Clobazam therapeutic drug monitoring: a comprehensive review of the literature with proposals to improve future studies

Antiseizure medications for Lennox-Gastaut Syndrome: Comprehensive review and proposed consensus treatment algorithm

Lennox-Gastaut syndrome (LGS) is a severe, childhood-onset developmental and epileptic encephalopathy characterized by multiple drug-resistant seizure types, specific electroencephalogram (EEG) patterns, and significant cognitive and behavioral impairments. To date, eight anti-seizure medications (ASMs) have been specifically approved by the U.S. Food and Drug Administration (FDA) for the treatment of LGS: clonazepam, felbamate, lamotrigine, topiramate, rufinamide, clobazam, cannabidiol, and fenfluramine. Additionally, several other ASMs, including valproate, are frequently used off-label for LGS management. As the therapeutic landscape for LGS expands, clinicians are increasingly faced with complex decisions regarding optimal ASM selection. This narrative review explores evolving treatment strategies, offering a consensus-based treatment algorithm designed by a panel of U.S.- based experts. We analyze both FDA-approved and off-label ASMs, drawing on data from randomized controlled trials, open-label extensions, and real-world studies to assess each drug's efficacy and safety profile. A key challenge in comparing ASMs lies in the heterogeneity of study designs and outcome measures. This review addresses these limitations and considers crucial factors influencing ASM selection, such as seizure outcomes, safety profiles, cognitive and behavioral outcomes, drug-drug interactions, and rational polypharmacy. Barriers to access, including economic and regulatory hurdles, are also discussed. The proposed treatment algorithm emphasizes a personalized approach to LGS management, recommending valproate or clobazam as first-line treatments, followed by individualized combinations based on the specific patient profile and associated comorbidities.

Pharmacokinetic variability and use of therapeutic drug monitoring of cannabidiol in patients with refractory epilepsy

OBJECTIVE

Cannabidiol (CBD) (Epidyolex) is a new antiseizure medication (ASM) for rare and severe epileptic syndromes. We aimed to investigate the pharmacokinetic variability of CBD to elucidate relationships between doses, serum concentrations, metabolites, and biochemical markers of toxicity by using therapeutic drug monitoring (TDM) data.

METHODS

Data on serum concentrations of all ASMs, CBD, and the active metabolite 7-hydroxy-cannabidiol (7-OH-CBD) were collected (January 2022 to June 2023) at the Section for Clinical Pharmacology, National Centre for Epilepsy, Oslo University Hospital.

RESULTS

Data from 52 patients were included: 122 serum concentration measurements (1-7 per patient); 48% female, mean age 23 (range 3-55) years. At maintenance (n = 34), the mean daily dose was 535 (SD 224) mg, that is, 10.03 (standard deviation [SD] .49) mg/kg/day, serum concentration .26 (SD .14) for CBD and .13 (SD .10) μmol/L for 7-OH-CBD. Reference ranges of .15-.50 μmol/L for CBD and .04-.25 μmol/L for 7-OH-CBD are proposed, which included 80% of measurements. There was a linear correlation between CBD dose to concentration and CBD to CBD-7-OH concentrations (r2 = .39 and .38) (p < .05). The hepatic marker alanine aminotransferase (ALT) increased on average 37%, demonstrating a moderate effect on liver function. Intra-individual coefficients of variation (CVs) were 32% (SD 17) for CBD and 48% (SD 24) for 7-OH-CBD (n = 15, ≥3 measurements). Twenty different ASMs were used: clobazam (n = 24), valproate (n = 17), and stiripentol (n = 8) were most common. The mean concentration ratio of desmethyl-clobazam/clobazam increased by 140% (7.29-17.5; p < .05) but was variable, pointing to enzyme inhibition by CBD.

SIGNIFICANCE

This observational study with TDM data revealed extensive pharmacokinetic variability of CBD in patients with refractory epilepsy. The results demonstrate the need for close follow-up and use of TDM, including biochemical markers of toxicity, for individualized treatment with CBD.

Comparison of various doses of oral cannabidiol for treating refractory epilepsy indications: a network meta-analysis

Aim

To evaluate the comparative efficacy and safety of various doses of oral cannabidiol (CBD) in treating refractory epilepsy indications, thus providing more informative evidence for clinical decision-making.

Methods

A literature search of PubMed, Embase, the Cochrane library, and Web of Science (WoS) was performed to retrieve relevant randomized controlled trials (RCTs) that compared different doses of oral CBD with placebo or each other in refractory epilepsy indications. The search was limited from the inception of each database to January 3, 2023. Relative risk [RR] with a 95% confidence interval [CI] was used to express results. STATA/SE 14 was employed for network meta-analysis.

Results

Six RCTs involving 972 patients were included in the final data analysis. Network meta-analysis showed that, CBD10 (10 mg/kg/day) (RR: 1.77, 95%CI: 1.28 to 2.44), CBD20 (20 mg/kg/day) (RR: 1.91, 95%CI: 1.49 to 2.46), CBD25 (25 mg/kg/day) (RR: 1.61, 95%CI: 0.96 to 2.70), and CBD50 (50 mg/kg/day) (RR: 1.78, 95%CI: 1.07 to 2.94) were associated with higher antiseizure efficacy although the pooled result for CBD25 was only close to significant. In addition, in terms of the risk of treatment-emergent adverse events (TEAEs), the difference between different doses is not significant. However, CBD20 ranked first in terms of antiseizure efficacy, followed by CBD50, CBD10, and CBD25. For TEAEs, CBD25 ranked first, followed by CBD10, CBD50, CBD5, and CBD20.

Conclusion

For refractory indications, CBD20 may be optimal option for antiseizure efficacy; however, CBD25 may be best for TEAEs. Therefore, an appropriate dose of oral CBD should be selected based on the actual situation. Due to the limitations of eligible studies and the limited sample size, more studies are needed in the future to validate our findings.

Spanish consensus on the management of concomitant antiseizure medications when using cenobamate in adults with drug-resistant focal seizures

OBJECTIVE

Cenobamate is an antiseizure medication (ASM) associated with high rates of seizure freedom and acceptable tolerability in patients with focal seizures. To achieve the optimal cenobamate dose for maximal potential effectiveness while avoiding or minimizing drug-related adverse events (AEs), the administration of cenobamate with other ASMs must be managed through concomitant ASM load reduction. A panel of Spanish epilepsy experts aimed to provide a Spanish consensus on how to adjust the dose of concomitant ASMs in patients with drug-resistant epilepsy (DRE) in order to improve the effectiveness and tolerability of adjunctive cenobamate.

METHODS

A three-stage modified Delphi consensus process was undertaken, including six Spanish epileptologists with extensive experience using cenobamate. Based on current literature and their own expert opinion, the expert panel reached a consensus on when and how to adjust the dosage of concomitant ASMs during cenobamate titration.

RESULTS

The expert panel agreed that tailored titration and close follow-up are required to achieve the best efficacy and tolerability when initiating cenobamate in patients receiving concomitant ASMs. When concomitant clobazam, phenytoin, phenobarbital, and sodium channel blockers are taken at high dosages, or when the patient is receiving two or more sodium channel blockers, dosages should be proactively lowered during the cenobamate titration period. Other concomitant ASMs should be reduced only if the patient reports a moderate/severe AE at any stage of the titration period.

