Levetiracetam. A review of its adjunctive use in the management of partial onset seizures

Reactive metabolites of the anticonvulsant drugs and approaches to minimize the adverse drug reaction

Several generations of antiepileptic drugs (AEDs) are available in the market for the treatment of seizures, but these are amalgamated with acute to chronic side effects. The most common side effects of AEDs are dose-related, but some are idiosyncratic adverse drug reactions (ADRs) that transpire due to the formation of reactive metabolite (RM) after the bioactivation process. Because of the adverse reactions patients usually discontinue the medication in between the treatment. The AEDs such as valproic acid, lamotrigine, phenytoin etc., can be categorized under such types because they form the RM which may prevail with life-threatening adverse effects or immune-mediated reactions. Hepatotoxicity, teratogenicity, cutaneous hypersensitivity, dizziness, addiction, serum sickness reaction, renal calculi, metabolic acidosis are associated with the metabolites of drugs such as arene oxide, N-desmethyldiazepam, 2-(1-hydroxyethyl)-2-methylsuccinimide, 2-(sulphamoy1acetyl)-phenol, E-2-en-VPA and 4-en-VPA and carbamazepine-10,11-epoxide, etc. The major toxicities are associated with the moieties that are either capable of forming RM or the functional groups may itself be too reactive prior to the metabolism. These functional groups or fragment structures are typically known as structural alerts or toxicophores. Therefore, minimizing the bioactivation potential of lead structures in the early phases of drug discovery by a modification to low-risk drug molecules is a priority for the pharmaceutical companies. Additionally, excellent potency and pharmacokinetic (PK) behaviour help in ensuring that appropriate (low dose) candidate drugs progress into the development phase. The current review discusses about RMs in the anticonvulsant drugs along with their mechanism vis-a-vis research efforts that have been taken to minimize the toxic effects of AEDs therapy.

Tailor-made amino acids in the design of small-molecule blockbuster drugs

The role of amino acids (AAs) in modern health industry is well-appreciated. Residues of individual AAs, or their chemical modifications, such as diamines and amino alcohols, are frequently found in the structures of modern pharmaceuticals. The goal of this review article, is to emphasize that, currently, tailor-made AAs serve as key structural features in many most successful pharmaceuticals, so-called blockbuster drugs. In the present article, we profile 14 small-molecule drugs, underscoring the breadth of structural variety of AAs applications in numerous therapeutic areas. For each compound, we provide spectrum of biological activity, medicinal chemistry discovery, and synthetic approaches.

Early intervention with levetiracetam prevents the development of cortical hyperexcitability and spontaneous epileptiform activity in two models of neurotrauma in rats

This study examined the antiepileptogenic potential of the antiseizure drug (ASD) levetiracetam (LEV) using the in vitro traumatized-slice and in vivo controlled cortical impact (CCI) models of traumatic brain injury (TBI) in rats when administered early after the injury. For the in vitro model, acute coronal slices (400-450 μm) of rat neocortex (P21-32) were injured via a surgical cut that separated the superficial layers from the deeper regions. Persistent stimulus-evoked epileptiform activity developed within 1-2 h after trauma. In randomly selected slices, LEV (500 μM) was bath-applied for 1 h starting immediately or delayed by 30-80 min after injury. Treated and untreated slices were examined for epileptiform activity via intracellular and extracellular recordings. For the in vivo model, rats (P24-32) were subjected to a non-penetrating, focal, CCI injury targeting the neocortex (5.0 mm diameter; 2.0 mm depth). Immediately after injury, rats were given either a single dose of LEV (60-150 mg/kg, i.p.) or the saline vehicle. At 2-3 weeks after the injury, ex vivo cortical slices were examined for epileptiform activity. The results from the traumatized-slice experiments showed that in vitro treatment with LEV within 60 min of injury significantly reduced (> 50%) the proportion of slices that exhibited stimulus-evoked epileptiform activity. LEV treatment also increased the stimulus intensity required to trigger epileptiform bursts in injured slices by 2-4 fold. Consistent with these findings, LEV treatment of CCI-injured rats (n = 15) significantly reduced the proportion of animals that exhibited spontaneous and stimulus-evoked epileptiform bursts in ex vivo cortical slices compared to saline-treated controls (n = 15 rats), and also significantly increased the stimulus intensity required to evoke epileptiform bursts. These results suggest that early administration of LEV has the potential to prevent or reduce posttraumatic epileptogenesis and that there may be a narrow therapeutic window for successful prophylactic intervention.

