Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Development of an online solid-phase extraction-liquid chromatography-mass spectrometric analysis of oxcarbazepine and its active metabolite licarbazepine from plasma with a direct injection step

We developed an online solid phase extraction procedure using a hydrophilic-lipophilic balance sorbent, with reversed-phase liquid chromatography-high-resolution mass spectroscopy for the determination of oxcarbazepine and its active metabolite licarbazepine in plasma samples. The analytes were detected using a high-resolution Q Orbitrap mass spectrometer with targeted-selected ion monitoring (t-SIM) in positive scan mode. Under the optimized conditions, the method was linear with R² values >0.99. The method was linear from 0.008 to 2.000 μg mL^-1 and the lower limit of quantification was 0.008 μg mL^-1 for both oxcarbazepine and licarbazepine. Recoveries ranged from 92.34 to 104.27% and from matrix-matched samples from 94.26 to 104.19%. The intraday and interday precision RSD values were <9.13% with an associated accuracy of 92.71 to 104.06%. The total time for the one step online procedure was only 8 min. This method provides a direct and accurate measurement for therapeutic drug monitoring of oxcarbazepine and its active metabolite licarbazepine.

Pharmacist impact on adherence of valproic acid therapy in pediatric patients with epilepsy using active education techniques

There is limited information on the impact of active education by a pharmacist in the population of pediatric patients with epilepsy (PWE) in China. The objective of this study was to assess the effect of education by pharmacists on medication adherence and percentage of valproic acid (VPA) samples reaching therapeutic reference range in these patients. This study was conducted at two teaching hospitals in Changsha, China. Patients were retrospectively identified from January 2016 to December 2017. Active education by a pharmacist in both oral and written formats was provided at the intervention hospital whereas standard passive pharmacist service (dispensing and answering questions) was provided at the control hospital. Medication adherence was assessed by the simplified medication adherence questionnaire (SMAQ), and serum concentrations of VPA were collected. The correlation between pharmacist education and medication adherence and percentage of VPA samples reaching therapeutic reference range were analyzed. A total of 2165 patients and 4343 serum VPA concentrations were included in the analysis. For the first therapeutic drug monitoring (TDM) measurement, there was no statistical difference between the two hospitals: 41.3% of VPA samples reached therapeutic range at the intervention hospital compared with 45.4% at the control hospital (χ² = 3.686, P > 0.05). After pharmacist intervention at the intervention hospital, however, there were significant differences in the percentage of therapeutic VPA samples reaching therapeutic range between the first and the second, third, fourth, and fifth TDM measurements (χ² = 9.756, P < 0.01; χ² = 22.840, P < 0.01; χ² = 15.816, P < 0.01; χ² = 27.613, P < 0.01). Based on the SMAQ adherence assessment, adherence increased from a minimum of 56.0% to a maximum of 73.9% with stabilization during the last six months of follow-up at the intervention hospital. Both the medication adherence rate and the percentage of VPA samples reaching therapeutic range increased as the result of active education by a pharmacist, suggesting that continuous pharmacist intervention had a positive impact in outpatient pediatric PWE.

Changes in drug load during lacosamide combination therapy: A noninterventional, observational study in German and Austrian clinical practice

Introduction

Effects of antiepileptic drug (AED) load changes in patients with focal seizures have not been well evaluated.

Methods

SP1065 (NCT01673282) was a noninterventional, prospective, observational study conducted in a clinical practice setting. Patients (aged ≥18 years) with focal seizures were enrolled within 7 days of being prescribed adjunctive lacosamide. Observation period was ~6 months. Drug load was assessed using percentage change in ratio of actual prescribed dose and World Health Organization defined daily dose (DDD) for concomitant AEDs and all AEDs (including lacosamide). Subgroups were defined for patients with at least one concomitant sodium channel–blocking AED (SCB [+]) and those without (SCB [−]).

Results

A total of 311 patients were assessed for safety, 302 for measurement of drug load, and 240 for effectiveness. Ratio of AED dose to DDD decreased for concomitant AEDs (−9.6%) and increased for all AEDs (including lacosamide; 15.5%). Median reduction in focal seizure frequency per 28 days was 100% (range: −100, 2275.8). 70.4% and 61.7% of patients had a ≥50% or ≥75% reduction in seizure frequency, respectively; 50.8% became seizure‐free. In the SCB (+) subgroup (n = 149), ratio of AED dose to DDD decreased for concomitant AEDs (−15.0%) and increased for all AEDs (10.7%). In the SCB (−) subgroup (n = 153), ratio of AED dose to DDD decreased for concomitant AEDs (−4.4%) and increased for all AEDs (20.2%). Fifty‐seven patients (18.3%) reported ADRs, most commonly dose >400 mg/d (7.1%). Seventeen patients (5.5%) had ADRs leading to discontinuation.

Significance

Addition of lacosamide resulted in reduction of concomitant AED drug load regardless of whether concomitant AEDs were SCB (+) or SCB (−). These results indicate that addition of lacosamide in patients with focal seizures could allow clinicians to withdraw or reduce the dose of less well‐tolerated or less effective AEDs.

Nonlinear protein binding of phenytoin in clinical practice: Development and validation of a mechanistic prediction model

AIMS

To individualize treatment, phenytoin doses are adjusted based on free concentrations, either measured or calculated from total concentrations. As a mechanistic protein binding model may more accurately reflect the protein binding of phenytoin than the empirical Winter-Tozer equation that is routinely used for calculation of free concentrations, we aimed to develop and validate a mechanistic phenytoin protein binding model.

METHODS

Data were extracted from routine clinical practice. A mechanistic drug protein binding model was developed using nonlinear mixed effects modelling in a development dataset. The predictive performance of the mechanistic model was then compared with the performance of the Winter-Tozer equation in 5 external datasets.