SIGNIFICANCE

Cenobamate is an effective ASM with a dose-dependent effect. To maximize effectiveness while maintaining the best tolerability profile, co-medication management is needed. The recommendations included herein provide practical guidance for proactive and reactive management of co-medication in cenobamate-treated patients with DRE and a high drug load.

PLAIN LANGUAGE SUMMARY

Patients with epilepsy may continue to have seizures even after treatment with several different antiseizure medications (ASMs). Cenobamate is an ASM that can reduce seizures in these patients. In this study, six Spanish experts in epilepsy discussed the best way to use cenobamate in drug-resistant epilepsy. They provide practical guidance on when and how the dose of other ASMs might be adjusted to reduce side effects and optimize the use of cenobamate.

Analysis of Factors Affecting Concentrations and Concentration-To-Dose Ratios of Trazodone

BACKGROUND

Trazodone is prescribed for several clinical conditions. Multiple factors may affect trazodone to reach its therapeutic reference range. The concentration-to-dose (C/D) ratio can be used to facilitate the therapeutic drug monitoring of trazodone. The study aimed to investigate factors on the concentrations and C/D ratio of trazodone.

METHODS

This study analyzed the therapeutic drug monitoring electronic case information of inpatients in the First Hospital of Hebei Medical University from October 2021 to July 2023. Factors that could affect the concentrations and C/D ratio of trazodone were analyzed, including body mass index, sex, age, smoking, drinking, drug manufacturers, and concomitant drugs.

RESULTS

A total of 255 patients were analyzed. The mean age was 52.44 years, and 142 (55.69%) were women. The mean dose of trazodone was 115.29 mg. The mean concentration of trazodone was 748.28 ng/mL, which was in the therapeutic reference range (700-1000 ng/mL). 50.20% of patients reached the reference range, and some patients (36.86%) had concentrations below the reference range. The mean C/D ratio of trazodone was 6.76 (ng/mL)/(mg/d). A significant positive correlation was found between daily dose and trazodone concentrations (r 2 = 0.2885, P < 0.001). Trazodone concentrations were significantly affected by dosage, sex, smoking, drinking, and concomitant drugs of duloxetine or fluoxetine. After dosage emendation, besides the above factors, it was influenced by age ( P < 0.05, P < 0.01, or P < 0.001).

CONCLUSIONS

This study identified factors affecting trazodone concentrations and C/D ratio. The results can help clinicians closely monitor patients on trazodone therapy and maintain concentrations within the reference range.

Pharmacokinetic Variability of Sulthiame: The Impact of Age, Drug-Drug Interactions, and Biochemical Markers of Toxicity in Patients with Epilepsy

PURPOSE

Sulthiame is an antiseizure medication increasingly used for epilepsy. The aim of this study was to investigate the pharmacokinetic variability of sulthiame in children and adults with epilepsy with respect to age, comedication, dose, serum concentration, and biochemical markers of toxicity in a clinical setting.

METHOD

Retrospective quantitative data from the therapeutic drug monitoring (TDM) database at the Section for Clinical Pharmacology, the National Center for Epilepsy, Norway (2015-2021), were used.

RESULTS

TDM data from 326 patients (127 female/199 male) were included [mean age, 11.4 (range 2-44) years; mean weight, 41 (range 14-109) kg]. Interindividual pharmacokinetic variability in the concentration/(dose/body weight) (C/(D/kg)) ratio was 16-fold; intraindividual variability was up to 8-fold (coefficient of variation = 10%-78%). Young children (younger than 6 years) had a significantly lower C/(D/kg) ratio than older age groups ( P < 0.05). Various comedications did not significantly affect the C/(D/kg) ratio, possibly owing to the small sample size. However, CYP2C19-mediated inhibition by sulthiame was indicated because patients using clobazam and sulthiame (n = 28) had a 3.5-fold higher N-desmethylclobazam C/(D/kg) ratio than those using neutral comedication (n = 45; P < 0.001). Patients with pH values below the adjusted normal range (7.32-7.42; n = 15) had a 33% higher sulthiame concentration than those with normal pH values (n = 22; P < 0.05). Blood gas measurements, especially pH, may serve as markers of toxicity and can be used in combination with clinical data when toxicity is suspected.

CONCLUSIONS

This study revealed the extensive intraindividual and interindividual pharmacokinetic variability of sulthiame, with age as a contributing factor. Sulthiame has clinically relevant interactions with clobazam. The use of TDM and pH as a biochemical marker may contribute to individualized and safe sulthiame treatment.

Pharmacokinetic correlates of clinical response in a naturalistic sample of escitalopram-treated patients

OBJECTIVE

We assessed pharmacokinetic correlates of treatment response to escitalopram using a large therapeutic drug monitoring database.

METHODS

A large naturalistic sample of patients receiving escitalopram was analyzed. Responders were defined as 'very much improved' or 'much improved' based on the Clinical Global Impression - Improvement score, CGI-I. We compared responders (n = 83) vs. non-responders (n = 388) with the primary outcome being the escitalopram plasma concentration and concentration corrected by the daily dose (C/D ratio). Effects of age, sex, body-mass-index (BMI), and C/D ratio were assessed in a multivariate logistic regression model predicting response.

RESULTS

There were no statistically significant differences in clinical and demographic characteristics between responders vs. non-responders. There were also no differences between escitalopram daily doses or plasma concentrations, while C/D ratios were significantly higher in non-responders than in responders (1.6 ± 1.7 vs. 1.2 ± 0.9 (ng/mL)/(mg/day), p = 0.007); C/D ratios (odds ratio 0.52, 95% confidence interval 0.34-0.80, p < 0.003) were associated with response to escitalopram, after controlling for age, sex, and BMI.

CONCLUSIONS

Patients with low clearance of escitalopram as reflected upon high C/D ratios may be less likely respond to escitalopram. Identifying these patients during dose titration may support clinical decision-making, including switching to a different antidepressant instead of increasing daily dose.

Elevations in Norclobazam Concentrations and Altered Mental Status in CYP2C19 Poor Metabolizer Phenotype: A Case Report

Clobazam is a 1,5-benzodiazepine frequently used as an adjunctive agent for refractory seizures and status epilepticus. Clobazam undergoes metabolism to an active metabolite norclobazam which is subsequently hydroxylated by CYP2C19, a cytochrome with several pharmacogenetic variants. Patients with poor metabolizer phenotypes may have elevated norclobazam levels and subsequent adverse effects. We present a case of an Asian American male receiving clobazam at a standard therapeutic dose for seizure disorder who became comatose secondary to significantly elevated norclobazam concentrations. Genetic testing revealed the patient was a poor CYP2C19 metabolizer, accounting for the impaired clearance. Clinicians should be aware of the patient populations at risk for these genetic polymorphisms and adjust initial doses based on package labeling or consider therapeutic drug monitoring to avoid adverse effects.

Study on the daily dose and serum concentration of clozapine in psychiatric patients and possible influencing factors of serum concentration

BACKGROUND

Clozapine is the most effective drug for treatment-resistant schizophrenia, and the dosage and concentration of clozapine in the treatment of mental illness vary greatly in different populations and are affected by many factors.

METHODS

The serum clozapine concentration of 3734 psychiatric patients was detected, and data on daily dose, sex, age and other medical records were collected for statistical analysis.