Quinolactacin Biosynthesis Involves Non-Ribosomal-Peptide-Synthetase-Catalyzed Dieckmann Condensation to Form the Quinolone-γ-lactam Hybrid

Quinolactacins are novel fungal alkaloids that feature a quinolone-γ-lactam hybrid, which is a potential pharmacophore for the treatment of cancer and Alzheimer's disease. Herein, we report the identification of the quinolactacin A2 biosynthetic gene cluster and elucidate the enzymatic basis for the formation of the quinolone-γ-lactam structure. We reveal an unusual β-keto acid (N-methyl-2-aminobenzoylacetate) precursor that is derived from the primary metabolite l-kynurenine via methylation, oxidative decarboxylation, and amide hydrolysis reactions. In vitro assays reveal two single-module non-ribosomal peptide synthetases (NRPs) that incorporate the β-keto acid and l-isoleucine, followed by Dieckmann condensation, to form the quinolone-γ-lactam. Notably, the bioconversion from l-kynurenine to the β-keto acid is a unique strategy employed by nature to decouple R*-domain-containing NRPS from the polyketide synthase (PKS) machinery, expanding the paradigm for the biosynthesis of quinolone-γ-lactam natural products via Dieckmann condensation.

Levetiracetam use during pregnancy in women with epilepsy: Preliminary observations from a tertiary care center in Northern India

INTRODUCTION

Data on efficacy and safety of levetiracetam (LEV) during pregnancy is still limited. We analyzed efficacy and safety of LEV during pregnancy in North Indian women with epilepsy (WWE) which is being presented here.

PATIENTS AND METHODS

This retrospective study included 99 WWE (on treatment with a single antiepileptic drug [AED]) who were evaluated in medical-surgical disorder antenatal clinic of the department of obstetrics and gynecology at a tertiary care teaching hospital and referral center in North India. All the obstetric and fetal data as well as data pertaining to epilepsy were noted meticulously.

RESULTS

In this study (n = 99), 35 women received carbamazepine, 28 received LEV, 15 received valproate (VPA), 13 received phenytoin (PHT), three each received oxcarbazepine and lamotrigine, respectively, and two received clobazam. Although the use of VPA was associated with significantly better control of seizures compared to LEV, its use was associated with higher risk of major congenital malformations (13.3%). The incidence of gestational hypertension was lower while incidence of fetal distress was significantly higher in WWE receiving PHT during pregnancy. None of the child born to pregnant women receiving LEV had any congenital malformation.

CONCLUSION

LEV is a first-line AED during pregnancy. Future prospective studies using therapeutic drug monitoring during pregnancy may further help in establishing its role during pregnancy.

Levetiracetam efficacy on frontal lobe dysfunctions and anger rumination in patients with epilepsy

This study compared the frontal lobe functioning and anger rumination between patients with epilepsy and healthy individuals. The second objective was to examine the efficacy of levetiracetam therapy on frontal lobe dysfunctions and anger rumination in patients with epilepsy. Participants (50 patients with epilepsy and 50 healthy individuals) completed the Frontal Assessment Battery (FAB) and Anger Rumination Scale (ARS). The patients had two testing sessions: pre- and post-levetiracetam therapies. The results showed that patients with epilepsy had frontal lobe dysfunctions in contrast with healthy individuals. Patients with epilepsy had higher anger rumination than healthy individuals. Compared with baseline performance, frontal lobe dysfunctions and anger rumination were significantly reduced after three months of levetiracetam therapy in patients with epilepsy. It is concluded that levetiracetam therapy may be beneficial in improving frontal lobe functioning and anger rumination thought pattern in patients with epilepsy. However, further studies are required to confirm this evidence.

