Felbamate

Treatment and care of women with epilepsy before, during, and after pregnancy: a practical guide

Women with epilepsy (WWE) wishing for a child represent a highly relevant subgroup of epilepsy patients. The treating epileptologist needs to delineate the epilepsy syndrome and choose the appropriate anti-seizure medication (ASM) considering the main goal of seizure freedom, teratogenic risks, changes in drug metabolism during pregnancy and postpartum, demanding for up-titration during and down-titration after pregnancy. Folic acid or vitamin K supplements and breastfeeding are also discussed in this review. Lamotrigine and levetiracetam have the lowest teratogenic potential. Data on teratogenic risks are also favorable for oxcarbazepine, whereas topiramate tends to have an unfavorable profile. Valproate needs special emphasis. It is most effective in generalized seizures but should be avoided whenever possible due to its teratogenic effects and the negative impact on neuropsychological development of in utero-exposed children. Valproate still has its justification in patients not achieving seizure freedom with other ASMs or if a woman decides to or cannot become pregnant for any reason. When valproate is the most appropriate treatment option, the patient and caregiver must be fully informed of the risks associated with its use during pregnancies. Folate supplementation is recommended to reduce the risk of major congenital malformations. However, there is insufficient information to address the optimal dose and it is unclear whether higher doses offer greater protection. There is currently no general recommendation for a peripartum vitamin K prophylaxis. During pregnancy most ASMs (e.g. lamotrigine, oxcarbazepine, and levetiracetam) need to be increased to compensate for the decline in serum levels; exceptions are valproate and carbamazepine. Postpartum, baseline levels are reached relatively fast, and down-titration is performed empirically. Many ASMs in monotherapy are (moderately) safe for breastfeeding and women should be encouraged to do so. This review provides a practically oriented overview of the complex management of WWE before, during, and after pregnancy.

Cenobamate tablets as a treatment for focal-onset seizures in adults

Introduction: Despite the introduction of numerous new antiseizure medications (ASMs) still about one-third of epilepsies remain drug-resistant. Therefore, new compounds with advanced efficacy are urgently needed. Cenobamate (CNB) is a new ASM that has been recently introduced in the United States for the treatment of adults with focal-onset seizures. The approval in Europe is under way.Areas covered: This review covers the pharmacological profile of CNB, the proof-of-concept trial, the two double-blind, placebo-controlled phase 2 trials investigating adjunct CNB in adults with focal-onset seizures, one open-label safety trial, and a variety of published abstract material that provided additional post hoc data.Expert opinion: In two placebo-controlled randomized multicenter phase 2 trials adjunct CNB showed unusually high efficacy with rates of seizure-free people with epilepsy (PWE) partially beyond 20%. However, during the clinical program cases of drug-related reactions with eosinophilia and systemic symptoms (DRESS syndrome) occurred. Therefore, an open-label safety study was performed in more than 1300 PWE with particularly slower titration schedules which did not add more cases with similar reactions. Taking into consideration the promising efficacy and the safety experience from the open-label trial, CNB applied according to the meanwhile recommended titration strategy, might offer a new prospect.

[Cenobamate-a new perspective for epilepsy treatment]

In spite of the introduction of numerous new antiseizure drugs (ASD) over the last decades, the percentage of drug-resistant epilepsies has remained almost stable. To achieve seizure freedom in such patients with any modified ASD regimen is an exception. Cenobamate (CNB) is a new ASD that showed unusually high efficacy in the pivotal placebo controlled, randomized trials. In both studies (C013 and C017), the rate of seizure-free patients was sometimes more than 20% and thus in a range never reached over the last decades in comparable trials with other new ASDs. This suggests that CNB which is already approved in the USA might actually offer a new and encouraging perspective for epilepsy treatment concerning efficacy. In this review the pharmacological profile, the currently known mode of action, and the results of the clinical trials are summarized.

Urolithiasis in patients on high dose felbamate

PURPOSE

We report 4 cases of felbamate urolithiasis. We identified only 1 prior case report of a felbamate stone. Felbamate is an antiepileptic drug used to treat refractory seizures and has minor side effects when given in recommended doses. We analyzed the characteristics, evaluation, treatment and outcomes in this challenging group of patients.