RESULTS

The mean daily dose, mean serum concentration and mean C/D (concentration/dose) ratio of clozapine were 191.02 ± 113.47 mg/day, 326.15 ± 235.66 ng/mL and 1.94 ± 1.25 ng/mL per mg/day, respectively. There was difference in daily dose between sexes, and females had higher daily dose (p <0.01), higher serum clozapine concentrations (p < 0.01) and higher C/D ratios (p < 0.01). There were significant differences in daily dose (p < 0.001), serum drug concentration (p < 0.001) and C/D ratio (p < 0.001) among different age groups. The daily dose decreased with age (p for trend < 0.001), and the C/D ratio increased with age (p for trend < 0.001). Inpatients and outpatients had no difference in daily dose, but inpatients had higher serum concentration (p < 0.001) and C/D ratio (p < 0.001). There was no difference in daily dose among different occupations, but there were significant differences in serum concentration (p < 0.001) and C/D ratio (p < 0.001), and unemployed patients may have higher serum concentration and C/D ratio. Duration of disease, comorbidity, marital status, and psychotic type may influence the daily dose and serum concentration.

CONCLUSIONS

The effective daily dose and serum concentration of clozapine in the study area may be lower than recommended levels, and women have higher serum concentrations and slower metabolic rates. With increasing age, the daily dose decreases, and the metabolic rate slows. Inpatient status and occupation of patients may influence the serum concentration and metabolic rate of clozapine.

The effect of anti-seizure medications on lipid values in adults with epilepsy

PURPOSE

Certain anti-seizure medications (ASMs) adversely impact lipid values. Here, we explored the impact of ASMs on lipid values in adults with epilepsy.

METHODS

A total of 228 adults with epilepsy were divided into four groups based on ASMs used: strong EIASMs, weak EIASMs, non-EIASMs, and no ASMs. Demographic information, epilepsy-specific clinical history, and lipid values were obtained through chart review.

RESULTS

While there was no significant difference in lipid values between groups, there was a significant difference in the proportion of participants with dyslipidemia. Specifically, more participants exhibited elevated low-density lipoprotein (LDL) level in the strong EIASM group compared to the non-EIASM group (46.7% vs 18%, p < 0.05). In addition, more participants showed elevated LDL level in the weak EIASM group compared to the non-EIASM group (38% vs 18%, p < 0.05). Users of strong EIASMs showed greater odds of high LDL level (OR 5.734, p = 0.005) and high total cholesterol level (OR 4.913, p = 0.008) compared to users of non-EIASMs. When we analyzed the impact of individual ASMs used by more than 15% of the cohort on lipid levels, participants using valproic acid (VPA) showed lower high-density lipoprotein (p = 0.002) and higher triglyceride levels (p = 0.002) compared to participants not using VPA.

CONCLUSION

Our study demonstrated a difference in the proportion of participants with dyslipidemia between ASM groups. Thus, adults with epilepsy using EIASMs should have careful monitoring of lipid values to address the risk of cardiovascular disease.

Clinical efficacy and safety of cannabidiol for pediatric refractory epilepsy indications: A systematic review and meta-analysis

Antiseizure medications (ASMs) are the mainstay for the treatment of seizure disorders. However, about one-third of people with epilepsy remain refractory to current ASMs. Cannabidiol (CBD) has recently been approved as ASM for three refractory epilepsy syndrome indications in children and adults. In this study, we evaluated the overall clinical potential of an oral CBD to treat refractory epilepsy in patients with Dravet syndrome (DS), Lennox-Gastaut syndrome (LGS), and tuberous sclerosis complex (TSC) through a systematic review and meta-analysis. A comprehensive search of databases was conducted, including randomized controlled trials (RCTs) assessing the effect of CBD in epilepsy patients. The review was conducted as per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The review focused on RCTs involving patients receiving highly purified oral CBD (Epidiolex, 10 to 50 mg/kg/day) for up to 16 weeks. A subgroup analysis by syndrome and CBD with or without concomitant clobazam was conducted. The key outcomes were reduction in seizure frequency, differences in 50% responder rates, adverse events, and interactions with clobazam as co-therapy. Odds ratio (OR) with 95% confidence interval (CI) were estimated. Of 1183 articles screened, we included 6 RCTs meeting our eligibility criteria. All studies were considered to have a low risk of bias. In the pooled analysis, CBD treatment was found to be more efficacious compared to placebo (OR = 2.45, 95% CI =1.81-3.32, p < 0.01). Subgroup analysis by syndrome demonstrated the odds of ≥50% reduction in seizures with CBD treatment in patients with DS (OR = 2.26, 95% CI:1.38-3.70), LGS (OR = 2.98, 95% CI:1.83-4.85) and TSC (OR = 1.99, 95% CI = 1.06-3.76). Compared with placebo, CBD was associated with increased adverse events (OR = 1.81, 95% CI = 1.33-2.46) such as diarrhea, somnolence, and sedation, and any serious adverse events (OR = 2.86, 95% CI = 1.63-5.05). Other factors, including dosage and clobazam co-therapy, were significantly associated with a greater effect on seizure control and side effects of CBD. In conclusion, the study shows that CBD is highly efficacious both as standalone and adjunct therapy with clobazam for controlling seizures in DS, LGS, and TSC conditions while limiting side effects. Further pharmacodynamic investigation of CBD actions, drug interaction assessments, and therapeutic management guidelines are warranted.

Dose-Related Reference Range as a Tool in Therapeutic Drug Monitoring

BACKGROUND

Therapeutic drug monitoring (TDM) aims to individualize drug therapy. This systematic review provides a state-of-the-art overview of the benefits of adding the dose-related reference range (DRR) as a second reference range to the set of tools used by TDM for measurement and evaluation. It discusses alternative pharmacokinetic approaches for individualization of drug therapy.

METHODS

Literature was searched in PubMed. Textbooks provided Bateman transformations for calculating expected drug concentrations at various times after drug application in "normal patients," that is, the population of phase II clinical trials. The review compiles conditions and prerequisites for these transformations to be valid.

RESULTS

Relating a measured drug concentration to the orienting therapeutic reference range provides pharmacodynamic information for improving the benefit-to-risk ratio of desired drug effects versus adverse drug effects. The discriminating DRR considers a patient's individual pharmacokinetic situation. DRR is statistically based on the pharmacokinetic parameters total clearance, time to reach maximal concentrations, and elimination half-life. Relating the measured drug concentration to a range rather than a particular value, DRR determines if individual patients do or do not belong to the population of "normal patients." Once a patient is identified to be outside the population of "normal patients," the clinical-pharmacological TDM report elaborates the cause. It consists of the measured value, the TDM 9-field-board, the elimination pathways table, and a medication recommendation taking into account clinical information. The internet-based platform KONBEST supports editing of the clinical-pharmacological TDM report. It is personally signed and send to the therapist.

CONCLUSIONS

The DRR embedded into a clinical-pharmacological TDM report allows adjusting a patient's medication to the patient's individual needs (individualization of drug therapy).

Retrospective analysis of metabolite patterns of clobazam and N-desmethylclobazam in human plasma by LC-MS/MS

Introduction

Clobazam is a benzodiazepine drug, used to treat Lennox-Gastaut syndrome in patients aged 2 years and older.

Objective

To support patient care, our laboratory developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the quantification of clobazam (CLB) and its major active metabolite N-desmethylclobazam (N-CLB) in human plasma or serum samples.

