Felbamate Levels in Patients with Epilepsy

The usefulness of felbamate (FBM) levels in managing epilepsy patients has not been determined. The purpose of the present study was to determine if FBM levels obtained at routine office visits correlated with side effects reported by patients. We determined FBM levels by high-pressure liquid chromatography (HPLC) of 46 epilepsy patient plasma specimens (41 patients) and assessed medication toxicity and seizure frequency by a questionnaire. Thirty-six patients were treated with other antiepileptic drugs (AEDs); concomitant AED levels not in ranges believed to cause toxicity. FBM levels ranged from 9 to 134 pg/ml, and were divided into three groups for analysis, resulting in low-range (9–36 pg/ml), mid-range (37–54 μg/ml), and high-level (44–134 pg/ml) groups. Anorexia and complaints of severe side effects were reported significantly more often in the high-level group as compared with the low- and midrange groups. Significantly more patients in the high-level group (1043) reported decreased seizure frequency, as compared with 12 of 30 of patients in the low-and midrange groups combined. FBM levels correlated linearly with doses overall, but most closely in FBM monotherapy patients.     

Monotherapy Trials of New Antiepileptic Drugs

Summary: A number of clinical trials that test the efficacy and safety of the newer antiepileptic drugs (AEDs) have recently been concluded. Two dose-response trials in inpatients with refractory partial seizures and outpatients with newly diagnosed partial epilepsy established the efficacy of gabapentin as monotherapy. Lamotrigine was found to have efficacy similar to that of phenytoin and carbamazepine (CBZ) and to be better tolerated than CBZ in patients with newly diagnosed epilepsy. It was also shown to have efficacy as monotherapy in partial seizures, based on the results of an active controlled trial, and in the treatment of absence seizures, based on the results of a responder-enriched study. Topiramate as monotherapy was found to be efficacious for treatment of partial-onset seizures, based on the results of a single-center dose-response trial. A dose-response trial that tested the efficacy of tiagabine monotherapy in patients with refractory partial epilepsy was uninformative. Oxcarbazepine was found to be safe and efficacious in four comparative trials in patients with newly diagnosed epilepsy as well as in one placebo-controlled inpatient trial in patients with refractory partial seizures.     

Antiepileptic Drug Therapy: General Treatment Principles and Application for Special Patient Populations

Summary: Over the past 10 years, the goal of treating epilepsy has evolved from attaining complete control of seizures, regardless of medication-related side effects or psychosocial problems, to enabling the patient to lead a lifestyle consistent with his or her capabilities. The recent introduction of new medications has brought hope to patients who have previously been unable to function optimally because of refractory seizures or side effects. A rational approach to selecting antiepileptic drug (AED) therapy for a particular patient would require a detailed understanding of the underlying cause(s) of seizures in that patient. Unfortunately, this is often not possible. Furthermore, currently available AEDs have been tested on the basis of seizure type rather than etiology. Nevertheless, an individualized empirical approach based on an open dialog with the patient and perseverance is often successful. There have also been significant advances in the understanding of seizures at the cellular level, notably in the role of γ-aminobutyric acid. Medical, social, and psychosocial issues relevant to particular patient populations (such as women of childbearing age and elderly patients) also must be considered when treatment plans are formulated. The recent addition of new AEDs, with unique mechanisms of action and favorable pharmacokinetic and tolerability profiles, has greatly widened the range of therapeutic options for patients.     

