Controversies in blood-level monitoring: reexamining its role in the treatment of epilepsy

Investigation of the Roles of New Antiepileptic Drugs and Serum BDNF Levels in Efficacy and Safety Monitoring and Quality of Life: A Clinical Research

Objective: We aimed to determine the therapeutic drug monitoring (TDM) features and the relation to Brain-Derived Neurotrophic Factor (BDNF) of frequently used new antiepileptic drugs (NADs) including lamotrigine (LTG), oxcarbazepine (OXC), zonisamide (ZNS) and lacosamide (LCM). Moreover, we investigated their effect on the quality of life (QoL).

Methods: Eighty epileptic patients who had been using the NADs, and thirteen healthy participants were included in this cross-sectional study. The participants were randomized into groups. The QOLIE-31 test was used for the assessment of QoL. We also prepared and applied “Safety Test”. HPLC method for TDM, and ELISA method for BDNF measurements were used consecutively.

Results: In comparison to healthy participants, epileptic participants had lower marriage rate (p=0.049), education level (p˂0.001), alcohol use (p=0.002). BDNF levels were higher in patients with focal epilepsy (p=0.013) and in those with higher education level (p=0.016). There were negative correlations between serum BDNF levels and serum ZNS levels (p=0.042) with LTG-polytherapy, serum MHD levels (a 10-monohydroxy derivative of OXC, p=0.041) with OXC-monotherapy. There was no difference in BDNF according to monotherapy-polytherapy, drug-resistant groups, regarding seizure frequency. There was a positive correlation between total health status and QoL (p˂0.001). QOLIE-31 overall score (OS) was higher in those with OXC-monotherapy (76.5±14.5). OS (p˂0.001), seizure worry (SW, p=0.004), cognition (C, p˂0.001), social function (SF, p˂0.001) were different in the main groups. Forgetfulness was the most common unwanted effect.

Conclusion: While TDM helps the clinician to use more effective and safe NADs, BDNF may assist in TDM for reaching the therapeutic target in epilepsy.

Limited care offered to people with epilepsy in Mwanza, Tanzania: need for intervention

Introduction

epilepsy is a very common neurological disorder which is associated with high socioeconomic burden. While up to 90% of people with epilepsy (PWE) in developing countries do not get appropriate treatment, there is limited information about care offered to PWE in Tanzania. This study aimed to describe available care offered to PWE in Mwanza.

Methods

a cross-sectional study involving health care workers (HCWs) and PWE attending five selected hospitals outpatient clinics of Mwanza region was done. HCWs completed self-administered questionnaires while PWE or caretakers were interviewed using structured questionnaires. Coded data were analyzed using SPSS.

Results

a total of 18 HCWs and 218 PWE (or their care takers) participated in this study. Health care workers rarely used investigations to confirm epilepsy diagnosis or explore its causes. 10/18 (55.6%) of HCWs reported that counseling was given to patients but counseling information was largely inadequate regarding the use of anti-epileptic drugs (AEDs). The AEDs prescriptions were dictated by drug availability and affordability to patients. Among 197 PWE, whose AEDs doses were revealed, 136 (69.0%) were under-medicated. No follow-up investigation was done to all PWE who were interviewed. There was discrepancy between hospitals and practitioners regarding withdrawal of AEDs.

Conclusion

people with epilepsy in Mwanza received limited care. Patients were not thoroughly investigated, counseled and followed-up, and had limited choice and accessibility to AEDs. Some patients particularly in district hospitals were under-medicated despite of seizure recurrence. We recommend short-course training about epilepsy management to the HCWs who diagnose and treat PWE regularly.

Reference ranges for antiepileptic drugs revisited: a practical approach to establish national guidelines

BACKGROUND AND OBJECTIVE

Laboratories sometimes use different reference ranges for the same antiepileptic drug (AED), particularly for new and poorly investigated drugs. This may contribute to misunderstandings, concerns or inappropriate dose changes, which in turn may affect therapeutic effect, drug safety or treatment adherence. Therefore, the Norwegian Association of Clinical Pharmacology wished to update and harmonize the reference ranges for AEDs and establish national guidelines for Norway.

METHODS

A working group collected information on the reference ranges used by Norwegian laboratories for all commonly used AEDs. These reference ranges were compared to recent recommendations by the International League Against Epilepsy, current literature, applicable clinical studies, reference ranges used by leading Northern European epilepsy centers outside of Norway, and routine data derived from Norwegian laboratory databases.

RESULTS

Reference ranges varied between laboratories for four of 23 available AEDs (lamotrigine, valproate, eslicarbazepine and oxcarbazepine). For four AEDs (brivaracetam, perampanel, stiripentol and sulthiame), reference ranges had not previously been established. In total, 13 reference ranges were either harmonized, updated or newly established. No changes were applied to the remaining 10 AEDs.

CONCLUSION

Updated and harmonized reference ranges are now available for 22 of the 23 AEDs available in Norway. The exception is vigabatrin (reference range not applicable). Revision of reference ranges is an important part of pharmacovigilance of AEDs and must be a continuous process based on current literature and clinical experience.

Pharmacokinetic Properties of New Antiepileptic Drugs

Eight new antiepileptic drugs (AEDs) have been approved for use within the United States within the past decade. They are felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, and zonisamide. These afford clinicians with more options to increase efficacy and tolerability in the treatment of patients with epilepsy. Pharmacokinetic properties and drug interactions with other AEDs and other medications taken for comorbidities are individually discussed for each of these new agents. Drug concentrations are not routinely monitored for these newer agents, and there have been few studies designed to investigate their concentration-effect relationships. For most of these medications, the concentrations observed in responders and nonresponders overlap considerably and levels associated with efficacy are often associated with adverse events, complicating the definition of target ranges. Also, epilepsy manifests itself sporadically causing difficulty in clinically monitoring efficacy of medications. Therapeutic drug monitoring provides for the individualization of treatment for these agents, which is important because they demonstrate significant variability in inter- and intraindividual pharmaco-kinetic properties. Therapeutic drug monitoring also allows for identification of noncompliance, drug interactions, and toxicity. Current knowledge of the relationships between efficacy, toxicity, and drug concentrations is discussed.

