Population pharmacokinetics of lorazepam and midazolam and their metabolites in intensive care patients on continuous venovenous hemofiltration

Clearance of Amlodipine, Fentanyl, Fluconazole, Methylprednisolone, and Midazolam by Continuous Renal Replacement Circuits

Critically ill pediatric patients on continuous renal replacement therapy (CRRT) have high mortality rates ranging from 30% to 70%, due in part to altered drug exposure from drug-CRRT circuit interactions. Drug loss within CRRT circuits can occur through both clearance by the hemofilter and adsorption to circuit components. Although these interactions are known to exist, their impact on the pharmacokinetics of most drugs is unknown, resulting in limited drug dosing guidance and increased risk for suboptimal drug exposure. In this study, we administered amlodipine, fentanyl, fluconazole, methylprednisolone, and midazolam individually and in combination with ex vivo, closed-loop, blood-primed CRRT circuits to quantify drug-circuit interactions. Circuits were dosed to drug-specific therapeutic concentrations, and drug concentrations in both plasma and effluent were measured over time. For all drugs administered individually, variable extraction by the CRRT circuit was observed (mean plasma recovery 0.4-49%). For drugs coadministered into a circuit, significant decreases in extraction and increases in drug recovery (2.5-109%) were found, suggesting dosing adjustments may be needed. This study highlights the need for additional studies of drug coadministration within CRRT circuits to describe complex drug-circuit and drug-drug interactions to provide dosing guidance in pediatric CRRT patients.

Association of NR1I2 Polymorphism with Midazolam Clearance in Mechanically Ventilated ICU Patients: A Population Pharmacokinetic and Pharmacogenetic Study

Background

Significant variability in the metabolism of midazolam (MDZ) exists among mechanically ventilated (MV) patients in the intensive care unit (ICU) due to complex clinical conditions and genetic factors. The NR1I2 gene (PXR), which encodes a nuclear receptor that regulates drug-metabolizing enzymes like CYP3A4, plays a critical role in MDZ metabolism. Polymorphisms in NR1I2, along with variations in genes such as CYP3A4, CYP3A5, and ABCB1, may influence enzyme activity and MDZ pharmacokinetics (PK). Understanding these factors is essential for optimizing MDZ dosing in high-risk patient populations.

Methods

We studied 61 MV ICU patients receiving continuous MDZ infusion. A population pharmacokinetic (PopPK) model was used to assess MDZ PK, with genetic factors (NR1I2 rs2461817, CYP3A4, CYP3A5, ABCB1, and other PXR polymorphisms) and clinical covariates (body weight (BW), aspartate aminotransferase (AST) levels) evaluated for their impact on MDZ clearance (CL).

Results

The PK of MDZ and its metabolite, 1-hydroxymidazolam (1-OH-MDZ), were accurately described using a one-compartment model. The estimated population means for MDZ and 1-OH-MDZ CL were 22.6 L/h (inter-individual variability [IIV] 59.4%) and 67.1 L/h (IIV 57.7%), respectively. MDZ CL was significantly associated with the NR1I2 rs2461817 polymorphism and AST levels, accounting for 11.3% of the variability. MDZ CL decreased by 32.7% as AST increased from 22 IU/L to 60 IU/L, and by 40.7% in patients homozygous for the NR1I2 rs2461817 variant. BW also influenced the CL of 1-OH-MDZ, demonstrating a 34.2% increase as weight increased from 54 kg to 65 kg. Simulations confirmed the significant impact of NR1I2 rs2461817 on MDZ CL.

Conclusion

The PopPK model highlights the significant impact of NR1I2 rs2461817 polymorphism on MDZ CL in Chinese MV patients, emphasizing the need to consider genetic and clinical factors for optimizing MDZ dosing in ICU settings.

The Clearance of Midazolam and Metabolites during Continuous Renal Replacement Therapy in Critically Ill Patients with COVID-19

INTRODUCTION

Midazolam-based continuous intravenous sedation in patients admitted to the intensive care unit (ICU) was a necessity during the COVID-19 pandemic. However, benzodiazepine-based sedation is associated with a high incidence of benzodiazepine-related delirium and additional days on mechanical ventilation. Due to the requirement of high midazolam doses in combination with the impaired renal clearance (CL) of the pharmacological active metabolite 1-OH-midazolam-glucuronide (10% compared to midazolam), ICU patients with COVID-19 and continuous renal replacement therapy (CRRT) were at risk of unintended prolonged sedation. Several CRRT-related factors may have influenced the delivered CL of midazolam and its metabolites. Therefore, the aim of the study was to identify and describe these CRRT-related factors.

METHODS

Pre-filter blood samples and ultrafiltrate samples were collected simultaneously. Midazolam, 1-OH-midazolam, and 1-OH-midazolam-glucuronide plasma samples were analyzed using an UPLC-MS/MS method. The prescribed CRRT dose was corrected for downtime and filter integrity using the urea ratio (urea concentration in effluent/urea concentration plasma). CL of midazolam and its metabolites were calculated with the delivered CRRT dose (corrected for downtime and saturation coefficient [SD]).