RESULTS

We found that in the clinically relevant concentration range, phenytoin protein binding is not only affected by serum albumin concentrations and presence of severe renal dysfunction, but is also concentration dependent. Furthermore, the developed mechanistic model outperformed the Winter-Tozer equation in 4 out of 5 datasets in predicting free concentrations in various populations.

CONCLUSIONS

Clinicians should be aware that the free fraction changes when phenytoin exposure changes. A mechanistic binding model may facilitate prediction of free phenytoin concentrations from total concentrations, for example for dose individualization in the clinic.

An evaluation of clobazam tablets and film (AQST-120) for the treatment of Lennox-Gastaut syndrome

Introduction: Lennox-Gastaut syndrome (LGS) is a chronic, epileptic encephalopathy, characterized by multiple seizure types, distinctive slow spike-wave patterns in the electroencephalogram (EEG), and severe cognitive and behavioral comorbidities. Seizures are typically refractory and long-term prognosis is poor. No antiseizure drug (ASD) is fully effective as a monotherapy. Clobazam (CLB) was licensed in the United States in 2011 as an adjunctive therapy for seizures in LGS. In 2018, a new formulation, CLB oral soluble film (COSF) (AQST-120), was approved by the Federal Drug Administration (FDA) for the same indication. Areas covered: The authors summarize current pharmacological options and guidelines for the management of seizures in LGS and efficacy and safety findings from phase II and III randomized controlled trials of adjunctive CLB in patients with LGS. An open-label extension trial is also considered. A pharmacokinetic comparison of COSF and CLB tablets is also undertaken. Expert opinion: CLB is partly effective as an add-on therapy in treating seizures in LGS. Adverse effects, pharmacokinetic interactions and the potential for tolerance with long-term treatment should be weighed against the clinical benefit when considering the introduction of CLB in this population. COSF has a similar pharmacokinetic profile to CLB tablets and may help to improve adherence to treatment.

Pharmacotherapy for Focal Seizures in Children and Adolescents

Focal-onset seizures are among the most common forms of seizures in children and adolescents and can be caused by a wide diversity of acquired or genetic etiologies. Despite the increasing array of antiseizure drugs available, treatment of focal-onset seizures in this population remains problematic, with as many as one-third of children having seizures refractory to medications. This review discusses contemporary concepts in focal seizure classification and pathophysiology and describes the antiseizure medications most commonly chosen for this age group. As antiseizure drug efficacy is comparable in children and adults, here we focus on pharmacokinetic aspects, drug-drug interactions, and side effect profiles. Finally, we provide some suggestions for choosing the optimal medication for the appropriate patient.

Quantitation of Oxcarbazepine Clinically in Plasma Using Surfaced-Enhanced Raman Spectroscopy (SERS) Coupled with Chemometrics

Nondestructive, sensitive, near-real-time quantitative analysis approaches are gaining popularity and attention, especially in clinical diagnosis and detection. There is a need to propose an alternative scheme using surface-enhanced Raman spectroscopy (SERS) assisted by chemometrics to improve some defects existing using other analytical instruments to meet clinical demands. In this study, clinical drug oxcarbazepine (OXC) in human blood plasma has been quantified and detected using this method. Partial least squares regression (PLSR) modeling was employed to assess the relationship between full SERS spectral data and OXC concentration. The calibration set's correlation coefficient of the model is > 0.9, the result suggests that this method is favorable and feasible. Furthermore, other multivariate calibration algorithms like Monte Carlo cross-validation (MCCV) sample set partitioning based on joint XY distances (SPXY), adaptive iteratively reweighted penalized least squares (AIR-PLS), moving window partial least squares regression (MWPLS), and leave-one-out cross-validation were used to handle these spectral data to obtain an accurate predictive model. The results achieved in this study provide a possibility and availability for us to apply SERS in combination with chemometrics to diagnosis detection.

Remedial dosing recommendations for delayed or missed doses of lamotrigine in pediatric patients with epilepsy using Monte Carlo simulations

OBJECTIVE

This study investigated the effect of delayed or missed doses on the pharmacokinetics (PK) of lamotrigine (LTG) in children with epilepsy and established remedial dosing recommendations for nonadherent patients.

METHODS

The Monte Carlo simulation based on a published LTG population PK model was used to assess the effect of different scenarios of nonadherence and the subsequently administered remedial regimens. The following three remedial approaches were investigated for each delayed dose: A) A partial dose was administered immediately, and the regular dose was administered at the next scheduled time. B) The delayed dose was administered immediately, followed by a partial dose at the next scheduled time. C) The delayed and partial doses were coadministered immediately, the next scheduled dose was skipped, and the regular dosing was resumed at the subsequent scheduled time. The most appropriate remedial regimen was that with the shortest deviation time from the individual therapeutic window.

RESULTS

The effect of nonadherence on PK was dependent on the delay duration and daily dose, and the recommended remedial dose was related to the delay duration and concomitant antiepileptic drugs. Remedial dosing strategies A and B were almost equivalent, whereas C showed a larger PK deviation time. If one dose was missed, double doses were not recommended for the next scheduled time.

CONCLUSIONS

Simulations provide quantitative insight into the remedial regimens for nonadherent patients, and clinicians should select the optimal regimen based on the status of patients.

