Placebo-controlled study of the efficacy and safety of lamotrigine in patients with partial seizures. U.S. Lamotrigine Protocol 0.5 Clinical Trial Group

New antiepileptic drugs. Overcoming the limitations of traditional therapy

Several new antiepileptic drugs have become available recently. Since seizures and epilepsy are common, primary care physicians are likely to encounter a patient who is taking one of these new medications. Successful medical management of epilepsy requires a proper understanding of medication half-life, indications, and side effects. Felbamate has a broad spectrum of efficacy but is limited by side effects and idiosyncratic reactions. Fosphenytoin has the efficacy of phenytoin and offers the advantage of intramuscular and intravenous dosing without the significant adverse effects associated with intravenous phenytoin; however, it is expensive. Gabapentin has minimal side effects and drug interactions yet has limited efficacy for seizures. Lamotrigine has broad seizure efficacy but requires a slow adjustment to therapeutic levels. Topiramate has minimal drug interactions, but therapy must be initiated slowly to avoid side effects. All of the new antiepileptics hold great promise in the management of patients with recurrent seizures.

The anticonvulsant lamotrigine in treatment-resistant manic-depressive illness

Anticonvulsants are used extensively in the treatment of bipolar disorder. Treating depression in bipolar disorder can be difficult because of the limited antidepressant effects of the standard mood stabilizers and the tendency of antidepressants to induce mania or decrease cycle length. Lamotrigine is a new anticonvulsant with few side effects that may have mood-stabilizing and elevating effects. Its mechanism of action probably involves the inhibition of excessive release of excitatory amino acids such as glutamate. Antiglutamatergic agents may be antidepressant and mood stabilizing. A case series of 16 patients treated with lamotrigine (dose range 50 mg to 250 mg, mean dose of responders = 141 mg) is presented along with two case reports. All patients were considered treatment-resistant bipolar type I or II. Patients were rated on average 5 weeks after starting lamotrigine using a semistructured follow-up form that included symptom rating, Clinical Global Impressions (CGI), and Global Assessment of Functioning (GAF) scores. Eight of 16 patients were rated as "responders" (CGI < or = 2) and had a mean increase of 16 in their GAF scores. Lamotrigine seems to have antidepressant and mood-stabilizing effects, but this requires confirmation in randomized, controlled trials.

Lamotrigine reduces voltage-gated sodium currents in rat central neurons in culture

PURPOSE

To study the mechanism or mechanisms of action of lamotrigine (LTG) and, in particular, to establish its effects on the function of NA+ channels in mammalian central neurons.

METHODS

Rat cerebellar granule cells in culture were subjected to the whole-cell mode of voltage clamping under experimental conditions designed to study voltage-gated Na+ currents.

RESULTS

Extracellular application of LTG (10-500 microM, n = 21) decreased in a dose-related manner a tetrodotoxin-sensitive inward current that was elicited by depolarizing commands (from -80 to +20 mV). The peak amplitude of this Na(+)-mediated current was diminished by 38.8 +/- 12.2% (mean +/- SD, n = 6) during application of 100 microM LTG, and the dose-response curve of this effect indicated an IC50 of 145 microM. The reduction in the inward currents produced by LTG was not associate with any significant change in the current decay, whereas the voltage dependency of the steady-state inactivation shifted toward more negative values (midpoint of the inactivation curve: -47.5 and -59.0 mV under control conditions and during application of 100 microM LTG, respectively, n = 4).

CONCLUSIONS

Our findings indicate that LTG reduces the amplitude of voltage-gated Na+ inward current in rat cerebellar granule cells and induces a negative shift of the steady-state inactivation curve. Both mechanisms may be instrumental in controlling the repetitive firing of action potentials (AP) that occurs in neuronal networks during seizure activity.

Recent advances in the pharmacotherapy of epilepsy

The therapeutic options for the treatment of epilepsy have expanded during the 1990s. Since 1993, four novel agents (felbamate, gabapentin, lamotrigine, and topiramate) have been approved by the US Food and Drug Administration, primarily for adjunctive treatment of partial seizures. In addition, a water-soluble pro-drug of phenytoin, fosphenytoin, and a sustained-release preparation of carbamazepine have been introduced. The novel anticonvulsants represent a potential improvement for patients whose seizures are incompletely controlled or who experience significant adverse effects with older anticonvulsants. Felbamate, lamotrigine, and topiramate appear to have a broad spectrum of action in seizure control, but felbamate use is limited by the potential for serious adverse effects. Gabapentin, lamotrigine, and topiramate are all well tolerated. Gabapentin has no known drug interactions, whereas lamotrigine and topiramate have limited interactions compared with older agents. The sustained-release preparation of carbamazepine may decrease the incidence of adverse effects and increase patient compliance. Fosphenytoin offers a safer method for intravenous administration of phenytoin and the added flexibility of intramuscular administration. Taken together, these recent advances in treatment may bring about improved efficacy and decreased adverse effects for many patients with epilepsy.

Reappraisal of polytherapy in epilepsy: a critical review of drug load and adverse effects

PURPOSE

We reviewed the literature to determine whether an analysis of published data could clarify the relationship between antiepileptic drug (AED) polytherapy and adverse affects (AE). We highlight the problems encountered.

METHODS

We made a Medline-search for articles published between 1974 and 1994 reporting the number of AE and doses or serum levels of every AED, per patient or treatment group, and used the PDD/DDD ratio to calculate AED load per patient from doses or the OSL/AToxL ratio to do so from serum levels of individual drugs. The PDD/DDD is the sum of ratios of the actual prescribed daily doses divided by the published average therapeutic dose of each drug. The OSL/AToxL is the sum of each observed serum level divided by its average toxic level.

RESULTS

We retrieved 118 trial reports. Most had to be excluded because of incomplete reporting of concomitant medication or AE. The data of the 15 articles selected for further analysis indicate a relationship between drug load and number of AE. We noted no relationship between the number of AEDs administered and AE. In add-on studies, the difference in neurotoxicity between the active and placebo arm may be obscured if the relative increase in drug load is small, as exemplified by the study of McGuire et al..