A Comparison of Antibiotic Serum Concentrations Drawn Simultaneously from Peripherally Inserted Central Catheters and Peripheral Veins in Children with Respiratory Infection

The purpose of the study was to evaluate serum concentration of antibiotics drawn from a peripherally inserted central catheter (PICC) compared with a peripheral venipuncture. This prospective comparative study included patients with ages 1month to 21years admitted with a respiratory infection requiring IV vancomycin or IV tobramycin via a newly placed PICC. The difference between the antibiotic levels from the venipuncture and PICC samples was statistically significant for both the peak and trough levels. However, the difference in values was not enough to impact antibiotic dosing and therefore was not clinically significant.

Therapeutic drug monitoring of antiepileptic drugs in a tertiary care hospital in India

INTRODUCTION

Therapeutic drug monitoring (TDM) helps to optimize the dose of antiepileptic drugs. Only limited information is available about the clinical utility of TDM of antiepileptic drugs in India. Hence, we aimed to study the clinical utility of antiepileptic TDM in a tertiary care hospital in India and to explore the association between the plasma drug levels and the occurrence of breakthrough seizures and drug toxicity.

METHODS

All patients taking antiepileptic drugs for whom TDM was done from January 2008 to December 2010 were included in the study. All relevant information was obtained from patient medical records. Trough levels were measured for all drugs using chemiluminescence assay. Drug levels were interpreted as within, below, and above the reference range, as recommended by the International League Against Epilepsy guidelines.

RESULTS

Of the 420 samples analyzed during this period, 396 samples were included in this study for analysis. The maximum number of requests was for phenytoin (50%) followed by valproic acid (26%). The most common indication for TDM was dosage adjustment (38%) followed by breakthrough seizures (34%). Among the 135 samples received with breakthrough seizures as indication, more than 50% had drug levels either within or above the reference range. Among the 62 samples referred with clinical symptoms of suspected toxicity, drug levels were above the reference range in only 52% of the samples.

CONCLUSIONS

Therapeutic drug monitoring was found to be useful in practice, in tailoring drug dosage in accordance with the needs of individual patient, in distinguishing nonresponders from noncompliants, and in aiding in making critical decisions. However, the "reference range" of these antiepileptic drugs was not reliable in predicting the occurrence of breakthrough seizures and clinical symptoms of suspected drug toxicity.

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.

Anticonvulsant prophylaxis for brain tumor surgery: determining the current best available evidence

Patients who undergo craniotomy for brain tumor resection are prone to experiencing seizures, which can have debilitating medical, neurological, and psychosocial effects. A controversial issue in neurosurgery is the common practice of administering perioperative anticonvulsant prophylaxis to these patients despite a paucity of supporting data in the literature. The foreseeable benefits of this strategy must be balanced against potential adverse effects and interactions with critical medications such as chemotherapeutic agents and corticosteroids. Multiple disparate metaanalyses have been published on this topic but have not been applied into clinical practice, and, instead, personal preference frequently determines practice patterns in this area of management. Therefore, to select the current best available evidence to guide clinical decision making, the literature was evaluated to identify meta-analyses that investigated the efficacy and/or safety of anticonvulsant prophylaxis in this patient population. Six meta-analyses published between 1996 and 2011 were included in the present study. The Quality of Reporting of Meta-analyses and Oxman-Guyatt methodological quality assessment tools were used to score these meta-analyses, and the Jadad decision algorithm was applied to determine the highest-quality meta-analysis. According to this analysis, 2 metaanalyses were deemed to be the current best available evidence, both of which conclude that prophylactic treatment does not improve seizure control in these patients. Therefore, this management strategy should not be routinely used.

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

BACKGROUND

Clobazam was recently approved for Lennox-Gastaut syndrome in the United States. There is no published review article focused on clobazam therapeutic drug monitoring (TDM) in English.

METHODS

More than 200 clobazam articles identified by a PubMed search were carefully reviewed for information on clobazam pharmacokinetics. Clobazam is mainly metabolized by a cytochrome P450 (CYP) isoenzyme, CYP3A4, to its active metabolite, N-desmethylclobazam. Then, N-desmethylclobazam is mainly metabolized by CYP2C19 unless the individual has no CYP2C19 activity [poor metabolizer (PM)].

RESULTS

Using a mechanistic approach to reinterpret the published findings of steady-state TDM and single-dosing pharmacokinetic studies, 4 different serum clobazam concentration ratios were studied. The available limited steady-state TDM data suggest that the serum N-desmethylclobazam/clobazam ratio can be useful for clinicians, including identifying CYP2C19 PMs (ratio >25 in the absence of inhibitors). There are 3 possible concentration/dose (C/D) ratios. The clobazam C/D ratio has the potential to measure the contribution of CYP3A4 activity to the clearance of clobazam from the body. The N-desmethylclobazam C/D ratio does not seem to be a good measure of clobazam clearance and should be substituted with the total (clobazam + N-desmethylclobazam) C/D ratio.

CONCLUSIONS

Future clobazam TDM studies need to use trough concentrations after steady state has been reached (>3 weeks in normal individuals and several months in CYP2C19 PMs). These future studies need to explore the potential of clobazam and total C/D ratios. Better studies on the relative potency of N-desmethylclobazam compared with the parent compound are needed to provide weighted total serum concentrations that correct for the possible lower N-desmethylclobazam pharmacodynamic activity. Standardization and more studies of C/D ratios from clobazam and other drugs can be helpful to move TDM forward.