Valproic acid concentrations in nursing mothers, mature milk, and breastfed infants in monotherapy and combination therapy

Valproic acid (VPA) is currently one of the four most often prescribed antiepileptic drugs (AEDs) in pregnancy. However, only a small number of studies have measured suckling infant serum levels of the drug. We studied the transport of VPA from breastfeeding mothers to the mature milk and breastfed infants and the influence of comedication with enzyme-inducing AEDs. The data of 30 nursing women treated by VPA were analyzed retrospectively. Mature milk, maternal, and infant serum levels were collected between the 6th and 32nd postnatal day and measured by gas chromatography during the years 1996-2017. Valproic acid levels varied from 5.4 to 69.0 mg/L (mean: 39.0 ± 16.1 mg/L) in the maternal serum, from <1.0 to 16.7 mg/L (mean: 1.6 ± 3.9 mg/L) in the milk, and from <1.0 to 17.5 mg/L (mean: 4.2 ± 4.3 mg/L) in the infant serum. The milk/maternal serum level ratio ranged from <0.03 to 0.25 (mean: 0.03 ± 0.06) and the infant/maternal serum level ratio from <0.03 to 0.61 (mean: 0.11 ± 0.13). Sixty-seven percent of milk and 33% of infant VPA concentrations were below the limit of quantification. No correlations were observed between maternal serum and milk levels or between maternal and infant serum levels. In conclusion, none of the milk or infant serum VPA levels reached the lower limit of the reference range used for the general population with epilepsy, so the degree of VPA exposure in breastfed infants is less than during gestation. Nevertheless, if signs of potential adverse reactions manifest, infant serum concentrations should be measured.

Stability indicating spectrophotometric methods for quantitative determination of carbamazepine and its degradation product, iminostilbene, in pure form and pharmaceutical formulations

A stressed study on the stability and degradation behavior under ICH forced degradation conditions of most widely used antiepileptic drug; carbamazepine (CMZ) is presented in this work. The research also includes studying spectrophotometric nature of CMZ and assaying it with mostly used spectrophotometric techniques. Six simple and sensitive spectrophotometric methods are introduced as stability indicating methods for quantitative determination of CMZ and its degradation product, one of its reported potential impurities; iminostilbene (IMS). Dual wavelength is method I where two wavelengths (215 and 270 nm for CMZ and 258 and 307 nm for IMS) were chosen for each component while absorbance difference is zero for the second one. Method II is isoabsorptive point method where the absorbance of CMZ at A_{225 nm} was measured in the range of 0.5-20 μg mL^-1. Method III is second derivative method which allows simultaneous determination of CMZ at 247 nm and IMS at 273 nm without any interference. Method IV based on measuring the peak amplitude of first derivative of ratio spectra (¹DD) at 280.5 and 253 nm for determination of CMZ and IMS, respectively. Method V is mean centering of the ratio spectra with good linearity for CMZ and IMS over 200-330 nm. Ratio difference method is method VI where good linearity was achieved for determination of CMZ and IMS by measuring differences in the amplitude of ratio spectra at 285, 258 nm and 258, 285 nm, respectively. The proposed methods show successful application in CMZ's pharmaceutical formulations.

Therapeutic drug monitoring of gabapentin in various indications

OBJECTIVES

Gabapentin has been increasingly used in various indications in recent years. Despite variable pharmacokinetics, therapeutic drug monitoring (TDM) is scarcely described in other indications than epilepsy. The aim of the study was to investigate the use and pharmacokinetic variability of gabapentin in epilepsy and non-epilepsy indications and to further evaluate the use of TDM in patients with restless legs syndrome (RLS).

MATERIALS & METHODS

Population-based data from the Norwegian Prescription Database, retrospective TDM data from the section for Clinical Pharmacology, the National Center for Epilepsy, Norway, and prospective observational data on patients with RLS were used.

RESULTS

The use of gabapentin increased by 30% from 2014 to 2017 (32 181 to 42 675 users). TDM data from 120 patients showed a 22-fold pharmacokinetic variability in concentration/dose ratios, and this ratio was elevated in elderly patients (≥65 years). The majority of elderly used gabapentin for non-epilepsy indications. In patients with RLS, intake in the evening/night only was common due to nocturnal symptoms, in contrast to regular dosing regimens in epilepsy. Thus, drug fasting concentrations do not reflect concentrations at the time of required therapeutic effect. TDM was still found useful in most patients to support dosage increase or evaluate adverse effects.

CONCLUSION

Due to extensive pharmacokinetic variability, TDM can benefit patients using gabapentin. Challenges with applying TDM in new indications such as RLS include different dosage regimens and consequently different interpretation of serum concentrations. Thus, TDM should be requested on clear clinical grounds and the service tailored according to the therapeutic indication.

Antiepileptic Drugs in Children : Current Concept

An epileptic seizure is defined as the transient occurrence of signs and/or symptoms due to abnormally excessive or synchronous neuronal activity in the brain. The type of seizure is defined by the mode of onset and termination, clinical manifestation, and by the abnormal enhanced synchrony. If seizures recur, that state is defined as epilepsy. Antiepileptic drugs (AEDs) are the mainstay of treatment. Knowledge about initiating and maintaining adequate AEDs is beneficial for the clinician who treats children with epilepsy. This article will delineate the general principles for selecting, introducing, and discontinuing AEDs and outline guidelines for monitoring adverse effects. In general, AED therapy following a first unprovoked seizure in children is not recommended. However, treatment should be considered after a second seizure. In children and adolescents, if they are seizure-free for at least 2 years, attempts to withdraw medication/s should be made, taking into account the risks vs. benefits for the individual patient. The decision on when and what AED to use should be tailored according to the patient. For optimal treatment, the selection of adequate AEDs can be achieved by considering the precise definition of the patient’s seizure and epilepsy syndrome. Continuous monitoring of both therapeutic and adverse effects is critical for successful treatment with AEDs.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Epilepsy: A 2018 Update

BACKGROUND

Antiepileptic drugs (AEDs) are the mainstay of epilepsy treatment. Since 1989, 18 new AEDs have been licensed for clinical use and there are now 27 licensed AEDs in total for the treatment of patients with epilepsy. Furthermore, several AEDs are also used for the management of other medical conditions, for example, pain and bipolar disorder. This has led to an increasingly widespread application of therapeutic drug monitoring (TDM) of AEDs, making AEDs among the most common medications for which TDM is performed. The aim of this review is to provide an overview of the indications for AED TDM, to provide key information for each individual AED in terms of the drug's prescribing indications, key pharmacokinetic characteristics, associated drug-drug pharmacokinetic interactions, and the value and the intricacies of TDM for each AED. The concept of the reference range is discussed as well as practical issues such as choice of sample types (total versus free concentrations in blood versus saliva) and sample collection and processing.