Methods

The chromatographic separation was achieved with an Agilent Zorbax Eclipse Plus C-18 RRHD column with mobile phase consisting of 0.05% formic acid in 5 mM ammonium formate, pH 3.0 and 0.1% formic acid in acetonitrile at a flow rate of 600 µL/minute and an injection volume of 5 µL. The detection was performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode to monitor precursor-to-product ion transitions in positive electrospray ionization mode.

Results

The method was validated over a concentration range of 20-2000 ng/mL for CLB and 200-10,000 ng/mL for N-CLB. The lower limit of quantification was 20 ng/mL for CLB and 200 ng/mL for N-CLB with good accuracy and precision. The method performance was successfully evaluated by comparison with two different external laboratories. Retrospective data analysis was performed to evaluate the positivity rate and metabolic patterns for clobazam from our patient population, as a reference laboratory. Among the positive samples, both parent and metabolite were detected in 96.4% of the samples.

Conclusion

The method was developed to support therapeutic drug monitoring and the data generated from retrospective analysis could be useful for result interpretation in conjunction with clinical patient information.

Cenobamate for treatment-resistant focal seizures: current evidence and place in therapy

Background

Cenobamate is newly approved for partial-onset seizures in adults, albeit the mechanism of its action remain poorly understood.

Methods

 This article aims to review the efficacy, safety, and tolerability of cenobamate in treating partial-onset seizures.

Data Collection:

The English language articles were searched in the National Institute of Health clinical trials registry, PubMed, and the Cochrane library between 2010 and June 2021 using the keywords cenobamate, YKP 3089, and seizure, and filter “trial” was applied.

Results:

A total of 31 articles were retrieved. Eventually, two randomized, double-blind, multicenter clinical trials involving 659 patients were analyzed. Cenobamate has shown significant reduction in seizure frequency compared to placebo. In cenobamate group, a greater number of participants showed ≥50% reduction in seizure frequency, adverse effects, and drug discontinuation compared to placebo. Multiple drug-drug interactions with other anti-seizure drugs were also observed.

Conclusions

Based on the findings of these trials, cenobamate seems to be an attractive option for treatment-resistant partial-onset seizures; however, multiple treatment-related adverse effects and drug-drug interactions are the areas of concern.

Is Cenobamate the Breakthrough We Have Been Wishing for?

Close to one-third of patients with epilepsies are refractory to current anti-seizure medications; however, trials with cenobamate suggest effectiveness in such patients with focal onset seizures. We searched for data published or otherwise reported on cenobamate and outlined these here. Despite being marketed in the USA, few studies are yet published in full, and trials are ongoing. Nevertheless, cenobamate showed potential for a high degree of efficacy in reducing seizures with an unprecedented seizure-free rate of up to 28%. Rare cases of hypersensitivity reactions seen in early trials seem to be avoided by the current recommended titration schedule. Other adverse events were rated mild-to-moderate and most commonly included dizziness, drowsiness, and headache. If data are confirmed in further published trials, cenobamate will be a welcome new treatment and further analyses may identify those that will benefit the most.

Determination of Clobazam and Its Major Metabolite N-desmethylclobazam in Human Plasma with High-Performance Liquid Chromatography

Clobazam (CLB) is a benzodiazepine that is used in many types of epilepsy. Although therapeutic drug monitoring (TDM) of CLB is not routine, there is evidence that TDM may be of value in conditions where pharmacokinetic alterations are suspected. Therefore, determination of both CLB and its active metabolite concentrations is essential for TDM. Herein, we present a simple and practical method for determination of CLB and N-desmethylclobazam (NDMCLB) in human plasma by high-performance liquid chromatography (HPLC). The drugs were extracted by hexane:dichloromethane (1:1, v/v) from 0.3 mL plasma. The separation was carried out with a C18 reverse phase column using a mobile phase of water:acetonitrile (57:43, v/v) pumped at 0.8 mL/min. The analytes were detected at 228 nm. The method was linear over the concentration range 20–500 ng/mL for CLB and 200–3000 ng/mL for NDMCLB. The intra-day coefficient of variation (CV) was <10% for CLB and <6% for NDMCLB, while the inter-day CV for CLB was <16%. The metabolite inter-day CV was <6%. The accuracy of intra- and inter-day assessments determined for CLB and NDMCLB was within ±10%. This paper describes a rapid, reliable, and simple method for measuring CLB and its metabolite NDMCLB in human plasma. This UV-HPLC procedure offers acceptable precision and accuracy to quantify CLB and its metabolite in human plasma.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Women with Epilepsy Before, During, and After Pregnancy

During pregnancy, the pharmacokinetics of an antiepileptic drug is altered because of changes in the clearance capacity and volume of distribution. These changes may have consequences for the frequency of seizures during pregnancy and fetal exposure to antiepileptic drugs. In 2009, a review was published providing guidance for the dosing and therapeutic drug monitoring of antiepileptic drugs during pregnancy. Since that review, new drugs have been licensed and new information about existing drugs has been published. With this review, we aim to provide an updated narrative overview of changes in the pharmacokinetics of antiepileptic drugs in women during pregnancy. In addition, we aim to formulate advice for dose modification and therapeutic drug monitoring of antiepileptic drugs. We searched PubMed and the available literature on the pharmacokinetic changes of antiepileptic drugs and seizure frequency during pregnancy published between January 2007 and September 2018. During pregnancy, an increase in clearance and a decrease in the concentrations of lamotrigine, levetiracetam, oxcarbazepine's active metabolite licarbazepine, topiramate, and zonisamide were observed. Carbamazepine clearance remains unchanged during pregnancy. There is inadequate or no evidence for changes in the clearance or concentrations of clobazam and its active metabolite N-desmethylclobazam, gabapentin, lacosamide, perampanel, and valproate. Postpartum elimination rates of lamotrigine, levetiracetam, and licarbazepine resumed to pre-pregnancy values within the first few weeks after pregnancy. We advise monitoring of antiepileptic drug trough concentrations twice before pregnancy. This is the reference concentration. We also advise to consider dose adjustments guided by therapeutic drug monitoring during pregnancy if the antiepileptic drug concentration decreases 15-25% from the pre-pregnancy reference concentration, in the presence of risk factors for convulsions. If the antiepileptic drug concentration changes more than 25% compared with the reference concentration, dose adjustment is advised. Monitoring of levetiracetam, licarbazepine, lamotrigine, and topiramate is recommended during and after pregnancy. Monitoring of clobazam, N-desmethylclobazam, gabapentin, lacosamide, perampanel, and zonisamide during and after pregnancy should be considered. Because of the risk of teratogenic effects, valproate should be avoided during pregnancy. If that is impossible, monitoring of both total and unbound valproate is recommended. More research is needed on the large number of unclear pregnancy-related effects on the pharmacokinetics of antiepileptic drugs.