Clinical outcomes associated with brand-to-generic phenytoin interchange

BACKGROUND

Concerns that antiepileptic brand-to-generic interchange results in disruption of seizure control are widespread. However, little within-patient evidence exists examining such interchanges.

OBJECTIVE

To compare within-patient seizure control before and after the interchange of a branded to a single-source generic phenytoin among patients with seizures in a managed care organization.

METHODS

This was a pre-post, self-controlled, retrospective study. Adults with a history of seizure who used Dilantin Kapseals 100 mg extended phenytoin sodium, USP, capsules and whose therapy was interchanged to Taro Pharmaceuticals' AB-rated generic extended phenytoin sodium capsules, USP, 100 mg between July 2007 and May 2008 were included. Study outcomes included the comparisons of the proportions of patients with at least emergency department (ED) visit/inpatient hospitalization and medical office visit/nonoffice consultation for acute seizure in the 6 months before and after interchange. Outcomes were confirmed with manual chart reviews and adjusted for potential confounding medication use.

RESULTS

A total of 222 patients were included in the study. Patients were primarily middle-aged (mean 56 years), equally mixed by sex (47% female); most had nonintractable seizures. The majority of patients (~70%) were on phenytoin as monotherapy and had equivalent rates of purchases for potentially confounding medications in both pre- and postinterchange time periods (all p > 0.05). Low serum concentrations were detected more often in the postinterchange study period (adjusted p < 0.001). Despite this, there were low proportions of patients with confirmed seizure events that resulted in an ED visit/inpatient hospitalization in both pre- and postinterchange periods (both 6.3%, adjusted p = 0.937). The proportion of patients with confirmed seizure events diagnosed at a medical office visit was not significantly different between the preinterchange and postinterchange periods (12.2% vs 11.3%, adjusted p = 0.545).

CONCLUSIONS

No increased proportion of seizures was observed within patients when branded phenytoin was interchanged to an AB-rated, single-source, generic equivalent. More rigorous studies should be conducted to more thoroughly evaluate patient tolerability and drug efficacy when antiepileptic drugs are interchanged from brand to generic formulations.

Modern methods for analysis of antiepileptic drugs in the biological fluids for pharmacokinetics, bioequivalence and therapeutic drug monitoring

Epilepsy is a chronic disease occurring in approximately 1.0% of the world's population. About 30% of the epileptic patients treated with availably antiepileptic drugs (AEDs) continue to have seizures and are considered therapy-resistant or refractory patients. The ultimate goal for the use of AEDs is complete cessation of seizures without side effects. Because of a narrow therapeutic index of AEDs, a complete understanding of its clinical pharmacokinetics is essential for understanding of the pharmacodynamics of these drugs. These drug concentrations in biological fluids serve as surrogate markers and can be used to guide or target drug dosing. Because early studies demonstrated clinical and/or electroencephalographic correlations with serum concentrations of several AEDs, It has been almost 50 years since clinicians started using plasma concentrations of AEDs to optimize pharmacotherapy in patients with epilepsy. Therefore, validated analytical method for concentrations of AEDs in biological fluids is a necessity in order to explore pharmacokinetics, bioequivalence and TDM in various clinical situations. There are hundreds of published articles on the analysis of specific AEDs by a wide variety of analytical methods in biological samples have appears over the past decade. This review intends to provide an updated, concise overview on the modern method development for monitoring AEDs for pharmacokinetic studies, bioequivalence and therapeutic drug monitoring.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Therapeutic Drug Monitoring of the Newer Anti-Epilepsy Medications

In the past twenty years, 14 new antiepileptic drugs have been approved for use in the United States and/or Europe. These drugs are eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, pregabalin, rufinamide, stiripentol, tiagabine, topiramate, vigabatrin and zonisamide. In general, the clinical utility of therapeutic drug monitoring has not been established in clinical trials for these new anticonvulsants, and clear guidelines for drug monitoring have yet to be defined. The antiepileptic drugs with the strongest justifications for drug monitoring are lamotrigine, oxcarbazepine, stiripentol, and zonisamide. Stiripentol and tiagabine are strongly protein bound and are candidates for free drug monitoring. Therapeutic drug monitoring has lower utility for gabapentin, pregabalin, and vigabatrin. Measurement of salivary drug concentrations has potential utility for therapeutic drug monitoring of lamotrigine, levetiracetam, and topiramate. Therapeutic drug monitoring of the new antiepileptic drugs will be discussed in managing patients with epilepsy.

Best practice in primary care pathology: review 12

This twelfth best practice review examines four series of common primary care questions in laboratory medicine: (i) antiepileptic drug monitoring; (ii) infectious diarrhoea; (iii) methicillin resistant Staphylococcus aureus; and (iv) brain natriuretic peptide. The review is presented in question–answer format, referenced for each question series. The recommendations represent a précis of guidance found using a standardised literature search of national and international guidance notes, consensus statements, health policy documents and evidence-based medicine reviews, supplemented by MEDLINE EMBASE searches to identify relevant primary research documents. They are not standards but form a guide to be set in the clinical context. Most are consensus rather than evidence-based. They will be updated periodically to take account of new information.

Drug treatment-related factors of inadequate seizure control

To optimize seizure control it is important to identify modifiable factors. We conducted a case-control study to explore to what extent drug treatment-related factors are associated with seizures. Eighty-six patients with epilepsy were evaluated: 45 cases (recently experienced a seizure) and 41 controls (seizure-free for at least 2 months). There was a significant association between low AED serum concentration and seizures (odds ratio (OR)=8.9, 95% confidence interval (CI)=1.7-47.8), compliance was not associated with seizures (OR=0.9, 95% CI=0.2-4.0), and changes in medication (mainly non-AEDs) were more frequently observed in the case group than in the control group (OR=4.1, 95% CI=0.9-18.3). These findings indicate that patients with low AED serum levels have a nine times higher risk of seizures compared with patients with therapeutic AED levels and that changes in medication regimens in patients with epilepsy should be made with care.