MATERIALS AND METHODS

Following institutional review board approval, we conducted a retrospective chart review of all patients who presented with a diagnosis of urolithiasis, were on felbamate and had stone analysis consistent with a felbamate origin.

RESULTS

All 4 patients had refractory seizures and 3 had severe developmental delay. Presentation ranged from an incidental finding to gross hematuria to agitation and pain. Stones were not visible on plain x-ray except in 1 case involving mixed stone composition. Decrease or cessation of the drug has not been feasible in 2 patients, and 3 patients have had recurrent stones. Initial stone analysis did not correctly identify the stone composition as felbamate in 2 cases, suggesting that the origin of these stones may not always be recognized.

CONCLUSIONS

We report the occurrence of felbamate stones in a series of patients on high dose felbamate therapy. Accurate diagnosis is made more difficult by the clinical complexity of the patient population (including severe developmental delay), the radiolucent nature of the stones and the possibility of inaccurate analysis of stone composition.

Use of Antiepileptic Drugs in Patients with Kidney Disease

The number of medications used to treat different types of seizures has increased over the last 10-15 years. Most of the newer antiepileptic drugs (AEDs) are likely to be unfamiliar to many nephrologists. For both the older and newer AEDs, basic pharmacokinetic information, recommendations for drug dosing in patients with reduced kidney function or who are on dialysis, and adverse renal and fluid-electrolyte effects are reviewed. Newer AEDs are less likely to have significant drug-drug interactions than older agents, but are more likely to need dosage adjustment in patients with reduced kidney function. The most common renal toxicities of these drugs include metabolic acidosis, hyponatremia, and nephrolithiasis; interstitial nephritis and other adverse effects are less common. Little is known about the clearance of most of the newer AEDs with high-efficiency hemodialyzers or with peritoneal dialysis. Monitoring of drug levels when available, careful clinical assessment of patients taking AEDs, and close collaboration with neurologists is essential to the management of patients taking AEDs.

New generation anticonvulsants for the treatment of epilepsy in children

In the last 12 years, 10 new anticonvulsants have been approved by the U.S. Food and Drug Administration and, as a result, the treatment options for children and adults with epilepsy have been expanded considerably. These new generation antiepileptic drugs offer equal efficacy with improved tolerability, pharmacokinetic properties, and side effect profiles compared with the traditional drugs. With many new medications available, the clinician treating children with epilepsy must be well versed in the application of these drugs to their patient population. This manuscript will review the indications, mechanism of action, pharmacokinetics, adverse effects, and dosing of the new generation of anticonvulsant medications.

Characteristics of patients initiated on the new antiepileptic drugs: a PADS study

Whereas randomized controlled trials remain a standard for evaluating and comparing efficacy and safety of the new antiepileptic drugs (AEDs), postmarketing drug research offers a useful means of comparing efficacy and safety of new AEDs. However, differences in baseline characteristics of patients in different drug groups create the potential for bias in drug comparison studies. In this study, baseline demographic characteristics of 1,386 patients initiating lamotrigine (LTG), tiagabine (TGB), or topiramate (TPM) were compared to identify patient characteristics that may influence AED use in epilepsy patients. Data were collected at 14 epilepsy centers and included medications, seizure types and syndromes, and prior adverse events. There were 402 patients in the LTG group, 725 TPM, and 259 TGB. The groups differed both in their number of concurrent AEDs (p<0.001) and in their number of prior AEDs (p<0.01). There was no difference in proportion with partial versus generalized epilepsy syndromes. The groups differed in the proportions of patients with complex partial seizures (p=0.049), primary generalized tonic-clonic seizures (p=0.01), and myoclonic seizures (p=0.03). Baseline behavioral adverse event rate was lowest in patients initiating TPM (p<0.01); LTG patients had the lowest rate of prior AED-related rash (p=0.02). There was no relationship between AED assignment and patient age, age of epilepsy onset, epilepsy duration, institutionalization status, gender, or psychiatric history. Numerous epidemiological differences were identified among patients placed on the new AEDs, including current and prior AED profiles, seizure types, and prior adverse event history. Accounting for these differences is of crucial importance because they may bias conclusions of nonrandomized post-marketing trials comparing the drugs.