RESULTS

Three patients on continuous venovenous hemodialysis (CVVHD) and 2 patients on continuous venovenous hemodiafiltration (CVVHDF) were included. Midazolam, 1-OH-midazolam, and 1-OH-midazolam-glucuronide concentrations were 2,849 (0-6,700) μg/L, 153 (0-295) μg/L, and 27,297 (1,727-39,000) μg/L, respectively. The SD was 0.03 (0.02-0.03) for midazolam, 0.05 (0.05-0.06) for 1-OH-midazolam, and 0.33 (0.23-0.43) for 1-OH-midazolam-glucuronide. The delivered CRRT CL was 1.4 (0-1.7) mL/min for midazolam, 2.7 (0-3.5) mL/min for 1-OH-midazolam, and 15.7 (4.0-27.7) mL/min for 1-OH-midazolam-glucuronide.

CONCLUSIONS

Midazolam and 1-OH-midazolam were not removed during CVVHD and CVVHDF. However, 1-OH-midazolam-glucuronide was removed reasonably, approximately up to 43%. CRRT modality, filter integrity, and downtime affect this removal. These data imply a personalized titration of midazolam in critically ill patients with renal failure and awareness for the additional sedative effects of its active metabolites.

The Impact of Continuous Veno-Venous Hemodiafiltration on the Efficacy of Administration of Prophylactic Doses of Enoxaparin: A Prospective Observational Study

BACKGROUND

Critically ill patients frequently require continuous renal replacement therapy (CRRT). During CRRT, particles up to 10 kDa in size, such as enoxaparin, may be removed. The aim of this study was to determine if patients receiving prophylactic doses of enoxaparin and treated with continuous veno-venous hemodiafiltration (CVVHDF) reach prophylactic values of anti-Xa factor activity.

METHODS

In this observational trial, we compared two groups: 20 patients treated with CVVHDF and 20 patients not treated with CVVHDF. All of them received prophylactic doses of 40 mg of enoxaparin subcutaneously. Anti-Xa factor activity was determined on the third day of receiving a prophylactic dose of enoxaparin. The first blood sample was taken just before the administration of enoxaparin, and other samples were taken 3 h, 6 h, and 9 h after the administration of a prophylactic dose of enoxaparin.

RESULTS

At 3 and 6 h after administration of enoxaparin in both groups, we observed a significant increase in anti-Xa factor activity from baseline, with the peak after 3 h of administration. There were no significant differences in the numbers of patients who had anti-Xa factor activity within the prophylactic range between CVVHDF and control groups.

CONCLUSION

CVVHDF has only a mild effect on the enoxaparin prophylactic effect measured by anti-Xa factor activity. Thus, it seems there is no need to increase the dose of enoxaparin for patients requiring CVVHDF.

Potential pharmacological confounders in the setting of death determined by neurologic criteria: a narrative review

Guidelines for the determination of death by neurologic criteria (DNC) require an absence of confounding factors if clinical examination alone is to be used. Drugs that depress the central nervous system suppress neurologic responses and spontaneous breathing and must be excluded or reversed prior to proceeding. If these confounding factors cannot be eliminated, ancillary testing is required. These drugs may be present after being administered as part of the treatment of critically ill patients. While measurement of serum drug concentrations can help guide the timing of assessments for DNC, they are not always available or feasible. In this article, we review sedative and opioid drugs that may confound DNC, along with pharmacokinetic factors that govern the duration of drug action. Pharmacokinetic parameters including a context-sensitive half-life of sedatives and opioids are highly variable in critically ill patients because of the multitude of clinical variables and conditions that can affect drug distribution and clearance. Patient-, disease-, and treatment-related factors that influence the distribution and clearance of these drugs are discussed including end organ function, age, obesity, hyperdynamic states, augmented renal clearance, fluid balance, hypothermia, and the role of prolonged drug infusions in critically ill patients. In these contexts, it is often difficult to predict how long after drug discontinuation the confounding effects will take to dissipate. We propose a conservative framework for evaluating when or if DNC can be determined by clinical criteria alone. When pharmacologic confounders cannot be reversed, or doing so is not feasible, ancillary testing to confirm the absence of brain blood flow should be obtained.

Renal medicine in the intensive care unit: a narrative review

Kidney disease, both acute and chronic, is commonly encountered on the intensive care unit. Due to the role the kidneys play in whole body homeostasis, it follows that their dysfunction has wide-ranging implications and can affect prescribing and therapeutic management. This narrative review discusses the pathophysiology of acute kidney injury and chronic kidney disease, and how this relates to critically unwell patients. We cover several aspects of the management of renal dysfunction on the critical care unit, exploring some of the recurrent themes within the literature, including type and timing of kidney replacement therapy, management of acute kidney injury, as well as discussing how novel biomarkers for acute kidney injury may help to identify patients suffering from acute kidney injury as well as risk stratifying these patients. We discuss how early involvement of specialist nephrology services can improve outcomes in patients with kidney disease as well as offer valuable diagnostic and specialist management advice, particularly for patients with established end stage kidney disease and patients who are already known to nephrology services. We also explore some of the ongoing research questions that need to be answered within this arena.

