Increases in metabolism of valproate and excretion of 6beta-hydroxycortisol in patients with traumatic brain injury

Steady-state pharmacokinetic simulation of intermittent vs. continuous infusion valproic acid therapy in non-critically ill and critically ill patients

OBJECTIVES

Valproic acid (VPA) is a broad-spectrum antiepileptic drug used for a variety of neurologic disorders. The relatively short half-life seen with intermittent intravenous bolus doing may lead to serum concentration variability. Continuous infusion VPA therapy is an approach to mitigate these effects. The objective of this study is to characterize the pharmacokinetics of continuous infusion of VPA in acutely ill patients and to determine dosing regimens that most frequently obtain goal steady-state serum concentrations.

METHODS

This is a retrospective pharmacokinetics study in adult patients receiving continuous infusion VPA per institutional protocol for seizure or status migrainosus. Pharmacokinetic parameters were reviewed for 234 patients (25 critically ill) and compared between the two groups (non-critically ill vs. critically ill). Intermittent and continuous infusion dosing strategies were modeled utilizing Monte Carlo simulations for both cohorts. Frequencies of serum concentration attainment were reported.

RESULTS

The percent target attainment for the non-critically ill group and critically ill group were 69.4 and 58.3% (p = 0.282) post-loading dose and 69.7 and 37.5% (p = 0.004) steady state, respectively. The volume of distribution was significantly different between the two groups (0.35 vs. 0.68 L/kg, p = < 0.0001). Highest frequency of target attainment (50-100 mcg/ml) occurred in the continuous infusion 2 mg/kg/h simulation for both critically ill (45.19%) and acutely ill (48.16%) groups.

DISCUSSION

Critically ill patients have an increased volume of distribution. Increasing the volume of distribution requires higher loading doses of VPA to obtain desired therapeutic concentrations. Continuous infusion VPA provides more consistent serum steady-state concentrations while mitigating pharmacokinetic variability.

Pharmacokinetics and Clinical Utility of Valproic Acid Administered via Continuous Infusion

INTRODUCTION

Valproic acid is a versatile antiepileptic drug that is often used in the acute care setting. Intravenous valproic acid lends itself well to a continuous infusion as it exhibits a relatively short half-life. We evaluated the pharmacokinetics and clinical efficacy of continuous infusion valproic acid in hospitalized patients with migraine and seizures.

METHODS

A retrospective cohort study was performed utilizing information from the medical records of patients receiving an intravenous continuous infusion of valproic acid. Patients were included if they were aged 1 month to 85 years and they received a continuous infusion of valproic acid. Therapeutic response, common adverse effects, and the pharmacokinetic profile of valproic acid were evaluated.

RESULTS

Continuous infusion valproic acid led to a concentration within the desired range (50-100 μg/ml) in 83.4% of patients, a rate that was higher in pediatric patients. The clinical response rate was also higher in pediatric patients with seizures or migraines and appeared to be better when the concentration was >75 μg/ml. Analysis of safety parameters suggests similar safety considerations to valproic acid when administered via intermittent infusion.

CONCLUSIONS

Continuous infusion valproic acid appears to be a safe, effective, and predictable manner by which to administer valproic acid to pediatric and adult patients admitted to the hospital.

Effect of Traumatic Brain Injury, Erythropoietin, and Anakinra on Hepatic Metabolizing Enzymes and Transporters in an Experimental Rat Model

In contrast to considerable data demonstrating a decrease in cytochrome P450 (CYP) activity in inflammation and infection, clinically, traumatic brain injury (TBI) results in an increase in CYP and UDP glucuronosyltransferase (UGT) activity. The objective of this study was to determine the effects of TBI alone and with treatment with erythropoietin (EPO) or anakinra on the gene expression of hepatic inflammatory proteins, drug-metabolizing enzymes, and transporters in a cortical contusion impact (CCI) injury model. Microarray-based transcriptional profiling was used to determine the effect on gene expression at 24 h, 72 h, and 7 days post-CCI. Plasma cytokine and liver protein concentrations of CYP2D4, CYP3A1, EPHX1, and UGT2B7 were determined. There was no effect of TBI, TBI + EPO, or TBI + anakinra on gene expression of the inflammatory factors shown to be associated with decreased expression of hepatic metabolic enzymes in models of infection and inflammation. IL-6 plasma concentrations were increased in TBI animals and decreased with EPO and anakinra treatment. There was no significant effect of TBI and/or anakinra on gene expression of enzymes or transporters known to be involved in drug disposition. TBI + EPO treatment decreased the gene expression of Cyp2d4 at 72 h with a corresponding decrease in CYP2D4 protein at 72 h and 7 days. CYP3A1 protein was decreased at 24 h. In conclusion, EPO treatment may result in a significant decrease in the metabolism of Cyp-metabolized drugs. In contrast to clinical TBI, there was not a significant effect of experimental TBI on CYP or UGT metabolic enzymes.

Effect of time, injury, age and ethanol on interpatient variability in valproic acid pharmacokinetics after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) results in an increase in hepatic metabolism. The increased metabolism is in significant contrast to a large body of in vitro and in vivo data demonstrating that activation of the host-defence response downregulates hepatic metabolism. Theoretically, this occurs because of activation of the pro-inflammatory cytokines tumour necrosis factor-alpha, interferon-gamma, interleukin (IL)-1 and IL-6. As part of a large double-blind, placebo-controlled clinical trial evaluating the use of valproic acid for prophylaxis of post-traumatic seizures, we obtained extensive valproic acid concentration-time data. Valproic acid is a hepatically metabolised, low extraction-ratio drug. Therefore, unbound clearance (CL(u)) is equal to intrinsic or metabolic clearance.

