Monostars: an aid to choosing an antiepileptic drug as monotherapy

Long-term response and response patterns to antiepileptic drugs in patients with newly diagnosed epilepsy

OBJECTIVE

This study investigated the long-term response and response patterns to antiepileptic drugs (AEDs) in patients with newly diagnosed epilepsy.

METHODS

Patients who had been newly diagnosed with epilepsy and had at least 3-year follow-up records were enrolled. Their long-term response and response patterns to AEDs were retrospectively analyzed. Patients were divided into two groups, a controlled group and an uncontrolled group, according to whether 3-year seizure freedom (3YSF) was achieved. Multiple logistic regression analyses were used to identify risk factors associated with a poor drug response.

RESULTS

Of the 472 patients with epilepsy, 180 achieved immediate seizure control, 36 achieved early seizure control, 118 achieved late seizure control, and 138 did not achieve 3YSF. Patients who achieved 3YSF (334/472, 70.8%) were categorized into the controlled group. Among them, 53.9% (180/334) achieved 3YSF immediately, 10.8% (36/334) achieved 3YSF within 6 months, and 35.3% (118/334) achieved 3YSF after 6 months. Also in this group, 228 (228/472, 48.3%), 84 (84/472, 17.8%), 15 (15/472, 3.2%), and 7 (7/472, 1.5%) patients achieved 3YSF on the first, second, third, and fourth regimen, respectively. Multivariate analyses showed that multiple seizure types (odds ratio [OR] = 3.903, 95% confidence interval [CI]: 2.098-7.264; P < 0.001] and polytherapy (OR = 5.093, 95% CI: 3.183-8.149; P < 0.001) were independent risk factors for a poor drug response.

CONCLUSION

The 3YSF rate in this cohort was 70.8%. More than half of the patients achieved long-term remission immediately after treatment. The probability of attaining 3YSF decreased with the increase in number of drug regimens, especially in patients who experienced failure of two treatment regimens.

Recent Advances in Epilepsy Management

One of the most common neurological disorders is epilepsy, which, approximately affecting more than 40 million people worldwide. The situation worsens in the affected patient when the epilepsy becomes intractable, that simply means failure of anti-epileptic drugs (AED) to achieve seizure freedom. It is also associated with an increased prevalence of mental health disorders including anxiety, depression, and suicidal thoughts. The present review is focused on the recent advances being utilized world over for the effective management of epilepsy patients. The review article discusses the efficacy and importance of recent AED drugs in use for management of epilepsy on one hand and on other hand highlights the use of modern advancements like High frequency oscillations, Network analysis, Seizure localization, Epilepsy surgery in curing intractable epilepsy.

Treating Newly Diagnosed Epilepsy: The Canadian Choice

Background:

Choosing an antiepileptic medication to treat a patient with epilepsy can be a complicated process during which the treating physician must base her or his decision on efficacy and safety of each of many available drugs. The lack of comparative studies between medications is one of the reasons.

Methods:

We conducted a survey on the management of newly diagnosed epilepsy in adult patients. The surveyed were adult and pediatric neurologists with a subspecialty interest in epilepsy who were working in academic institutions or private practice across Canada. Scenarios presented were grouped in categories according to the epilepsy syndrome (absence epilepsy, juvenile myoclonic epilepsy, undetermined idiopathic generalized epilepsy, symptomatic or cryptogenic partial epilepsy, and unclassified epilepsy), the patient's gender and age. First and second step in medical treatment for status epilepticus were surveyed as well.

Results:

Forty one of 64 experts responded the survey (responder rate of 66%). The results revealed a consensus among Canadian epileptologists that the first choice of antiepileptic medication in generalized epilepsies was between valproate in men (chosen by 88% of respondents) and lamotrigine in women. In localization-related epilepsies, carbamazepine was the preferred drug of choice (chosen by 90% of respondents). In the treatment of status epilepticus, an initial intravenous dose of lorazepam (95% of respondents), followed by a second dose of lorazepam or intravenous phenytoin in case the initial dose of lorazepam failed, were the treatments preferred.

