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

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.

Risk factors for hyperammonemia associated with valproic acid therapy in adult epilepsy patients

Hyperammonemia is one of the side effects of treatment with valproic acid (VPA), but the risk factors and mechanisms involved remain obscure. This study analyzed the risk factors for hyperammonemia associated with VPA therapy in adult epilepsy patients. A retrospective analysis of 2724 Japanese patients (1217 males and 1507 females aged from 16 to 76years) treated with VPA between January 2006 and December 2010 were analyzed. The ammonia level increased markedly in a VPA dose-dependent manner, and was significantly elevated in patients who also used hepatic enzyme inducers such as phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ), and combinations of these drugs. When a blood ammonia level exceeding 200μg/dl was defined as hyperammonemia, the risk factors for hyperammonemia according to multiple regression analysis were a VPA dose >20mg/kg/day (odds ratio (OR): 4.1; 95% confidence interval (CI): 1.6-10.8) and concomitant use of PHT (OR: 11.0; 95% CI: 3.1-38.7), concomitant PB (OR: 4.3; 95% CI: 1.0-17.9), concomitant CBZ (OR: 2.8; 95% CI: 0.6-11.9), and concomitant topiramate (OR: 2.8; 95% CI: 1.2-6.5). Regimens containing multiple inducers were associated with an increased risk of hyperammonemia. Identification of risk factors for hyperammonemia associated with VPA therapy can help to minimize side effects during its clinical use.

Pharmacotherapy of the third-generation AEDs: lacosamide, retigabine and eslicarbazepine acetate

INTRODUCTION

The search for new, more effective antiepileptic drugs (AEDs) continues. The three most recently approved drugs, the so-called third-generation AEDs, include lacosamide, retigabine and eslicarbazepine acetate and are licensed as adjunctive treatment of partial epilepsy in adults.

AREAS COVERED

For the above three AEDs, their mechanisms of action, pharmacokinetic characteristics, drug-drug interactions, pharmacotherapeutics, dose and administration and therapeutic drug monitoring are reviewed in this paper.

EXPERT OPINION

Lacosamide and retigabine act through novel mechanisms, while eslicarbazepine acetate, a pro-drug for eslicarbazepine, acts in a similar manner to several other AEDs. All three AEDs are associated with linear pharmacokinetic and rapid absorption and undergo metabolism. Their drug-drug interaction profile is low (lacosamide and retigabine) to modest (eslicarbazepine) in propensity. At the highest approved doses for the three AEDs, responder rates were similar. The most commonly observed adverse effects compared with placebo were dizziness, headache, diplopia and nausea for lacosamide; dizziness, somnolence and fatigue for retigabine and dizziness and somnolence for eslicarbazepine acetate. The precise role that these new AEDs will have in the treatment of epilepsy and whether they will make a significant impact on the prognosis of intractable epilepsy is not yet known and will have to await further clinical experience.

Therapeutic drug monitoring--the appropriate use of drug level measurement in the care of the neonate

Neonates and young infants are in a unique and dynamic pharmacokinetic state, in which they undergo relatively rapid maturational changes in drug absorption, distribution, metabolism, and excretion. In addition to these maturational changes, most drug pharmacokinetic studies in neonates show wide interindividual variability despite similar gestational and postnatal ages. Therapeutic drug monitoring is a necessary tool in the neonatal intensive care unit, despite the relative lack of outcome data. This article discusses therapeutic drug monitoring for several frequently used drugs in neonates.

Clinical decision support of therapeutic drug monitoring of phenytoin: measured versus adjusted phenytoin plasma concentrations

BACKGROUND

Therapeutic drug monitoring of phenytoin by measurement of plasma concentrations is often employed to optimize clinical efficacy while avoiding adverse effects. This is most commonly accomplished by measurement of total phenytoin plasma concentrations. However, total phenytoin levels can be misleading in patients with factors such as low plasma albumin that alter the free (unbound) concentrations of phenytoin. Direct measurement of free phenytoin concentrations in plasma is more costly and time-consuming than determination of total phenytoin concentrations. An alternative to direct measurement of free phenytoin concentrations is use of the Sheiner-Tozer equation to calculate an adjusted phenytoin that corrects for the plasma albumin concentration. Innovative medical informatics tools to identify patients who would benefit from adjusted phenytoin calculations or from laboratory measurement of free phenytoin are needed to improve safety and efficacy of phenytoin pharmacotherapy. The electronic medical record for an academic medical center was searched for the time period from August 1, 1996 to November 30, 2010 for patients who had total phenytoin and free phenytoin determined on the same blood draw, and also a plasma albumin measurement within 7 days of the phenytoin measurements. The measured free phenytoin plasma concentration was used as the gold standard.