The fetal safety of Levetiracetam: a systematic review

OBJECTIVE

To systematically review the available published evidence on the fetal safety of Levetiracetam with focus on birth defects.

RESULTS

Eight studies met the inclusion criteria; five pregnancy registries and one population based cohort study. A total of 27 major congenital malformations were reported among 1213 Levetiracetam monotherapy - exposed pregnant women, yielding an overall major malformation rate of 2.2% (27/1213) [95% confidence interval of 1.53-3.22]. In contrast, Levetiracetam polytherapy was associated with significantly higher malformation rate of 6.3% (34/541) [95% CI of 4.53-8.65] (P<0.001). Additionally 2 studies investigating child neurodevelopment in Levetiracetam - exposed children revealed that the measured achievements were well above those children exposed to valproic acid, and similar to unexposed controls.

CONCLUSIONS

The current evidence suggests that the overall risk of major malformation after first trimester exposure to Levetiracetam is within the population baseline risk of 1-3%, with no apparent adverse effects on long term child development.

Enantioselective Synthesis of Antiepileptic Drug: (-)-Levetiracetam—Synthetic Applications of the Versatile New ChiralN-Sulfinimine

We report an asymmetric synthesis of (-)-Levetiracetam (1) in six steps starting from versatile new chiralN-sulfinimine (3). The key step, stereoselective 1,2-addition of ethylmagnesium bromide (EtMgBr) to chiralN-sulfinimine derived from (R)-glyceraldehyde acetonide and (S)-t-BSA, gave the corresponding sulfonamide (2) in high diastereoselectivity. Simultaneous deprotection and deacetylation followed by NaIO4cleavage and reduction gaveβ-amino alcohol (6). Subsequent reactions yielded the targeted compound levetiracetam (1).

Enantioselective Synthesis of Antiepileptic Agent, (−)-Levetiracetam, through Evans Asymmetric Strategy

A practical and efficient enantioselective synthesis of antiepileptic drug, (−)-Levetiracetam, has been described in five steps (33.0% overall yield) and high optical purity (99.0%ee), using Evans asymmetric strategy forα-alkylation of carbonyl functionality as the key step. The simplicity of the experimental procedures and high stereochemical outcome make this method synthetically attractive for preparing the target compound on multigram scales.

The effects of music relaxation and muscle relaxation techniques on sleep quality and emotional measures among individuals with posttraumatic stress disorder

Posttraumatic stress disorder (PTSD), an anxiety disorder with lifetime prevalence of 7.8%, is characterized by symptoms that develop following exposure to traumatic life events and that cause an immediate experience of intense fear, helplessness or horror. PTSD is marked by recurrent nightmares typified by the recall of intrusive experiences and by extended disturbance throughout sleep. Individuals with PTSD respond poorly to drug treatments for insomnia. The disadvantages of drug treatment for insomnia underline the importance of non-pharmacological alternatives. Thus, the present study had three aims: first, to compare the efficiency of two relaxation techniques (muscular relaxation and progressive music relaxation) in alleviating insomnia among individuals with PTSD using both objective and subjective measures of sleep quality; second, to examine whether these two techniques have different effects on psychological indicators of PTSD, such as depression and anxiety; and finally, to examine how initial PTSD symptom severity and baseline emotional measures are related to the efficiency of these two relaxation methods. Thirteen PTSD patients with no other major psychiatric or neurological disorders participated in the study. The study comprised one seven-day running-in, no-treatment period, followed by two seven-day experimental periods. The treatments constituted either music relaxation or muscle relaxation techniques at desired bedtime. These treatments were randomly assigned. During each of these three experimental periods, subjects' sleep was continuously monitored with a wrist actigraph (Ambulatory Monitoring, Inc.), and subjects were asked to fill out several questionnaires concerned with a wide spectrum of issues, such as sleep, depression, and anxiety. Analyses revealed a significant increase in objective and subjective sleep efficiency and a significant reduction in depression level following music relaxation. Moreover, following music relaxation, a highly significant negative correlation was found between improvement in objective sleep efficiency and reduction in depression scale. The study's findings provide evidence that music relaxation at bedtime can be used as treatment for insomnia among individuals with PTSD.