CONCLUSIONS

Articles reporting add-on trials of new AEDs generally do not provide detailed information about the basic medication to which the new AED is added, which makes calculation of total drug load impossible. Furthermore, often only frequency of AE is reported, not severity or development of tolerance, making it difficult to judge the impact of AE. However, despite the paucity of available information, we present some evidence that toxicity in AED polytherapy may be related to total drug load, rather than to the number of drugs administered. Therefore, the present trend to reject polytherapy for fear of increased toxicity is not warranted, which removes one of the objections to initiating specific research to prove or disprove the value of AED combinations as long as the drug load is appropriate.

Utility of the lethargic (lh/lh) mouse model of absence seizures in predicting the effects of lamotrigine, vigabatrin, tiagabine, gabapentin, and topiramate against human absence seizures

PURPOSE

Traditional methods of preclinical screening have predicted the effects of a putative antiepileptic drug (AED) against human absence seizures by testing its efficacy against clonic seizures in the high-dose pentylenetetrazole (PTZ) model. This high-dose PTZ model correctly predicted the efficacy of ethosuximide (ESM), benzodiazepines, and valproate (VPA) and the lack of efficacy of phenytoin (PHT) and carbamazepine (CBZ). However, the high-dose PTZ model erred in predictions for (a) phenobarbital (PB) (PTZ: efficacy; human: nonefficacy); (b) lamotrigine (LTG) (PTZ: nonefficacy; human: efficacy); (c) vigabatrin (VGB) (PTZ: nonefficacy; human: proabsence effect); and (d) tiagabine (TGB) (PTZ: efficacy; human: possible proabsence). It also appears to have erred in predictions for gabapentin (GBP) (PTZ: efficacy) and topiramate (TPM) (PTZ: efficacy). Because the lh/lh genetic model of absence seizures correctly predicted effects of ESM, clonazepam, VPA, PHT, CBZ, and PB against human absence seizures, we performed this study to test the predictive utility of the lh/lh model for LTG, VGB, TGB, GBP, and TPM.

METHODS

Bipolar recording electrodes were implanted bilaterally into frontal neocortex of 8-week-old male lh/lh mice. With the exception of VGB, vehicle or drugs were administered intraperitoneally (i.p.) on alternating days, and an EEG was used to record effects on seizure frequency. With VGB, vehicle was administered i.p. on day 1, and gradually increasing doses of VGB were administered on successive days. Drug and vehicle effects were compared in corresponding 15-min epochs of the 150-min period after administration.

RESULTS

LTG (4.8-144 micromol/kg) significantly (p < 0.04) reduced seizure frequency (by 65%) compared with vehicle. In contrast, VGB (0.35-11 mmol/kg) and TGB (0.27-27 micromol/kg) significantly increased seizure frequency (300-700%) and seizure duration (1,700-1,800%; p < 0.001). GBP (18 micromol/kg to 1.8 mmol/kg) and TPM (8.9-295 micromol/kg) had no significant effect on seizure frequency.

CONCLUSIONS

In contrast to the high-dose PTZ model, the lh/lh model correctly predicted the antiabsence effect of LTG, the possible proabsence effects of VGB and TGB, and the lack of effect of GBP and TPM. The lh/lh model appears to be superior to the high-dose PTZ model in predicting efficacy of putative AEDs against human absence seizures.

A pharmacological and clinical review on topiramate, a new antiepileptic drug

Topiramate is a new antiepileptic drug which has recently become available in the United States and in a number of European countries. Pharmacological studies suggest that its mode of action is multifactorial and involves blockade of voltage-dependent sodium channels, potentiation of GABAergic transmission and inhibition of excitatory pathways through an action at AMPA receptor sites. Carbonic anhydrase inhibiting properties have also been demonstrated but they are considered not to be relevant to anticonvulsant activity. Topiramate is well absorbed from the gastrointestinal tract, peak plasma levels being usually attained in 2-3 hours. The drug is negligibly (9-17%) bound to plasma proteins and is eliminated partly by renal excretion in unchanged form and partly by oxidation and hydrolysis. In healthy volunteers, the half-life is about 20-30 hours, but elimination rate is accelerated in patients taking concomitant enzyme inducing drugs such as phenytoin, carbamazepine and barbiturates. Topiramate has no major effects on plasma levels of concurrent anticonvulsants, except for a rise in plasma phenytoin in occasional patients. In double-blind add-on trials in refractory partial epilepsy, a significant reduction in seizure frequency has been demonstrated in over 40% of topiramate-treated patients (vs about 10% of those treated with placebo), a response rate which compares favourably with that observed with other new antiepileptic drugs. Dosages found to be effective in add-on controlled trials range between 200 and 1000 mg day-1, although most patients are likely to benefit from receiving 400 mg day-1 or less. Preliminary data suggest that topiramate may be effective also in generalized epilepsies, but this needs to be confirmed in prospective studies. The most common adverse effects of topiramate are CNS-related and include dizziness, fatigue, visual disturbances, ataxia, mental slowing and impaired concentration. Paresthesias, anorexia, weight loss and increased risk of nephrolithiasis have been also reported. Many of these effects are related to dose and/or to rate of dose titration. Based on these data, topiramate appears to be a valuable new drug, whose main current indication is in the add-on management of refractory partial and secondarily generalized seizures. Studies on its potential-value as monotherapy are in progress.

Lamotrigine in childhood epilepsies

Lamotrigine (LTG) is one of the new generation of antiepileptic drugs (AEDs) that have been designed to perform specific physiological or pharmacological functions. Early laboratory testing revealed an AED profile auguring success in the management of generalized tonic-clonic seizures, partial seizures, and also absence, thus suggesting a broad spectrum of activity. The drug blocks voltage-sensitive sodium channels resulting in inhibition of excitatory neurotransmitter release. Randomized, controlled clinical trials confirmed effectiveness and the side effect profile was favorable. The use of LTG in childhood is based largely on anecdotal open-label derived information. To date it appears to have been successful in many of the most devastating childhood epilepsy syndromes but controlled trial information is needed to confirm that it may be not only successful as add-on in partial seizures but also in primary and secondarily generalized epilepsies as a primary agent.