Felbamate urolithiasis

PURPOSE

To report a case of felbamate (FBM) urolithiasis.

METHODS

Urographic imaging [sonography, abdominal computed tomography (CT), intravenous pyelogram, voiding cystourethrogram] and urologic procedures (cystoscopy with lithotripsy, ureteral stent) to define and capture the stones. Stone identification was by infrared spectroscopy and gas chromatography/mass spectrometry.

RESULTS

A 15-year-old boy had painful hematuria, bilateral ureteral obstruction, and urinary retention. Kidney, bladder, and ureteral stones were found, and ureteral stent placement was required to relieve obstruction. The stone material was identified as FBM by chemical analysis. Stone formation ceased with discontinuation of FBM.

CONCLUSIONS

FBM urolithiasis can occur, and possible contributory factors include high felbamate dosage, drug polypharmacy, and risk factors for forming stones of other types. FBM urolithiasis may be heralded by crystalluria.

Effect of antiepileptic drugs on sleep

The interactions between sleep and epilepsy are well known. A nodal point of the relationship between sleep and epilepsy is represented by pharmacological treatment. Sleep disturbances such as drowsiness are among the most frequent side effects of treatment with antiepileptic drugs, since they can deeply modify both sleep architecture and the sleep-wake cycle. Severe daytime somnolence affects patients' activities and it may facilitate the occurrence of seizures. These considerations underline the importance of antiepileptic drugs having anticonvulsant properties that do not negatively influence sleep and daytime somnolence. In this paper we review some relevant aspects of the effects of antiepileptic drugs on sleep.

Nonfocal generalized tonic-clonic seizures: response during long-term topiramate treatment. Topiramate YTC/YTCE Study Group

PURPOSE

A total of 131 adults and children (mean age, 27 years; range, 3-59 years) with generalized tonic-clonic seizures (GTCS) of nonfocal origin resistant to other antiepileptic drugs (AEDs) were treated with open-label topiramate (TPM) after completing double-blind placebo-controlled trials.

RESULTS

The mean duration of open-label TPM treatment was 387 days (range, 14-909 days); the mean TPM dose was 7 mg/kg/day (range, 1-16 mg/kg/day). At the last study visit, the frequency of GTCS was reduced > or =50% from baseline in 63% of patients and by > or =75% in 44%. Among patients treated > or =6 months, 16% were GTCS free > or =6 months despite a pretreatment seizure frequency of one GTCS/week (median). Treatment with TPM was being continued in 82% of patients (n = 107) at the last visit. During treatment periods of up to 2.5 years, 11 (8%) patients discontinued TPM because of adverse events and seven (5%) because of inadequate seizure control.

CONCLUSIONS

TPM therapy was well tolerated, and seizure control was maintained with long-term, open-label therapy in patients with GTCS, leading to prolonged seizure-free intervals in some patients with seizures previously resistant to AED therapy.

Helping patients who say they cannot sleep. Practical ways to evaluate and treat insomnia

Why do some people spend most of the night tossing and turning while others drop off as quickly as a cat in the sun? There are many possible explanations for problems with falling and staying asleep and, sometimes, patients actually get a lot more sleep than they think they do. Each type of insomnia has its own set of symptoms, which can be used, along with appropriate diagnostic tools, to help in identification. In this article, Dr. Attarian describes differential diagnosis and summarizes the best treatment approaches to the common causes of insomnia.