Cost-utility analysis of levetiracetam and phenytoin for posttraumatic seizure prophylaxis

BACKGROUND

The standard for early posttraumatic brain injury (TBI) seizure prophylaxis is phenytoin. Despite its effectiveness, some argue for the use of newer antiepileptics (e.g., levetiracetam) because phenytoin requires close monitoring to maintain its therapeutic window and is associated with rare cutaneous hypersensitivity reactions. The purpose of this study was to evaluate whether phenytoin or levetiracetam would be more cost-effective in preventing early post-TBI seizures and reducing their negative impact on TBI outcomes.

METHODS

Cost-effectiveness analysis with the following base case assumptions: (1) phenytoin patients receive 1.0 g fosphenytoin load + 3 days of 100 mg three times a day (TID), have level drawn on day 3, "therapeutic" patients receive 100 mg TID on days 4 to 7, and "subtherapeutic" patients receive 200 mg TID on days 4 to 7; (2) levetiracetam patients receive 500 mg load + 7 days of 500 mg two times a day. Glasgow Outcome Scale (GOS) scores 4 to 5 represent good outcome, and GOS scores 2 to 3 represent poor outcome. Patients who develop early seizures: 40% good outcome, 50% poor outcome, and 10% death. Those who do not develop seizures: 75% good outcome, 20% poor outcome, and 5% death. Quality of life outcomes by GOS: good = 0.7, poor = 0.3, and death = 0.0. Severe adverse events and those impacting costs are rare for each agent. Assumptions were obtained through hospital query and exhaustive literature review.

RESULTS

The cost of a 7-day course of fosphenytoin, phenytoin, and free phenytoin level was $37.50, whereas the cost of a 7-day course of levetiracetam was $480.00. Literature review noted phenytoin to be as effective as levetiracetam in preventing early post-TBI seizures (and more effective in subclinical seizures). Quality-adjusted life years (QALY) were 23.6 for phenytoin and 23.2 for levetiracetam. As a result, the cost/effectiveness ratios were $1.58/QALY for phenytoin and $20.72/QALY for levetiracetam. All sensitivity analyses favored phenytoin unless levetiracetam prevented 100% of seizures and cost <$400 for 7-day course.

CONCLUSIONS

Phenytoin is more cost-effective than levetiracetam at all reasonable prices and at all clinically plausible reductions in post-TBI seizure potential.

Levetiracetam: a review of its use in epilepsy

Levetiracetam (Keppra®, E Keppra®) is an established second-generation antiepileptic drug (AED). Worldwide, levetiracetam is most commonly approved as adjunctive treatment of partial onset seizures with or without secondary generalization; other approved indications include monotherapy treatment of partial onset seizures with or without secondary generalization, and adjunctive treatment of myoclonic seizures associated with juvenile myoclonic epilepsy and primary generalized tonic-clonic (GTC) seizures associated with idiopathic generalized epilepsy. Levetiracetam has a novel structure and unique mechanisms of action. Unlike other AEDs, the mechanisms of action of levetiracetam appear to involve neuronal binding to synaptic vesicle protein 2A, inhibiting calcium release from intraneuronal stores, opposing the activity of negative modulators of GABA- and glycin-gated currents and inhibiting excessive synchronized activity between neurons. In addition, levetiracetam inhibits N-type calcium channels. Levetiracetam is associated with rapid and complete absorption, high oral bioavailability, minimal metabolism that consists of hydrolysis of the acetamide group, and primarily renal elimination. It lacks cytochrome P450 isoenzyme-inducing potential and is not associated with clinically significant pharmacokinetic interactions with other drugs, including other AEDs. The efficacy of oral immediate-release levetiracetam in controlling seizures has been established in numerous randomized, double-blind, controlled, multicentre trials in patients with epilepsy. Adjunctive levetiracetam reduced the frequency of seizures in paediatric and adult patients with refractory partial onset seizures to a significantly greater extent than placebo. Monotherapy with levetiracetam was noninferior to that with carbamazepine controlled release in controlling seizures in patients with newly diagnosed partial onset seizures. Levetiracetam also provided seizure control relative to placebo as adjunctive therapy in patients with idiopathic generalized epilepsy with myoclonic seizures or GTC seizures. In addition, patients receiving oral levetiracetam showed improvements in measures of health-related quality of life relative to those receiving placebo. Although treatment-emergent adverse events were commonly reported in the clinical trials of levetiracetam, the overall proportion of patients who experienced at least one treatment-emergent adverse event was broadly similar in the levetiracetam and placebo treatment groups, with most events being mild to moderate in severity. Levetiracetam is not associated with cognitive impairment or drug-induced weight gain, but has been associated with behavioural adverse effects in some patients.