RESULTS

In this study, the standard Sheiner-Tozer formula for calculating an estimated (adjusted) phenytoin level more frequently underestimates than overestimates the measured free phenytoin relative to the respective therapeutic ranges. Adjusted phenytoin concentrations provided superior classification of patients than total phenytoin measurements, particularly at low albumin concentrations. Albumin plasma concentrations up to 7 days prior to total phenytoin measurements can be used for adjusted phenytoin concentrations.

CONCLUSIONS

The results suggest that a measured free phenytoin should be obtained where possible to guide phenytoin dosing. If this is not feasible, then an adjusted phenytoin can supplement a total phenytoin concentration, particularly for patients with low plasma albumin.

What is quality improvement and why should child neurologists care?

In this article, the authors discuss the 6 domains of care identified by the Institute of Medicine report, Crossing the Chasm, with examples and questions that are especially relevant to physicians caring for children who have neurologic disorders and their families.

Drug interaction and pharmacokinetic modeling of oxcarbazepine in korean patients with epilepsy

OBJECTIVES

To determine first whether there was a clear relationship between concentrations of the active metabolite of oxcarbazepine (OXC), 10-hydroxycarbamazepine (OHC), and dose adjusted for weight, and second, whether the clearance of OHC was influenced by comedication with enzyme-inducing antiepileptic drugs (EIAED).

METHODS

We analyzed 254 cases (patients 3-80 years of age) of OXC therapeutic drug monitoring, retrospectively. The cases were categorized into OXC monotherapy (n = 78), OXC in combination with EIAED (n = 73), and OXC in combination with non-EIAED (n = 103). The serum OHC concentrations of predose samples were measured by high-performance liquid chromatography. A population pharmacokinetic model was developed using NONMEM.

RESULTS

The mean ± SD serum concentration of OHC was 14.47 ± 8.28 μg/mL at a mean daily dose of 16.22 ± 7.99 mg/kg. The serum concentration of OHC was correlated with the OXC dose per body weight (r = 0.6005; P < 0.0001). No association was found between OHC concentration and patient age, weight, sex, or seizure type. The concentration-to-dose ratio on OXC in combination with EIAED was significantly lower than that on OXC monotherapy (P = 0.002) or OXC in combination with non-EIAED (P < 0.0001). In population pharmacokinetic modeling, the apparent clearance of OHC was higher by 31.2% in combination with EIAED than in other groups.

CONCLUSIONS

The serum concentration of OHC was statistically significantly correlated with the dose of OXC and negatively correlated with comedication of EIAED. Population pharmacokinetic analysis showed that the apparent clearance of OHC increased with comedication with EIAEDs.

No pharmacokinetic interaction between lacosamide and valproic acid in healthy volunteers

Two open-label, randomized, multiple-dose clinical studies evaluated the potential for pharmacokinetic interaction between the antiepileptic drugs lacosamide and valproic acid. The influence of lacosamide on valproic acid pharmacokinetics (trial A) and valproic acid on lacosamide pharmacokinetics (trial B) was investigated in 32 healthy male volunteers, 16 in each trial. Volunteers in trial A received valproic acid (300 mg bid) with randomization to either early or late addition of lacosamide (200 mg bid). Those in trial B received lacosamide (200 mg bid) with randomization to either early or late addition of valproic acid (300 mg bid). Area under the concentration-time curve during a 12-hour dosing interval at steady state (AUC(τ,ss)) and maximum steady-state plasma drug concentration (C(max,ss)) were measured for each drug alone and together and tested for equivalence. The point estimates (90% confidence intervals) for AUC(τ,ss) and C(max,ss) were 104% (99%-109%) and 101% (97%-107%), respectively, for valproic acid and 100% (98%-103%) and 101% (96%-107%), respectively, for lacosamide, which were within the generally accepted equivalence range of 80% to 125%. No changes in the rate or extent of absorption, terminal half-life, or time to maximum concentration were observed. These results suggest that lacosamide and valproic acid have no relevant pharmacokinetic drug-drug interaction.