METHODS

The present review is based on published articles and searches in PubMed and Google Scholar, last searched in March 2018, in addition to references from relevant articles.

RESULTS

In total, 171 relevant references were identified and used to prepare this review.

CONCLUSIONS

TDM provides a pragmatic approach to epilepsy care, in that bespoke dose adjustments are undertaken based on drug concentrations so as to optimize clinical outcome. For the older first-generation AEDs (carbamazepine, ethosuximide, phenobarbital, phenytoin, primidone, and valproic acid), much data have accumulated in this regard. However, this is occurring increasingly for the new AEDs (brivaracetam, eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, piracetam, pregabalin, rufinamide, stiripentol, sulthiame, tiagabine, topiramate, vigabatrin, and zonisamide).

Silymarin as a flavonoid-type P-glycoprotein inhibitor with impact on the pharmacokinetics of carbamazepine, oxcarbazepine and phenytoin in rats

P-glycoprotein (P-gp) is an efflux transporter involved in drug-resistant epilepsy and some flavonoids have been targeted as effective P-gp inhibitors. Herein, we assessed the impact of silymarin on the pharmacokinetics of three antiepileptic drugs (AEDs) in rats. Animals were pretreated with silymarin, verapamil (positive control) or vehicle (negative control) 1 h before AEDs administration (carbamazepine (25 mg/kg), oxcarbazepine (OXC) (50 mg/kg), or phenytoin (100 mg/kg)). Multiple blood samples were collected after AED dosing, and a non-compartmental analysis was performed. An independent study was also conducted to investigate the effects of silymarin on the OXC plasma-to-brain distribution. Silymarin altered the pharmacokinetics of OXC, increasing its peak plasma concentration by 50% and its extent of systemic exposure by 41%, which had also impact on brain drug concentrations. These findings support that the co-administration of silymarin and OXC should continue to be explored as a strategy to reverse the pharmacoresistance in epilepsy.

Influence of Inflammation on the Pharmacokinetics of Perampanel

BACKGROUND

It is well-known that the pharmacokinetics of various drugs are influenced by inflammation. This study evaluated the relationship between C-reactive protein (CRP; an inflammation marker) and the pharmacokinetics of perampanel.

METHODS

Among 111 patients who underwent measurement of both CRP and perampanel, 23 patients had a serum CRP level exceeding 1.5 mg/dL (CRP-positive). We compared the concentration/dose ratio (CD ratio) of perampanel in these 23 patients between the times when they were CRP-positive and CRP-negative. To evaluate the effect of CRP on the CD ratio, multiple regression analysis was performed with the following covariates: CRP-positive status, body weight, and use of phenytoin, carbamazepine, or phenobarbital, and combinations of these drugs.

RESULTS

In 10 patients using enzyme-inducing antiepileptic drugs (AEDs), the mean CD ratio increased by 53.5% [from 1389 to 2132 (ng/mL)/(mg/kg)] when they were CRP-positive. In 13 patients without enzyme-inducing AEDs, the mean CD ratio increased by 100.8% [from 3826 ng/mL to 7683 (ng/mL)/(mg/kg)] when they were CRP-positive. By multiple regression analysis, the CRP level was a significant independent determinant of the CD ratio of perampanel. Despite a marked increase of the CD ratio, no adverse events were reported.

CONCLUSIONS

Irrespective of concomitant administration of enzyme-inducing AEDs, the serum perampanel concentration showed a marked increase in patients with inflammation. However, this increase was not associated with central nervous system toxicity. Although it is unknown whether the concentration of free and/or bound perampanel was increased, it seems likely that dose reduction is unnecessary for elevation of the serum perampanel level in patients with inflammation.

Pharmacokinetic considerations for anti-epileptic drugs in children

Epilepsy is a chronic and debilitating neurological disease, with a peak of incidence in the first years of life. Today, the vast armamentarium of antiepileptic drugs (AEDs) available make even more challenging to select the most appropriate AED and establish the most effective dosing regimen. In fact, AEDs pharmacokinetics is under the influence of important age-related factors which cannot be ignored. Areas covered: Physiological changes occurring during development age (different body composition, immature metabolic patterns, reduced renal activity) can significantly modify the pharmacokinetic profile of AEDs (adsorption, volume of distribution, half-life, clearance), leading to an altered treatment response. We reviewed the main pharmacokinetic characteristics of AEDs used in children, focusing on age-related factors which are of relevance when treating this patient population. Expert opinion: To deal with this pharmacokinetic variability, physicians have at their disposal two tools: 1) therapeutic drug concentration monitoring, which may help to set the optimal therapeutic regimen for each patient and to monitor eventual fluctuation, and 2) the use of extended-release drug formulations, when available. In the next future, the development of 'ad-hoc' electronic dashboard systems will represent relevant decision-support tools making the AED therapy even more individualized and precise, especially in children.

Collaboration of Care for Women with Epilepsy in their Reproductive Years

Over half a million women of childbearing age have epilepsy, many of which will require family planning care at some point in their reproductive years. Matters relating to contraception, pregnancy, fertility, and sexual functioning are all impacted to varying degrees by the use of antiepileptic drugs (AEDs) to treat epilepsy and require active management by a woman's neurologist. It is important that a woman's obstetrician/gynecologist (OBGYN) and internist are aware of the way in which their care may be related to her epilepsy care and how this can be successfully comanaged with her neurologist. This includes the impact AED therapies have on pregnancy, such as risk of teratogenicity, changes to AED clearance rates during pregnancy and postpartum, and risk of seizure worsening while pregnant; interactions of hormonal contraceptives and AEDs; side effects of AED treatment on hormonal systems and sexual functioning; and matters of fertility and infertility treatments. The current editorial discusses these relationships between AED choice, dose, and family planning matters for women with epilepsy in their childbearing years to support the collaboration of care between her neurologist, OBGYN, and internist.