An in vivo [18F]MK-9470 microPET study of type 1 cannabinoid receptor binding in Wistar rats after chronic administration of valproate and levetiracetam

There is substantial evidence that the endocannabinoid system and in particular the type 1 cannabinoid receptor (CB1R) is involved in epilepsy. We evaluated the in vivo effect of chronic administration of the anti-epileptic drugs valproate (VPA) and levetiracetam (LEV) on rat brain CB1 receptors using the positron emission tomography (PET) tracer [(18)F]MK-9470. Six Wistar rats were treated with VPA (200mg/kg) or LEV (50mg/kg) IP daily for 2 weeks. Dynamic imaging after intravenous injection of 18 MBq [(18)F]MK-9470 was performed on a FOCUS 220 microPET at baseline and after chronic treatment. Six animals were used as controls and were injected with saline, using the same protocol. Parametric images based on standardized uptake values (SUV) were generated and were spatially normalized to Paxinos space. These CB1R images were analyzed using a predefined volume of interest (VOI)-based analysis. Differences in SUV values between chronic and baseline scans in each condition (saline, VPA and LEV treatment) were calculated in each VOI. Direct binding affinity of the drugs at CB1R was assessed by competitive binding assay in Chinese hamster ovarian cells expressing human CB1R. Chronic injections of saline did not produce significant changes in global [(18)F]MK-9470 binding (p=0.43), nor in tracer binding in individual VOIs. We found a significant increase in global cerebral [(18)F]MK-9470 binding after chronic VPA administration compared to sham treated animals (+32.5%, p<0.001), as well as in tracer binding in all individual VOIs. After chronic administration of LEV, there was no significant change in global cerebral CB1R binding (+6.9%, p=0.81), nor in tracer binding in individual VOIs. As VPA does not exhibit high affinity for CB1R (displacement of [(3)H]-SR141716A 1.3+/-14.0%), such upregulation is most likely caused by an indirect effect on the endocannabinoid system. This increase in CB1R tracer binding and possibly signaling may represent a supplementary and new mechanism of VPA, but not LEV, since activation of CB1Rs has been shown to decrease excitability and excitotoxicity on-demand.

Monotherapy for partial epilepsy: focus on levetiracetam

Levetiracetam (LEV), the S-enantiomer of alpha-ethyl-2-oxo-1-pyrollidine acetamide, is a recently licensed antiepileptic drug (AED) for adjunctive therapy of partial seizures. Its mechanism of action is uncertain but it exhibits a unique profile of anticonvulsant activity in models of chronic epilepsy. Five randomized, double-blind, placebo-controlled trials enrolling adult or pediatric patients with refractory partial epilepsy have demonstrated the efficacy of LEV as adjunctive therapy, with a responder rate (>/=50% reduction in seizure frequency) of 28%-45%. Long-term efficacy studies suggest retention rates of 60% after one year, with 13% of patients seizure-free for 6 months of the study and 8% seizure-free for 1 year. More recent studies illustrated successful conversion to monotherapy in patients with refractory epilepsy, and its effectiveness as a single agent in partial epilepsy. LEV has also efficacy in generalized epilepsies. Adverse effects of LEV, including somnolence, lethargy, and dizziness, are generally mild and their occurrence rate seems to be not significantly different from that observed in placebo groups. LEV also has no clinically significant pharmacokinetic interactions with other AEDs, or with commonly prescribed medications. The combination of effective antiepileptic properties with a relatively mild adverse effect profile makes LEV an attractive therapy for partial seizures.