Long-term safety and efficacy of lamotrigine (Lamictal) in paediatric patients with epilepsy

This study was initiated to evaluate the long-term safety, tolerability and effect on seizure control of lamotrigine (Lamictal) in paediatric patients with epilepsy. A total of 155 children (aged 2-19 years) with treatment-resistant epilepsy received add-on therapy or monotherapy lamotrigine for up to four years. Patients had already experienced benefit from lamotrigine treatment in an open one-year study before entering this open continuation study of up to three additional years of treatment. Overall, including both these studies, patients were treated with lamotrigine for 53-221 weeks, representing 417.9 patient-years of experience. The physician's global assessment of seizure control compared to the three-month period before lamotrigine treatment, indicated that seizure control was generally maintained during long-term lamotrigine treatment for up to four years. For 19 patients, the investigator recorded a subjective improvement in behaviour, alertness, seizure severity, quality of life and mobility with lamotrigine treatment, sometimes independent of seizure control. In total, 34 patients received lamotrigine monotherapy; 22 of these were maintained on lamotrigine monotherapy for at least one year. Lamotrigine was well tolerated. The majority of adverse experiences were classified by the physician as being mild in intensity and only six patients (4%) withdrew from the study due to adverse experiences.

Efficacy of topiramate as adjunctive therapy in refractory partial seizures: United States trial experience

In companion double-blind, placebo-controlled, dose-ranging trials performed in the United States, topiramate (TPM) daily target dosages of 200-1,000 mg/day were evaluated as add-on therapy in adults with refractory partial seizures with or without becoming secondarily generalized. Net reductions in median monthly seizure frequency (active drug minus placebo) with the most efficacious dosages of TPM were 35% in the low-dose trial and 40% in the high-dose trial. Substantial reductions in secondarily generalized seizures were also observed with TPM. TPM appears to be an efficacious new antiepileptic drug in the management of partial epilepsy.

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.

Clinical efficacy of topiramate as add-on therapy in refractory partial epilepsy: the European experience

In three randomized, double-blind, placebo-controlled add-on European trials, target daily topiramate (TPM) dosages of 400, 600, and 800 mg/day (200, 300, and 400 mg bid) were evaluated in adults with refractory partial seizures with or without becoming secondarily generalized. Median reductions from baseline in monthly seizure rate were 41% with TPM 400 mg/day vs. 1% with placebo (n = 0.065), 46% with TPM 600 mg/day compared to -12% (a 12% increase) with placebo (p < or = 0.005), and 36% with TPM 800 mg/day versus -18% (an 18% increase) with placebo (p < 0.001). Differences between TPM and placebo with respect to percent responders (percent of patients demonstrating a 50% or greater reduction in seizures) significantly favored TPM (p < 0.05) at all three target dosages. Significant reductions in secondarily generalized tonic-clonic seizures compared to placebo were also observed with 400 mg/day (p = 0.002) and 800 mg/day (p < 0.05) of TPM. TPM appears to be a promising new antiepileptic drug for use as adjunctive therapy in adults with refractory partial epilepsy.

Lamotrigine adjunctive therapy in childhood epileptic encephalopathy (the Lennox Gastaut syndrome)

PURPOSE

We assessed efficacy and safety of adjunctive lamotrigine (LTG) therapy in patients with the Lennox-Gastaut syndrome (LGS).

METHODS

The study was a single-center, retrospective chart review of open-label adjunctive LTG therapy in patients with LGS. Initial LTG dose and titration was dependent on concomitant antiepileptic drugs (AEDs). Efficacy was based on the change in seizure frequency between the initiation of LTG therapy and December 1, 1995 (or LTG discontinuation). Seizure diaries were used to count patient seizures. A secondary evaluation of efficacy was a parental or guardian assessment of the patient's global status. The evaluation of safety involved chart review for treatment-emergent adverse events (AE).

RESULTS

Data from 16 LGS patients were analyzed. Fifty-three percent (8 of 15) had a > 50% reduction in seizure frequency with LTG adjunctive therapy. Tonic, atonic, generalized tonic-clonic (GTCS), and atypical absence seizure frequency but not myoclonic seizure frequency decreased significantly during LTG therapy. Fifty-three percent of the patient's parents (8 of 15) reported that their child's quality of life (QOL) was much or very much improved during the study. The major treatment-emergent AE were infection (50%, 8 of 16) and sleep disturbance (19%, 3 of 16). A rash was noted in 13% (2 of 16) of the patients and resulted in LTG discontinuation in 1. No clinically significant changes were noted in neurologic examination or laboratory tests during the study.

CONCLUSIONS

Our results indicate that LTG adjunctive therapy is effective and well tolerated in patients with LGS.

Management of epilepsy in the elderly

Epilepsy in elderly patients is a growing worldwide challenge; as the population ages, the prevalence of epilepsy increases. Management of epilepsy in elderly patients requires an understanding of their unique medical and pharmacologic characteristics. Accurate assessment of seizures, thorough neurologic assessment to define etiology, and evaluation of concomitant illnesses and living situations are necessary for comprehensive treatment planning and informed management. Expect elderly patients to present challenges to treatment that include concomitant diseases, obligatory polypharmacy with accompanying drug interactions, and age-related changes in renal and hepatic physiology that alter drug metabolism and elimination. Elderly patients have declining intellectual function, motor impairment, or altered special sensory function that make them susceptible to dose-related CNS side effects of antiepileptic drugs (AEDs). When AEDs are added to the medical regimen of an elderly patient, the physician must review all prescribed drugs. Drugs prescribed for concomitant illnesses such as behavioral problems, cardiovascular disease, hypertension, and infection may alter the distribution and metabolism of AEDs, with an impact on efficacy and occurrence of adverse effects. AEDs tend to induce metabolism of other drugs, leading to a decline in target response. Optimal care of elderly patients with epilepsy includes use of free levels to monitor AED concentrations, careful dose selection, and physician sensitivity to patients' social problems.