Buprenorphine-cannabis interaction in patients undergoing opioid maintenance therapy

Buprenorphine is a partial μ-opioid agonist widely used for opioid maintenance therapy (OMT). It is mainly metabolized to pharmacologically active norbuprenorphine by the cytochrome P450 (CYP) isozyme 3A4. This may give rise to drug-drug interactions under combinations with inhibitors or inducers of CYP3A4. Cannabis is a potential inhibitor of CYP3A4, and there is a large degree of concomitant cannabis use among OMT patients. We performed a retrospective analysis on liver healthy OMT patients substituted with buprenorphine, either with (n = 15) or without (n = 17) concomitant use of cannabis. Patients with additional illicit drugs or medications affecting CYP3A were excluded. Measured blood concentrations of buprenorphine and norbuprenorphine were compared between the two groups. Cannabis users and non-users received similar doses, but users had 2.7-fold higher concentrations of buprenorphine (p < 0.01) and 1.4-fold for norbuprenorphine (1.4-fold, p = 0.07). Moreover, the metabolite-to-parent drug ratio was 0.98 in non-users and 0.38 in users (p = 0.02). Female gender did not produce significant effects. These findings indicate that cannabis use decreases the formation of norbuprenorphine and elevates buprenorphine and norbuprenorphine concentrations in blood most probably by inhibition of CYP3A4. The pharmacokinetic interaction may give rise to enhanced or altered opioid activity and risk of intoxications. Physicians should inform patients about this risk and supervise cannabis users by regular control of buprenorphine blood levels, i.e., by therapeutic drug monitoring.

Cannabidiol efficacy independent of clobazam: Meta-analysis of four randomized controlled trials

OBJECTIVE

The efficacy of cannabidiol (CBD) with and without concomitant clobazam (CLB) was evaluated in stratified analyses of four large randomized controlled trials, two in Lennox-Gastaut syndrome, and two in Dravet syndrome.

METHODS

Each trial of CBD (Epidiolex^® in the US; Epidyolex^® in the EU; 10 and 20 mg/kg/day) was evaluated by CLB use. The treatment ratio was analyzed using negative binomial regression for changes in seizure frequency and logistic regression for the 50% responder rate, where the principle analysis combined both indications and CBD doses in a stratified meta-analysis. Pharmacokinetic data were examined for an exposure/response relationship based on CLB presence/absence. Safety data were analyzed using descriptive statistics.

RESULTS

The meta-analysis favored CBD vs. placebo regardless of CLB use. The treatment ratio (95% CI) of CBD over placebo for the average reduction in seizure frequency was 0.59 (0.52, 0.68; P < .0001) with CLB and 0.85 (0.73, 0.98; P = .0226) without CLB, and the 50% responder rate odds ratio (95% CI) was 2.51 (1.69, 3.71; P < .0001) with CLB and 2.40 (1.38, 4.16; P = .0020) without CLB. Adverse events (AEs) related to somnolence, rash, pneumonia, or aggression were more common in patients with concomitant CLB. There was a significant exposure/response relationship for CBD and its active metabolite.

CONCLUSIONS

These results indicate CBD is efficacious with and without CLB, but do not exclude the possibility of a synergistic effect associated with the combination of agents. The safety and tolerability profile of CBD without CLB show a lower rate of certain AEs than with CLB.

Review and Consensus on Pharmacogenomic Testing in Psychiatry

The implementation of pharmacogenomic (PGx) testing in psychiatry remains modest, in part due to divergent perceptions of the quality and completeness of the evidence base and diverse perspectives on the clinical utility of PGx testing among psychiatrists and other healthcare providers. Recognizing the current lack of consensus within the field, the International Society of Psychiatric Genetics assembled a group of experts to conduct a narrative synthesis of the PGx literature, prescribing guidelines, and product labels related to psychotropic medications as well as the key considerations and limitations related to the use of PGx testing in psychiatry. The group concluded that to inform medication selection and dosing of several commonly-used antidepressant and antipsychotic medications, current published evidence, prescribing guidelines, and product labels support the use of PGx testing for 2 cytochrome P450 genes (CYP2D6, CYP2C19). In addition, the evidence supports testing for human leukocyte antigen genes when using the mood stabilizers carbamazepine (HLA-A and HLA-B), oxcarbazepine (HLA-B), and phenytoin (CYP2C9, HLA-B). For valproate, screening for variants in certain genes (POLG, OTC, CSP1) is recommended when a mitochondrial disorder or a urea cycle disorder is suspected. Although barriers to implementing PGx testing remain to be fully resolved, the current trajectory of discovery and innovation in the field suggests these barriers will be overcome and testing will become an important tool in psychiatry.

Cenobamate: A New Adjunctive Agent for Drug-Resistant Focal Onset Epilepsy

OBJECTIVE

To review the pharmacology, efficacy, and safety of oral cenobamate in the treatment of uncontrolled focal epilepsy.

DATA SOURCES

The PubMed database and ClinicalTrials.gov were searched using the following terms: cenobamate, Xcopri, and YKP3089.

STUDY SELECTION AND DATA EXTRACTION

Articles published in English between January 2000 and April 2020 related to pharmacology, safety, and clinical trials were assessed.

DATA SYNTHESIS

In a phase 2 trial, cenobamate reduced the median percentage change in seizure frequency from baseline by 56% compared with 22% for placebo (P < 0.0001). In another phase 2 trial of multiple cenobamate doses, cenobamate reduced seizure frequency by 36% (P = 0.0071) in the 100-mg group and 55% (P < 0.0001) in both the 200- and 400-mg groups, compared to 24% with placebo. Adverse effects of cenobamate appear to be similar to those of other antiseizure medications and primarily affect the neurological system.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

In patients taking antiseizure medications who continue to have focal seizures, cenobamate has efficacy at multiple doses and is generally well tolerated. Cenobamate may be distinguished from other antiseizure medications by high rates of seizure freedom not seen in previous placebo-controlled trials, which has the potential to significantly improve quality of life. However, despite this efficacy, Drug Reaction with Eosinophilia and Systemic Symptoms may remain a significant concern with cenobamate.

CONCLUSION

As seen in clinical trials, cenobamate as an adjunctive, once-daily treatment represents an efficacious and generally well-tolerated therapy for patients with drug-resistant focal epilepsy.

Does cannabidiol have antiseizure activity independent of its interactions with clobazam? An appraisal of the evidence from randomized controlled trials

Four pivotal randomized placebo-controlled trials have demonstrated that adjunctive therapy with cannabidiol (CBD) improves seizure control in patients with Dravet syndrome (DS) and Lennox-Gastaut syndrome (LGS). Between 47% and 68% of patients allocated to CBD treatment in these trials were receiving clobazam (CLB), which shows complex interactions with CBD resulting, in particular, in a 3.4- to 5-fold increase in plasma concentration of the active metabolite norclobazam. This raises concern as to the role played by these interactions in determining the reduction in seizure frequency in CBD-treated patients, and the question of whether CBD per se has clinically evident antiseizure effects. We appraised available evidence on the clinical consequences of the CBD-CLB interaction, focusing on subgroup analyses of seizure outcomes in patients on and off CLB comedication in the pivotal CBD trials, as provided by the European Medicines Agency Public Assessment Report. Evaluation of the results of individual trials clearly showed that improvement in seizure control over placebo was greater when CBD was added on to CLB than when it was added on to other medications. However, seizure control was also improved in patients off CLB, and despite the small sample size the difference vs placebo was statistically significant for the 10 mg/kg/d dose in one of the two LGS trials. Stronger evidence for an antiseizure effect of CBD independent of an interaction with CLB emerges from meta-analyses of seizure outcomes in the pooled population of LGS and DS patients not receiving CLB comedication. Although these results need to be interpreted taking into account methodological limitations, they provide the best clinical evidence to date that CBD exerts therapeutic effects in patients with epilepsy that are independent of its interaction with CLB. Greater antiseizure effects, and a greater burden of adverse effects, are observed when CBD is combined with CLB.