The Impact of Suboptimal 25-Hydroxyvitamin D Levels and Cholecalciferol Replacement on the Pharmacokinetics of Oral Midazolam in Control Subjects and Patients With Chronic Kidney Disease

The aim of this study was to investigate the impact of suboptimal 25-hydroxyvitamin D (25-VitD) and cholecalciferol (VitD3 ) supplementation on the pharmacokinetics of oral midazolam (MDZ) in control subjects and subjects with chronic kidney disease (CKD). Subjects with CKD (n = 14) and controls (n = 5) with suboptimal 25-VitD levels (<30 ng/mL) were enrolled in a 2-phase study. In phase 1 (suboptimal), subjects were administered a single oral dose of VitD3 (5000 IU) and MDZ (2 mg). In phase 2 (replete) subjects who achieved 25-VitD repletion after receiving up to 16 weeks of daily cholecalciferol were given the identical single oral doses of VitD3 and MDZ as in phase 1. Concentrations of MDZ and metabolites, 1'-hydroxymidazolam (1'-OHMDZ), and 1'-OHMDZ glucuronide (1'-OHMDZ-G) were measured by liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis was performed. Under suboptimal 25-VitD, reductions in MDZ clearance and renal clearance of 47% and 87%, respectively, and a 72% reduction in renal clearance of 1'-OHMDZ-G were observed in CKD vs controls. In phase 1 versus phase 2, MDZ clearance increased in all control subjects, with a median (interquartile range) increase of 10.5 (0.62-16.7) L/h. No changes in MDZ pharmacokinetics were observed in subjects with CKD between phases 1 and 2. The effects of 25-VitD repletion on MDZ disposition was largely observed in subjects without kidney disease. Impaired MDZ metabolism and/or excretion alterations due to CKD in a suboptimal 25-VitD state may not be reversed by cholecalciferol therapy. Suboptimal 25-VitD may augment the reductions in MDZ and 1'-OHMDZ-G clearance values observed in patients with CKD.

A Clinician's Guide to Dosing Analgesics, Anticonvulsants, and Psychotropic Medications in Continuous Renal Replacement Therapy

Acute kidney injury (AKI) requiring continuous renal replacement therapy (CRRT) is a common complication in critical illness and has a significant impact on pharmacokinetic factors determining drug exposure, including absorption, distribution, transport, metabolism, and clearance. In this review, we provide a practical guide to drug dosing considerations in critically ill patients undergoing CRRT, focusing on the most commonly used analgesic, anticonvulsant, and psychotropic medications in the clinical care of critically ill patients. A literature search was conducted to identify articles in which drug dosing was evaluated in adult patients receiving CRRT between the years 1980 and 2020. We included articles with pharmacokinetic/pharmacodynamic analyses and those that described medication clearance via CRRT. A summary of the data focused on practical pharmacokinetic and pharmacodynamic principles is presented, with recommendations for drug dosing of analgesics, anticonvulsants, and psychotropic medications. Pharmacokinetic and pharmacodynamic studies to guide drug dosing of analgesics, anticonvulsants, and psychotropic medications in critically ill patients receiving CRRT are sparse. Considering the widespread use of these medications, narrow therapeutic index of these drug classes, and risks of over- and underdosing, additional studies in patients receiving CRRT are needed to inform drug dosing.

Management of status epilepticus in patients with liver or kidney disease: a narrative review

Introduction: Status epilepticus (SE) is a neurologic and medical emergency with significant related morbidity and mortality. Hepatic or renal dysfunction can considerably affect the pharmacokinetics of drugs used for SE through a variety of direct or indirect mechanisms.Areas Covered: This review aims to focus on the therapeutic management of SE in patients with hepatic or renal impairment, highlighting drugs' selection and dose changes that may be necessary due to altered drug metabolism and excretion. The references for this review were identified by searches of PubMed and Google Scholar until May 2020.Expert opinion: According to literature evidence and clinical experience, in patients with renal disease, the authors suggest considering lorazepam as the drug of choice in pre-hospital and intra-hospital early-stage SE, phenytoin in definite SE, propofol in refractory or super-refractory SE. In patients with liver disease, the authors suggest the use of lorazepam as drug of choice in pre-hospital and intra-hospital early-stage SE, lacosamide in definite SE, propofol in refractory or super-refractory SE. A list of preferred drugs for all SE stages is provided.