Clinical administration of new antiepileptic drugs: an overview of safety and efficacy

Gabapentin, lamotrigine, tiagabine, topiramate, vigabatrin, and zonisamide are all administered as add-on therapy for treatment of patients with refractory epilepsy. To date, no comparative randomized trials have been performed that could potentially allow an evidence-based choice to be made between these antiepileptic drugs (AEDs). We report a series of meta-analyses of placebo-controlled, randomized add-on trials in patients with partial epilepsy. Results of these meta-analyses are compared, thus giving broad estimates of the comparative efficacy and tolerability of these AEDs. The efficacy outcome is the odds ratio for the number of patients with a > or = 50% reduction in seizure frequency. Reported side effects are also used as tolerability outcomes, and study withdrawal is used as a global outcome measure. Results are summarized as odds ratios with 95% confidence intervals (CIs). When each outcome is compared among drugs, the 95% CIs overlap. Therefore, no conclusive evidence of a difference in efficacy or tolerability between these AEDs was derived, even though the apparently most effective agent (topiramate) may be twice as effective as the apparently least effective agent (lamotrigine). Comparative randomized studies are needed to further evaluate these drugs.

New antiepileptic drugs: a systematic review of their efficacy and tolerability

OBJECTIVES

To evaluate the efficacy and tolerability of the newly developed antiepileptic drugs gabapentin, lamotrigine, tiagabine, topiramate, vigabatrin, and zonisamide in patients with refractory partial epilepsy.

DESIGN

Systematic review of published and unpublished randomised controlled trials of add-on treatment with new antiepileptic drugs.

SUBJECTS

20 published and eight unpublished trials representing 3883 patients with refractory partial epilepsy.

MAIN OUTCOME MEASURES

Proportion of patients who (a) showed 50% or greater reduction in frequency of seizures (50% responders) and (b) withdrew from each study for any reason.

RESULTS

Odds ratios (95% confidence intervals) relative to placebo for 50% responders were 2.29 (1.53 to 3.43) for gabapentin, 2.32 (1.47 to 3.68) for lamotrigine, 3.03 (2.01 to 4.58) for tiagabine, 4.22 (2.80 to 6.35) for topiramate, 3.68 (2.45 to 5.51) for vigabatrin, and 2.47 (1.36 to 4.47) for zonisamide. Odds ratios for withdrawal were 1.36 (0.75 to 2.49) for gabapentin, 1.19 (0.79 to 1.79) for lamotrigine, 1.81 (1.21 to 2.70) for tiagabine, 2.42 (1.43 to 4.11) for topiramate, 2.58 (1.26 to 5.27) for vigabatrin, and 5.70 (1.76 to 18.49) for zonisamide. Comparing results for each drug showed that all of the 95% confidence intervals overlapped, indicating that they were not significantly different in terms of efficacy and tolerability.

CONCLUSIONS

All six drugs were significantly better than placebo at reducing frequency of seizures. These results do not allow an evidence based choice between these drugs as we have no conclusive indication of differences in efficacy or tolerability.

Current developments in neurology, Part I: Advances in the pharmacotherapy of headache, epilepsy, and multiple sclerosis

When caring for patients with disorders of the central nervous system such as migraine headaches, epilepsy, or MS, clinicians are faced with increasingly complex pharmacotherapeutic options. Pharmacotherapeutic strategies directed toward prevention, reversal, or cure of these diseases are hampered by an incomplete understanding of the underlying pathophysiology. In this decade of the brain, basic science research combined with difficult but necessary clinical trials may answer some seemingly overwhelming questions for these devastating illnesses.

Serum concentrations of lamotrigine in epileptic patients: the influence of dose and comedication

Lamotrigine (LTG) is a new antiepileptic drug (AED), chemically unrelated to the drugs in current use. Previous studies have shown that LTG has only a limited effect on other AEDs, but its own metabolism can be strongly induced or inhibited by the comedication. We investigated the influences of carbamazepine (CBZ), phenytoin (PHT), phenobarbital (PB), valproic acid (VPA), and combinations of these drugs on the serum concentration of LTG. A total of 588 blood samples from 302 patients were analyzed. The mean duration of LTG therapy was 141 +/- 137 days (mean +/- SD). A patient was only considered twice in this study if his or her comedication had been changed. The LTG serum concentration in relation to LTG dose/body weight (level-to-dose ratio, LDR, microgram/ml/mg/kg) was calculated and compared for different drug combinations. The results showed that comedication had a highly significant (p < 0.001) influence on the LTG serum concentrations. The mean LDR for LTG was 0.32 (LTG + PHT) < 0.52 (LTG + PB) approximately equal to 0.57 (LTG + CBZ) < 0.98 (LTG mono) approximately equal to 0.99 (LTG + VPA + PHT) < 1.67 (LTG + VPA + CBZ) approximately equal to 1.80 (LTG + VPA + PB) < 3.57 (LTG + VPA (<, p < 0.05; approximately equal to, p > 0.05, multiple comparisons). The mean LTG concentrations in patients on comedication with VPA were about two times higher than on patients on LTG monotherapy or on comedication without VPA (5.0 vs. 2.6 micrograms/ml), despite the LTG doses being half as high (3.0 vs. 5.9 mg/kg). The correlations of the serum concentrations and doses of CBZ, PB, PHT, and VPA with the LDR of LTG were only weak or not significant. Furthermore, the distribution of LTG serum concentrations and dosages was compared with the tentative therapeutic range for the LTG concentration (1-4 micrograms/ml), proposed by some investigators, and the recommendations for the LTG dosage. Remarkable discrepancies were observed. The comedication has an important influence on the LTG concentration and should be considered in LTG dosage.