Prioritizing treatment attributes and their impact on selecting an oral triptan: Results from the TRIPSTAR project

Seven oral triptans, which differ on a range of attributes important for treatment selection, are now available for treating migraine. US neurologists were surveyed to assess the relative importance of treatment attributes, prespecified by clinical relevance and availability of controlled study data, for selecting among oral triptans. Using a multiattribute decision model, we combined these data on the importance of treatment attributes with information on the relative performance of the oral triptans derived from a recent meta-analysis of controlled clinical trials.

Efficacy and tolerability of conversion to monotherapy with lamotrigine compared with valproate and carbamazepine in patients with epilepsy

OBJECTIVE

This randomized, open-label study was designed to compare the efficacy and tolerability of lamotrigine monotherapy with those of valproate and carbamazepine monotherapy in patients with epilepsy whose seizures were uncontrolled on their prestudy antiepileptic drug monotherapy.

METHODS

Patients meeting eligibility criteria were randomized 2:1 to lamotrigine:carbamazepine or lamotrigine:valproate. The treatment phase was divided into a 4-week dose-escalation phase (Weeks 1-4), during which lamotrigine, carbamazepine, or valproate was added to patient's prestudy monotherapy; an 8-week add-on phase (Weeks 5-12), during which patients were stabilized on both the study medication and their prestudy antiepileptic therapy; an 8-week withdrawal phase (Weeks 13-20), during which prestudy antiepileptic therapy could be withdrawn if clinically appropriate; and an 8-week monotherapy phase (Weeks 21-28), during which patients could be treated with study medication as monotherapy.

RESULTS

The numbers of patients randomized to the carbamazepine and valproate arms of the study were 144 (98 lamotrigine, 46 carbamazepine) and 158 (105 lamotrigine, 53 valproate), respectively. Successful monotherapy sustained for at least 7 weeks was achieved in comparable percentages of patients in the lamotrigine group (56%) and the carbamazepine group (54%) and in more patients in the lamotrigine group (49%) than the valproate group (40%). Among monotherapy completers, the percentage of patients with zero seizures during the monotherapy phase was comparable for lamotrigine (41%) and carbamazepine (30%) and significantly higher (P<0.05) with lamotrigine (32%) than with valproate (11%). No differences between treatments were observed with respect to time to treatment failure or time to first seizure. Lamotrigine was also better tolerated than carbamazepine or valproate.

CONCLUSION

Lamotrigine monotherapy was as effective as and better tolerated than carbamazepine or valproate monotherapy in patients whose seizures were uncontrolled on their prestudy antiepileptic drug monotherapy.

Epilepsy in low-grade gliomas: the impact on cognitive function and quality of life

Low-grade gliomas frequently are associated with epilepsy. The purpose of this study is to determine the impact of epilepsy and antiepileptic drug (AED) treatment on cognitive functioning and health-related quality of life (HRQOL) in these patients. One hundred fifty-six patients without clinical or radiological signs of tumor recurrence for at least 1 year after histological diagnosis and with an epilepsy burden (based on seizure frequency and AED use) ranging from none to severe were compared with healthy controls. The association between epilepsy burden and cognition/HRQOL was also investigated. Eighty-six percent of the patients had epilepsy and 50% of those using AEDs actually were seizure-free. Compared with healthy controls, glioma patients had significant reductions in information processing speed, psychomotor function, attentional functioning, verbal and working memory, executive functioning, and HRQOL. The increase in epilepsy burden that was associated with significant reductions in all cognitive domains except for attentional and memory functioning could primarily be attributed to the use of AEDs, whereas the decline in HRQOL could be ascribed to the lack of complete seizure control. In conclusion, low-grade glioma patients suffer from a number of neuropsychological and psychological problems that are aggravated by the severity of epilepsy and by the intensity of the treatment.

Building and evaluation of a structured representation of pharmacokinetics information presented in SPCs: from existing conceptual views of pharmacokinetics associated with natural language processing to object-oriented design

OBJECTIVE

Develop a detailed representation of pharmacokinetics (PK), derived from the information in Summaries of Product Characteristics (SPCs), for use in computerized systems to help practitioners in pharmaco-therapeutic reasoning.