Single antiepileptic drug levels do not predict adherence and nonadherence

OBJECTIVES

To investigate the significance of "subtherapeutic" vs "therapeutic" antiepileptic drug (AED) plasma levels with respect to treatment adherence.

MATERIAL AND METHODS

One hundred and seventy patients with refractory temporal lobe epilepsy who underwent video-EEG monitoring in view of a surgical indication had their AEDs (carbamazepine, phenobarbital, phenytoin, and valproate) rapidly withdrawn following a standardized schedule. Plasma levels were measured at admission, and during the 2 days of drug withdrawal. Adherence and nonadherence were identified by the development of plasma levels from day 1 through day 3. Frequencies of an initial level below the reference range in both groups were compared.

RESULTS

Adherence was found in 73.2% of cases, and nonadherence in 26.8%. Low levels were seen equally often (about 1/4 of cases) in adherent and nonadherent cases. The vast majority (73.7%) of low levels had another explanation than nonadherence (eg low-dose treatment or enzyme induction). Of 42 nonadherent cases, the vast majority of 76.2% had unsuspicious plasma levels at admission.

CONCLUSIONS

"Subtherapeutic" AED plasma levels only rarely are caused by nonadherence whereas levels in the "therapeutic range" by no means prove that the patient is adherent to treatment. For meaningful interpretation, any level needs to be compared with other levels of the same patient. Our findings strongly emphasize the principle of individualized therapeutic AED monitoring as promoted by the Therapeutic Strategies Commission of the ILAE.

Integrated Microfluidic Devices Fabricated in Poly (Methyl Methacrylate) (PMMA) for On-site Therapeutic Drug Monitoring of Aminoglycosides in Whole Blood

On-site therapeutic drug monitoring (TDM) is important for providing a quick and accurate dosing to patients in order to improve efficacy and minimize toxicity. Aminoglycosides such as amikacin, gentamicin, and tobramycin are important antibiotics that have been commonly used to treat infections of chronic bacterial infections in the urinary tract, lung, and heart. However, these aminoglycosides can lead to vestibular and auditory dysfunction. Therefore, TDM of aminoglycosides is important due to their ototoxicity and nephrotoxicity. Here, we have developed a hot embossed poly (methyl methacrylate) (PMMA) microfluidic device featuring an electrokinetic size and mobility trap (SMT) to purify, concentrate, and separate the aminoglycoside antibiotic drugs amikacin, gentamicin, and tobramycin. These drugs were separated successfully from whole blood within 3 min, with 30-fold lower detection limits compared to a standard pinched injection. The limit of detections (LOD) were 3.75 µg/mL for gentamicin, 8.53 µg/mL for amikacin, and 6.00 µg/mL for tobramycin. These are sufficient to cover the therapeutic range for treating sepsis of 6⁻10 μg/mL gentamicin and tobramycin and 12⁻20 μg/mL of amikacin. The device is simple and could be mass produced via embossing or injection molding approaches.

Topiramate plus Cooling for Hypoxic-Ischemic Encephalopathy: A Randomized, Controlled, Multicenter, Double-Blinded Trial

BACKGROUND AND OBJECTIVES

Therapeutic interventions to improve the efficacy of whole-body cooling for hypoxic-ischemic encephalopathy (HIE) are desirable. Topiramate has been effective in reducing brain damage in experimental studies. However, in the clinical setting information is limited to a small number of feasibility trials. We launched a randomized controlled double-blinded topiramate/placebo multicenter trial with the primary objective being to reduce the antiepileptic activity in cooled neonates with HIE and assess if brain damage would be reduced as a consequence.

STUDY DESIGN

Neonates were randomly assigned to topiramate or placebo at the initiation of hypothermia. Topiramate was administered via a nasogastric tube. Brain electric activity was continuously monitored. Topiramate pharmacokinetics, energy-related and Krebs' cycle intermediates, and lipid peroxidation biomarkers were determined using liquid chromatography-mass spectrometry and MRI for assessing brain damage.

RESULTS

Out of 180 eligible patients 110 were randomized, 57 (51.8%) to topiramate and 53 (48.2%) to placebo. No differences in the perinatal or postnatal variables were found. The topiramate group exhibited less seizure burden in the first 24 h of hypothermia (topiramate, n = 14 [25.9%] vs. placebo, n = 22 [42%]); needed less additional medication, and had lower mortality (topiramate, n = 5 [9.2%] vs. placebo, n = 10 [19.2%]); however, these results did not achieve statistical significance. Topiramate achieved a therapeutic range in 37.5 and 75.5% of the patients at 24 and 48 h, respectively. A significant association between serum topiramate levels and seizure activity (p < 0.016) was established. No differences for oxidative stress, energy-related metabolites, or MRI were found.

CONCLUSIONS

Topiramate reduced seizures in patients achieving therapeutic levels in the first hours after treatment initiation; however, they represented only a part of the study population. Our results warrant further studies with higher loading and maintenance dosing of topiramate.

Closed-loop Neuropharmacology for Epilepsy: Distant Dream or Future Reality?

Epilepsy is considered the most frequent severe neurological condition but most patients treated with medication become seizure free. The management of treatment, however, is highly empirical, mainly relying on observation. A closed-loop therapy for epilepsy would be very valuable for more efficient treatment regimens. Here we discuss monitoring treatment (therapeutic drug monitoring) and the potential developments in this field, as well as providing a review of potential biomarkers that could be used to monitor the disease activity. Finally, we consider the pharmacogenetic input in epilepsy treatment.