Controlled trial of lamotrigine (Lamictal) for treatment-resistant partial seizures

The antiepileptic effect of lamotrigine (Lamictal) was assessed in a double-blind, placebo-controlled, crossover trial in 56 adult patients with refractory partial seizures. Lamotrigine or placebo was added to the patients' existing antiepileptic drugs (AEDs). The dose of lamotrigine varied from 75 to 400 mg daily. Thirty-eight patients completed the trial and 7 withdrew because of adverse experiences. There was a statistically significant reduction in seizure counts on lamotrigine compared with placebo for total seizures (30.3% reduction, 95% CI 8.4%, 47.0%), complex partial seizures (29.2% reduction, 95% CI 3.8%, 47.9%) and secondary generalised seizures (37.9%, CI 18.9%, 52.4%). The analysis of total seizure days showed a similar significant reduction during lamotrigine treatment for the same seizure categories. There was no statistically significant difference in reporting of adverse events between lamotrigine and placebo except for dizziness which was reported more frequently on lamotrigine than on placebo. There were no differences in abnormal haematological or biochemical findings between lamotrigine and placebo, and lamotrigine had no effect on plasma concentrations of concomitant AEDs.

Lamotrigine high-dose tolerability and safety in patients with epilepsy: a double-blind, placebo-controlled, eleven-week study

PURPOSE

This study was undertaken to evaluate the dose tolerability and safety of a chronic ascending twice-daily (b.i.d.) dosage regimen of < or = 700 mg/day lamotrigine (LTG) and to include determination of the LTG pharmacokinetic profile at doses > or = 500 mg/day in patients receiving concomitant enzyme-inducing antiepileptic drugs (AEDs).

METHODS

Twelve adult male epileptic patients treated with enzyme-inducing AEDs received < or = 700 mg/day (b.i.d.) oral LTG (n = 8) or placebo (controls, n = 4). For 3 weeks, as outpatients they had their LTG dosage increased from 100 to 400 mg/day. Then, in a clinical research study unit, patients received regimens of 500, 600, and 700 mg/day for 1 week each. Controls received matching placebo in the same sequence. At study end, dosages were tapered in 2 weeks. Follow-up evaluations were made 7 days later.

RESULTS

Five LTG patients tolerated 700 mg/day for 1 week. LTG was reduced to 600 mg/day in a patient with mild diplopia and to 500 mg/day in a patient with mild oscillopsia and diplopia. One patient discontinued 300 mg/day therapy with a moderately intense diffuse papular skin rash, attributed to LTG. Headache, drowsiness, faintness, and diplopia, the common adverse events (AEs), were mild to moderate in intensity and occurred in 50-75% of patients in both groups (except for diplopia, occurring only with LTG). Concomitant AED plasma concentrations were not markedly changed by LTG. LTG pharmacokinetics were linear over the range of 500-700 mg/day.

CONCLUSIONS

LTG doses < or = 700 mg/day can be tolerated in patients receiving concomitant enzyme-inducing AEDs.

Bidirectional interaction of valproate and lamotrigine in healthy subjects

OBJECTIVE

To evaluate the steady-state pharmacokinetics of lamotrigine and valproate at three dosing levels of lamotrigine in normal volunteers receiving steady-state therapeutic doses of valproate.

METHODS

This was an open-label, randomized, three-way crossover study of 18 normal male volunteers. Subjects received oral valproate (500 mg Depakote twice a day) throughout the study. Each subject subsequently received three oral dosage regimens of lamotrigine (50, 100, or 150 mg/day) for 1 week each, with a 2-week washout period between lamotrigine treatment periods. Valproate and lamotrigine trough plasma samples were determined by a capillary gas chromatography method and immunofluorometric assay, respectively. Urine samples were assayed for 11 valproate metabolites by gas chromatography/mass spectrometry.

RESULTS

When compared to other studies in which lamotrigine was administered with no concurrent antiepileptic drug, concomitant valproate markedly increased the half-life of lamotrigine and decreased lamotrigine clearance, without substantial alteration in the linear kinetics of the drug. The addition of lamotrigine was associated with a small but significant 25% decrease in steady-state valproate plasma concentration. Oral clearance of valproate was increased (from 7.2 +/- 1.1 ml/hr/kg before lamotrigine treatment to 9.0 +/- 2.0 ml/hr/kg on day 28; p < 0.05). The formation clearance of the hepatotoxic valproate metabolites, 2-n-propyl-4-pentenoic acid (4-ene-valproate) and 2-propyl-2,4-pentadienoic acid [2(E),4-diene-valproate], was unaffected by lamotrigine administration.

CONCLUSIONS

As a consequence of the interaction between lamotrigine and sodium valproate, a dosage reduction of lamotrigine should be considered in patients taking a combination of valproate and lamotrigine.

Safety of topiramate: adverse events and relationships to dosing

To date, 1,809 individuals have been exposed to topiramate (TPM), primarily adults with partial-onset seizures. Of this total, 665 patients have been treated for more than 1 year, 177 for more than 3 years, and 67 for more than 5 years. The profile of treatment-emergent adverse reactions (TEAEs) observed with TPM at various dosages is based primarily on data from five double-blind, placebo-controlled trials in which 360 patients received TPM at target doses of 200-1,000 mg/day. Long-term safety is assessed on the basis of 1,001 patients treated with TPM in controlled and open trials for up to 5.3 years. Most of the commonly reported TEAEs were related to the central nervous system and were observed with greater frequency at dosages above the 200-600-mg/day range found to be optimal in dose ranging trials. Nephrolithiasis not requiring surgery was seen in 1.5% of patients, and mild, dose-related weight loss was associated with TPM therapy. No clinically significant treatment-related abnormalities were observed in clinical laboratory parameters or in neurologic, electrocardiographic, ophthalmologic, or audiologic tests.