Population pharmacodynamic modelling of midazolam induced sedation in terminally ill adult patients

Aims

Midazolam is the drug of choice for palliative sedation and is titrated to achieve the desired level of sedation. A previous pharmacokinetic (PK) study showed that variability between patients could be partly explained by renal function and inflammatory status. The goal of this study was to combine this PK information with pharmacodynamic (PD) data, to evaluate the variability in response to midazolam and to find clinically relevant covariates that may predict PD response.

Method

A population PD analysis using nonlinear mixed effect models was performed with data from 43 terminally ill patients. PK profiles were predicted by a previously described PK model and depth of sedation was measured using the Ramsay sedation score. Patient and disease characteristics were evaluated as possible covariates. The final model was evaluated using a visual predictive check.

Results

The effect of midazolam on the sedation level was best described by a differential odds model including a baseline probability, Emax model and interindividual variability on the overall effect. The EC50 value was 68.7 μg l^–1 for a Ramsay score of 3–5 and 117.1 μg l^–1 for a Ramsay score of 6. Comedication with haloperidol was the only significant covariate. The visual predictive check of the final model showed good model predictability.

Conclusion

We were able to describe the clinical response to midazolam accurately. As expected, there was large variability in response to midazolam. The use of haloperidol was associated with a lower probability of sedation. This may be a result of confounding by indication, as haloperidol was used to treat delirium, and deliria has been linked to a more difficult sedation procedure.

Considerations for Medication Management and Anticoagulation During Continuous Renal Replacement Therapy

Providing safe and high-quality care to critically ill patients receiving continuous renal replacement therapy (CRRT) includes adequate drug dosing and evaluation of patients' response to medications during therapy. Pharmacokinetic drug studies in acute kidney injury and CRRT are limited, considering the number of medications used in critical care. Therefore, it is important to understand the basic principles of drug clearance during CRRT by evaluating drug properties, CRRT modalities, and how they affect medication clearance. Few published studies have addressed drug disposition and clinical response during CRRT. Additionally, clotting in the CRRT circuit is a concern, so a few options for anticoagulation strategies are presented. This article reviews (1) the CRRT system and drug property factors that affect medication management, (2) the evidence available to guide drug dosing, and (3) anticoagulation strategies for critically ill patients receiving CRRT.

Emergency medicine evaluation and management of the end stage renal disease patient

BACKGROUND

End stage renal disease (ESRD) is increasing in the U.S., and these patients demonstrate greater all-cause mortality, cardiovascular events, and hospitalization rates when compared to those with normal renal function. These patients may experience significant complications associated with loss of renal function and dialysis.

OBJECTIVE

This review evaluates complications of ESRD including cardiopulmonary, neurologic, infectious disease, vascular, and access site complications, as well as medication use in this population.

DISCUSSION

ESRD incidence is rapidly increasing, and patients commonly require renal replacement therapy including hemodialysis (HDS) or peritoneal dialysis (PD), each type with specific features. These patients possess greater risk of neurologic complications, cardiopulmonary pathology, infection, and access site complications. Focused history and physical examination are essential. Neurologic issues include uremic encephalopathy, cerebrovascular pathology, and several others. Cardiopulmonary complications include pericarditis, pericardial effusion/tamponade, acute coronary syndrome, sudden cardiac death, electrolyte abnormalities, pulmonary edema, and air embolism. Infections are common, with patients more commonly presenting in atypical fashion. Access site infections and metastatic infections must be treated aggressively. Access site complications include bleeding, aneurysm/pseudoaneurysm, thrombosis/stenosis, and arterial steal syndrome. Specific medication considerations are required for analgesics, sedatives, neuromuscular blocking agents, antimicrobials, and anticoagulants.

CONCLUSIONS

Consideration of renal physiology with complications in ESRD can assist emergency providers in the evaluation and management of these patients. ESRD affects many organ systems, and specific pharmacologic considerations are required.

Hypoalbuminaemia and decreased midazolam clearance in terminally ill adult patients, an inflammatory effect?

AIMS

Midazolam is the drug of choice for palliative sedation and is titrated to achieve the desired level of sedation. Because of large inter-individual variability (IIV), however, the time it takes to achieve adequate sedation varies widely. It would therefore greatly improve clinical care if an individualized dose could be determined beforehand. To find clinically relevant parameters for dose individualization, we performed a pharmacokinetic study on midazolam, 1OH-midazolam (1-OH-M) and 1OH-midazolam-glucuronide (1-OH-MG) in terminally ill patients.

METHODS

Using nonlinear mixed effects modelling (NONMEM 7.2), a population pharmacokinetic analysis was conducted with 192 samples from 45 terminally ill patients who received midazolam either orally or subcutaneously. The covariates analysed were patient characteristics, co-medication and blood chemistry levels.