Add-on lacosamide: a retrospective study on the relationship between serum concentration, dosage, and adverse events

We performed a retrospective study in patients with poorly controlled epilepsy treated with add-on lacosamide (LCM) to investigate the relationship of LCM-related adverse events with LCM serum concentration and weight-dependent dosage. We collected serum concentrations, weight-related dosages, and occurrences of the seven most frequent adverse events according to the randomized double-blind, placebo-controlled trials. Seventy of 131 patients could be sufficiently evaluated. LCM serum concentrations and weight-related dosages in patients with and without typical adverse events did not differ significantly. Closer analysis of the data suggested that dizziness as the leading adverse event occurred significantly more often if LCM was combined with classic sodium channel blockers. There was a significant correlation between LCM serum concentrations and co-medication, so there is still evidence for dependent variables that might have a relevant impact in individual cases. However, our data do not allow definition of a safety range for LCM.

Optimal sampling strategy development methodology using maximum a posteriori Bayesian estimation

Maximum a posteriori Bayesian (MAPB) pharmacokinetic parameter estimation is an accurate and flexible method of estimating individual pharmacokinetic parameters using individual blood concentrations and prior information. In the past decade, many studies have developed optimal sampling strategies to estimate pharmacokinetic parameters as accurately as possible using either multiple regression analysis or MAPB estimation. This has been done for many drugs, especially immunosuppressants and anticancer agents. Methods of development for optimal sampling strategies (OSS) are diverse and heterogeneous. This review provides a comprehensive overview of OSS development methodology using MAPB pharmacokinetic parameter estimation, determines the transferability of published OSSs, and compares sampling strategies determined by MAPB estimation and multiple regression analysis. OSS development has the following components: 1) prior distributions; 2) reference value determination; 3) optimal sampling time identification; and 4) validation of the OSS. Published OSSs often lack all data necessary for the OSS to be clinically transferable. MAPB estimation is similar to multiple regression analysis in terms of predictive performance but superior in flexibility.

Antiepileptic drug combinations--have newer agents altered clinical outcomes?

In 2000, 332 (20.5%) of 1617 patients registered with the Western Infirmary Epilepsy Unit required antiepileptic drug (AED) polytherapy to remain seizure-free for at least 1 year. The analysis was repeated 10 years later. Of 2379 seizure-free patients, 20.4% (n=486 - 254 women, 232 men, aged 18-95 years [median age 49 years]) were receiving combination therapy. Two AEDs were taken by 395 (81.3%) patients in 2010, and by 287 (86.4%) in 2000. Sodium valproate with lamotrigine was the commonest of 64 successful pairings. As a combination, mean daily doses of both AEDs were lower (n=96; sodium valproate 1200 mg, lamotrigine 155 mg) than when sodium valproate was taken with carbamazepine or levetiracetam (n=42; 1621 mg; p<0.001), and lamotrigine was combined with topiramate or levetiracetam (n=33; 430 mg; p<0.001), suggesting possible synergism. In 2010, a higher percentage of patients (n=85) remained seizure-free on 3 AEDs (17.5% in 2010, 12.7% in 2000) in 57 separate regimens. Only 0.9% (n=3) of patients in 2000, and 1.2% (n=6) in 2010 responded to 4 AEDs. Levetiracetam (n=109; 10.2%) and topiramate (n=81; 7.6%) were the newer agents most commonly represented in successful combinations. These data tend to imply that drug substitution rather than addition has largely led to these marginally improved results. In the last decade, when used as adjunctive therapies, newer agents appear not to have impacted substantially on the likelihood of producing seizure freedom. An alternative approach to AED development may be required to change this disappointing scenario.

Hyperammonemic encephalopathy related to valproate, phenobarbital, and topiramate synergism

We present a woman with epilepsy secondary to a lesion in the left frontal lobe. She developed episodes of disorientation and behavioral changes. She was taking valproic acid (1500 mg/day), topiramate (200 mg/day), and phenobarbital (100 mg/day). During an episode, the EEG revealed moderate encephalopathy and ammonia levels were increased (195 μg/dL, reference range: 11-60 μg/dL). Episodes ceased after withdrawal of valproic acid.