Expanding antiepileptic drug options: clinical efficacy of new therapeutic agents

Results of double-blind, placebo-controlled, add-on trials of topiramate (TPM), lamotrigine (LTG), and vigabatrin (VGB) in refractory partial epilepsy were reviewed. In three European multicenter studies of TPM, the clinical efficacy of 400-, 600-, and 800-mg/day target dosages was demonstrated. In a similarly designed United States trial, LTG was significantly superior to placebo at a 500-mg/day dosage but not at a 300-mg/day dosage. A meta-analysis of a number of smaller trials of VGB suggests that a > or = 50% reduction in seizures is observed in approximately 45% of patients with refractory partial epilepsy. All of these newer antiepileptic drugs have shown efficacy in well-controlled trials and should contribute significantly to our ability to manage partial epilepsy.

Double-blind, placebo-controlled trial of topiramate as add-on therapy in patients with refractory partial seizures

In a double-blind, randomized, parallel-group trial, we compared topiramate (TPM) with placebo as add-on therapy in patients with refractory partial epilepsy. TPM was titrated either to the target dosage of 800 mg/ day [400 mg twice daily (b.i.d)] or to the maximal tolerated dose if lower. Twenty-eight (28) patients were randomized to each treatment group. In the intent-to-treat analysis, the net median percent reduction relative to placebo in average monthly seizure rate was 54% for patients in the TPM group (p < 0.001). None of the placebo-treated patients and 43% of the patients treated with TPM experienced > or = 50% reduction in seizures (p = 0.001), and 36% of patients assigned to TPM had a 75-100% reduction in seizures (p < 0.01). Secondarily generalized seizures were also significantly reduced in the TPM group (p = 0.044). The most common adverse events (AE) reported in the TPM group were fatigue, impaired concentration, weight loss, dizziness, and paresthesias. AE occurring either during the rapid titration of TPM or at high dosages led 21% of TPM-treated patients to withdraw from the study. Half of these occurred during the titration study period. No serious AE or clinically important changes in clinical laboratory measures were observed. The present study further establishes the favorable profile and good benefit/risk ratio of TPM in resistant partial epilepsy.

A cost minimization study comparing vigabatrin, lamotrigine and gabapentin for the treatment of intractable partial epilepsy

Epilepsy is one of the commonest of the serious neurological disorders. The total economic burden of epilepsy in the United Kingdom has been estimated to be 1930 m pounds, with around 32 m pounds spent on antiepileptic drug therapy alone. Despite the high level of expenditure on drug therapy for epilepsy there is very little information regarding the relative cost-effectiveness of the different drugs available. It is important to establish the relative cost-effectiveness of therapies to provide decision makers with the information necessary to allocate resources in a rational manner and thus achieve the highest benefit for available resources. In this study the cost-effectiveness of lamotrigine, vigabatrin and gabapentin was estimated by a cost minimization analysis for the first year of drug therapy using data based on published studies. In general, there was little difference between the initial direct costs of treatment, however, the fewer side-effects associated with gabapentin is reflected in the lower total costs of treatment in the first year resulting in savings of 18.52 pounds per patient compared with lamotrigine and 47.18 pounds compared with vigabatrin. Based on incidence data estimates this translates to estimated direct cost savings to the UK of between 166,680 pounds and 424,620 pounds per annum.

The National Hospital Seizure Severity Scale: a further development of the Chalfont Seizure Severity Scale

Seizure severity scales have recently been identified as an important additional outcome measure in trials of new antiepileptic drugs (AEDs). The National Hospital Seizure Severity Scale (NHS3) is presented as a refined version of the Chalfont Seizure Severity Scale. The principal advantages of the new version are that it is quicker and simpler to apply, the limits of reliability are now clearly defined, and construct validity for the scale is available. The scale is administered by a health professional during an interview with a patient and a witness to the seizures. It contains seven seizure-related factors and generates a score from 1 to 27. An intraclass correlation coefficient of 0.90 was obtained during interobserver and test-retest reliability assessment, suggesting that the scale is sufficiently reliable for group studies. Scores for an individual patient should be interpreted with caution in light of the limits of agreement obtained. Validation experiments indicate that NHS3 measures seizure severity in a manner compatible with the subjective impression of people with epilepsy. We suggest that the NHS3 is a valid, easily applicable measure of seizure severity that is acceptably reliable for use in trials of novel AEDs.

A randomised open multicentre comparative trial of lamotrigine and carbamazepine as monotherapy in patients with newly diagnosed or recurrent epilepsy

The efficacy and safety of lamotrigine and carbamazepine as monotherapy in patients with untreated, newly diagnosed or recurrent partial and/or generalised tonic-clonic seizures, were compared in a randomised, open, multicentre study. Patients received 24 weeks' treatment with oral lamotrigine 100 mg (LTG 100, n = 115) or 200 mg (LTG 200, n = 111) or carbamazepine 600 mg (CBZ 600, n = 117). Efficacy measurements were comparable between the three treatment groups, although the higher lamotrigine dose was possibly most effective, with 60.4% completing seizure free compared with 51.3% (LTG 100) and 54.7% (CBZ 600). Both dosage regimens of lamotrigine were well tolerated. More patients on CBZ 600 reported adverse experiences, 66% versus 53% (LTG 100) and 58% (LTG 200), and of these a greater proportion were attributed to CBZ 600 treatment, 53% versus 23% (LTG 100) and 28% (LTG 200). Similarly, a greater proportion of the CBZ 600 group required a change in dose, 47% versus 20% (LTG 100) and 17% (LTG 200) or withdrew completely due to adverse experiences, 10.3% versus 4.3% (LTG 100) and 4.5% (LTG 200). The most common adverse experience leading to withdrawal was rash, with approximately double the proportion of reports occurring in patients on CBZ 600 (5.1%) compared with lamotrigine (1.7% on LTG 100 and 2.7% on LTG 200). Overall lamotrigine appeared equally effective but better tolerated compared with carbamazepine.