RESULTS

The data were accurately described by a one compartment model for midazolam, 1-OH-M and 1-OH-MG. The population mean estimates for midazolam, 1-OH-M and 1-OH-MG clearance were 8.4 l h^-1 (RSE 9%, IIV 49%), 45.4 l h^-1 (RSE 12%, IIV 60.5%) and 5.1 l h^-1 (RSE 11%, IIV 49.9%), respectively. 1-OH-MG clearance was correlated with the estimated glomular filtration rate (eGFR) explaining 28.4% of the IIV in 1-OH-MG clearance. In addition, low albumin levels were associated with decreased midazolam clearance, explaining 18.2% of the IIV.

CONCLUSION

Our study indicates albumin levels and eGFR as relevant clinical parameters to optimize midazolam dosing in terminally ill patients. The correlation between low albumin levels and decreased midazolam clearance is probably a result of inflammatory response as high CRP levels were correlated in a similar way.

Antiepileptic Drug Removal by Continuous Renal Replacement Therapy: A Review of the Literature

Continuous renal replacement therapy (CRRT) is used for managing acute kidney injury in critically ill patients. Removal of antiepileptic drugs (AEDs) by CRRT could be significant and may complicate patients' intensive care unit stay. The objective of the current review was to summarize the available evidence for AED removal by CRRT. An electronic literature search of PubMed (1946 to May 2016), Medline (1946 to May 2016), and Embase (1974 to May 2016) databases for studies discussing AED removal by CRRT was conducted. A total of 31 case reports discussing 32 patients were found. AEDs reported were levetiracetam (n = 3), valproic acid (n = 9), carbamazepine (n = 10), phenytoin (n = 3), phenobarbital (n = 4), lacosamide (n = 1), gabapentin (n = 1), and topiramate (n = 1). Two-thirds of the reports were about using CRRT in drug overdose and one-third was about AED removal by CRRT during therapy. Based on the current limited evidence and pharmacokinetic characteristics of AEDs, renally eliminated AEDs and/or AEDs with limited protein binding such as levetiracetam are more likely to be removed by CRRT than AEDs that are mainly metabolized and extensively protein bound such as carbamazepine. In conclusion, there is not enough evidence to provide robust dosing recommendations for AEDs in patients undergoing CRRT. Further studies are needed.

Clinical Pharmacology Studies in Critically Ill Children

Developmental and physiological changes in children contribute to variation in drug disposition with age. Additionally, critically ill children suffer from various life-threatening conditions that can lead to pathophysiological alterations that further affect pharmacokinetics (PK). Some factors that can alter PK in this patient population include variability in tissue distribution caused by protein binding changes and fluid shifts, altered drug elimination due to organ dysfunction, and use of medical interventions that can affect drug disposition (e.g., extracorporeal membrane oxygenation and continuous renal replacement therapy). Performing clinical studies in critically ill children is challenging because there is large inter-subject variability in the severity and time course of organ dysfunction; some critical illnesses are rare, which can affect subject enrollment; and critically ill children usually have multiple organ failure, necessitating careful selection of a study design. As a result, drug dosing in critically ill children is often based on extrapolations from adults or non-critically ill children. Dedicated clinical studies in critically ill children are urgently needed to identify optimal dosing of drugs in this vulnerable population. This review will summarize the effect of critical illness on pediatric PK, the challenges associated with performing studies in this vulnerable subpopulation, and the clinical PK studies performed to date for commonly used drugs.

Antibiotic Dosing in Critically Ill Patients Undergoing Renal Replacement Therapy

Continuous renal replacement therapy is frequently used to manage acute renal failure in critically ill patients. Antibiotic drugs used to treat infections in critically ill patients need to be dosed on the basis of the method of renal replacement therapy to be used, degree of residual renal function, and the sensitivity of the organism to be treated. Antibiotic dosing regimens must then be continuously monitored and adjusted according to modifications made to the renal replacement circuit and the patient’s underlying condition.

Effects of anesthetics, sedatives, and opioids on ventilatory control

This article provides a comprehensive, up to date summary of the effects of volatile, gaseous, and intravenous anesthetics and opioid agonists on ventilatory control. Emphasis is placed on data from human studies. Further mechanistic insights are provided by in vivo and in vitro data from other mammalian species. The focus is on the effects of clinically relevant agonist concentrations and studies using pharmacological, that is, supraclinical agonist concentrations are de-emphasized or excluded.

Clinical practice guidelines for the management of pain, agitation, and delirium in adult patients in the intensive care unit

OBJECTIVE

To revise the "Clinical Practice Guidelines for the Sustained Use of Sedatives and Analgesics in the Critically Ill Adult" published in Critical Care Medicine in 2002.