Metabolism and excretion of mood stabilizers and new anticonvulsants

1. The mood stabilizers lithium, carbamazepine (CBZ), and valproate (VPA), have differing pharmacokinetics, structures, mechanisms of action, efficacy spectra, and adverse effects. Lithium has a low therapeutic index and is renally excreted and hence has renally-mediated but not hepatically-mediated drug-drug interactions. 2. CBZ has multiple problematic drug-drug interactions due to its low therapeutic index, metabolism primarily by a single isoform (CYP3A3/4), active epoxide metabolite, susceptibility to CYP3A3/4 or epoxide hydrolase inhibitors, and ability to induce drug metabolism (via both cytochrome P450 oxidation and conjugation). In contrast, VPA has less prominent neurotoxicity and three principal metabolic pathways, rendering it less susceptible to toxicity due to inhibition of its metabolism. However, VPA can increase plasma concentrations of some drugs by inhibiting metabolism and increase free fractions of certain medications by displacing them from plasma proteins. 3. Older anticonvulsants such as phenobarbital and phenytoin induce hepatic metabolism, may produce toxicity due to inhibition of their metabolism, and have not gained general acceptance in the treatment of primary psychiatric disorders. 4. The newer anticonvulsants felbamate, lamotrigine, topiramate, and tiagabine have different hepatically-mediated drug-drug interactions, while the renally excreted gabapentin lacks hepatic drug-drug interactions but may have reduced bioavailability at higher doses. 5. Investigational anticonvulsants such as oxcarbazepine, vigabatrin, and zonisamide appear to have improved pharmacokinetic profiles compared to older agents. 6. Thus, several of the newer anticonvulsants lack the problematic drug-drug interactions seen with older agents, and some may even (based on their mechanisms of action and preliminary preclinical and clinical data) ultimately prove to have novel psychotropic effects.

Electrophysiological effects of felbamate

Felbamate is a broad spectrum antiepileptic drug recently introduced into clinical practice for controlling seizures in patients affected by Lennox-Gastaut epilepsy, complex partial seizures or otherwise intractable epilepsies. However, the cellular mechanisms by which the drug exerts its anticonvulsant actions are not fully understood. The aim of the present article is to outline the possible mechanisms of action of felbamate as suggested by findings obtained with electrophysiological approaches.

Pharmacotherapeutic issues for women of childbearing age with epilepsy

OBJECTIVE

To provide an overview of key pharmacotherapeutic issues in epilepsy for the woman of childbearing potential.

DATA SOURCES

A MEDLINE search (1966-1997) was done to identify pertinent literature. Chapters in epilepsy textbooks, pregnancy registries, and their respective bibliographies were also evaluated.

STUDY SELECTION AND DATA EXTRACTION

All identifiable sources written in English were evaluated.

DATA SYNTHESIS

Epilepsy is a common neurologic disorder. It is estimated that nearly 1 million American women of childbearing age have epilepsy. There are many women's health issues in epilepsy. These include menstrual cycle influences on seizure activity, contraceptive-antiepileptic drug interactions, pharmacokinetic changes during pregnancy, teratogenicity of antiepileptic drugs, breast-feeding, and quality of life. These issues challenge both the woman with epilepsy and the many healthcare providers involved in her care. This article reviews these issues and makes recommendations. It addresses both the first-generation antiepileptic drugs (phenobarbital, phenytoin, carbamazepine, valproic acid) and the newer or second-generation agents (felbamate, gabapentin, lamotrigine, topiramate, tiagabine).

CONCLUSIONS/RECOMMENDATIONS

Drug interactions between enzyme-inducing antiepileptic drugs and contraceptives are well documented. Higher doses of oral contraceptives or a second contraceptive method are suggested if epileptic women use an enzyme-inducing antiepileptic drug. Planned pregnancy is highly recommended and counseling before conception is crucial. Prepregnancy counseling should include, but is not limited to, folic acid supplementation, optimal control of seizure activity, monotherapy with the lowest effective antiepileptic drug dose, and medication adherence. Patient information should be provided about the risk of teratogenicity and the importance of prenatal care. Antiepileptic drug dosage adjustments may be necessary and should be based on clinical symptoms, not solely on serum drug concentrations. While the future holds promise for many aforementioned women's issues in epilepsy, many questions remain to be answered.

New drugs for epilepsy

Seizure freedom with no side-effects is the aim of treatment, and new antiepileptic drugs have not lived up to expectations; only a few patients with chronic epilepsy have been rendered seizure-free. These treatments have side-effects but their safety profile may be better than older alternatives, although chronic effects have not yet been established. This article reviews newly marketed antiepileptic drugs. It concentrates on shortcomings of current antiepileptic treatment and on the way drugs are developed. A new approach to treatment is long overdue. The development of rational antiepileptic treatments should be strongly encouraged. More clinically relevant paradigms need to be developed and incorporated into clinical trial programmes as these are presently biased in their designs towards regulatory issues.