Value of therapeutic drug level monitoring and unbound (free) levels

Therapeutic drug monitoring (TDM) has declined with newer anti-epileptic drugs (AEDs) having no therapeutic window. Use of unbound (free) fraction has almost completely disappeared. The case reported highlights its importance and offers sound reason for its retention. A 66-year-old Caucasian man with known epilepsy was admitted with vomiting, ataxia and nystagmus presumably due to AED toxicity. Medications included valproate (VPA) 1g bd; phenytoin (PHT) 200mg tds; carbamazepine (CBZ) 400mg mane, 200mg midi, 400mg nocte; levetiracetam (LEV) 250mg bd. Initial AED-TDM revealed total serum levels of CBZ: 27micromol/L; PHT: 37micromol/L; VPA 499micromol/L, therapeutic or subtherapeutic. Free levels were subsequently measured demonstrating CBZ: 8.2micromol/L; PHT: 5micromol/L; VPA 93micromol/L. Consequently, VPA was initially omitted and dosage reduced with cessation of toxicity. AED regimen was greatly simplified and remained efficacious. This case highlights the value of TDM with polypharmacy and suggested AED toxicity. Total AED levels failed to identify the cause, which the unbound, free fraction identified. While total PHT was borderline subtherapeutic (37micromol/L; range: 40-80) the free level was therapeutic (5micromol/L; range: 4-8) and while VPA was therapeutic (VPA 499micromol/L; range: 300-750) the free level was supratherapeutic (93micromol/L; range: 30-75). Acknowledgement of discordance between total and free levels for highly protein-bound AED is highlighted.

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

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Therapeutic monitoring of antiepileptic drugs during pregnancy and in the postpartum period: is it useful?

As in all patient populations, epilepsy is common in pregnant women. Consequently, approximately 1 in 200 pregnancies is exposed to antiepileptic drugs (AEDs). Although exposure to AEDs in utero has been associated with an increased risk of major fetal malformations, most women with epilepsy require medication throughout pregnancy, since seizures themselves may be potentially harmful not only for the mother but also for the developing fetus. Physiological changes during pregnancy result in a reduction in the serum concentrations of most AEDs, particularly in late pregnancy. Changes in protein binding lead to a greater reduction in total than free (active) drug concentrations. Pharmacokinetic changes in pregnancy show interindividual variability and are not well understood for most newer AEDs. However, recent studies have shown that changes in lamotrigine clearance are particularly marked, with increases in each trimester and a significant fall in plasma concentrations, leading to consequent breakthrough seizures in some women. Concentrations may then rise precipitously after delivery, leading to symptoms of lamotrigine toxicity. Therapeutic drug monitoring could theoretically guide adjustment of AED dosage to achieve good seizure control while minimising fetal exposure, although there are several limitations to such monitoring. Firstly, there are wide interindividual variations in serum drug concentrations, with seizure control often correlating poorly with a given therapeutic range. Secondly, therapeutic ranges have not been well defined for newer AEDs and their measurement is often not always available. Thirdly, for highly protein-bound drugs, although measurement of free drug concentrations may more accurately reflect drug availability during pregnancy than total drug concentrations, assays for this are not always available and may be unreliable. Thus, it may be useful, prior to pregnancy, to establish the total and free drug concentrations required to achieve optimal seizure control in a given individual. Regular monitoring of AEDs has been advocated in each trimester and shortly after delivery, with adjustment of dosage to avoid seizure precipitation during pregnancy or symptoms of toxicity after birth. More frequent monitoring has been recommended for lamotrigine. However, aggressive drug monitoring of any AED has yet to be proven to be effective in improving seizure control or care. Furthermore, higher doses may be associated with a greater potential for teratogenicity and it is not yet known whether longer term adverse effects may be related to in utero exposure in the latter half of pregnancy. There is limited evidence about the relationship of maternal serum drug concentrations and teratogenicity. While there is a theoretical role for therapeutic drug monitoring in improving the risk-to-benefit ratio of AED therapy during pregnancy, there are many practical limitations. Future work is needed to clarify its role in improving seizure control during pregnancy and identifying serum drug concentrations that may be considered safe for fetal exposure.

Conventional and sustained-release valproate in children with newly diagnosed epilepsy: a randomized and crossover study comparing clinical effects, patient preference and pharmacokinetics

OBJECTIVE

It has been suggested that sustained-release valproate (VPA) formulations may be more effective and better tolerated than conventional VPA due to better compliance and lower fluctuations in VPA serum concentrations, but comparative trials with conventional VPA in children are scarce. This randomized and crossover trial compared the efficacy (complete control of seizures), the tolerability, and the patient (or parents) preference of conventional VPA twice daily (CVbid) with those of sustained-release chrono VPA twice daily (ChVbid), once daily in the morning (ChVom) or once daily in the evening (ChVoe) in monotherapy.

METHODS

The study was carried out in 48 children (29 girls), aged 5-14 years, with newly diagnosed partial epilepsy (n=26), or idiopathic generalized epilepsy (n=22). The study duration was 16 months (four phases of 4 months each). VPA pharmacokinetics data were also compared in the different regimens. Mean VPA dosage was of approximately 870 mg/day (approximately 22 mg/kg/day) and mean VPA concentration was of approximately 89 mg/l at 12 h post-dose and of 54 mg/l at 24 h post-dose.

RESULTS

By intention in treatment there were no significant differences in efficacy (73%, 83%, 77% and 75%, respectively) or in adverse reaction frequency (56%, 58%, 67% and 46%, respectively). There were significant differences, however, in patient (or parents) preference, the order being ChVoe (31%) > ChVom (25%) > CVbid (17%) > ChVbid (8%). The mean VPA serum concentration fluctuation between 4 h and 0 h post-morning-dose was nonsignificantly lower after CVbid than after ChVbid. Fluctuation was significantly higher after ChVom than after CVbid or ChVbid. The mean VPA serum concentration difference between 12 h and 24 h post-dose was approximately 40 mg/l.