Psychotic and severe behavioural reactions with vigabatrin: a review

Behavioural disturbances and psychotic reactions are commoner in patients with epilepsy than in the general population and may be precipitated by the majority of antiepileptic drugs, including the newer ones. These reactions may be more frequent in patients with complex partial seizures, reflecting underlying temporal lobe pathology. A review of the literature on vigabatrin found an incidence of severe abnormal behaviour in controlled trials in adults of 3.4%. In children open studies gave an incidence of around 6%. This may be related to dosage and speed of introduction. Such reactions may be related to changes in seizure control, either unaccustomed good control (force normalisation) or breakdown in control, implying non-specific causative mechanisms. Alternatively, any relationship to control may be fortuitous and specific, unknown pharmacological mechanisms may be involved. Appropriate risk reduction measures include slow introduction, limiting the dose to that required for seizure control, slow withdrawal and increased vigilance in those on polytherapy or with psychiatric histories. Such advice is pertinent to all antiepileptic medications. Additionally, vigabatrin is probably contraindicated in idiopathic generalised epilepsies. Behavioural reactions are uncommon with vigabatrin, and have not been shown to be greater with it than with other antiepileptic agents. Therefore, it maybe inappropriate to withhold the drug from those who may benefit from it.

New antiepileptic drugs--an explosion of activity

The low therapeutic index of established antiepileptic drugs coupled with a better understanding of the pathophysiology of seizure production has led to the development of a range of new therapeutic agents for the treatment of epilepsy. In this review, the three drugs recently licensed in the UK (vigabatrin, lamotrigine and gabapentin) are profiled, together with several of the more promising up-and-coming compounds (oxcarbazepine, felbamate, tiagabine, stiripentol, remacemide and topiramate). Future avenues for clinical research in the pharmacological management of the epilepsies involve their rational use both singly and in combination.

Antiepileptic drugs in pediatric practice

Several factors characterize the current medical treatment of epilepsy during childhood. Children do not present the same types of seizures or epilepsies as adults, and certain epilepsy syndromes are seen only during childhood. Accordingly, the choice of antiepileptic drugs (AEDs) may differ in children. In addition, certain medical therapies, such as ACTH or pyridoxine, are used only in children. It is also common practice to prescribe AEDs in children for indications that are "off-label," such as the treatment of partial-onset seizures with carbamazepine before the age of 6 years. The natural history of epilepsy and the risk for seizure recurrence may be different in the pediatric age range, and this may influence the decision to institute chronic prophylactic therapy in children. Similar considerations may apply to the decision to discontinue AED therapy. The pharmacokinetics of several AEDs are age-dependent, and dosages are more variable among patients. The adverse effects of AEDs may be age-dependent, and the pattern of exacerbation of certain seizures by AEDs may be different in children. In addition, several new AEDs are now available, or are about to be released, and the preferential sequence of AEDs of choice in children with epilepsy will need to be reassessed as experience grows and as the results of comparative studies become available.

Lamotrigine: an antiepileptic agent for the treatment of partial seizures

OBJECTIVE

To review the current literature on lamotrigine and its use as an antiepileptic drug (AED).

DATA SOURCES

MEDLINE and bibliographic literature searches pertaining to lamotrigine were performed. Additionally, Burroughs Wellcome provided a comprehensive bibliography, data on file, and investigator's brochure.

DATA SELECTION

The selection of reported data for this review includes both controlled and uncontrolled studies as well as case reports and unreported data from both European and US trials.

DATA SYNTHESIS

Lamotrigine is effective as an adjunctive agent in the treatment of complex and simple partial seizures with or without secondary generalization. Anecdotal reports suggest that the spectrum of activity may include other seizure types, but controlled studies substantiating these reports are needed. Lamotrigine has a favorable pharmacokinetic profile, including a long half-life, low serum protein binding, and lack of mixed-function oxidase enzyme induction. It is likely that the drug induces metabolism through the glucuronidation pathway, although probably not to a clinically significant extent. Concurrent use of enzyme-inducing AEDs increase lamotrigine's clearance, whereas valproic acid decreases it. Adverse effects are primarily central nervous system-related, with dizziness, diplopia, ataxia, and somnolence reported in at least 10% of the patients treated. The incidence of these effects is higher in patients treated concomitantly with carbamazepine and may represent a pharmacodynamic interaction. The occurrence of rash may limit lamotrigine's use and was the most common cause for discontinuation in clinical trials (2.3%). The incidence of rash is higher in patients comedicated with valproic acid.

CONCLUSIONS

Lamotrigine appears to be a safe and effective new AED for patients with refractory partial seizures when used as an adjunctive agent. It has a favorable pharmacokinetic profile allowing for once- or twice-daily dosing and adverse effects appear mild and transient. Additional studies are required to confirm efficacy in other seizure types.

Lamotrigine

Lamotrigine (LTG) is a novel antiepileptic drug (AED) with a spectrum of activity in animal models of epilepsy similar to that of phenytoin and carbamazepine. In some models it appears to have a broader spectrum and better tolerability than these agents, however. One mechanism of action of LTG is the marked inhibition of release of the excitatory neurotransmitters glutamate and aspartate under conditions of sustained repetitive firing. LTG appears to do this by blocking voltage-sensitive sodium channels and has no direct effect on N-methyl-D-aspartate (NMDA) receptors. In clinical trials as add-on therapy in medically refractory partial seizure patients, LTG has consistently produced a 50% reduction in seizure frequency in 25-34% of subjects. LTG is well tolerated, even in the add-on situation. In part, this appears to be related to positive behavioral effects. Desirable pharmacologic properties of LTG include low protein binding (55%), an absence of enzyme induction, and linear pharmacokinetics. The most significant adverse effect is rash, leading to a withdrawal rate of 2% of patient exposures in clinical trials.

Gabapentin: a new agent for the management of epilepsy

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of gabapentin, a new antiepileptic drug (AED). Gabapentin's potential role in the treatment of epilepsy also was assessed.