Antiepileptic drug interactions - principles and clinical implications

Antiepileptic drugs (AEDs) are widely used as long-term adjunctive therapy or as monotherapy in epilepsy and other indications and consist of a group of drugs that are highly susceptible to drug interactions. The purpose of the present review is to focus upon clinically relevant interactions where AEDs are involved and especially on pharmacokinetic interactions. The older AEDs are susceptible to cause induction (carbamazepine, phenobarbital, phenytoin, primidone) or inhibition (valproic acid), resulting in a decrease or increase, respectively, in the serum concentration of other AEDs, as well as other drug classes (anticoagulants, oral contraceptives, antidepressants, antipsychotics, antimicrobal drugs, antineoplastic drugs, and immunosupressants). Conversely, the serum concentrations of AEDs may be increased by enzyme inhibitors among antidepressants and antipsychotics, antimicrobal drugs (as macrolides or isoniazid) and decreased by other mechanisms as induction, reduced absorption or excretion (as oral contraceptives, cimetidine, probenicid and antacides). Pharmacokinetic interactions involving newer AEDs include the enzyme inhibitors felbamate, rufinamide, and stiripentol and the inducers oxcarbazepine and topiramate. Lamotrigine is affected by these drugs, older AEDs and other drug classes as oral contraceptives. Individual AED interactions may be divided into three levels depending on the clinical consequences of alterations in serum concentrations. This approach may point to interactions of specific importance, although it should be implemented with caution, as it is not meant to oversimplify fact matters. Level 1 involves serious clinical consequences, and the combination should be avoided. Level 2 usually implies cautiousness and possible dosage adjustments, as the combination may not be possible to avoid. Level 3 refers to interactions where dosage adjustments are usually not necessary. Updated knowledge regarding drug interactions is important to predict the potential for harmful or lacking effects involving AEDs.

Efficacy and safety of methylphenidate in treating ADHD symptoms in children and adolescents with uncontrolled seizures: a Brazilian sample study and literature review

OBJECTIVE

Attention-deficit/hyperactivity disorder (ADHD) is observed in 30% of children and adolescents with epilepsy. Recent studies have demonstrated the safety of methylphenidate (MPH) in patients with controlled epilepsy. There are few studies of patients with uncontrolled epilepsy. The goal was to study the efficacy and safety of MPH use in children and adolescents diagnosed with ADHD and uncontrolled epilepsy.

METHODS

We evaluated 24 patients ranging from 7 to 16 years of age who took MPH for 6 months. Inclusion criteria were at least two epileptic seizures in the previous 6 months and a diagnosis of ADHD based on DSM-IV criteria.

CONCLUSION

Patients were classified according to ADHD subtype as follows: 41.7% inattentive type, 37.5% combined, and 20.8% hyperactive/impulsive type; 58.3% had partial epilepsy and 41.7% generalized epilepsy. There was an overall improvement in ADHD symptoms in 70.8% of patients, and there was no increase in frequency of epileptic seizures in 22 patients (91.6%).

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.

Phenobarbital for neonatal seizures in hypoxic ischemic encephalopathy: a pharmacokinetic study during whole body hypothermia

PURPOSE

Therapeutic hypothermia has recently been introduced to treat term newborns with hypoxic-ischemic encephalopathy, of whom more than half have seizures. Phenobarbital is widely used to treat neonatal seizures, but it is unknown whether its pharmacokinetics is affected by hypothermia. We evaluated the influence of hypothermia on phenobarbital pharmacokinetics in asphyxiated newborns.

METHODS

Nineteen term asphyxiated newborns treated with mild whole body hypothermia, started within 6 h after birth and protracted for 72 h, received phenobarbital for clinical seizures. Treatment schedule consisted of a loading dose of 20 mg/kg, titrated to response, up to a maximum dose of 40 mg/kg, followed by a maintenance dose of 2.5 or 1.5 mg/kg every 12 h. Phenobarbital concentrations were measured on 28 dried blood spots in each newborn.

KEY FINDINGS

Eighteen newborns showed plasma concentrations within the reference range after receiving a loading dose of 20 mg/kg. In the remaining newborn, who had received a loading dose of 35 mg/kg, phenobarbital concentrations exceeded the upper reference limit. Phenobarbital concentrations reached a virtual steady state in all newborns. Pharmacokinetic parameters were then calculated. Minimum and maximum concentration (24.7 ± 8.8 and 30.63 ± 10.3 mg/L), average plasma concentration (27.37 ± 9.4 mg/L), and half-life (173.9 ± 62.5 h) were considerably higher than reported in literature for normothermic newborns. Pharmacokinetic parameters did not differ significantly between infants receiving different maintenance doses.

SIGNIFICANCE

Phenobarbital administered to newborns under whole body hypothermia results in higher plasma concentrations and longer half-lives than expected in normothermic newborns.