CONCLUSION

Although our results should be confirmed by a larger study, they suggest that the efficacy and tolerability of chrono valproate is similar to that of conventional valproate, and that the main advantage is the once-daily administration.

Does It Really Matter When a Blood Sample for Valproic Acid Concentration is Taken Following Once-Daily Administration of Divalproex-ER?

Divalproex sodium extended-release (divalproex-ER) is a novel formulation intended for once-daily oral administration, either morning or evening. Questions have risen concerning the optimal time for obtaining a blood sample for valproic acid (VPA) concentration in relation to the dose. Trough sampling is easily achieved just before a morning daily dose, but the best time to sample after an evening daily dose is unclear, because collecting a blood sample 21 to 24 hours later may be limited by the operational hours of the laboratory. This investigation provides practical guidance regarding blood sample timing. Steady-state plasma VPA concentration-time profiles from 5 published divalproex-ER studies (healthy subjects and epilepsy patients) were analyzed. The concentration-time profile for each subject/patient was expressed as a percentage of his/her trough concentration and summary statistics computed. Typically, when taking divalproex-ER once daily in the morning, a blood sample collected 21 to 24 hours later is expected to have a concentration within 3% of the trough value. Conversely, for divalproex-ER dosed once-daily in the evening, for example 8 PM, a blood draw 12 to 15 hours later (ie, 8 to 11 AM) will give a plasma VPA concentration value that is 18% to 25% higher, on average, than the trough value. However, waiting longer, (for example 18 to 21 hours, ie 2 to 5 PM) will result in concentration values that are merely 3% to 13% higher than trough values, which may provide acceptable information for monitoring purposes. The greatest deviation from trough VPA concentration occurs around the peak, that is 3 to 15 hours after a once-daily divalproex-ER dose; sampling during this time period is recommended only if a clinical need exists to test for a higher VPA concentration. Despite the apparent smoothness of the VPA concentration-time profile after a once-daily divalproex-ER dose, the timing of the blood sample does matter and impacts the proper interpretation of the VPA concentration.

Long-lasting antiepileptic effects of levetiracetam against epileptic seizures in the spontaneously epileptic rat (SER): differentiation of levetiracetam from conventional antiepileptic drugs

PURPOSE

Some evidence suggests that levetiracetam (LEV) possesses antiepileptogenic characteristics. The purpose of this study was to investigate the time course of seizure protection by LEV compared with that of phenytoin (PHT), phenobarbital (PB), valproate (VPA), and carbamazepine (CBZ) in the spontaneously epileptic rat (SER). The SER is a double mutant (tm/tm, zi/zi) showing both tonic convulsions and absence-like seizures.

METHODS

The effect of single (40, 80, and 160 mg/kg, i.p.) and 5-day (80 mg/kg/day, i.p.) administration of LEV on tonic convulsions and absence-like seizures in SERs were studied. Tonic convulsions induced by blowing air onto the animal's head at 5-min intervals for 30 min and spontaneous absence-like seizures characterized by 5- to 7-Hz spike-wave-like complexes in the cortical and hippocampal EEG were recorded for 30 min. In the single-administration study, observations for seizure activity were performed once before and 3 times (45, 75, and 135 min) after drug administration. In the 5-day administration study, seizure observation was performed 4 times for 30 min (once before and 3 times after drug administration) during the 5-day drug-administration period, and continued once a day until 8 days after the final administration. The antiepileptic effects of 5-day administration of conventional AEDs (PHT, PB, VPA, and CBZ) were examined by using similar methods.

RESULTS

Tonic convulsions and absence-like seizures were inhibited by a single administration of LEV at 80 and 160 mg/kg, i.p., but not significantly at 40 mg/kg, i.p. When LEV was repeatedly administered at 80 mg/kg/day, i.p., for 5 days to SERs, the inhibitory effects on seizures increased with administration time. The number of tonic convulsions and absence-like seizures were significantly reduced to 39.1% and 38.4% compared with previous values, respectively, after 5-day LEV administration. Furthermore, significant inhibition of tonic convulsions was detected <or=3 days after the final administration, and significant inhibition of absence-like seizures was still observed 8 days after the final injection of LEV. This demonstrates long-lasting seizure protection by LEV after cessation of treatment. PHT, PB, VPA, and CBZ inhibited tonic convulsions more potently compared with LEV in SERs. The maximal antiseizure effects of these drugs were reached after the initial administration, with almost the same antiseizure effects observed through day 5, despite continued drug administration. Moreover, a long-lasting treatment effect was not observed with any of these drugs except for PHT and CBZ, both of which showed moderately prolonged antiseizure effects.

CONCLUSIONS

These results show that LEV is effective in the treatment of both convulsive and absence-like seizures in SERs after single- and multiple-dose administration. Interestingly, in the 5-day administration study, it was found that the antiepileptic effects for tonic convulsions and absence-like seizures were observed both during the drug-administration period and <or=8 days after the final administration of LEV. This long-lasting effect suggests that LEV may possess an antiepileptogenic effect that it does not share with PHT, PB, VPA, and CBZ.

Quantitative determination of vigabatrin and gabapentin in human serum by gas chromatography-mass spectrometry

BACKGROUND

Published methods for routine clinical monitoring of vigabatrin and gabapentin are often very laborious. A simple GC-MS method was developed for the simultaneous quantitative determination of vigabatrin and gabapentin in human serum.

METHODS

After protein precipitation, the compounds are derivatized by methylation and analysed on a polydimethylsiloxane column using splitless injection. Cyclobarbital is used as the internal standard. To attain maximal sensitivity, detection is performed in selected ion monitoring mode.