METHODS

The American College of Critical Care Medicine assembled a 20-person, multidisciplinary, multi-institutional task force with expertise in guideline development, pain, agitation and sedation, delirium management, and associated outcomes in adult critically ill patients. The task force, divided into four subcommittees, collaborated over 6 yr in person, via teleconferences, and via electronic communication. Subcommittees were responsible for developing relevant clinical questions, using the Grading of Recommendations Assessment, Development and Evaluation method (http://www.gradeworkinggroup.org) to review, evaluate, and summarize the literature, and to develop clinical statements (descriptive) and recommendations (actionable). With the help of a professional librarian and Refworks database software, they developed a Web-based electronic database of over 19,000 references extracted from eight clinical search engines, related to pain and analgesia, agitation and sedation, delirium, and related clinical outcomes in adult ICU patients. The group also used psychometric analyses to evaluate and compare pain, agitation/sedation, and delirium assessment tools. All task force members were allowed to review the literature supporting each statement and recommendation and provided feedback to the subcommittees. Group consensus was achieved for all statements and recommendations using the nominal group technique and the modified Delphi method, with anonymous voting by all task force members using E-Survey (http://www.esurvey.com). All voting was completed in December 2010. Relevant studies published after this date and prior to publication of these guidelines were referenced in the text. The quality of evidence for each statement and recommendation was ranked as high (A), moderate (B), or low/very low (C). The strength of recommendations was ranked as strong (1) or weak (2), and either in favor of (+) or against (-) an intervention. A strong recommendation (either for or against) indicated that the intervention's desirable effects either clearly outweighed its undesirable effects (risks, burdens, and costs) or it did not. For all strong recommendations, the phrase "We recommend …" is used throughout. A weak recommendation, either for or against an intervention, indicated that the trade-off between desirable and undesirable effects was less clear. For all weak recommendations, the phrase "We suggest …" is used throughout. In the absence of sufficient evidence, or when group consensus could not be achieved, no recommendation (0) was made. Consensus based on expert opinion was not used as a substitute for a lack of evidence. A consistent method for addressing potential conflict of interest was followed if task force members were coauthors of related research. The development of this guideline was independent of any industry funding.

CONCLUSION

These guidelines provide a roadmap for developing integrated, evidence-based, and patient-centered protocols for preventing and treating pain, agitation, and delirium in critically ill patients.

Scaling of pharmacokinetics across paediatric populations: the lack of interpolative power of allometric models

AIM

The objective of this investigation was to assess the performance of an allometric model as the basis for interpolating drug exposure in the context of pharmacokinetic bridging across paediatric subpopulations.

METHODS

Midazolam was selected as a paradigm compound. Two nonlinear mixed effects models were developed to describe midazolam pharmacokinetics in infants, toddlers and adults (model 1) and in children and adolescents (model 2). Subsequently, systemic drug exposure, expressed in terms of the area under the concentration vs. time curve (AUC), in children and adolescents was interpolated based on pharmacokinetic parameter distributions obtained from the model describing infants, toddlers and adults (model 1). Results were compared with the values obtained from modelling of the data in the corresponding population (model 2).

RESULTS

The two pharmacokinetic models accurately described midazolam exposure in the population on which they were built. However, the model based on data from infants, toddlers and adults failed to predict the exposure observed in children and adolescents: the mean difference between the predicted and estimated AUC(0-180) was of -17.8%, with a range of -6.8 to -38.4%.The discrepancy between estimated and interpolated exposure increased proportionally with body weight.

CONCLUSIONS

The current results indicate that irrespective of whether extrapolation or interpolation methods are to be applied during paediatric drug development, model predictions beyond the range of the data used for parameter estimation may be biased. For accurate inter- or extrapolation to different populations, the assumption of identical parameter-covariate correlations across age groups may not be taken for granted.

CYP3A-dependent drug metabolism is reduced in bacterial inflammation in mice

BACKGROUND AND PURPOSE

Gene expression of Cyp3a11 is reduced by activation of Toll-like receptors (TLRs) by Gram-negative or Gram-positive bacterial components, LPS or lipoteichoic acid (LTA) respectively. The primary adaptor protein in the TLR signalling pathway, TIRAP, plays differential roles in LPS- and LTA-mediated down-regulations of Cyp3a11 mRNA. Here, we have determined the functional relevance of these findings by pharmacokinetic/pharmacodynamic (PK/PD) analysis of the Cyp3a substrate midazolam in mice. Midazolam is also metabolized by Cyp2c in mice.

EXPERIMENTAL APPROACH

Adult male C57BL/6, TIRAP+/+ and TIRAP-/- mice were pretreated with saline, LPS (2 mg·kg⁻¹) or LTA (6 mg·kg⁻¹). Cyp3a11 protein expression, activity and PK/PD studies using midazolam were performed.

KEY RESULTS

Cyp3a11 protein expression in LPS- or LTA-treated mice was reduced by 95% and 60% compared with saline-treated mice. Cyp3a11 activity was reduced by 70% in LPS- or LTA-treated mice. Plasma AUC of midazolam was increased two- to threefold in LPS- and LTA-treated mice. Plasma levels of 1'-OHMDZ decreased significantly only in LTA-treated mice. Both LPS and LTA decreased AUC of 1'-OHMDZ-glucuronide. In the PD study, sleep time was increased by ∼2-fold in LPS- and LTA-treated mice. LTA-mediated decrease in Cyp3a11 protein expression and activity was dependent on TIRAP. In PK/PD correlation, AUC of midazolam was increased only in LPS-treated mice compared with saline-treated mice.