Optimization and validation of bioanalytical SPE – HPLC method for the simultaneous determination of carbamazepine and its main metabolite, carbamazepine-10, 11-epoxide, in plasma

Carbamazepine is widely used as an antiepileptic drug in the treatment of partial and generalized tonic-clonic seizures. Carbamazepine 10,11-epoxide is the most important metabolite of carbamazepine, because it is a pharmacologically active compound with anticonvulsant properties. According to that, the routine analysis of carbamazepine 10,11-epoxide along with carbamazepine may provide optimal therapeutic monitoring of carbamazepine treatment. The aim of this study was to optimize and validate a simple and reliable solid - phase extraction method followed by RP-HPLC for the simultaneous determination of plasma levels of carbamazepine and carbamazepine-10,11-epoxide, in order to assure the implementation of the method for therapeutic monitoring. The extraction of the analytes from the plasma samples was performed by means of a solid-phase extraction procedure. The separation was carried out on a reversed-phase column using isocratic elution with acetonitrile and water (35:65, v/v) as a mobile phase. The temperature was 30°C and UV detection was set at 220 nm. The extraction yield values were more than 98% for all analytes, measured at four concentration levels of the linear concentration range. The method displayed excellent selectivity, sensitivity, linearity, precision and accuracy. Stability studies indicate that stock solutions and plasma samples were stabile under different storage conditions at least during the observed period. The method was successfully applied to determine the carbamazepine and carbamazepine-10,11-epoxide in plasma of epileptic patients treated with carbamazepine as monotherapy and in polytherapy. In conclusion, the proposed method is suitable for application in therapeutic drug monitoring of epileptic patients undergoing treatment with carbamazepine.

Lacosamide neurotoxicity associated with concomitant use of sodium channel-blocking antiepileptic drugs: a pharmacodynamic interaction?

Lacosamide is a new antiepileptic drug (AED) apparently devoid of major pharmacokinetic interactions. Data from a small postmarketing assessment suggest people who had lacosamide co-prescribed with a voltage-gated sodium channel (VGSC)-blocking AED seemed more likely to discontinue lacosamide because of tolerability problems. Among 39 people with refractory epilepsy who developed neurotoxicity (diplopia, dizziness, drowsiness) on lacosamide treatment given in combination with VGSC-blocking AEDs, we identified 7 (17.9%) without any changes in serum levels of other AEDs in whom the symptoms were ameliorated by dose reduction of the concomitant VGSC-blocking AED. Symptoms in these people seem to have arisen from a pharmacodynamic interaction between lacosamide and other VGSC-blocking AEDs. Slow-inactivated VGSCs targeted by lacosamide might be more sensitive to the effects of conventional VGSC-blocking AEDs. Advising people to reduce concomitantly the conventional VGSC-blocking AEDs during lacosamide uptitration in cases of neurotoxicity might improve the tolerability of combination treatment.

The impact of an educational intervention, the New GP Contract and NICE guidelines on anti-epilepsy therapeutic drug monitoring

BACKGROUND

Since the early 1970s therapeutic drug monitoring (TDM) of anti-epilepsy drug (AED) levels has been available to assist in the review process of patients with epilepsy. Routine blood levels were not part of the Quality and Outcomes Framework in the New GP Contract, neither have they been generally recommended in National Guidelines (NICE and SIGN) for the management of patients with epilepsy.

AIM

To assess the impact of an educational intervention, the New GP Contract and NICE guidelines on the number of requests for TDM.

DESIGN

Retrospective study.

SETTING

39 general practices serving Chester (13), the Rural area surrounding Chester (13) and Ellesmere Port (13).

METHODS

An educational intervention took place in the individual Chester practices between December 2001 and March 2003. For the Rural and Ellesmere Port practices there was one combined event in March 2004 and in March 2007, respectively. Practices were encouraged, not to routinely request TDM, except in certain circumstances. The number of TDM requests for Chester, Rural and Ellesmere Port were obtained from the local laboratory in Chester, plus other nearby hospitals, to provide control groups.

MAIN OUTCOME MEASURES

The number of TDM requests from primary care for Chester, Rural, Ellesmere Port, Wirral, Crewe, Warrington and Wrexham, April to April, 2002 through to 2008, where available.

RESULTS

There has been a fall in the number requests in all districts. The most significant falls were in Chester (47%), Rural (34%) and Ellesmere Port (47%), and corresponded to the time of their educational intervention. The fall has been less marked in Wirral (25%), Crewe (27%), Wrexham (10%) and Warrington (9%). In 2004, the first year after the introduction of the New GP Contract, TDM in Chester and the Rural fell significantly, while those in Ellesmere Port, Wirral, Crewe and Wrexham increased. TDM dropped significantly in Ellesmere Port in the year after their educational intervention. Despite the valproate assay being clinically unhelpful there were still 611 requests in the areas studied in 2007/2008.