RESULTS

The method was fully validated and linear calibration curves were obtained in the concentration ranges from 5 to 80 microg/mL for vigabatrin and from 5 to 30 microg/mL for gabapentin. The within-day and day-to-day relative standard deviations at three different concentration levels were <10% and <15%, respectively. The limit of quantitation was 2 mug/mL for both compounds.

CONCLUSIONS

The presented method provides high chromatographic resolution, good sensitivity and unequivocal identification potential and can be used for simultaneous analysis of both antiepileptics.

Nonparametric population modeling of valproate pharmacokinetics in epileptic patients using routine serum monitoring data: implications for dosage

Therapeutic drug monitoring (TDM) of valproate (VAL) is important in the optimization of its therapy. The aim of the present work was to evaluate the ability of TDM using model-based, goal-oriented Bayesian adaptive control for help in planning, monitoring, and adjusting individualized VAL dosing regimens. USC*PACK software and routine TDM data were used to estimate population and individual pharmacokinetics of two commercially available VAL formulations in epileptic adult and pediatric patients on chronic VAL monotherapy. The population parameter values found were in agreement with values reported earlier. A statistically significant (P < 0.001) difference in median values of the absorption rate constant was found between enteric-coated and sustained-release VAL formulations. In our patients (aged 0.25-53 years), VAL clearance declined with age until adult values were reached at about age 10. Because of the large interindividual variability in PK behavior, the median population parameter values gave poor predictions of the observed VAL serum concentrations. In contrast, the Bayesian individualized models gave good predictions for all subjects in all populations. The Bayesian posterior individualized PK models were based on the population models described here and where most patients had two (a peak and a trough) measured serum concentrations. Repeated consultations and adjusted dosage regimens with some patients allowed us to evaluate any possible influence of dose-dependent VAL clearance on the precision of total VAL concentration predictions based on TDM data and the proposed population models. These nonparametric expectation maximization (NPEM) population models thus provide a useful tool for planning an initial dosage regimen of VAL to achieve desired target peak and trough serum concentration goals, coupled with TDM soon thereafter, as a peak-trough pair of serum concentrations, and Bayesian fitting to individualize the PK model for each patient. The nonparametric PK parameter distributions in these NPEM population models also permit their use by the new method of 'multiple model' dosage design, which allows the target goals to be achieved specifically with maximum precision. Software for both types of Bayesian adaptive control is now available to employ these population models in clinical practice.

Correlation of Lamotrigine Concentrations Between Serum and Saliva

STUDY OBJECTIVE

To compare the relationship between serum and salivary concentrations of lamotrigine in pediatric and adult epilepsy populations.

DESIGN

Paired-sample pharmacokinetic study.

SETTING

University neurology clinic.

PATIENTS

Thirty-seven patients with epilepsy, aged 2-60 years, who were taking lamotrigine and whose physicians had ordered a lamotrigine serum concentration.

MEASUREMENTS AND MAIN RESULTS

Patients spit a minimum of 0.25 ml into a cup to provide saliva samples. Blood samples were obtained by phlebotomy. Serum and salivary lamotrigine concentrations were determined by high-performance liquid chromatography. Linear regression analysis was used to evaluate correlations. Six patients' results were omitted due to the lack of a serum or saliva specimen or clearly erroneous results, leaving 31 patients for analysis. There was a strong correlation between the serum results reported by two reference laboratories (coefficient of correlation [r] = 0.988). The correlations between salivary and serum lamotrigine concentrations were similar for reference laboratory A (r = 0.81) and reference laboratory B (r = 0.84). Saliva:serum concentration ratios ranged from 0.41-1.26 (mean +/- SD 0.62 +/- 0.19) for reference laboratory A and from 0.40-1.19 ((mean +/- SD 0.64 +/- 0.18) for reference laboratory B.

CONCLUSION

There is a good correlation between salivary and serum concentrations for lamotrigine. However, there is wide interpatient variability in the saliva:serum ratio. The data suggest that salivary monitoring may play a role in the monitoring of lamotrigine for adult and pediatric patients.

Postictal serum levels of antiepileptic drugs for detection of noncompliance

Medication noncompliance (NC) is thought to be a major cause of insufficient seizure control. In an explorative study we investigated whether postictal serum levels (PISLs) of antiepileptic drugs (AEDs) are a reliable indicator of NC. Young adults with epilepsy on a stable AED regimen were asked to contact medical service as soon as possible when a seizure occurred to obtain serum levels of their AEDs. PISLs were compared with the mean value of two routine serum levels of the same medication. PISLs lower than 50% of the individual reference value were regarded as an indicator of NC. PISL samples in 61 seizures of 52 patients treated mainly with carbamazepine, valproic acid, or lamotrigine were evaluated. A drop in serum levels >50% indicating NC was noted in 44.3% of the seizures. Determination of PISLs seems to be a simple and useful method for detecting or ruling out irregular intake patterns as a cause of "breakthrough" seizures.

Simultaneous isocratic HPLC determination of vigabatrin and gabapentin in human plasma by dansyl derivatization

A rapid and low-cost assay for simultaneous vigabatrin (VGA) and gabapentin (GBP) determination is described that can be performed with simple HPLC instrumentation. The method involves derivatization of the primary amine group of VGA and GBP with dansyl chloride followed by isocratic separation (column: microBondapak C-18, 10 microm, 300 x 3.9 mm; mobile phase: 50 mmol/L NaH(2)PO(4) in 40% acetonitrile) at 50 degrees C and fluorometric detection (excitation and emission wavelength: 318 and 510 nm, respectively) of the fluorescent product, which is stable for at least 7 days. Correlation coefficients of the calibration curves are >0.999 with a lower limit of detection of 0.3 microg/mL. Between- and within-run coefficients of variation are below 4.5%, and assay time is 15 minutes. This method may be used for therapeutic drug monitoring in the case of GBP and to control patient compliance in the case of VGA.