METHODS

Available knowledge about PK was studied to identify main PK concepts and organize them in a preliminary generic model. The information from 1950 PK SPC-texts in the French language was studied using a morpho-syntactic analyzer. It produced a list of candidate terms (CTs) from which those describing main PK concepts were selected. The contexts in which they occurred were explored to discover co-occurring CTs. The regrouping according to CT semantic types led to a detailed object-oriented model of PK. The model was evaluated. A random sample of 100 PK texts structured according to the model was judged for completeness and semantic accuracy by 8 experts who were blinded to other experts' responses.

RESULTS

The PK text file contained about 300000 words, and the morpho-syntactic analysis extracted 17520 different CTs. The context of 592 CTs was studied and used to deduce the PK model. It consists of four entities: the information about the real PK process, the experimental protocol, the mathematical modeling, and the influence of factors causing variation. Experts judged that the PK model represented the information in 100 sample PK texts completely in 89% of cases and nearly completely in the other 11%. There was no distortion of meaning in 98% of cases and little distortion in the remainder.

CONCLUSION

The PK model seems to be applicable to all SPCs and can be used to retranscribe legal information from PK sections of SPCs into structured databases.

[A practical study of the efficacy of a delayed-action preparation of carbamazepine (Tegretol CR 400) in the treatment of patients with partial epilepsy ]

INTRODUCTION

Carbamazepine (CBZ) is the first choice antiepileptic drug in the treatment of partial seizures. Many clinical studies show high efficacy and good tolerance of CBZ in the majority of patients. However, poor water solubility and erratic absorption as well as autoinduction of its metabolism, cause wide and unpredictable fluctuations in CBZ serum concentration. In order to avoid these problems controlled-release formulations of CBZ (Tegretol CR 400) were developed.

PURPOSE

The aim of this study was to evaluate the efficacy, tolerance and practicality of the therapy of partial seizures in adults with controlled-release CBZ (Tegretol CR 400).

PATIENTS AND METHODS

Over a three-year period we conducted an open pragmatic study of controlled-release CBZ in the therapy of 141 adult patients with established diagnosis of localized related epilepsy. Patients with progressive brain or systemic disease were excluded. All patients had unacceptable seizure frequency and were divided into four groups: 1) 34 with newly-diagnosed epilepsy; 2) 42 with chronic epilepsy and no previous antiepileptic medication; 3) 27 with chronic epilepsy previously treated with conventional preparations of carbamazepine (CBZ); and 4) 38 with chronic epilepsy previously treated with other antiepileptic medications. Patients were switched to controlled-release CBZ and the dosage was slowly adjusted. Baseline evaluation included the analysis of efficacy, tolerance and practicality of the controlled-release CBZ therapy. Three categories of efficiency were defined: 1) successful (patients without seizures); 2) partially successful (patients with improvement of at least 50% in frequency and severity of seizures); and 3) unsuccessful therapy (same or worse than before controlled-release CBZ). Tolerance and practicity were evaluated through the analysis of side effects and frequency of daily doses, respectively. These variables were compared to the corresponding ones after a period of at least three months of full dosage controlled-release CBZ therapy.

RESULTS

In all four groups the therapy was successful in 76%, 52%, 30% and 29%, partially successful in 18%, 43%, 30% and 32%, and unsuccessful in 6%, S%, 40% and 39%, respectfully. Side effects occurred less frequently in all 4 groups during the therapy with controlled-release CBZ. We found reduced frequency of drug administration (once or twice daily) in 97.9% of our patients.

DISCUSSION

Due to its slow and irregular absorption, short half life, wide and unpredictable fluctuation in plasma levels CBZ has decreased ability to control seizures, with the appearance of the intermittent side-effects such as diplopia, ataxia, headache and dizziness. Controlled-release formulation of CBZ sustains stable absorption and reduces fluctuations in carbamazepine serum concentration. Steady serum levels permit to the majority of patients to tolerate a higher total daily dose by reducing peak-dependent side-effects and improve compliance as a result of less frequent daily doses (1 or 2).

CONCLUSION

In patients with partial seizures controlled-release vs. conventional carbamazepine had better efficiency, based on an excellent tolerance, favorable daily dosage and superior compliance.