CONCLUSIONS AND IMPLICATIONS

LPS or LTA altered PK/PD of midazolam. This is the first study to demonstrate mechanistic differences in regulation of metabolite formation of a clinically relevant drug by Gram-negative or Gram-positive bacterial endotoxins.

Understanding renal replacement therapy and dosing of drugs in pediatric patients with kidney disease

Multifaceted factors need to be considered when prescribing renal replacement therapy (RRT) and dosing of drugs in pediatric patients with kidney disease. RRTs in pediatrics such as intermittent hemodialysis, continuous venovenous hemofiltration, continuous venovenous hemodialysis, and continuous venovenous hemodiafiltration affect solute and drug clearance. Drug properties such as molecular weight, molecular charge, volume of distribution, and protein binding affect drug clearance. RRT prescription parameters such as blood flow rate, ultrafiltration rate, membrane size, and pore size can also influence drug clearance. Furthermore, the pediatric patient presents additional concerns because of developmental factors in children that affect both pharmacokinetics of drugs.

[Study of factors affecting drug extraction during continuous hemofiltration and hemodiafiltration, and the contribution of extraction to systemic clearance]

The aim of this study was to elucidate the factors affecting dialysis clearance and the need for additional doses of drugs during and after continuous hemofiltration (CHF) and hemodiafiltration (CHDF). We performed a literature search of MEDLINE using the terms hemofiltration OR hemodiafiltration AND pharmacokinetics to obtain the clearances of CHF and CHDF in a clinical setting. The relationships between molecular weight, the unbound fraction (fuB), ultrafiltration flow rate (UFR) and dialysis flow rate were analyzed. The need for additional doses of certain drugs was also discussed based on the ratio of dialysis and systemic clearances. The clearance of CHF for 32 reported drugs was significantly correlated with the product of fuB×UFR (r=0.841, p<0.001), and furthermore the plots obtained lay on a line of y=x. The clearance of CHDF also showed good correlation with the product of fuB×UFR (r=0.795, p<0.001), but the plots were higher than the line for y=x, suggesting that additional clearance by dialysis was not negligible. The elimination by both forms of dialysis for drugs excreted mainly via the kidneys, and with a higher fuB, was considerable. The extent of drug clearance by both CHF and CHDF is determined mainly by fuB and UFR. The ratio of dialysis clearance to systemic clearance should be estimated to determine the contribution of CHF and CHDF.

Management of the dialysis patient in general intensive care

The incidence of end-stage renal disease (ESRD) is rising and represents an important group of patients admitted to intensive care units (ICU). ESRD patients have significant co-morbidities and specific medical requirements. Renal replacement therapy (RRT), cardiovascular disease, disorders of electrolytes, drug metabolism, and sepsis are discussed. This review provides a practical approach to problems specific to the ESRD patient and common problems on ICU that require special consideration in ESRD patients. ESRD patients are at risk of hyperkalaemia. I.V. insulin and nebulized salbutamol lower serum potassium until definitive treatment with RRT is instituted. ESRD patients are prone to hypocalcaemia, which requires i.v. replacement if associated with complications. Midazolam has delayed metabolism and elimination in renal impairment and should be avoided. Morphine and its derivatives accumulate in renal failure and shorter-acting opiates are preferable. The use of diuretics is limited to patients with residual urine output. When required, therapeutic systemic anticoagulation should be achieved with unfractionated heparin as it is reversible and its metabolism and clearance are independent of renal function. The risk of sepsis is higher among ESRD patients when compared with patients with normal renal function. Empiric treatment should include both Gram-positive and Gram-negative cover, and methicillin-resistant Staphylococcus aureus cover if the patient has a dialysis catheter. Cardiovascular events account for the majority of deaths among ESRD patients. Troponin-I and CK-MB in combination should be used as markers of acute myocardial damage in the appropriate context, whereas B-type natriuretic peptide and troponin-T values are of less value.

The impact of continuous renal replacement therapy on drug therapy

Critically ill patients with multisystem organ failure often require daily administration of large volumes of fluid to provide electrolyte and nutrition support, medications, and blood products. This often results in fluid overload, which has historically been managed with intermittent hemodialysis (IHD). Unfortunately, IHD entails a high rate of fluid and solute removal that often exacerbates hemodynamic instability. Accordingly, continuous renal replacement therapy (CRRT), involving slow and continuous removal of water and solutes from the plasma, is currently preferred for managing these patients.