CONCLUSION

The overall number of TDM requests has fallen since 2004 with the introduction of the New GP Contract and National Guidelines on the management of patients with epilepsy. The reduction has been more significant in areas where the changes were supplemented by an educational intervention. PCTs should endeavour to facilitate the introduction of National Guidelines with a supportive educational process, facilitated by educators with an interest and stake hold in those specific dillnesses. There is a significant cost to the NHS of inappropriate requests for TDM. Further study is required to quantify the indications for current requests for TDM.

A high-performance liquid chromatography assay to monitor the new antiepileptic drug lacosamide in patients with epilepsy

A simple high-performance liquid chromatographic micromethod is described for the quantitation of the new antiepileptic drug lacosamide in serum of patients. Serum (100 microL) was first precipitated with 10 microL 60% perchloric acid and 10 microL supernatant injected directly into the high-performance liquid chromatograph. Chromatographic separation was achieved by use of a steel cartridge column (125 x 3 mm inside diameter) packed with Hypersil BDS C-18, at 40 degrees C, and with a gradient elution system comprising methanol, formic acid and water. The eluent was monitored at 215 nm by diode array detection and the calibration curve was linear in the range of 10 to 250 micromol/L. Recovery ranged from 99% to 106%. The limit of quantification was 1 micromol/L and the intrabatch and interbatch coefficients of variation were less than 5%. No interference from commonly prescribed antiepileptic drugs (clobazam, clonazepam, carbamazepine, carbamazepine-10,11-epoxide, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, primidone, pregabalin, valproic acid, and vigabatrin) was observed, so the method can be used to routinely monitor lacosamide in patients on polytherapy antiepileptic drug regimens.

Saliva and serum lacosamide concentrations in patients with epilepsy

PURPOSE

Lacosamide is a new antiepileptic drug that has a novel mechanism of action, linear pharmacokinetics, and proven efficacy in the adjunctive treatment of partial-onset seizures. We ascertained the relationship between serum and saliva lacosamide concentrations so as to determine whether saliva may be a useful alternative to serum for therapeutic drug monitoring.

METHODS

Blood samples were obtained from 98 people with intractable epilepsy (51 male; mean age 43 ± 12; range 19-76 years) prescribed lacosamide as adjunctive therapy. For 48 patients, concurrent saliva samples were also collected. Lacosamide concentrations in serum (free and total) and in saliva were determined by high performance liquid chromatography (HPLC).

RESULTS

Linear regression analysis showed a good correlation between lacosamide dose and both total (r(2) = 0.825; n = 32) and free (r(2) = 0.815; n = 29) serum concentrations, and lacosamide serum total and free concentrations were linearly related (r(2) = 0.721; n = 97). There was also a good correlation between saliva lacosamide and both total (r(2) = 0.842; n = 49) and free (r(2) = 0.828; n = 47) serum lacosamide concentrations. Based on the saliva data, the protein binding of lacosamide in serum is calculated to be 87 ± 4% and is comparable to the value calculated by direct measurement of the free and total lacosamide concentration in serum (91 ± 4%).

DISCUSSION

These data support the use of saliva as a viable alternative to serum for monitoring lacosamide therapy in patients with epilepsy.

Attention deficit and hyperactivity disorder in people with epilepsy: diagnosis and implications to the treatment

The association between attention deficit and hyperactivity disorder (ADHD) and epilepsy can cause significant impact on the social life of affected individuals and their families. Clinical studies suggest that 30-40% of people with epilepsy also have ADHD. There are no studies which demonstrate that short or long-term treatment with methylphenidate increases the risk of seizures. Some studies attempt to relate drug interactions between methylphenidate and antiepileptic drugs, but adverse effects of methylphenidate have not been shown clearly. This review presents some neurobiological and physiopathogenic aspects, common to ADHD and epilepsy, from recent research studies, related to pharmacology, neuroimaging and electroencephalography. Possible risk of occurrence of seizures associated with the use of methylphenidate are also discussed.

Effect of CPS14217C>A genotype on valproic-acid-induced hyperammonemia

BACKGROUND

In order to clarify the factors causing hyperammonemia and to predict occurrences during treatment with valproic acid (VPA), we investigated the effect of the genetic polymorphism of carbamoyl-phosphate synthase 1 (CPS14217C>A) on susceptibility of hyperammonemia, together with the effect of coadministration of other anticonvulsants.