Monotherapy or Polytherapy for Epilepsy Revisited: A Quantitative Assessment

Summary: Some investigators argue that treating epilepsy with several antiepileptic drugs (AEDs) simultaneously (polytherapy) may give rise to more adverse effects than monotherapy, but this argument lacks supporting quantitative data. To reexamine this issue, we recruited a cohort of patients from the outpatients of the Special Centres for Epilepsy in The Netherlands and from the outpatients of the Department of Neurology, Nijmegen University, The Netherlands. Two tools were used for analysis. All daily doses of antiepileptic drugs (AEDs) were standardized by the ratio of prescribed daily dose to defined daily dose (PDD/DDD). The DDD is the assumed average effective daily dose for a drug used for its main indication in adults. The assignment of DDD Values is the task of the World Health Organization (WHO) Collaborating Centre for Drugs Statistics Methodology and Nordic Council on Medicines, which regularly publishes Guidelines for Defined Daily Doses. The severity of adverse effects (AE) was assessed by using the Neurotoxicity Index and the Systemic Toxicity Index as developed by the VA Cooperative Study Group for their recent studies comparing the efficacy and tolerability of AEDs. One hundred sixty-one patients received monotherapy; all had a PDD/DDD ratio ≤2/day; 128 of 262 patients receiving polytherapy also had ≤2 PDD/DDD ratios/day. The mono- and polytherapy groups were stratified according to the PDD/DDD ratio. The prevalence of neurological AE for patients with similar PDD/DDD ratios was 50–80% for monotherapy patients and 50–80% for polytherapy patients. The difference between the mono- and polytherapy groups was not significant. The prevalence of neurological AE for patients receiving polytherapy with a PDD/DDD ratio >2.0 was 71–100%, whereas all patients with a PDD/DDD ratio >4.0 had neurological AE. This difference between patients with a PDD/DDD ratio ≤2.0 and those with >2.0 was statistically significant; p < 0.05. The severity of neurological AE also increased with dose, but appeared to peak at ～3.5 PDD/DDD ratio. Our study underscores the usefulness of applying quantitative methods to the analysis of drug AE. Comparison of monotherapy and polytherapy showed no difference for equipotent doses. Because distribution of the AED doses was uneven between the groups receiving mono- and polytherapy, our study permits only a tentative statement that the frequency and severity of AE is independent of the use of either. In addition, frequency and intensity of AE apparently are not very sensitive to changes in dose. An experimental prospective study is planned to verify or refute the conclusions of this observational pilot study.     

Felbamate

Summary: After the first year of clinical experience, felbamate (FBM) appears to be a valuable antiepileptic drug (AED) for the treatment of intractable epilepsy. However, many patients experience side effects that may discourage continued usage. These may be decreased by using a slower dose-escalation schedule and/or by being more aggressive in decreasing co-medication. The most common troublesome side effects are nausea and insomnia. With the recent observation of aplastic anemia, FBM should be considered only for persons with intractable epilepsy under the care of a physician familiar with FBM. Nevertheless, many patients have benefited significantly from FBM and have made a decision to continue receiving FBM at the presently known risk profile. A few more years of experience may be needed to more accurately determine the final place of FBM in the treatment of epilepsy.     

Felbamate: A Clinical Trial for Complex Partial Seizures

We performed a randomized, double-blind, three-period cross-over study of felbamate (FBM, 2-phenyl-1,3-propanediol dicarbamate: Carter-Wallace 554) in patients with complex partial seizures. Patients continued carbamazepine (CBZ) throughout the study and were observed in the hospital for the entire trial period. The entry criteria required at least six seizures in a 3-week baseline period (and no more than 1 week with a single seizure) with CBZ alone. Thirty subjects were randomized. Two left the study after randomization, 1 owing to seizure exacerbation, and 1 owing to hyponatremia, which may have been related to CBZ therapy. The daily dosage of 50 mg/kg (maximum 3,000 mg) FBM per day was well tolerated by all 28 patients who completed the study. Only mild adverse experience were observed during the trial. FBM reduced CBZ level (p less than 0.0001; 95% confidence interval -28%, -20%). There was no significant difference in seizure frequency between placebo and FBM periods (one-sided p = 0.172), but when a correction was made for the lower CBZ level noted during FBM periods, the data suggested a strong antiseizure effect of FBM.     