Management strategies for refractory localization-related seizures

Localization-related epilepsy, the most common type of seizure disorder, often provides major management problems. Five new antiepileptic drugs (AEDs) with different mechanisms of action have been licensed in the United Kingdom in the 1990s for adjunctive use in the management of poorly controlled partial seizures. These were, in chronologic order, vigabatrin, lamotrigine, gabapentin, topiramate, and tiagabine. Their practical deployment is explored here. Mention also is made of clobazam and acetazolamide. Combination therapy with two or even three AEDs having complementary pharmacologic effects can provide an essential contribution to the management of partial seizures. This article discusses some of the pharmacologic strategies used in treating patients with refractory localization-related epilepsy.

Oxcarbazepine, an antiepileptic agent

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The mechanisms of action of commonly used antiepileptic drugs

In the past decade, nine new drugs have been licensed for the treatment of epilepsy. With limited clinical experience of these agents, the mechanisms of action of antiepileptic drugs may be an important criterion in the selection of the most suitable treatment regimens for individual patients. At the cellular level, three basic mechanisms are recognised: modulation of voltage-dependent ion channels, enhancement of inhibitory neurotransmission, and attenuation of excitatory transmission. In this review, we will attempt to introduce the concepts of ion channel and neurotransmitter modulation and, thereafter, group currently used antiepileptic drugs according to their principal mechanisms of action.

Seizures in the adult intensive care unit

Seizures are a common occurrence in the intensive care unit (ICU). The presentation of seizures is usually as focal or generalized motor convulsions, but other seizure types may occur. Etiologies of the seizures are typically secondary either to primary neurologic pathology or a consequence of critical illness and clinical management. Particularly important as precipitants of seizures are hypoxia/ischemia, drug toxicity, and metabolic abnormalities. It is important to properly diagnose the seizure type and its cause to ensure appropriate therapy. Most seizures occur singly, and recurrence is usually prevented with initiation of anticonvulsant therapy. However, status epilepticus may develop, which requires emergent treatment before irreversible brain injury occurs. Treatment with anticonvulsants is not without untoward risks, however, and primary toxicities of these agents is reviewed. After traumatic head injury, brain surgery, or cerebrovascular accidents, many patients are at risk for seizures. Current data on the benefits of prophylactic therapy for such patients is also reviewed.

Neuropsychological effects of epilepsy and antiepileptic drugs

Epilepsy and its treatment can have deleterious cognitive and behavioural consequences. Affected individuals have a higher prevalence of neuropsychological dysfunction than the general population because of complex interactions among several multifaceted and overlapping influences--for example, underlying neuropathologies, ictal and interictal neuronal discharges, a plethora of antiepileptic drugs, and numerous psychosocial issues. Research into the clinical relevance of these factors has been dogged by a range of methodological pitfalls including lack of standardisation of neuropsychological tests, small numbers and multiple testing, and statistical failure to appreciate differential effects of interactive elements in individual patients. Although antiepileptic drugs can impair neuropsychological functioning, their positive effect on seizure control might improve cognition and behaviour. Each person should be assessed individually with respect to factors unique to his or her seizure disorder and its treatment.

The star systems: overview and use in determining antiepileptic drug choice

An explosion in antiepileptic drug (AED) therapy began in the 1990s with the licensing of 9 new chemical entities and more to come. Important differences between AEDs may not be detected by regulatory trials, which are designed to satisfy licensing requirements and often diverge considerably from everyday clinical practice. The Star Systems have been developed as evidence-based yet pragmatic and flexible models for comparing AEDs. Each drug has been judged across a range of criteria, including mechanism of action, pharmacokinetics, ease of use, efficacy, tolerability, safety, interaction profile and a 'comfort factor'. A score has been allocated under each category and systems have been devised for patients with newly diagnosed epilepsy and those with difficult-to-control seizures requiring combination therapy. The choice of treatment should involve assessment of patient-related factors, accurate classification of seizure type and syndrome, married with an understanding of the pharmacology of the AEDs. A staged management plan should be formulated when initiating treatment with the aim of preventing the development of refractory epilepsy. When using combinations of AEDs, the mechanism of action of each agent should be taken into consideration. Such an individualised approach to management will optimise the chance of attaining remission and help many more patients achieve a fulfilling life.