OBJECTIVE

The objective of this study was to evaluate the time-dependent effects of TBI on the pharmacokinetics of total and unbound valproic acid with the goal of identifying patient factors that may predict changes in total clearance (CL) and CL(u). In addition, by determining the factors that influence the magnitude and time course of induction of hepatic metabolism and understanding their interaction with the host-defence mediators, we can further our insight into the mechanism(s) responsible for the changes in CL and CL(u).

STUDY DESIGN

Valproic acid plasma concentration data were obtained from 158 TBI patients. Unbound valproic acid plasma concentrations were estimated using total valproic acid plasma and albumin concentrations following a Scatchard equation binding model previously developed in a subset of TBI patients. The effect of 13 patient factors on CL and CL(u) was evaluated initially in a univariate analysis. The significant factors were then included in a multiple linear regression analysis by use of step-wise selection and forward selection procedures.

RESULTS

CL and CL(u) were significantly increased after TBI in a time-dependent manner. The average increase was >75% by weeks 2 and 3 post-injury. The magnitude of the induction of CL was increased with decreased albumin concentrations, in addition to the presence of ethanol on admission, increased severity of head injury, tube feeding and total parenteral nutrition (TPN). The magnitude of induction of CL(u) was increased by older age, presence of ethanol on admission, increased severity of head injury, tube feeding, TPN, and if the patient had a post-injury neurosurgical procedure. The time to normalisation of CL(u) was significantly longer in patients with head injury plus other injuries compared with those with head injury alone.

CONCLUSIONS

As has been reported with other drugs, TBI results in a significant increase in the metabolism of valproic acid. The patient factors identified in this study that resulted in an increase in the magnitude and time course of the induction of CL(u) (ethanol, older age, presence of a neurosurgical procedure, severity of TBI and presence of multiple non-TBI injuries) have all been reported to cause a shift to the anti-inflammatory mediators IL-4 and IL-10. This suggests that the increase in hepatic metabolism after TBI may be due to the increased presence of anti-inflammatory mediators in contrast to the inhibition effect of the pro-inflammatory mediators in non-TBI inflammation and infection.

Agitation After Traumatic Brain Injury

Posttraumatic agitation is a challenging problem for acute and rehabilitation staff, persons with traumatic brain injury, and their families. Specific variables for evaluation and care remain elusive. Clinical trials have not yielded a strong foundation for evidence-based practice in this arena. This review seeks to evaluate the present literature (with a focus on the decade 1995-2005) and employ previous clinical experience to deliver a review of the topic. We will discuss definitions, pathophysiology, evaluation techniques, and treatment regimens. A recommended approach to the evaluation and treatment of the person with posttraumatic agitation will be presented. The authors hope that this review will spur discussion and assist in facilitating clinical care paradigms and research programs.

Cytochrome P-450 activity is differentially altered in severely injured patients

OBJECTIVE

To assess whether changes in cytochrome P-450 (CYP) activity of specific CYP enzymes occur in severely injured patients and to assess changes in CYP activity during recovery.

DESIGN

Prospective clinical study.

SETTING

University-affiliated, level I trauma center and trauma critical care unit.

PATIENTS

Twenty-three multiply injured patients admitted to a trauma critical care unit were compared with healthy volunteers.

INTERVENTIONS

CYP metabolizing activity was assessed using the probe drugs mephenytoin (CYP-2C19), chlorzoxazone (CYP-2E1), dapsone (multiple CYP enzymes), and flurbiprofen (CYP-2C9).

MEASUREMENTS AND MAIN RESULTS

Mephenytoin metabolism was profoundly suppressed after injury and increased during postinjury recovery, whereas chlorzoxazone metabolism was suppressed to a lesser degree. Measures of dapsone and flurbiprofen metabolism were elevated throughout the study. Chlorzoxazone and mephenytoin metabolism correlated with the multiple organ dysfunction score and with the multiple organ failure score.

CONCLUSIONS

CYP isoform activity is differentially altered by shock and trauma in injured patients. The metabolic activity of selected CYP isoforms may have potential for evaluating acute hepatic dysfunction in critically ill trauma patients.

Apparent autoinduction of valproate beta-oxidation in humans

AIMS

The study aimed to show whether autoinduction of valproate (VPA) along its beta-oxidation pathway occurred upon chronic dosing in humans.

METHODS

Twelve young volunteers without active illness took sodium valproate (NaVPA) 200 mg orally 12 hourly for 3 weeks. On days 7 and 21, serial blood samples and all urine passed over an interdosing interval from 08.00 to 20.00 h were collected for analysis of VPA and certain metabolites.

RESULTS

Plasma AUC(0,12 h) of VPA was significantly lower on day 21 than on day 7 (2.40 vs 2.84 micromol ml-1 h, 95% CI for the difference 0.13-0.81 micromol ml-1 h). Significant differences in plasma AUC(0,12 h) of the beta-oxidation metabolites E-2-en-VPA and 3-oxo-VPA were not found. However, formation clearances of plasma VPA to urinary E-2-en-VPA and 3-oxo-VPA were significantly increased from day 7 to day 21 (0. 010 vs 0.024 and 2.57 vs 3.60 ml kg-1 h-1, respectively, 95% CI for the differences -0.025 to -0.004 and -1.72 to -0.34 ml kg-1 h-1, respectively). Formation clearances to VPA-glucuronide (0.534 vs 0. 505 ml kg-1 h-1) and 4-OH-VPA (0.112 vs 0.110 ml kg-1 h-1) were not significantly different.

CONCLUSIONS

Regular low dose VPA intake in humans over a period of 3 weeks appears to be associated with a small induction of its metabolism by the beta-oxidation pathway, but not by glucuronidation or 4-hydroxylation.