Persistent Hypersomnolence Following Clobazam in a Child With Epilepsy and Undiagnosed CYP2C19 Polymorphism

We describe an 11-year-old female who presented with severe hypersomnolence after receiving 1 week of modest doses of clobazam (CLB). In reviewing the above case, we considered that the hypersomnolence could be related to a pharmacodynamic, pharmacokinetic, or pharmacogenomic issue associated with CLB or to a combination of these factors. Although serum concentrations of CLB and its active metabolite are sensitive to factors that affect cytochrome-dependent metabolism, drug-drug interactions were omitted as a cause of the hypersomnolence. Subsequent DNA analysis of the cytochrome P450 2C19 gene revealed the patient as *2/*2 genotype with poor metabolizer enzyme activity. Because genetic testing of all patients treated with CLB is currently not practical, CLB dose/concentration ratios and pharmacokinetic drug-drug interaction impact models may be indicated. Genetic testing should be considered when an adverse effect suggests the possibility of a polymorphism important to drug metabolism.

GABAergic modulation of secondary hyperalgesia: A randomized controlled 4-way crossover trial with the α2-subunit preferring GABA positive allosteric modulator, N-desmethyl-clobazam in healthy volunteers

The antihyperalgesic and sedative effects of the α2-subunit preferring GABA_A positive allosteric modulator (GAM), N-desmethyl-clobazam (NDMC), 20 and 60 mg, were assessed in a randomized, placebo and active-controlled (clonazepam 1,5 mg), 4-way crossover study, in healthy volunteers, using the ultraviolet B-induced experimental pain model. Single (20, 40, 60 mg) and repeated doses (20 mg over 15 days) of NDMC pharmacokinetics were evaluated. Thirty-two subjects participated in the study. Primary outcome parameter was maximal change in the area of cutaneous UVB irradiation-induced secondary hyperalgesia (ASH). ASH decreased under all treatments. Mean (SD) relative change was 79 (22)%, 83 (24)%, 77 (30)% and 92 (16)% for placebo, NDMC20, NDMC60 and clonazepam, respectively. Neither absolute change nor relative change in ASH was significantly different between NDMC60 and placebo (mean difference = 2.3 cm² [95% CI 4.0-8.5], p = .462 and 0.4% [-11.9 to 12.6], p = .952, respectively). An overall treatment effect was found on level of sedation. Compared to placebo, sedation was higher under clonazepam (mean difference = 39 mm [30-49] on a visual analogue scale, p < .001) while NDMC was free of sedative effect. NDMC pharmacokinetics after single doses showed poor absorption, but was linear. Steady-state plasma concentrations of NDMC20 were attained within 14 days, with low between-subjects variability. Mean steady-state concentration (C_S-S , SD) reached 209 (22) ng/ml. NDMC absence of sedative effect and its overall well-characterized safety coming from years of utilization as a metabolite from clobazam, raise the prospect of dose escalating trials in patients to quantify its clinical utility. SIGNIFICANCE: This article, presenting the Phase I data of the new antihyperalgesic compound, α2-subunit GABA_A positive allosteric modulator, N-desmethyl-clobazam (NDMC) is exploring the modulation of a new target in the treatment of neuropathic pain. Based on these results and on its preclinical properties NDMC would qualify as a good tool compound to seek confirmation of the clinical utility of selective GABA allosteric modulators in neuropathic pain patients.

Drug-drug interactions with cannabidiol (CBD) appear to have no effect on treatment response in an open-label Expanded Access Program

OBJECTIVE

We have previously shown that cannabidiol (CBD; Epidiolex®) significantly affects levels of clobazam/N-desmethylclobazam, rufinamide, topiramate, zonisamide, and eslicarbazepine. In the present study, we tested whether the presence of concomitant clobazam affected seizure frequency and severity (treatment response) 12 weeks after initiation of therapy with CBD in patients with treatment-resistant epilepsy (TRE). The secondary questions were whether the presence of any of the other antiepileptic drugs (AEDs) had an effect on seizure frequency or severity at 12, 24, or 48 weeks after therapy initiation.

METHODS

One hundred and thirty-two adults and children with TRE receiving CBD were studied prospectively. Participants were separated into two groups - either taking (CBD + clobazam) or not taking concomitant clobazam (CBD - clobazam). In the secondary analyses, participants were divided into groups depending on whether they were taking at least 1/4 of the other AEDs shown to interact with CBD (iAED). Seizure counts and Chalfont Seizure Severity Scale (CSSS) were obtained at baseline, 12, 24, and 48 weeks. Groups were compared at each respective time point in the study using generalized estimating equations (GEE) analyses.

RESULTS

All groups demonstrated statistically significant reductions in seizure frequency and severity from baseline (all P < 0.05). When participants on CBD + clobazam were compared with CBD - clobazam, there were no significant differences in seizure frequency and severity reduction between the groups at 12 weeks (both P > 0.05). When comparing groups with iAEDs vs. group without iAEDs, independent of coadministration of clobazam, no differences in treatment response were observed (all P > 0.05). Longitudinal analyses up to 48 weeks after therapy initiation did not reveal any differences in treatment response between groups.

CONCLUSION

These analyses suggest that concomitant to CBD, AEDs may not have an effect on reducing seizure frequency and severity in patients with TRE.

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.

Hypothermia in an Adolescent Due to Probable Drug-Drug Interaction Involving Clobazam

We report on a 16-year-old female who developed hypothermia as a result of a drug-drug interaction that produced supratherapeutic serum concentrations of clobazam. Although clobazam and its active metabolite (N-desmethylclobazam) are metabolized by cytochrome 2C19 (CYP2C19), literature suggests that clobazam-associated drug interactions involving this isoenzyme are not clinically relevant because of its wide therapeutic index. This report describes clobazam-associated hypothermia due to supratherapeutic serum concentrations of clobazam that resulted from the combination of 2 CYP2C19 inhibitors.

Clinical consequences related to a defective elimination of clobazam caused by homozygous mutated CYP2C19 allele

Introduction: Voluntary drug intoxication with benzodiazepines is common and in most cases without consequences. We report an interesting case of voluntary drug intoxication with clobazam (CLB) in a patient with a homozygous mutated CYP2C19 genotype. Case report: A 63-year-old Caucasian man was admitted to an intensive care unit for voluntary drug intoxication with CLB (1200 mg) complicated by prolonged hospitalization (46 days). The levels of CLB and N-desmethylclobazam (NCLB) in plasma were initially 8.3 and 14.8 mg/L. The persistence of a high concentration of NCLB (14.3 mg/L on day 30) suggested a lack of elimination. A homozygous mutated allele of CYP2C19*2 without enzyme activity was discovered. To overcome this phenotype, NCLB metabolism was induced by administering 100 mg of phenobarbital for 10 days, allowing patient improvement. Discussion: NCLB is the major active metabolite of CLB with a longer half-life and much higher steady-state plasma concentrations compared to the parent drug. The half-life elimination of CLB is 18 h that of NCLB is between 40 and 50 h. However, there is considerable inter-individual variation in the metabolism of CLB and of the report NCLB/CLB under the dependence of genotype of CYP2C19. These polymorphisms are not generally well-known by physicians and may lead to severe poisoning.