Primary Generalized Epilepsies

For pure childhood absence epilepsy (CAE), ethosuximide (ESM) remains the drug of first choice. Although valproic acid (VPA) is of equal efficacy, it is more toxic, and is reserved for those patients with accompanying convulsions. Lamotrigine (LTG) is effective as both add-on and monotherapy for CAE. If any of these three drugs fails, one of the other two can be used as monotherapy. Rarely, when ESM, VPA, or LTG does not effectively control CAE, phenytoin (PHT), primidone (PRM), and phenobarbital (PB) may be partially effective, although carbamazepine (CBZ) may worsen absence seizures. Experience is limited with the newer AEDs. Tiagabine (TGB) may induce absence status epilepticus in PGE. Oxcarbazepine (OXC) and vigabatrin (VGB) may worsen absence seizures. Felbamate (FBM) is probably effective, but is potentially fatal. Lifelong therapy is not anticipated. For juvenile absence epilepsy (JAE), VPA is the drug of first choice. LTG is also of proven efficacy. The risks of VPA-induced teratogenicity (possibly lessened by the concurrent use of folic acid) and weight gain are potentially unacceptable in young women of childbearing age. Not enough data exists on the safety of LTG in pregnancy. A combination of VPA and LTG can be used if either drug alone is unsuccessful. For juvenile myoclonic epilepsy (JME), VPA is the traditional drug of first choice in most patients. As in JAE, side effects may make VPA an unacceptable choice in many patients, especially young women. In clinical practice, TPM is being increasingly used as monotherapy for JME. Many patients appreciate the accompanying weight loss seen with TPM, but it has potentially troubling side effects, has not been well studied as monotherapy for JME, and its safety in pregnancy has yet to be confirmed. PHT and CBZ may worsen myoclonus when used alone, but they may have a role as add-on treatment to VPA, LTG, or TPM, especially when generalized tonic-clonic seizures (GTCSs) are not controlled. PB and PRM may also be useful as add-on treatment, but often have unacceptable side effects. Clonazepam may be useful as adjunctive treatment for resistant myoclonic jerks. OXC and VGB both worsen myoclonic seizures. GBP is not useful in JME and can make seizures worse. The efficacy of FBM and TGB in JME is largely unknown. Lifelong AED therapy is necessary. In epilepsy with generalized tonic-clonic seizure (GTCS) on awakening (EGA), VPA is the drug of choice, especially if other seizure types (absence and myoclonic) are present. If only GTCSs are present, then PB, PHT, and CBZ may be as effective as VPA; however, the use of PHT and CBZ may "unearth" other seizure types (absence and myoclonic) in those patients with EGA, although PB is poorly tolerated. As for JME, LTG, and TPM may both be effective monotherapy for EGA, although the use of other AEDs in EGA has not been well studied. Lifelong AED treatment is necessary.

Epilepsy after the first drug fails: substitution or add-on?

When and how a combination of antiepileptic drugs (AEDs) should be used in patients unresponsive to monotherapy is not known. We followed up prospectively 248 patients in whom treatment with the first AED was unsuccessful. When treatment failed due to intolerable adverse events, a second (substituted) drug was prescribed. When failure was due to lack of efficacy, either AED substitution or combination (add-on) was undertaken. Patients were considered to be seizure-free if they had no seizures for at least 1 year. Among patients with inadequate seizure control on the first well tolerated AED, those who received substituted monotherapy (n= 35) and those who received add-on treatment (n= 42) had similar seizure-free rates (substitution vs. add-on: 17% vs. 26%) and incidence of intolerable side effects (substitution vs. add-on: 26% vs. 12%). Based on the drugs' perceived primary mode of action, more patients became seizure-free when the combination involved a sodium channel blocker and a drug with multiple mechanisms of action (36%) compared to other combinations (7 %, P= 0.05). None of the 11 patients who received add-on treatment after a second drug had also failed became seizure-free, compared to 26% in those who received add-on as soon as the first tolerated AED proved to be ineffective (n= 42, P= 0.05). These preliminary observations have generated verifiable hypotheses regarding the early management of epilepsy. A randomized study comparing substitution and combination after the failure of the first AED is underway.