Conversion to High Dose Gabapentin Monotherapy in Patients with Medically Refractory Partial Epilepsy

Summary: Purpose: To evaluate the safety and efficacy of high dose gabapentin (GBP) monotherapy (3,0004,800 mg/ day) in patients with medically refractory partial epilepsy.
Methods: GBP monotherapy at daily doses up to 4,800 mg was attempted in patients participating in the open-label phase of a double-blind, dose-controlled, GBP monotherapy trial. For those who achieved monotherapy, the types and severity of adverse events were assessed and the average seizure frequency per 28 days while maintained on the highest daily GBP dose was compared to the seizure frequency during the baseline phase of the double blind trial. Correlation analysis between GBP serum level, total daily dose, and percentage of seizure change from baseline was performed.
Results: A total of 45 patients participated in the open-label phase of the trial and 23 (51%) were converted successfully to GBP monotherapy. In those patients, the average daily gabapentin dose was 3,900 mg and the mean length of follow-up was 252 days. Compared to baseline, there was a mean reduction of 54%, 43%, and 14% for simple partial, complex partial and secondarily generalized seizures respectively, while maintained on high-dose GBP monotherapy. A significant linear correlation between daily GBP dosage (2,4004,800 mg) and resultant mean serum levels was found (r = 0.51; p < 0.01). There was no significant correlation between seizure frequency and total daily GBP dose or with serum levels. High-dose GBP monotherapy was well tolerated; only one patient exited the trial because of adverse events. The most common adverse event was tiredness/sleepiness and was not dose-related.
Conclusions: GBP monotherapy is well tolerated in daily doses of up to 4,800 mg and is effective in a subgroup of patients with medically refractory partial epilepsy.     

Prototype Antiepileptic Drug Clinical Development Plan

Antiepileptic drug (AED) development has been generally difficult owing to many factors: regulatory requirements for demonstration of efficacy and safety, subject availability, traditional trial designs, and physicians' beliefs about epilepsy and its treatment. The U.S. Food and Drug Administration (FDA) regulations require a new drug to be shown safe and effective for its intended use before it can be marketed. The unambiguous proof required is a formidable hurdle for AED development. We report a recent clinical development plan highlighting innovations in clinical trial design that have addressed these requirements, discuss alternative endpoints, and compare the results of various trial designs at various stages of development. This model clinical development plan includes trials relevant to all three clinically relevant contexts in which an AED might be used: as an adjunct to an existing regimen, as a substitution for much of an existing AED regimen, and as monotherapy.     

Felbamate: Successful Development of a New Compound for the Treatment of Epilepsy

Summary: Felbamate (FBM) is an effective and safe novel antiepileptic drug (AED) for add-on treatment in adults with refractory partial seizures as shown in three pivotal controlled trials. In addition, FBM is effective and safe in monotherapy in adults with refractory partial seizures. FBM is also effective and safe as add-on therapy for children and adults with refractory Lennox-Gastaut syndrome. The effective daily dosage is ˜30–45 mg/kg divided into three or four doses with resulting plasma concentrations of 50–80 mg/L. The safety profile of FBM is limited to mild gastrointestinal complaints, insomnia, and nonspecific CNS symptoms. Six pivotal controlled trials, with both classic and innovative design, showed that FBM is a useful AED.     

Response to Antiepileptic Drug Therapy: Winners and Losers

Summary:  Recent evidence suggests that the vast majority of people with epilepsy will respond to their first or second treatment regimen or will be refractory de novo. Two patients with symptomatic epilepsy secondary to underlying cortical dysplasias are presented to illustrate these different scenarios. Clinical observations can provide insights to the processes underlying pharmacoresistance.     