Antiepileptic drugs as a cause of worsening seizures

PURPOSE

Although the paradoxical ability of antiepileptic drugs (AEDs) to increase seizure activity has been recognized for decades, the underlying mechanisms are poorly understood and few systematic studies have addressed this problem. This article is intended to provide a critical review of available literature on this topic.

METHODS

Information was collected by means of computerized literature searches, screening of journals and textbooks, and consultation with colleagues. Mechanisms which potentially might precipitate underlying drug-induced exacerbation of seizures were considered based on available pharmacologic and clinical knowledge.

RESULTS

The reviewed information suggests that a paradoxical increase in seizure frequency may occur as a result of at least two separate mechanisms. The first appears to involve a nonspecific manifestation of drug intoxication; seizure-worsening in this context is usually reversible by dosage reduction or elimination of unnecessary polypharmacy. Conversely, the other mechanism may involve a distinct adverse primary action of the drug in specific seizure types or in syndromic forms. Carabamazepine, in particular, has been reported to precipitate or exacerbate a variety of seizures, most notably absence, atonic, or myoclonic seizures in patients with generalized epilepsies characterized by bursts of diffuse and bilaterally synchronous spike-and-wave EEG activity. Phenytoin and vigabatrin also have been implicated in worsening of seizures, particularly generalized seizures, whereas gabapentin has been associated repeatedly with precipitation of myoclonic jerks. Benzodiazepines occasionally have been reported to precipitate tonic seizures, especially when given intravenously to control other seizure types in patients with Lennox-Gastaut syndrome. Seizure deterioration has been reported also with other drugs; though in most cases evidence is still insufficient for meaningful conclusions to be drawn.

CONCLUSIONS

Drug-induced exacerbation of seizures is a serious and common clinical problem that is often unrecognized or overlooked by the treating physician. Its occurrence appears to be related to three possible causes: an incorrect diagnosis of seizure type or syndromic form, lack of knowledge about certain drugs that are contraindicated in specific types of epilepsies, or to prescription of excessive drug dosages and drug combinations. Further studies are required to evaluate the prevalence of this phenomenon of drug-induced exacerbation of seizures, to investigate its mechanisms in greater detail and to characterize additional prognostic factors that may be used for early identification of patients at risk.

Anticonvulsant activity of felbamate in amygdala kindling model of temporal lobe epilepsy in rats

PURPOSE

Previous studies have demonstrated that felbamate (FBM, 2-phenyl-1,3-propanediol dicarbamate) at nontoxic doses exerts potent anticonvulsant activity in a variety of animal epilepsy or seizure models. We further characterized the anticonvulsant activity of FBM by using the kindling model of temporal lobe epilepsy (TLE).

METHODS

The experiments were performed in fully kindled rats. The anticonvulsant effect of FBM was assessed by determining seizure severity, afterdischarge (AD) duration and seizure duration either at the focal seizure threshold, or after suprathreshold stimulation. In addition, the neurological performance of kindled rats after FBM administration was evaluated in the open field and by the rotorod test.

RESULTS

FBM at doses of 12.5-50 mg/kg, given intraperitoneally (i.p.) 60 min before testing, dose-dependently increased the AD threshold (ADT). The maximal effect was achieved after the highest dose tested and reached almost 600% of the control ADT. This dose of FBM significantly diminished other seizure parameters, e.g., seizure severity, seizure duration, and AD duration. When the rats were stimulated with suprathreshold current (500 microA) seizure severity was moderately but significantly reduced. No behavioral abnormalities were noted in kindled rats after administration of either of the doses.

CONCLUSIONS

FBM potently increases the threshold for focal seizures and reduces seizure severity, seizure duration, and AD duration at doses that produce no adverse behavioral effects in amygdala-kindled rats. These data are thus compatible with clinical experience with FBM in TLE and substantiate that kindling is a good predictor of anticonvulsant activity against TLE.

A review of the newer antiepileptic drugs and the ketogenic diet

Since 1994, three new antiepileptic drugs, felbamate, lamotrigene, and gabapentin, have been released for the treatment of epilepsy. The present paper provides an overview of these three drugs and reviews their potential uses in pediatric epilepsy even though felbamate is the only one with an approved use in children. Topiramate and vigabatrin, which are under investigation, are briefly reviewed. In addition, a discussion of the ketogenic diet is included because of its recent publicity. Patient examples included provide clinical illustrations for the reader.