METHODS

Seventy-nine patients with epilepsy were enrolled, and five of them had hyperammonemia. Univariate and multivariate logistic regression analyses were performed.

RESULTS

The aspartate aminotransferase level in the patients with hyperammonemia was significantly higher than that in those without hyperammonemia. The risk of hyperammonemia was significantly influenced by the number of anticonvulsants concomitantly administered with VPA. Also, the distribution of the CPS14217C>A genotype differed depending on whether the patients had hyperammonemia or not. No significant effects of CPS14217 genotypes and the number of anticonvulsants coadministered with VPA on the serum concentrations of VPA were observed. The multivariate logistic regression analysis showed that the concomitant administration of two or more anticonvulsants with VPA and the heterozygous or homozygous carrier state of the A allele of the CPS14217C>A polymorphism were independent risk factors for developing hyperammonemia.

CONCLUSIONS

These findings suggested that in epileptic patients undergoing VPA therapy, CPS14217A polymorphism and the number of coadministered anticonvulsants would be considered as risk factors for hyperammonemia, even if the serum VPA concentrations were controlled.

Neurocognitive effects of brivaracetam, levetiracetam, and lorazepam

PURPOSE

Brivaracetam (BRV) is a new anticonvulsant under development. Although BRV is an analog of levetiracetam (LEV), in addition to being an SV2A ligand, it also inhibits sodium channels in a voltage-dependent manner. The cognitive effects of BRV are uncertain.

METHODS

A randomized, double-blind, placebo-controlled, four-way cross-over design was employed in 16 healthy volunteers comparing acute dosing (i.e., two doses) of BRV 10 mg, LEV 500 mg, lorazepam (LZP) 2 mg, and placebo. The primary outcome was the summary score from the cognitive neurophysiologic test (CNT), which combines electrophysiologic and performance measures. Secondary outcomes included CNT cognitive and electrophysiologic subscores, traditional neuropsychological measures, and treatment-emergent adverse events (TEAEs).

RESULTS

Compared to BRV, LEV, and placebo, LZP adversely affected the CNT summary score and the majority of CNT subscores and neuropsychological measures. In contrast, BRV did not differ from placebo or LEV on any measure. More TEAEs occurred with LZP compared to each of the other treatment conditions.

DISCUSSION

The differential pattern of drug effects was consistent across multiple electrophysiologic, cognitive, and subjective measures. The profile of cognitive, subjective, and electrophysiologic effects for BRV was similar to the analog compound LEV and to placebo. The findings suggest that BRV should be tolerated well from a neuropsychological perspective, but additional studies are needed.

Update on anticonvulsant drugs

In 2009, the US Food and Drug Administration approved three medications for the treatment of epilepsy: rufinamide, lacosamide, and vigabatrin. In addition, extended-release formulations of lamotrigine and levetiracetam were approved recently. When added to the dozen medications for treating epilepsy, the choice is a luxury in terms of additional options, but also a challenge for practitioners to use them all with expertise. Recently, there has been much interest surrounding medications for epilepsy and their possible association with osteoporosis, safety during pregnancy, biological equivalence to generic versions, and possible association with higher rates of suicidality. This review discusses these issues and provides a current overview for the medical management of epilepsy.

[Therapeutic drug monitoring of clobazam]

Clobazam is a 1,5 benzodiazepine available in France since 1975, used in add-on with the other anticonvulsant drugs in the treatment of refractory epilepsies of child and adult and for the treatment of anxiety of adult. It is mainly metabolized in desmethylclobazam, or norclobazam, active metabolite, present in a concentration approximately eight times superior to that of the parent drug, but with an activity of the order of 20 to 40% of that of clobazam. Elimination half-life of clobazam is of 18 h while that of norclobazam is from 40 to 50 h. There is a large interindividual variability in the plasma concentrations. Furthermore, clobazam being prescribed in add-on with the other anticonvulsant drugs in resistant epilepsies, concentration-effect relationship is difficult to bring to light, since, in many studies, the patients who did not answer received the highest doses. Adverse reactions are moderated, appearing more often for the highest concentrations; also the phenomenon of tolerance seems more frequent in high concentrations. However, because of the kinetic interactions, a dosage of clobazam and norclobazam can be useful in certain cases. There is no validated therapeutic range, but the usual concentrations are in the range of 100-300 microg/L for the parent drug and about ten times more for the metabolite. The level of proof of the interest of the Therapeutic Drug Monitoring for this molecule is estimated in: rather useless.