Therapeutic drug monitoring of the newer antiepileptic drugs

The aim of the present review is to discuss the potential value of therapeutic drug monitoring (TDM) of the newer antiepileptic drugs (AEDs) felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, and zonisamide. Studies of the relationship between serum concentrations and clinical efficacy of these drugs are reviewed, and the potential value of TDM of the drugs is discussed based on their pharmacokinetic properties and mode of action. Analytical methods for the determination of the serum concentrations of these drugs are also briefly described. There are only some prospective data on the serum concentration-effect relationships, and few studies have been designed primarily to study these relationships. As TDM is not widely practiced for the newer AEDs, there are no generally accepted target ranges for any of these drugs, and for most a wide range in serum concentration is associated with clinical efficacy. Furthermore, a considerable overlap in drug concentrations related to toxicity and nonresponse is reported. Nevertheless, the current tentative target ranges for felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine (10-hydroxy-carbazepine metabolite), tiagabine, topiramate, vigabatrin, and zonisamide are 125 to 250 micromol/L, 70 to 120 micromol/L, 10 to 60 micromol/L, 35 to 120 micromol/L, 50 to 140 micomol/L, 50 to 250 nmol/L, 15 to 60 micromol/L, 6 to 278 micromol/L, and 45 to 180 micromol/L, respectively. Further systematic studies designed specifically to evaluate concentration-effect relationships of the new AEDs are urgently needed. Although routine monitoring in general cannot be recommended at present, measurements of some of the drugs is undoubtedly of help with individualization of treatment in selected cases in a particular clinical setting.

[Antiepileptic drugs used in childhood. New products and new concepts]

INTRODUCTION

Eight new antiepileptic drugs (AED) have been marketed in Spain since 1990 and others will soon follow.

OBJECTIVE

To review the concepts underlying the development of the new drugs, as well as their indications, efficacy and safety.

DEVELOPMENT

Pharmacologic antiepileptic intervention is no longer solely directed towards an anticonvulsant effect, but also to epileptogenic prevention, disease modification and reversal of pharmacoresistance. The development of new AED, initially based on the screening of putative products in animal models, changed during the last half of the century to a rational design based on known facts about excitatory /inhibitory neuronal mechanisms. More recently, attention has focussed on pharmacogenetics. The new AED were initially indicated for partial epilepsies, but some have been shown to have a broader clinical spectrum. Some show the ideal pharmacokinetic mechanisms, avoiding hepatic metabolism and protein binding. Drug interactions and adverse effects, especially severe idiosyncratic adverse effects, are rare, although there are some exceptions. In most cases, however, seizure control does not seem to be better than with the classic AED. Because of the specific characteristics of childhood epilepsy and pharmacokinetics, as well as the regulations governing the development of clinical trials, the use of new products in children is circumspect, which in turn delays the access of such patients to a possible therapeutic benefit.

Liquid chromatography tandem mass spectrometry assay for topiramate analysis in plasma and cerebrospinal fluid: validation and comparison with fluorescence-polarization immunoassay

SUMMARY

The authors report the development and validation of a liquid chromatography tandem mass spectrometry assay (LC/MS/MS assay) for the analysis of topiramate (2,3:4,5-bis-o-(-1-methyl)-beta-D-fructopyranose sulfamate) in plasma and cerebrospinal fluid (CSF). Comparison is made with the commercially available fluorescence-polarization immunoassay (FPIA).

LC/MS/MS ASSAY

Using the internal standard, 1,2:3,4-bis-o-(1-methylethylidene-alpha-D-galactopyranose sulfamate), a structural isomer, the calibration curve in plasma was linear in the concentration range of 0.02-20.0 mg/L (r(2) = 0.9998). The coefficients of variation in plasma were < or = 3%, and the accuracy ranged from 100% to 101% in the therapeutically relevant concentration range of 0.4-16.0 mg/L. In CSF, the mean recovery was 98%, and there was linearity between the nominal and the estimated concentration in the range of 1.5-20.0 mg/L (r(2)= 0.9996). FPIA: The calibration curve was linear in the concentration interval of 1.6-24.3 mg/L (r(2) = 0.9994), and the mean recovery was 96%. Accuracy in plasma was 99- 104%, and precision was 3.2-6.0%. In CSF, there was linearity between the nominal concentration and the estimated concentration in the range of 1.5-20.0 mg/L (r(2) = 0.9995), and the mean recovery was 100%. COMPARISON BETWEEN FPIA AND LC/MS/MS: There was a high correlation between the FPIA and the LC/MS/MS assay (r(2) = 0.9965 in plasma and r(2) = 0.9996 in CSF, P < 0.001 for both). In plasma and CSF, the two methods showed equal results, evaluated as the ratio between the two methods (plasma: median ratio = 1.00; 95% confidence interval [CI], 0.98-1.02, paired-sample test, P = 0.79; and CSF: median ratio = 1.00, 95% CI, 0.99-1.02, paired-sample test, P = 0.75). The coefficient of variation on the ratios between the two methods had similar levels: 5% in plasma and 3% in CSF.

CONCLUSION

The new LC/MS/MS assay has favorable characteristics, being highly precise and accurate. FPIA also proved precise and accurate, and there was a high agreement with the LC/MS/MS assay in plasma and CSF. Either method displayed sufficient precision and accuracy and may thus be implemented in daily routine.

Add-on phenytoin fails to prevent early seizures after surgery for supratentorial brain tumors: a randomized controlled study

PURPOSE

To determine the potential effectiveness of phenytoin (PHT) in preventing early postoperative seizures in patients undergoing craniotomy for supratentorial brain tumors.