Clinical review: Drug metabolism and nonrenal clearance in acute kidney injury

Decreased renal drug clearance is an obvious consequence of acute kidney injury (AKI). However, there is growing evidence to suggest that nonrenal drug clearance is also affected. Data derived from human and animal studies suggest that hepatic drug metabolism and transporter function are components of nonrenal clearance affected by AKI. Acute kidney injury may also impair the clearance of formed metabolites. The fact that AKI does not solely influence kidney function may have important implications for drug dosing, not only of renally eliminated drugs but also of those that are hepatically cleared. A review of the literature addressing the topic of drug metabolism and clearance alterations in AKI reveals that changes in nonrenal clearance are highly complicated and poorly studied, but they may be quite common. At present, our understanding of how AKI affects drug metabolism and nonrenal clearance is limited. However, based on the available evidence, clinicians should be cognizant that even hepatically eliminated drugs and formed drug metabolites may accumulate during AKI, and renal replacement therapy may affect nonrenal clearance as well as drug metabolite clearance.

Pharmacokinetics and clinical efficacy of midazolam in children with severe malaria and convulsions

AIM

To investigate the pharmacokinetics and clinical efficacy of intravenous (IV), intramuscular (IM) and buccal midazolam (MDZ) in children with severe falciparum malaria and convulsions.

METHODS

Thirty-three children with severe malaria and convulsions lasting ≥5 min were given a single dose of MDZ (0.3 mg kg⁻¹) IV (n = 13), IM (n = 12) or via the buccal route (n = 8). Blood samples were collected over 6 h post-dose for determination of plasma MDZ and 1′-hydroxymidazolam concentrations. Plasma concentration–time data were fitted using pharmacokinetic models.

RESULTS

Median (range) MDZ C_max of 481 (258–616), 253 (96–696) and 186 (64–394) ng ml⁻¹ were attained within a median (range) t_max of 10 (5–15), 15 (5–60) and 10 (5–40) min, following IV, IM and buccal administration, respectively. Mean (95% confidence interval) of the pharmacokinetic parameters were: AUC(0,∞) 596 (327, 865), 608 (353, 864) and 518 (294, 741) ng ml⁻¹ h; V_d 0.85 l kg⁻¹; clearance 14.4 ml min⁻¹ kg⁻¹, elimination half-life 1.22 (0.65, 1.8) h, respectively. A single dose of MDZ terminated convulsions in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration. Four children (one in the IV, one in the IM and two in the buccal groups) had respiratory depression.

CONCLUSIONS

Administration of MDZ at the currently recommended dose resulted in rapid achievement of therapeutic MDZ concentrations. Although IM and buccal administration of MDZ may be more practical in peripheral healthcare facilities, the efficacy appears to be poorer at the dose used, and a different dosage regimen might improve the efficacy.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Midazolam (MDZ), a water-soluble benzodiazepine, can be administered via several routes, including intravenously (IV), intramuscularly (IM) and buccal routes to terminate convulsions. It may be a suitable alternative to diazepam to stop convulsions in children with severe malaria, especially at peripheral healthcare facilities. The pharmacokinetics of MDZ have not been described in African children, in whom factors such as the aetiology and nutritional status may influence the pharmacokinetics.

WHAT THIS STUDY ADDS

Administration of MDZ (IV, IM, or buccal) at the currently recommended dose (0.3 mg kg⁻¹) resulted in rapid achievement of median maximum plasma concentrations of MDZ within the range 64–616 ng ml⁻¹, with few clinically significant cardio-respiratory effects. A single dose of MDZ rapidly terminated (within 10 min) seizures in all (100%), 9/12 (75%) and 5/8 (63%) children following IV, IM and buccal administration, respectively. Although IM and buccal MDZ may be the preferred treatment for children in the pre-hospital settings the efficacy appears to be poorer.

Clinical Pharmacokinetic Monitoring of Midazolam in Critically Ill Patients

Midazolam is a commonly used sedative in critically ill, mechanically ventilated patients in intensive care unit (ICU) settings worldwide. We used a nine-step decision-making algorithm to determine whether therapeutic monitoring of midazolam in the ICU is warranted. Midazolam has a higher clearance and shorter half-life than other benzodiazepines, and prolonged sedation is achieved with continuous infusion. There appears to be very good correlation between plasma concentrations of both midazolam and its active metabolite, alpha1-hydroxymidazolam, and the degree of sedation. However, due to high interpatient variability, it is not possible to predict the level of sedation in any given individual based on plasma concentration of midazolam or its metabolites. Moreover, no simple and practical assay is available to quantitate midazolam plasma concentrations in the acute ICU setting. Many scales are available to assess the sedative effects of midazolam. Because the plasma concentration of midazolam required to achieve a constant level of sedation is highly variable, it is usually more prudent for the clinician to monitor for sedation with a validated clinical scale than by plasma concentrations alone. Various physiologic parameters, including age-related effects, compromised renal function, and liver dysfunction affect the pharmacokinetics of midazolam and alpha1-hydroxymidazolam. Although routine drug monitoring for all critically ill patients receiving midazolam is not recommended, this practice is likely beneficial in patients with neurologic damage in whom sedation cannot be assessed and in patients who have renal failure with a prolonged time to awakening.