Impact of Drug Interactions on Clobazam and N-Desmethylclobazam Concentrations in Pediatric Patients With Epilepsy

BACKGROUND

Clobazam (CLB) is approved as adjunctive treatment for seizures associated with Lennox-Gastaut syndrome in patients aged 2 years and older. It is converted to an active metabolite N-desmethylclobazam (NCLB) by CYP3A4, which is then broken down to an inactive metabolite by CYP2C19. This study characterizes the impact of CYP3A4 and CYP2C19 drug interactions on CLB and NCLB serum concentrations (Cp) and concentration/dose (Cp/D) ratios in pediatric patients with epilepsy.

METHODS

This was a retrospective chart review including patients older than 1 month, who received CLB between April 2012 and March 2017. Extracted data included patient demographics, CLB daily dose, CLB and NCLB Cp, calculated CLB and NCLB Cp/Cp and Cp/D ratios, and all concomitant drugs.

RESULTS

The study included 995 CLB concentration sets from 302 patients (median age 7.6 years and range 0.2-40.1 years). Pharmacokinetic variability was extensive, as seen by widespread ranges of CLB and NCLB Cp, NCLB/CLB Cp ratio, and 3 Cp/D ratios (CLB, NCLB, and CLB + NCLB). Comedications, described as CYP3A4 inducers and/or CYP2C19 inhibitors (carbamazepine, eslicarbazepine, felbamate, (fos)phenytoin, oxcarbazepine, pentobarbital, phenobarbital, rufinamide, and topiramate), generally increased NCLB/CLB Cp ratio (267%-400%), NCLB Cp/D ratio (167%-202%), and CLB + NCLB Cp/D ratio (142%-185%) and decreased CLB Cp/D ratio (47%-76%) compared with a group of concentration sets in patients receiving only neutral comedications (P < 0.025 for all comparisons). Older age was associated with higher Cp/D ratios (mg/kg), indicative of decreased clearance.

CONCLUSIONS

Pharmacokinetic variability of CLB in pediatric patients is extensive, and it is influenced by drug-drug interactions and age. Therapeutic drug monitoring of CLB and active metabolite NCLB with calculation of various Cp/Cp and Cp/D ratios can provide useful insight into CLB pharmacokinetics and help differentiate between causes of variability.

Efficacy, tolerability, and blood concentration of zonisamide in daily clinical practice

We aimed to evaluate the efficacy, tolerability, and blood concentration of zonisamide (ZNS) used in daily clinical practice. This was a retrospective study performed at a single epilepsy center and included 149 patients with epilepsy. The efficacy and retention of ZNS for 52 weeks, percentage of patients who were seizure free for 26 weeks, and the 5-year retention rate were analyzed. The tolerability was assessed based on treatment-emergent adverse effects (AEs) and the adverse effect profile (AEP). More than 70% (105/149) of patients were on ZNS polytherapy. The mean dose of ZNS was 300 ± 170.6 mg/day, and the antiepileptic drug (AED) load was 2.0 ± 1.1 (median 1.8, range 0.2-5.3). The retention rate for 52 weeks and the percentage of patients who were seizure-free for 26 weeks were 73% and 42%, respectively. The retention rate decreased with time and reached 43% in 5 years. Younger age of onset was a significant variable affecting retention rate for 52 weeks (p = 0.044), whereas fewer concomitant AEDs were significantly associated with being seizure free for 26 weeks (p = 0.0006). AEs were reported in 24% (36/147) of patients. The number, mechanism of action, or drug load of the AEDs did not predict the development of AEs; however, blood concentration of ZNS was significantly higher in patients with AEs (p = 0.0011) than in those without AEs. ZNS is a well-tolerated and effective AED in daily clinical practice, and several clinical factors may predict the efficacy and tolerability of ZNS.

Levetiracetam circulating concentrations and response in status epilepticus

INTRODUCTION

Intravenous levetiracetam (LEV) is broadly used in the treatment of status epilepticus (SE). A loading dose is usually infused, aiming to reach quickly the range of plasma concentrations considered as therapeutic (12-46 mg/l). The aim of the study was to evaluate the response to LEV in SE, correlated exposure assessed by plasma concentration monitoring, as well as calculated exposure parameters.

MATERIALS & METHODS

We retrospectively analyzed a SE registry, including patients since 2015 with at least one available LEV plasma level measured less than 36 h after loading. A Bayesian maximum likelihood approach based on a population pharmacokinetic model was used to estimate LEV exposure parameters. We compared plasma levels and pharmacokinetics parameter estimates between responders and nonresponders. Therapeutic response was defined as SE cessation within 24 h following LEV introduction without a need for additional antiepileptic drug (AED).

RESULTS

We included 29 patients (45 plasma levels). Variability was salient in LEV loading doses (ranging between 17 and 38 mg/kg) and monitoring practice. There was no difference in median plasma concentrations (19.5 versus 21.5 mg/l; p = 0.71), median estimated LEV exposure (25.8 versus 37.0 mg/l; p = 0.61), peak (30.4 versus 41.5 mg/l; p = 0.36), or residual levels after loading dose (14.4 versus 20.5 mg/l; p = 0.07) between responders and nonresponders.

CONCLUSIONS

Levetiracetam exposure does not seem to differ significantly between responders and nonresponders; greater exposure was not associated with better outcome. Loading doses of 30 mg/kg seem, however, appropriate to quickly reach the target exposure level. The short LEV half-life makes standardized sampling measurement necessary to obtain directly interpretable LEV levels.

Correlation between ABCB1 gene polymorphisms, antiepileptic drug concentrations and treatment response

Aim: A possible molecular mechanism of clinically defined multidrug-resistant epilepsy involves drug efflux transporters such as P glycoprotein (P-gp), a member of the ATP-binding cassette subfamily B1 (ABCB1). We have investigated the prevalence of the C3435T, G 2677T/A, and T129C single-nucleotide polymorphisms in the promoter region of MDR1 gene, in Romanian epileptic patients.