Effectiveness of First Antiepileptic Drug

PURPOSE: To investigate the interaction among efficacy, tolerability, and overall effectiveness of the first antiepileptic drug (AED) in patients with newly diagnosed epilepsy. METHODS: The 470 patients were diagnosed, treated and followed up from January 1984 at a single center. Outcome was classified as seizure freedom for at least the last year or failure of initial treatment because of inadequate seizure control, adverse events, or for other reasons. RESULTS: Overall, 47% of patients became seizure-free with the first prescribed AED. A higher proportion (p = 0.025) of patients with symptomatic or cryptogenic epilepsy changed treatment because of intolerable side effects (17%), and a lower proportion (p = 0.007) became seizure-free (43.5%) compared with those with idiopathic epilepsy (8.5% and 58%, respectively). Most patients (83%) received carbamazepine (CBZ; n = 212), sodium valproate (VPA; n = 101), or lamotrigine (LTG; n = 78). The majority of seizure-free patients required only a moderate daily AED dose (93.1% with < or =800 mg CBZ, 91.3% with < or =1,500 mg VPA, 93.8% with < or =300 mg LTG), with commonest dose ranges being 400-600 mg for CBZ, 600-1,000 mg for VPA, and 125-200 mg for LTG. Most withdrawals due to poor tolerability also occurred at or below these dose levels (CBZ: 98%; VPA: 100%; LTG: 75%). Patients taking CBZ (27%) had a higher incidence of adverse events necessitating a change of treatment than did those treated with VPA (13%) or LTG (10%), resulting in fewer becoming seizure-free (CBZ vs. VPA, p = 0.02; CBZ vs. LTG, p = 0.002). CONCLUSIONS: Nearly 50% of newly diagnosed patients became seizure-free on the first-ever AED, with >90% doing so at moderate or even modest dosing. Tolerability was as important as efficacy in determining overall effectiveness.     

Antiepileptic Drug Interactions

Summary: This article reviews the potential interactions of antiepileptic drugs (AEDs) and the pharmacokinetic and pharmacodynamic principles involved. It describes the absorptive and distributive properties of AEDs and the effects on protein binding, hepatic metabolism, and elimination resulting from co-administration of AEDs with food or other drugs. Drug behavior is a function of absorption, metabolism, distribution, and elimination. Administration of either multiple AEDs or a combination of AEDs plus drugs for other conditions can modify any of these physiologic processes, possibly resulting in complex interactions. These may include alterations in the bioavailability and absorption of a drug and changes in half-life and serum level through induction or inhibition of hepatic metabolism. In most cases, increases or decreases in serum concentrations will signal a drug interaction. In other cases, clinically significant drug interactions remain undetected owing to apparently stable serum concentrations. Co-administration of drugs may affect the rate of clearance of one or both drugs. The effect on clearance varies, owing to genetic factors, patient characteristics (age and presence of co-morbidities), and individual responses. AEDs that induce hepatic metabolism can also influence the metabolism of concomitantly administered non-epilepsy medications and can interfere with oral contraceptives, as well as vitamins D and K. Patients with renal insufficiency or advanced age may experience incomplete renal excretion and should receive reduced dosages of drug. Understanding the pharmacokinetics and pharmacodynamic properties of AEDs and the route of metabolism of all competing drugs is important for optimal management of patients with epilepsy and for prevention of avoidable drug interactions.     

Antiepileptic Drug Hypersensitivity Syndrome

Summary: : The antiepileptic drug hypersensitivity syndrome (AHS) is an adverse drug reaction associated with the aromatic antiepileptic drugs (AEDs) phenytoin (PHT), carbamazepine (CBZ), phenobarbital (PB), and primidone. The syndrome is defined by the triad of fever, skin rash, and internal organ involvement. It can also be caused by other drugs, such as sulfonamides, dapsone, minocycline, terbinafine, azathioprine, and allopurinol. Diagnosis of AHS may be difficult because of the variety of clinical and laboratory abnormalities and manifestations and because the syndrome may mimic infectious, neoplastic, or collagen vascular disorders. The incidence is approximately 1 in 3,000 exposures. AHS starts with fever, rash, and lymphadenopathy, within the fist 2–8 weeks after initiation of therapy. Internal manifestations include, among others, agranulocytosis, hepatitis, nephritis, and myostitis. AHS is associated with a relative excess of reactive oxidative metabolites of the AED. Insufficient detoxification may lead to cell death or contribute to the formation of antigen that triggers an immune reaction. Crossreactivity among PHT, CBZ, and PB is as high as 70–80%.