Management of epilepsy in adolescents and adults

Epilepsy is the most common serious neurological disorder affecting an estimated 50 million people worldwide. Particular focus should be placed on a safe diagnosis, seizure and syndrome classification, and choice of pharmacological and surgical options for a range of patient populations with different health-care requirements. Eight new antiepileptic drugs were licensed in the 1990s with more to come. These new drugs along with earlier resective surgery have led to a better outcome for many more people with this condition.

Early identification of refractory epilepsy

BACKGROUND

More than 30 percent of patients with epilepsy have inadequate control of seizures with drug therapy, but why this happens and whether it can be predicted are unknown. We studied the response to antiepileptic drugs in patients with newly diagnosed epilepsy to identify factors associated with subsequent poor control of seizures.

METHODS

We prospectively studied 525 patients (age, 9 to 93 years) who were given a diagnosis, treated, and followed up at a single center between 1984 and 1997. Epilepsy was classified as idiopathic (with a presumed genetic basis), symptomatic (resulting from a structural abnormality), or cryptogenic (resulting from an unknown underlying cause). Patients were considered to be seizure-free if they had not had any seizures for at least one year.

RESULTS

Among the 525 patients, 333 (63 percent) remained seizure-free during antiepileptic-drug treatment or after treatment was stopped. The prevalence of persistent seizures was higher in patients with symptomatic or cryptogenic epilepsy than in those with idiopathic epilepsy (40 percent vs. 26 percent, P=0.004) and in patients who had had more than 20 seizures before starting treatment than in those who had had fewer (51 percent vs. 29 percent, P<0.001). The seizure-free rate was similar in patients who were treated with a single established drug (67 percent) and patients who were treated with a single new drug (69 percent). Among 470 previously untreated patients, 222 (47 percent) became seizure-free during treatment with their first antiepileptic drug and 67 (14 percent) became seizure-free during treatment with a second or third drug. In 12 patients (3 percent) epilepsy was controlled by treatment with two drugs. Among patients who had no response to the first drug, the percentage who subsequently became seizure-free was smaller (11 percent) when treatment failure was due to lack of efficacy than when it was due to intolerable side effects (41 percent) or an idiosyncratic reaction (55 percent).

CONCLUSIONS

Patients who have many seizures before therapy or who have an inadequate response to initial treatment with antiepileptic drugs are likely to have refractory epilepsy.

Gabapentin in the management of convulsive disorders

Gabapentin, in clinical use since 1993, is indicated as an adjunctive antiepileptic drug (AED) for treatment of complex partial seizures, with or without secondary generalization, in patients over 12 years of age. Although several cellular actions have been described in the literature, the molecular mechanism(s) of action responsible for the anticonvulsant effect of gabapentin has not been conclusively determined. It is likely that gabapentin has multiple concentration-dependent actions that combine in a unique manner to produce antiepileptic efficacy. The pharmacokinetic properties of this water-soluble, amino-acid AED are generally favorable. Absorption appears to be dependent on transport by the L-system amino acid transporter. Elimination of unmetabolized drug occurs by the renal route. Although its therapeutic range is not well characterized, gabapentin has a broad therapeutic index. This implies that a wide range of doses can be used, based on individual patient needs, without significant limitation due to dose-dependent side effects. Gabapentin has few drug-drug interactions, none of which is clinically limiting. Several studies have demonstrated the long-term efficacy of gabapentin with no systematic evidence of tachyphylaxis. In addition, there is increasing evidence to support the use of gabapentin as monotherapy. Gabapentin is safe and is generally well tolerated. To date, nearly 3 million patients have been treated in studies and in open use without causal relationship to a specific life-threatening organ toxicity. Seizure control superior to that observed in well-controlled trials has been reported at higher doses used in clinical practice and in studies. Therefore, gabapentin dosing must be optimized on an individual basis to achieve an adequate trial of the drug and obtain the best seizure control.