Methods: 70 epileptic patients evaluated in the Neurology Department of Cluj County Hospital were included in the study. The response to treatment was assessed by reviewing the seizure diaries and the patients were classified as responders or non-responders. Antiepileptic drug (AED) plasmatic concentrations were measured and the patients were divided into 2 groups: first group with AED concentrations in therapeutic range and the second one with sub-optimal AED concentrations. Genotyping the DNA samples, we investigated MDR1 gene polymorphism by polymerase chain reaction (PCR). Results were expressed as genotype and allele frequencies per response group and compared between subgroups.

Results: 33 patients (47.14%) were classified as responders, while the remaining 37 patients (52.86%) were classified as non-responders. A comparison of responders and non-responders revealed no significant difference in genotype frequency for any of the three mutations studied. The CT heterozygote for ABCB1 T129C had significantly lower AED concentrations (p=0.041), with no significant difference for the other polymorphisms studied.

Conclusions: In our study we found an association of CT variant in ABCB1 C129T with lower AED plasmatic concentrations and no association between ABCB1 variants and the drug responsiveness.

Therapeutic drug monitoring of levetiracetam in daily clinical practice: high-performance liquid chromatography versus immunoassay

Objectives

Although levetiracetam presents an easy dosing and tolerability, therapeutic drug monitoring may be recommended in certain situations. Measurement of levetiracetam in serum plasma is commonly done by high performance liquid chromatography (HPLC). After ARK Diagnostics marketed an enzyme immunoassay (IA) for levetiracetam in serum or plasma, automated determinations are possible. In this study, the performance of this immunoassay and the impact of automation on the follow-up in patients treated with levetiracetam is evaluated. We also detected those subpopulations of patients who may benefit the most from this therapeutic drug monitoring.

Methods

Samples from 50 outpatients diagnosed with epilepsy and treated with levetiracetam were collected. This new IA was performed on the Architect c4000 analyser and compared with the HPLC. Then, a retrospective observational study that included serum samples of levetiracetam for 24 months, was conducted to evaluate the impact of automattion and the influence of some variables (age, sex, renal function, and co-administration of valproic acid and glucuronidation-inducing drugs) in levetiracetam apparent oral clearance (CLp/F) by a multivariate linear regression.

Results

The mean high-performance liquid chromatography quantified concentration (CpHPLC) was 18.43 mcg/mL (95% CI: 15.48 to 21.39) and immunoassay concentration (CpEI) was 18.35 mcg/mL (95% CI: 15.20 to 21.50) (P=0.861). The Pearson's linear correlation coefficient obtained in the analysis was r²=0.88, according to the following equation: CpHPLC=-0.29+1.01 CpEI. The intraclass correlation coefficient was 0.95 (95% CI: 0.91 to 0.97). After IA implementation, the number of levetiracetam determinations increased in 76.27%. The median of Clp/F was higher (P<0.001) in inducers (4.36 L/h; IQR:3.29-5.44) and lower (P<0.001) in glomerular filtration rate (GFR) <60 mL/min (2.7 L/h; IQR: 0.58-3.85).

Conclusions

The Ark method performed on the Architect is fully acceptable and can be used routinely to measure levetiracetam plasmatic concentration levels. It has demonstrated the need for closer monitoring in patients with renal failure or co-administration of glucuronidation-inducing drugs.

The effect of serum levetiracetam concentrations on therapeutic response and IL1-beta concentration in patients with epilepsy

OBJECTIVE

Assessment of the relevance between serum drug concentration to its therapeutic response is a valid monitoring strategy for the clinical efficacy of antiepileptic drugs (AEDs). Levetiracetam (LEV) is a broad spectrum AED with a possible anti-inflammatory effect. We aimed to determine the relationship between LEV concentrations and its therapeutic response, and the effect of LEV on IL1-beta concentrations in patients with epilepsy.

METHODS

Patients on monotherapy (n = 7) or polytherapy (n = 15) with LEV for their seizures management were included. Blood samples of each patient were collected: just before LEV intake, 1 h, 2 h, 4 h and 8 h following the last dose. Serum LEV concentrations were measured by liquid chromatography mass spectrometry and IL1-beta concentrations by chemiluminescent immunometric assay. Concentration to dose (C/D) ratio values was used for analyses. LEV concentrations were compared between responders (≤1 seizure/month) and non-responders (>1 seizure/month) and patients with or without adverse reactions. IL1-beta concentrations before and at 2 h following LEV ingestion were compared in order to detect the effect of the increase in serum LEV concentration on IL1-beta.

RESULTS

Although there was no change in LEV (C/D) ratio or LEV maximum concentration (Cmax)/D ratio of the responders and non-responders, the C/D ratio following 1 h of LEV intake (2.17 ± 0.59 kg.day/L) and Cmax/D ratio (2.25 ± 0.56 kg.day/L) in the patients with adverse effects was significantly higher than for the patients without adverse effects (1.09 ± 0.12 kg.day/L and 1.49 ± 0.14 kg.day/L respectively). A statistically significant decrease was found in the IL1-beta concentration to LEV (C/D) ratio with the increase in LEV concentration in patients on LEV monotherapy.

CONCLUSION

The possible relationship between LEV Cmax and its therapeutic response or IL1-beta concentrations may be an importance indication of LEV antiepileptic efficacy. Consequently, monitoring LEV Cmax values may enhance LEV adherence because patients would be less likely to develop adverse effects.