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.

Pharmacokinetics of clobazam oral soluble film

OBJECTIVE

Clobazam oral soluble film (COSF) is a novel dosage form under development for the adjunctive treatment of seizures associated with Lennox-Gastaut syndrome. The present study was undertaken to assess the pharmacokinetics of clobazam administered as single doses of COSF 20 and 10 mg compared with clobazam tablets (CTAB) 20 and 10 mg in healthy adults. A secondary objective was to assess the safety and tolerability of single doses of COSF 20 and 10 mg.

METHODS

A total of 51 adult volunteers were enrolled in a single-dose, open-label, randomized four-sequence, four-period, crossover study with treatments (A) COSF 20 mg, (B) CTAB 20 mg, (C) COSF 10 mg, and (D) CTAB 10 mg. Pharmacokinetic sampling for clobazam and N-desmethylclobazam was carried out until 21 days postdose with a 28-day washout. Subjects were monitored for adverse events (AEs) throughout the study. Visual inspections of the administration site were performed before and after COSF administration to monitor for mucosal irritation.

RESULTS

COSF at single doses of 10 and 20 mg was bioequivalent to CTAB at equivalent doses for both clobazam and its active metabolite N-desmethylclobazam. The pharmacokinetics of both formulations was dose-proportional at doses of 10 and 20 mg. The number of AEs and the number of subjects experiencing AEs were dose-related across the treatment groups, with somnolence the most common event. None of these events was severe or serious, and most were mild. There was no evidence for local irritation at the administration site following COSF.

SIGNIFICANCE

COSF is a novel clobazam dosage form that is bioequivalent to CTAB. Because of its ease of administration, COSF may be expected to improve adherence, reduce likelihood of dosing error, and provide more accurate dosing than formulations of clobazam that are currently available.

Pharmacodynamics and common drug-drug interactions of the third-generation antiepileptic drugs

INTRODUCTION

Anticonvulsants that belong to the third generation are considered as 'newer' antiepileptic drugs, including: eslicarbazepine acetate, lacosamide, perampanel, brivaracetam, rufinamide and stiripentol. Areas covered: This article reviews pharmacodynamics (i.e. mechanisms of action) and clinically relevant drug-drug interactions of the third-generation antiepileptic drugs. Expert opinion: Newer antiepileptic drugs have mechanisms of action which are not shared with the first and the second generation anticonvulsants, like inhibition of neurotransmitters release, blocking receptors for excitatory amino acids and new ways of sodium channel inactivation. New mechanisms of action increase chances of controlling forms of epilepsy resistant to older anticonvulsants. Important advantage of the third-generation anticonvulsants could be their little propensity for interactions with both antiepileptic and other drugs observed until now, making prescribing much easier and safer. However, this may change with new studies specifically designed to discover drug-drug interactions. Although the third-generation antiepileptic drugs enlarged therapeutic palette against epilepsy, 20-30% of patients with epilepsy is still treatment-resistant and need new pharmacological approach. There is great need to explore all molecular targets that may directly or indirectly be involved in generation of seizures, so a number of candidate compounds for even newer anticonvulsants could be generated.

Therapeutic Drug Monitoring of Clobazam and Its Metabolite-Impact of Age and Comedication on Pharmacokinetic Variability

BACKGROUND

Clobazam (CLB) has been used as an antiepileptic drug for several decades. There is still insufficient data regarding its pharmacokinetic variability in clinical practice. The purpose of this study was to investigate pharmacokinetic variability of CLB with emphasis on the impact of age and comedication in patients with epilepsy.

METHODS

Serum concentration measurements of CLB and its metabolite N-desmethylclobazam (NCLB), as well as demographic and clinical data were retrieved from the routine therapeutic drug monitoring service at the National Center for Epilepsy, Norway, 2009-2013. NCLB/CLB and total (CLB + NCLB), CLB and NCLB concentration/dose (C/D) ratios were calculated.

RESULTS

550 patients (296 women/254 men), average age 27 years (range 1-86), were included. The interindividual pharmacokinetic variability was extensive, as illustrated by a 100-fold variability in serum concentration compared with dose (total C/D ratio 0.03-3.29 µmol·L·mg). The CLB C/D ratio was 36% lower in young children (2-9 years) than in adults (18-64 years), reflecting a higher clearance. In patients receiving phenytoin, felbamate, stiripentol, oxcarbazepine or eslicarbazepine acetate, valproate, phenobarbital, zonisamide or carbamazepine one or more of the calculated ratios were significantly different from that in patients receiving no or neutral comedications. The mean values for the different groups were in the order of 20%-230% of C/D ratios in the neutral group and 200%-950% of the NCLB/CLB ratio.

CONCLUSIONS

The pharmacokinetic variability of CLB and its metabolite NCLB in clinical practice is extensive, and is influenced by drug-drug interactions, age, and pharmacogenetics. Therapeutic drug monitoring of CLB and NCLB is therefore valuable in patient management.

The Pharmacology and Toxicology of Third-Generation Anticonvulsant Drugs

Epilepsy is a neurologic disorder affecting approximately 50 million people worldwide, or about 0.7% of the population [1]. Thus, the use of anticonvulsant drugs in the treatment of epilepsy is common and widespread. There are three generations of anticonvulsant drugs, categorized by the year in which they were developed and released. The aim of this review is to discuss the pharmacokinetics, drug-drug interactions, and adverse events of the third generation of anticonvulsant drugs. Where available, overdose data will be included. The pharmacokinetic properties of third-generation anticonvulsant drugs include relatively fewer drug-drug interactions, as well as several unique and life-threatening adverse events. Overdose data are limited, so thorough review of adverse events and knowledge of drug mechanism will guide expectant management of future overdose cases. Reporting of these cases as they occur will be necessary to further clarify toxicity of these drugs.

In vivo Raman measurement of levofloxacin lactate in blood using a nanoparticle-coated optical fiber probe

Monitoring drug concentrations in vivo is very useful for adjusting a drug dosage during treatment and for drug research. Specifically, cutting-edge "on-line" drug research relies on knowing how drugs are metabolized or how they interact with the blood in real-time. Thus, this study explored performing in vivo Raman measurements of the model drug levofloxacin lactate in the blood using a nanoparticle-coated optical fiber probe (optical fiber nano-probe). The results show that we were able to measure real-time changes in the blood concentration of levofloxacin lactate, suggesting that this technique could be helpful for performing drug analyses and drug monitoring in a clinical setting without repeatedly withdrawing blood from patients.