DATA SOURCE

A MEDLINE search was performed to identify all published literature (manuscripts and abstracts). Abstracts presented at the American Epilepsy Society, International Epilepsy Congress, and American Academy of Neurology meetings from 1991 to 1993 also were reviewed. A copy of the proceedings from the Food and Drug Administration Peripheral and Central Nervous System Advisory Committee meeting and package insert were obtained from Parke Davis.

STUDY SELECTION

All pertinent literature was reviewed. Emphasis was placed on published information, particularly placebo-controlled clinical trials.

DATA SYNTHESIS

Gabapentin is effective as adjunctive treatment for patients with partial seizures with or without secondary generalization refractory to the standard AEDs. It has a unique pharmacokinetic profile for an AED, including no binding to plasma proteins, primary elimination by the kidney, and dose-dependent oral absorption at high dosages. No drug interactions occur with the other AEDs. The most frequent adverse reactions noted in patients receiving gabapentin have been mild and transient central nervous system effects. No serious hypersensitivity or systemic reactions have been observed.

CONCLUSIONS

Gabapentin appears to be a useful new AED. Further studies evaluating its use as monotherapy, in higher dosages, and in pediatric and elderly patients are required to better delineate its therapeutic role relative to that of other AEDs.

New antiepileptic drugs for children: felbamate, gabapentin, lamotrigine, and vigabatrin

After a 15-year hiatus, several new antiepileptic drugs have been approved or are under Food and Drug Administration investigation for use in the United States. This article reviews four of these new drugs--felbamate, gabapentin, lamotrigine, and vigabatrin. Although these drugs have been primarily developed for use in adults with partial seizures, they will also likely be used in children with partial epilepsy. Pediatric experience with several of these drugs has demonstrated safety and efficacy in other seizure types and epilepsy syndromes. These drugs will be an important addition to the therapeutic armamentarium for pediatric epilepsy. Additional studies are needed to fully explore the safety and efficacy of these drugs in a variety of pediatric epilepsies and to compare them to existing antiepileptic drugs.

Vigabatrin and lamotrigine in refractory epilepsy

Epilepsy arises from an imbalance of inhibitory and excitatory influences in the brain. Vigabatrin (VIG) decreases the breakdown of the inhibitory neurotransmitter gamma-aminobutyric acid, whereas lamotrigine (LTG) reduces presynaptic excitatory amino acid release. 22 patients with refractory epilepsy, treated with an anticonvulsant regimen containing VIG, entered a balanced, double blind, placebo controlled, crossover trial of additional LTG. Treatment periods of 12 weeks (25 mg, 50 mg, 100 mg LTG twice daily for four weeks at each dose, and matched placebo) were followed by wash out intervals of four weeks. 14 of the 20 patients completing the study improved, resulting in a significant fall in seizure days and numbers. Analysis of seizure type confirmed a beneficial effect on partial and secondary generalised tonic-clonic seizures. At the highest LTG dose (200 mg daily) there was a median fall of 37% in seizure count with nine (45%) patients reporting > 50% reduction. Three of these patients were seizure free during this month of treatment. Side effects were minimal throughout the study. Concentrations of other antiepileptic drugs, including those of carbamazepine 10,11-epoxide, were not modified by LTG. This study suggests a substantial efficacy for a regimen containing VIG and LTG. Combinations of drugs with complementary modes of action may provide a rational pharmacological approach to the management of refractory epilepsy.

Newer antiepileptic drugs. Towards an improved risk-benefit ratio

Epilepsy is one of the most common neurological disorders. Even though existing antiepileptic drugs can render 80% of newly diagnosed patients seizure free, a significant number of patients have chronic intractable epilepsy causing disability with considerable socioeconomic implications. There is, therefore, a need for more potent and effective antiepileptic drugs and drugs with fewer adverse effects, particularly CNS effects. Drugs for the treatment of partial seizures are particularly needed. With major advances in our understanding of the basic neuropathology, neuropharmacology and neurophysiology of epilepsy, numerous candidate novel antiepileptic drugs have been developed in recent years. This review comparatively evaluates the pharmacokinetics, efficacy and adverse effects of 12 new antiepileptic drugs namely vigabatrin, lamotrigine, gabapentin, oxcarbazepine, felbamate, tiagabine, eterobarb, zonisamide, remacemide, stiripentol, topiramate and levetiracetam (ucb-L059). Of the 12 drugs, vigabatrin, lamotrigine and gabapentin have recently been marketed in the UK. Five of these new drugs have known mechanisms of action (vigabatrin, lamotrigine, tiagabine, oxcarbazepine and eterobarb), which may provide for a more rational approach to the treatment of epilepsy. Oxcarbazepine, remacemide and eterobarb are prodrugs. Vigabatrin, gabapentin and topiramate are more promising on the basis of their pharmacokinetic characteristics in that they are excreted mainly unchanged in urine and not susceptible to significant pharmacokinetic interactions. In contrast, lamotrigine, felbamate and stiripentol exhibit significant drug interactions. Essentially, all the drugs are effective in partial or secondarily generalised seizures and are effective to varying degrees in other seizure types. Particularly welcome is the possible effectiveness of zonisamide in myoclonus and felbamate in Lennox-Gastaut syndrome. In relation to adverse effects, CNS effects are observed with all drugs, however, gabapentin, remacemide and levetiracetam appear to exhibit least. There is also the possibility of rational duotherapy, using drugs with known mechanisms of action, as an additional therapeutic approach. The efficacy of these 12 antiepileptic drug occurs despite the fact that candidate antiepileptic drugs are evaluated under highly unfavourable conditions, namely as add-on therapy in patients refractory to drug management and with high seizure frequency. Thus, whilst candidate drugs which do become licensed are an advance in that they are effective and/or are associated with less adverse effects than currently available antiepileptic drugs in these patients, it is possible that these drugs may exhibit even more improved risk-benefit ratios when used in normal clinical practice.