METHODS

Two hundred patients requiring elective craniotomy for supratentorial brain tumors were randomized to two groups of equal size, with a prospective, open-label, controlled design. One group received PHT (18 mg/kg as an intravenous intraoperative load, followed by additional daily doses aimed at maintaining serum PHT concentrations within the 10- to 20-aeg/ml range) for 7 consecutive days. In the other group, PHT was not administered. More than 90% of patients in both groups continued to take preexisting anticonvulsant medication (AEDs) with carbamazepine or phenobarbital throughout the study. The primary efficacy end point was the number of patients remaining free from seizures during the 7-day period after the operation.

RESULTS

Of 100 patients allocated to PHT, 13 experienced seizures during the 7-day observation period, compared with 11 of 100 patients in the placebo group (p > 0.05). Most seizures occurred in the first day after surgery in both groups. There were no differences between groups in the proportion of patients experiencing more than one seizure, but there was a trend for generalized seizures to be more common in PHT-treated patients than in controls (11 vs. five patients, respectively). Status epilepticus occurred in one patient in the PHT group and in two patients in the control group. Of the 13 PHT-treated seizure patients, 11 had serum PHT concentrations within the target range, and only two had concentrations below range on the days their seizures occurred.

CONCLUSIONS

PHT, given at dosages producing serum concentrations within the target range, failed to prevent early postoperative seizures in patients treated with concomitant AEDs. Prophylactic administration of PHT cannot be recommended in these patients.

Simultaneous determination of four antiepileptic drugs in serum by high-performance liquid chromatography

A high-performance liquid chromatographic method has been developed for the simultaneous determination of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoin. After protein precipitation by acetonitrile, the supernatant was analysed on a C18 reversed-phase HPLC column. Antiepileptic drugs and oxazepam (internal standard) were detected by ultraviolet absorbance at 240 nm. Linearity was established for the whole concentration range for each compound. Quantitation limits of oxcarbazepine, 10-hydroxycarbamazepine, epoxycarbamazepine, carbamazepine, phenobarbital and phenytoin were 0.58, 3.5, 2.35, 0.66, 1.02 and 3.13 microg/mL, respectively, and mean recoveries added to serum were 105.15, 84.76, 94, 45, 96.52, 98.62 and 95.08%, respectively. This method has been used for the simultaneous determination of steady-state serum concentration of antiepileptic drugs in patients treated by one or more anticonvulsive treatment.

Stupor from lamotrigine toxicity

PURPOSE

To report that acute lamotrigine poisoning may result in severe encephalopathy.

METHODS

A 55-year-old woman became stuporous after overdose with lamotrigine (LTG) and valproic acid (VPA) tablets. Evaluation revealed elevated serum LTG levels and no other etiology for encephalopathy.

RESULTS

LTG was withheld, and the patient experienced a complete recovery in conjunction with reduced serum levels.

CONCLUSIONS

LTG overdose may result in a severe but reversible encephalopathy, a previously undescribed phenomenon. LTG toxicity should be considered in patients taking this drug who have depressed mental status.

Oxcarbazepine, an antiepileptic agent

BACKGROUND

Epilepsy is a common neurologic condition. Many of the currently approved pharmacologic agents for its treatment are associated with numerous adverse drug reactions and drug interactions.

OBJECTIVE

This review describes the pharmacology and therapeutic use of oxcarbazepine, an analogue of the well-known antiepileptic agent carbamazepine.

METHODS

Articles for review were identified through a search of MEDLINE, International Pharmaceutical Abstracts, and EMBASE for the years 1980 through 2000. The terms used individually and in combination were oxcarbazepine, carbamazepine, epilepsy, and seizures.

RESULTS

Oxcarbazepine and its primary metabolite have been effective in animal models of epilepsy that generally predict efficacy in generalized tonic-clonic seizures and partial seizures in humans. The exact mechanism of action of oxcarbazepine is unknown, although as with carbamazepine, it is believed to involve blockade of voltage-gated sodium channels. The pharmacokinetic profile of oxcarbazepine is less complicated than that of carbamazepine, with less metabolism by the cytochrome P450 system, no production of an epoxide metabolite, and lower plasma protein binding. The clinical efficacy and tolerability of oxcarbazepine have been demonstrated in trials in adults, children, and the elderly. In a double-blind, randomized, crossover trial in adults, oxcarbazepine 300 mg was associated with a decrease in the mean frequency of tonic seizures (21.4 vs 30.5 seizures during steady-state periods) and tonic-clonic seizures (8.2 vs 10.4) compared with carbamazepine 200 mg (P = 0.05). A multinational, multicenter, double-blind, placebo-controlled, randomized, 28-week trial assessed the efficacy and tolerability of oxcarbazepine at doses of 600, 1200, and 2400 mg as adjunctive therapy in patients with uncontrolled partial seizures. All 3 oxcarbazepine groups demonstrated a reduction in seizure frequency per 28-day period compared with placebo (600 mg, 26% reduction; 1200 mg, 40% reduction; 2400 mg, 50% reduction; placebo, 7.6% reduction; all, P < 0.001). A trial in children assessed the efficacy and toxicity of oxcarbazepine (median dose, 31.4 mg/kg/d) as adjunctive therapy for partial seizures. Patients receiving oxcarbazepine experienced a 35% reduction in seizure frequency, compared with a 9% reduction in the placebo group (P < 0.001). The most common adverse effects associated with oxcarbazepine are related to the central nervous system (eg, dizziness, headache, diplopia, and ataxia) and the gastrointestinal system (eg, nausea and vomiting). Compared with carbamazepine, there is an increased risk of hyponatremia with oxcarbazepine. The frequency and severity of drug interactions are less with oxcarbazepine than with carbamazepine or other antiepileptic agents.

CONCLUSIONS

Oxcarbazepine may be considered an appropriate alternative to carbamazepine for the treatment of partial seizures in patients who are unable to tolerate carbamazepine. Its use in nonseizure disorders remains to be examined in large-scale clinical trials, and pharmacoeconomic comparisons of oxcarbazepine with other antiepileptic agents, particularly carbamazepine, are needed.