Seizures and cancer: drug interactions of anticonvulsants with chemotherapeutic agents, tyrosine kinase inhibitors and glucocorticoids

Patients with cancer commonly experience seizures. Combined therapy with anticonvulsant drugs (AEDs) and chemotherapeutic drugs or tyrosine kinase inhibitors carries inherent risks on drug-drug interactions (DDIs). In this review, pharmacokinetic studies of AEDs with chemotherapeutic drugs, tyrosine kinase inhibitors, and glucocorticoids are discussed, including data on maximum tolerated dose, drug clearance, elimination half-life, and organ exposure. Enzyme-inducing AEDs (EIAEDs) cause about a 2-fold to 3-fold faster clearance of concurrent chemotherapeutic drugs metabolized along the same pathway, including cyclophosphamide, irinotecan, paclitaxel, and teniposide, and up to 4-fold faster clearance with the tyrosine kinase inhibitors crizotinib, dasatinib, imatinib, and lapatinib. The use of tyrosine kinase inhibitors, particularly imatinib and crizotinib, may lead to enzyme inhibition of concurrent therapy. Many of the newer generation AEDs do not induce or inhibit drug metabolism, but they can alter enzyme activity by other drugs including AEDs, chemotherapeutics and tyrosine kinase inhibitors. Glucocorticoids can both induce and undergo metabolic change. Quantitative data on changes in drug metabolism help to apply the appropriate dose regimens. Because the large individual variability in metabolic activity increases the risks for undertreatment and/or toxicity, we advocate routine plasma drug monitoring. There are insufficient data available on the effects of tyrosine kinase inhibitors on AED metabolism.

Three patients needing high doses of valproic Acid to get therapeutic concentrations

Valproic acid (VPA) can autoinduce its own metabolism. Cases requiring VPA doses >4000 mg/day to obtain therapeutic plasma concentrations, such as these 3 cases, have never been published. Case 1 received VPA for seizures and schizophrenia and had >50 VPA concentrations in 4 years. A high dose of 5,250 mg/day of VPA concentrate was prescribed for years but this dose led to an intoxication when switched to the enterocoated divalproex sodium formulation, requiring a normal dose of 2000 mg/day. VPA metabolic capacity was significantly higher (t = −9.6; df = 6.3, p < 0.001) during the VPA concentrate therapy, possibly due to autoinduction in that formulation. Case 2 had VPA for schizoaffective psychosis with 10 VPA concentrations during an 8-week admission. To maintain a VPA level ≥50 μg/mL, VPA doses increased from 1500 to 4000 mg/day. Case 3 had tuberous sclerosis and epilepsy and was followed up for >4 years with 137 VPA concentrations. To maintain VPA concentrations ≥50 μg/mL, VPA doses increased from 3,375 to 10,500 mg/day. In Cases 2 and 3, the duration of admission and the VPA dose were strongly correlated (r around 0.90; p < 0.001) with almost no change after controlling for VPA concentrations, indicating progressive autoinduction that increased with time.

The effects of antiepileptic inducers in neuropsychopharmacology, a neglected issue. Part I: A summary of the current state for clinicians

The literature on inducers in epilepsy and bipolar disorder is seriously contaminated by false negative findings. This is part i of a comprehensive review on antiepileptic drug (AED) inducers using both mechanistic pharmacological and evidence-based medicine to provide practical recommendations to neurologists and psychiatrists concerning how to control for them. Carbamazepine, phenobarbital and phenytoin, are clinically relevant AED inducers; correction factors were calculated for studied induced drugs. These correction factors are rough simplifications for orienting clinicians, since there is great variability in the population regarding inductive effects. As new information is published, the correction factors may need to be modified. Some of the correction factors are so high that the drugs (e.g., bupropion, quetiapine or lurasidone) should not co-prescribed with potent inducers. Clobazam, eslicarbazepine, felbamate, lamotrigine, oxcarbazepine, rufinamide, topiramate, vigabatrin and valproic acid are grouped as mild inducers which may (i)be inducers only in high doses; (ii)frequently combine with inhibitory properties; and (iii)take months to reach maximum effects or de-induction, definitively longer than the potent inducers. Potent inducers, definitively, and mild inducers, possibly, have relevant effects in the endogenous metabolism of (i)sexual hormones, (ii) vitamin D, (iii)thyroid hormones, (iv)lipid metabolism, and (v)folic acid.

On the Slow Diffusion of Point-of-Care Systems in Therapeutic Drug Monitoring

Recent advancements in point-of-care (PoC) technologies show great transformative promises for personalized preventative and predictive medicine. However, fields like therapeutic drug monitoring (TDM), that first allowed for personalized treatment of patients' disease, still lag behind in the widespread application of PoC devices for monitoring of patients. Surprisingly, very few applications in commonly monitored drugs, such as anti-epileptics, are paving the way for a PoC approach to patient therapy monitoring compared to other fields like intensive care cardiac markers monitoring, glycemic controls in diabetes, or bench-top hematological parameters analysis at the local drug store. Such delay in the development of portable fast clinically effective drug monitoring devices is in our opinion due more to an inertial drag on the pervasiveness of these new devices into the clinical field than a lack of technical capability. At the same time, some very promising technologies failed in the clinical practice for inadequate understanding of the outcome parameters necessary for a relevant technological breakthrough that has superior clinical performance. We hope, by over-viewing both TDM practice and its yet unmet needs and latest advancement in micro- and nanotechnology applications to PoC clinical devices, to help bridging the two communities, the one exploiting analytical technologies and the one mastering the most advanced techniques, into translating existing and forthcoming technologies in effective devices.

Effects of CYP2C19 and P450 oxidoreductase polymorphisms on the population pharmacokinetics of clobazam and N-desmethylclobazam in japanese patients with epilepsy

BACKGROUND

Clobazam (CLB) is a 1,5-benzodiazepine with antiepileptic properties. More than 70% of administered CLB is dealkylated to yield N-desmethylclobazam (N-CLB), a pharmacologically active metabolite, by cytochrome P450 (CYP) 3A4 and CYP2C19. The subsequent inactivation of N-CLB is primarily catalyzed by CYP2C19. Meanwhile, P450 oxidoreductase (POR) is the obligatory electron donor to all microsomal CYP enzymes. The aim of this study was to evaluate the impact of the CYP2C19 and POR genotypes on the pharmacokinetic parameters of CLB and N-CLB.

METHODS

This retrospective study included 85 Japanese patients with epilepsy who were treated with CLB. CYP2C19*2, *3, and P450 oxidoreductase (POR) *28 (rs1057868C>T) polymorphisms were evaluated. A total of 128 steady-state concentrations for both CLB and N-CLB were collected from the patients. A nonlinear mixed-effects model identified the pharmacokinetics of CLB and N-CLB; the covariates included CYP2C19 and POR genotypes, weight, gender, daily CLB dose, and coadministered antiepileptic drugs.

RESULTS

Among the 85 patients, the allele frequencies of CYP2C19*2, CYP2C19*3, and POR*28 were 27.6%, 12.9%, and 41.2%, respectively. A one-compartment model with first-order absorption and/or elimination showed that the clearance of CLB and N-CLB was significantly lower by 18.1% and 84.9%, respectively, in the CYP2C19 poor metabolizers compared with the homozygous extensive metabolizers. The CLB clearance was 44% higher in subjects homozygous for the POR*28 T allele than in those homozygous for the POR*28 C allele, although the genotypes did not affect the N-CLB clearance. The concomitant use of phenobarbital, phenytoin, and zonisamide significantly affected the CLB clearance, whereas that of carbamazepine, phenytoin, and valproic acid affected the N-CLB clearance. The weight also significantly influenced the CLB clearance and volume of distribution of both CLB and N-CLB.

CONCLUSIONS

Our results showed that the CYP2C19 and/or POR genotypes have an impact on the CLB and/or N-CLB clearance. These results suggest that determining the CYP2C19 and/or POR genotypes is helpful for obtaining appropriate serum CLB and N-CLB concentrations and preventing an overdose when starting CLB therapy.