Lamotrigine pharmacokinetics in patients receiving felbamate

Drug interactions can significantly complicate the management of patients receiving multiple medications. It is essential therefore that potential pharmcokinetic interactions be evaluated as new antiepileptic medications are introduced. Lamotrigine (LTG) is a recently marketed medication whose pharmacokinetics are significantly influenced by concomitant drugs. Felbamate (FBM), another relatively new antiepileptic agent has been associated with multiple interactions including both enzyme induction and inhibition. The purpose of the present pilot study was to evaluate potential differences in lamotrigine kinetics in six patients concomitantly receiving FBM compared to five patients receiving lamotrigine as monotherapy. There was no statistically significant differences in either apparent LTG oral clearance (0.026 +/- 0.005 vs. 0.024 +/- 0.01 l/kg per h, respectively), or in mean elimination half-life (33.7 +/- 7.5 vs. 40.2 +/- 15.05 h, respectively). Oral clearance values in our patients are also consistent with data reported previously in the literature. Data from this pilot study suggest that a marked effect of FBM upon lamotrigine pharmacokinetics is unlikely.

Tiagabine

Tiagabine is a novel antiepileptic drug that was designed to block gamma-aminobutyric acid uptake by presynaptic neurons and glial cells. It has been shown to be effective against partial seizures in adults and adolescents. Preliminary pediatric data are also encouraging. This article reviews the available animal and human data on the pharmacokinetics, efficacy, and safety of tiagabine.

Overview of the safety of newer antiepileptic drugs

Standard antiepileptic drugs (AEDs) are associated with a wide variety of acute and chronic adverse events and with many interactions with each other and with non-AEDs that complicate patient management. The safety and interaction profiles of the newer AEDs have also been intensively studied. Safety data are available for six of the newer AEDs, lamotrigine (LTG), vigabatrin (VGB), gabapentin (GBP), tiagabine (TGB), felbamate (FBM), and topiramate (TPM). The potential for the most recently developed AEDs for producing rare idiosyncratic reactions cannot be ascertained until additional patient exposures have been reported from careful postmarketing surveillance.

Pharmacokinetic interactions of the new antiepileptic drugs

Therapy with traditional antiepileptic drugs is associated with a wide range of pharmacokinetic drug-drug interactions. In particular, enzyme induction, enzyme inhibition and displacement from protein binding may result in important changes in serum concentrations of antiepileptics. Relevant interactions have also been described for some new antiepileptics. Felbamate increases serum concentrations of phenytoin, phenobarbital and valproic acid (sodium valproate). On the other hand, it reduces concentrations of carbamazepine and increases concentrations of its metabolite carbamazepine-10,11-epoxide. Concentrations of felbamate itself are reduced by phenytoin and carbamazepine. Concentrations of lamotrigine are considerably increased by valproic acid and decreased by phenytoin, carbamazepine and phenobarbital (phenobarbitone). Vigabatrin reduces serum concentrations of phenytoin by approximately 20%. On the other hand, some new antiepileptics have the important advantage of not interfering with the metabolism of other antiepileptics; this is the case for gabapentin, lamotrigine and oxcarbazepine. Furthermore, the pharmacokinetics of gabapentin, oxcarbazepine and vigabatrin are independent of concomitant drugs. These aspects are especially important as, until now, new antiepileptics have been most often utilised as add-on therapy.

Rational polypharmacy

The medical treatment of seizure disorders is a complex process, requiring extensive interaction and co-operation between physician and patient. The physician must have an accurate diagnosis of the patient's illness and a comprehensive understanding of seizures and seizure disorders. The physician must consider specific individual characteristics of the patient, especially those that will influence the choice of medical therapy, and the interrelationship between the patient's lifestyle and the seizure disorder must be appreciated to maintain an optimal quality of life. Finally, the physician must have a thorough understanding of the pharmacology of antiepileptic drugs (AEDs) and experience with their therapeutic applications. It is important for patients to be fully involved in the treatment of their illness. Each patient should be informed about their disorder, should be involved in all therapeutic plans and strategies, and should be a responsible and active participant in treatment.