Curcumin ameliorates cognitive dysfunction and oxidative damage in phenobarbitone and carbamazepine administered rats

The antiepileptic drugs, phenobarbitone and carbamazepine are well known to cause cognitive impairment on chronic use. The increase in free radical generation has been implicated as one of the important mechanisms of cognitive impairment by antiepileptic drugs. Curcumin has shown antioxidant, anti-inflammatory and neuro-protective properties. Therefore, the present study was carried out to investigate the effect of chronic curcumin administration on phenobarbitone- and carbamazepine-induced cognitive impairment and oxidative stress in rats. Pharmacokinetic interactions of curcumin with phenobarbitone and carbamazepine were also studied. Vehicle/drugs were administered daily for 21days to male Wistar rats. Passive avoidance paradigm and elevated plus maze test were used to assess cognitive function. At the end of study period, serum phenobarbitone and carbamazepine, whole brain malondialdehyde and reduced glutathione levels were estimated. The administration of phenobarbitone and carbamazepine for 21days caused a significant impairment of learning and memory as well as an increased oxidative stress. Concomitant curcumin administration prevented the cognitive impairment and decreased the increased oxidative stress induced by these antiepileptic drugs. Curcumin co-administration did not cause any significant alteration in the serum concentrations of both phenobarbitone as well as carbamazepine. These results show that curcumin has beneficial effect in mitigating the deterioration of cognitive functions and oxidative damage in rats treated with phenobarbitone and carbamazepine without significantly altering their serum concentrations. The findings suggest that curcumin can be considered as a potential safe and effective adjuvant to phenobarbitone and carbamazepine therapy in preventing cognitive impairment associated with these drugs.

Difficulties in Treatment and Management of Epilepsy and Challenges in New Drug Development

Epilepsy is a serious neurological disorder that affects around 50 million people worldwide. Almost 30% of epileptic patients suffer from pharmacoresistance, which is associated with social isolation, dependent behaviour, low marriage rates, unemployment, psychological issues and reduced quality of life. Currently available antiepileptic drugs have a limited efficacy, and their negative properties limit their use and cause difficulties in patient management. Antiepileptic drugs can provide only symptomatic relief as these drugs suppress seizures but do not have ability to cure epileptogenesis. The long term use of antiepileptic drugs is limited due to their adverse effects, withdrawal symptoms, deleterious interactions with other drugs and economic burden, especially in developing countries. Furthermore, some of the available antiepileptic drugs may even potentiate certain type of seizures. Several in vivo and in vitro animal models have been proposed and many new antiepileptic drugs have been marketed recently, but large numbers of patients are still pharmacoresistant. This review will highlight the difficulties in treatment and management of epilepsy and the limitations of available antiepileptic drugs and animal seizure models.

Rufinamide: a novel broad-spectrum antiepileptic drug

The last 20 years have witnessed a tremendous explosion in the number of antiepileptic drugs (AEDs) as well as the introduction of AEDS developed for specific epilepsy syndromes. The study of the efficacy and side effect profile of AEDs for unique epilepsy syndromes has allowed neurologists to utilize evidence-based medicine when treating patients. In late 2008, the Food and Drug Administration approved rufinamide for adjunctive use in the treatment of seizures associated with Lennox-Gastaut syndrome. This unique chemical compound is also the first new AED to reach the market in the United States having a pediatric indication prior to approval for adults. Rufinamide appears to have a broad spectrum of efficacy, is well tolerated, and may be rapidly initiated--properties that will likely extend its use outside of Lennox-Gastaut syndrome.

Extended-release formulations of antiepileptic drugs: rationale and comparative value

Extended-release products are designed to prolong the absorption of drugs with short half-lives, thereby allowing longer dosing intervals while minimizing fluctuations in serum drug levels. The relationship between serum drug concentration and clinical effects of antiepileptic drugs (AEDs) can be complex and reducing fluctuations in serum drug levels is not equally advantageous for all AEDs. Extended-release formulations have been shown to be particularly valuable for carbamazepine, whereas for other AEDs advantages, other than prolongation of the dosing interval, have not been clearly demonstrated. Differences in bioavailability may exist between extended-release and immediate-release formulations and among different brands of extended-release products. Therefore, when switching from one formulation to another, careful monitoring of clinical response and attention to the need for dose adjustment are warranted.

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.