stay.

RESULTS

Therapeutic anti-factor Xa levels among patients receiving vasopressors were observed. In hemodynamically normal patients, subtherapeutic concentrations were detected during the first 48 hours of fondaparinux administration.

CONCLUSIONS

Vasopressor therapy does not appear to affect fondaparinux bioavailability or to reduce anti-factor Xa levels. Subtherapeutic concentrations were detected during the first 48 hours of fondaparinux administration in hemodynamically stable patients. The clinical significance of reduced levels during the first 2 days of fondaparinux administration remains unknown.

Management of aminoglycosides in the intensive care unit

Antibacterial resistance is increasing throughout the world, while the development of new agents is slowly progressing. In addition, the increasing prevalence of fluoroquinolone resistance may force many practitioners to choose an aminoglycoside agent in gram-negative regimens. Aminoglycosides are bactericidal agents with potent activity against gram-negative infections and activity against gram-positive infections when added to a cell wall active antimicrobial-based regimen. These agents may be dosed multiple times a day or consolidated as high-dose, extended-interval dosing to maximize pharmacokinetic and pharmacodynamic properties to achieve possible improved efficacy with reduced toxicity. Clinical application includes the treatment of bacteremia, endocarditis, health-care and nosocomial pneumonias, intra-abdominal infections, and others. Nephrotoxicity and ototoxicity are potential risks of aminoglycoside therapy that may be minimized with serum monitoring and short courses of therapy.

Off-label medication use in adult critical care patients

PURPOSE

This study evaluated the use of off-label medications in the intensive care unit (ICU) setting and their varying levels of evidence.

MATERIALS AND METHODS

Thirty-seven ICUs from 24 US sites participated in this prospective, multicenter, observational study during a single 24-hour period. All medication orders were evaluated for Food and Drug Administration-labeled indications, strength of evidence, and strength of recommendation. Off-label medication orders were evaluated for indication, dose, route of administration, duration of therapy, and whether they were supported by institutional guidelines.

RESULTS

A total of 414 patients were enrolled, yielding 5237 medication orders for analysis. Of these, 1897 orders (36.2%) were off-label. The 3 drug classes that accounted for the most off-label orders were bronchorespiratory, gastrointestinal, and immunology. The majority of off-label medication orders (89.1%) were initiated after patient admission to the ICU. Nine hundred twenty-eight (48.3%) of the off-label medication orders had grade C or no evidence.

CONCLUSIONS

The use of off-label medication therapies in the US adult critical care units is common, a majority of which are initiated after admission to the ICU and a significant portion of which are supported with inferior levels of evidence.

Intravenous to Oral Conversion of Antihypertensives: A Toolkit for Guideline Development

Objective:

To provide a toolkit of information for hospitals to use in developing intravenous to oral conversion protocols for antihypertensives.

Data Sources:

Articles describing intravenous to oral conversion protocols for any therapeutic category were identified in an English-language MEDLINE search (1990-April 2010) using a wide variety of MeSH terms. References from selected articles were reviewed for additional material.

Study Selection and Data Extraction:

Experimental and observational English-language studies and review articles that focused on oral transition of intravenous drugs were selected.

Data Synthesis:

Most of the literature on conversion from intravenous to oral formulations involves antimicrobials. There is considerable evidence documenting reduced costs and improved patient flow through the health-care system following implementing these protocols with drugs like antimicrobials, histamine-2 receptor antagonists, and proton pump inhibitors. Although antihypertensives have not been studied, principles and implementation strategies used for other drug classes can be applied to antihypertensives. Guidance is provided on framing the problem, issues surrounding oral absorption principles, information pertaining to oral conversion in specific disease slates, and implementation and documentation strategies. Detailed tables of oral and intravenous antihypertensives are provided.

Conclusions:

We recommend that hospitals consider developing protocols on conversion of intravenous to oral antihypertensives in an attempt to reduce unnecessarily prolonged intravenous therapy. Information contained in this article can be used as a toolkit to select information specific to the characteristics of individual health-care systems.

Drug disposition in obesity and protein–energy malnutrition

Clinical response to medication can differ between patients. Among the known sources of variability is an individual's nutrition status. This review defines some pharmacokinetic terms, provides relevant body size metrics and describes the physiologic influences of protein–energy malnutrition and obesity on drug disposition. Weight-based drug dosing, which presumes a healthy BMI, can be problematic in the protein–energy malnourished or obese patient. The use of total body weight, lean body weight, or an adjusted body weight depends on the drug and how it is differently handled in malnutrition or obesity. Most of the recognized influences are seen in drug distribution and drug elimination as a result of altered body composition and function. Distribution characteristics of each drug are determined by several drug-related factors (e.g. tissue affinity) in combination with body-related factors (e.g. composition). Drug elimination occurs through metabolic and excretory pathways that can also vary with body composition. The current data are limited to select drugs that have been reported in small studies or case reports. In the meantime, a rational approach to evaluate the potential influences of malnutrition and obesity can be used clinically based on available information. Antimicrobials are discussed as a useful example of this approach. Further advancement in this field would require collaboration between experts in body composition and those in drug disposition. Until more data are available, routine monitoring by the clinician of the protein–energy malnourished or obese patient receiving weight-based drug regimens is necessary.

Common drug interactions leading to adverse drug events in the intensive care unit: management and pharmacokinetic considerations

Critically ill patients are predisposed to drug interactions because of the complexity of the drug regimens they receive in the intensive care setting. Drugs may affect the absorption, distribution, metabolism, and/or elimination of an object drug and consequently alter the intended pharmacologic response and potentially lead to an adverse event. Certain disease states that afflict critically ill patients may also amplify an intended pharmacologic response and potentially result in an unintended effect. A team approach is important to identify, prevent, and address drug interactions in the intensive care setting and optimize patient outcomes.

Pharmacokinetics of intravenous omeprazole in critically ill paediatric patients

The proton pump inhibitors are first-line drugs for the treatment of a number of gastrointestinal diseases. These drugs have a good safety profile, making it possible to use them in paediatric patients. Although their pharmacokinetics in children has not been extensively studied, research performed suggests that the dose used should be varied as a function of age, as this factor affects the drug's metabolism. Proton pump inhibitors can be used in critically ill children for the prophylaxis and treatment of gastrointestinal haemorrhage, although there is still little experience with this. The most widely used proton pump inhibitor at the present time is omeprazole. As there are specific characteristics of these patients that could alter the pharmacokinetics of the drugs, studies need to be performed to determine the most suitable dose and dosage interval.

Impaired glucose and nutrient absorption in critical illness: is gastric emptying only a piece of the puzzle?

This commentary highlights the contribution of the article by Chapman and colleagues assessing the relationships between glucose absorption, glycaemia and gastric emptying during critical illness. In addition to several more expected findings, their data suggest that factors other than slow gastric emptying may limit glucose absorption during critical illness. This hypothesis has received little attention so far, although numerous small intestinal abnormalities possibly interfering with absorption are known to occur in intensive care patients. Future work should focus on further validation of tools to assess nutrient absorption in the critically ill, before defining the precise causes and mechanisms that are involved.