Pharmacogenetics-based population pharmacokinetic analysis of gabapentin in patients with chronic pain: Effect of OCT2 and OCTN1 gene polymorphisms

Gabapentin (GAB) is eliminated unchanged in urine, and organic cation transporters (OCT2 and OCTN1) have been shown to play a role in GAB renal excretion. This prospective clinical study aimed to evaluate the genetic polymorphisms effect on GAB pharmacokinetic (PK) variability using a population pharmacokinetic approach. Data were collected from 53 patients with chronic pain receiving multiple doses of GAB. Patients were genotyped for SLC22A2 c.808G>T and SLC22A4 c.1507C>T polymorphisms. Both polymorphisms' distribution followed the Hardy-Weinberg equilibrium. An one-compartment model with first-order absorption and linear elimination best described the data. The absorption rate constant, volume of distribution, and clearance estimated were 0.44 h^-1 , 86 L, and 17.3 × (estimated glomerular filtration ratio/89.58)^1.04  L/h, respectively. The genetic polymorphism SLC22A4 c.1507C>T did not have a significant influence on GAB absorption, distribution or elimination. Due to the low minor allelic frequency of SLC22A2 c.808G>T, further studies require higher number of participants to confirm its effect on GAB renal elimination. In conclusion, GAB clinical pharmacokinetics are strongly influenced by renal function and absorption process, but not by the OCTN1 (SLC22A4 c.1507C>T) polymorphism.

Quality, origins and limitations of common therapeutic drug reference intervals

Therapeutic drug monitoring (TDM) is used to manage drugs with a narrow window between effective and toxic concentrations. TDM involves measuring blood concentrations of drugs to ensure effective therapy, avoid toxicity and monitor compliance. Common drugs for which TDM is used include aminoglycosides for infections, anticonvulsants to treat seizures, immunosuppressants for transplant patients and cardiac glycosides to regulate cardiac output and heart rate. An essential element of TDM is the provision of accurate and clinically relevant reference intervals. Unlike most laboratory reference intervals, which are derived from a healthy population, TDM reference intervals need to relate to clinical outcomes in the form of efficacy and toxicity. This makes TDM inherently more difficult to develop as healthy individuals are not on therapy, so there is no "normal value". In addition, many of the aforementioned drugs are old and much of the information regarding reference intervals is based on small trials using methods that have changed. Furthermore, individuals have different pharmacokinetics and drug responses, particularly in the context of combined therapies, which exacerbates the challenge of universal TDM targets. This focused review examines the origins and limitations of existing TDM reference intervals for common drugs, providing targets where possible based on available guidelines.

Effects of carbamazepine on the P-gp and CYP3A expression correlated with PXR or NF-κB activity in the bEnd.3 cells

Drug-resistant epilepsy (DRE) is present in 20-30% of all patients who develop epilepsy. Growing evidences demonstrated that glutamate released during seizures to increase the brain P-glycoprotein (P-gp) expression. Carbamazepine (CBZ) is known to influence the P-gp and cytochrome P450 (CYP) expression. However, the exact molecular mechanism is still unknown. We investigated that the effects of NF-κB and pregnane X receptor (PXR) activity on P-gp and CYP3A expression in mouse brain endothelial (bEnd.3) cells treated with l-glutamate (mimicking the seizure conditions), CBZ (mimicking the AED treating conditions) or both (l-glutamate plus CBZ) through qPCR and Western blotting assay. Mean fluorescence intensity was used to observe P-gp efflux function by analysis of intracellular Rhodamine123 (Rho123) accumulation. P-gp, CYP3A, PXR and NF-κB p65 were elevated in bEnd.3 cells incubated with l-glutamate, CBZ or CBZ pretreated by l-glutamate for 30 min. Both the mRNA and protein levels of P-gp and CYP3A were remarkably reduced by PXR or NF-κB p65 knock-down by siRNA transfections. The decreased intracellular accumulation of Rho123 suggested that the expression of P-gp was enhanced in bEnd.3 cells. These data suggested that overexpression of P-gp and CYP3A during seizures and treated with CBZ may be regulated by PXR or NF-κB p65 activity and expression, which revealed a mechanism underlying the development of DRE.

Pharmacokinetics and Drug Interaction of Antiepileptic Drugs in Children and Adolescents

Selecting the most appropriate antiepileptic drug (AED) or combination of drugs for each patient and identifying the most suitable therapeutic regimen for their needs is increasingly challenging, especially among pediatric populations. In fact, the pharmacokinetics of several drugs vary widely in children with epilepsy because of age-related factors, which can influence the absorption, distribution, metabolism, and elimination of the pharmacological agent. In addition, individual factors, such as seizure type, associated comorbidities, individual pharmacokinetics, and potential drug interactions, may contribute to large fluctuations in serum drug concentrations and, therefore, clinical response. Therapeutic drug concentration monitoring (TDM) is an essential tool to deal with this complexity, enabling the definition of individual therapeutic concentrations and adaptive control of dosing to minimize drug interactions and prevent loss of efficacy or toxicity. Moreover, pharmacokinetic/pharmacodynamic modelling integrated with dashboard systems have recently been tested in antiepileptic therapy, although more clinical trials are required to support their use in clinical practice. We review the mechanism of action, pharmacokinetics, drug-drug interactions, and safety/tolerability profiles of the main AEDs currently used in children and adolescents, paying particular regard to issues of relevance when treating this patient population. Indications for TDM are provided for each AED as useful support to the clinical management of pediatric patients with epilepsy by optimizing pharmacological therapy.

The critical interaction between valproate sodium and warfarin: case report and review

BACKGROUND

Valproic acid (VPA) and warfarin are commonly prescribed for patients with epilepsy and concomitant atrial fibrillation (AF). When VPA and warfarin are prescribed together, clinically important interactions may occur. VPA may replace warfarin from the protein binding sites and result in an abnormally increased anticoagulation effect. This is commonly underrecognized.

CASE PRESENTATION

In our case, we report a 78-year-old woman with a glioma who presented with status epilepticus. The patient was on warfarin to prevent cardiogenic embolism secondary to AF. Intravenous loading dose of VPA was administered, but international normalized ratio (INR) increased significantly to 8.26. Intravenous vitamin K1 was then given and the patient developed no overt bleeding during the hospitalization.

CONCLUSION

By reviewing the literature and discussing the critical interaction between valproate sodium and warfarin, we conclude that intravenous VPA and the co-administrated warfarin may develop critical but underrecognized complications due to effects on the function of hepatic enzymes and displacement of protein binding sites.