Effects of levetiracetam in lipid peroxidation level, nitrite-nitrate formation and antioxidant enzymatic activity in mice brain after pilocarpine-induced seizures

: Oxidative stress has been implicated in a large number of human degenerative diseases, including epilepsy. Levetiracetam (LEV) is a new antiepileptic agent with broad-spectrum effects on seizures and animal models of epilepsy. Recently, it was demonstrated that the mechanism of LEV differs from that of conventional antiepileptic drugs. Objectifying to investigate if LEV mechanism of action involves antioxidant properties, lipid peroxidation levels, nitrite-nitrate formation, catalase activity, and glutathione (GSH) content were measured in adult mice brain. The neurochemical analyses were carried out in hippocampus of animals pretreated with LEV (200 mg/kg, i.p.) 60 min before pilocarpine-induced seizures (400 mg/kg, s.c.). The administration of alone pilocarpine, 400 mg/kg, s.c. (P400) produced a significant increase of lipid peroxidation level in hippocampus. LEV pretreatment was able to counteract this increase, preserving the lipid peroxidation level in normal value. P400 administration also produced increase in the nitrite-nitrate formation and catalase activity in hippocampus, beyond a decrease in GSH levels. LEV administration before P400 prevented the P400-induced alteration in nitrite-nitrate levels and preserved normal values of catalase activity in hippocampus. Moreover, LEV administration prevented the P400-induced loss of GSH in this cerebral area. The present data suggest that the protective effects of LEV against pilocarpine-induced seizures can be mediated, at least in part, by reduction of lipid peroxidation and hippocampal oxidative stress.

Modulation of AMPA Receptors in Cultured Cortical Neurons Induced by the Antiepileptic Drug Levetiracetam

PURPOSE

The present study explores the hypothesis that the antiepileptic mechanism of action of levetiracetam (LEV) is related to effects on alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor channels in mouse cortical neurons in culture.

METHODS

The neurons were subjected to the whole-cell configuration of the patch-clamp recording technique and were 8-12 days old in culture.

RESULTS

Kainate elicited concentration-dependent (EC(50)= 80 microM) inward currents in all the patched cells. LEV (5-200 microM) itself did not induce inward or outward currents on all patched neurons, whereas it was effective on the kainate- and AMPA-induced current because it significantly decreased the amplitude of these currents. LEV was also able to significantly decrease the total membrane conductance during kainate perfusion, indicating that its effect was not dependent on the cellular voltage membrane potential. Further evidence that LEV modulated the ionotropic non-NMDA receptors came from the analysis of miniature excitatory postsynaptic currents (mEPSCs). In fact, LEV significantly decreased both the amplitude and the frequency of mEPSCs, as shown by the relative cumulative distributions.

CONCLUSIONS

These results reveal that AMPA receptors are modulated by LEV because a significant decrease in the kainate- and AMPA-induced currents and a decrease in amplitude and in frequency of mEPSCs have been observed in cortical neurons in culture. The described effect of LEV on AMPA receptors in cortical neurons is probably due to the etheromeric composition of the receptors and may be considered as a possible new antiepileptic mechanism of action.

Levetiracetam is neuroprotective in murine models of closed head injury and subarachnoid hemorrhage

OBJECTIVES

Prophylactic treatment with antiepileptic drugs is common practice following subarachnoid hemorrhage (SAH) and traumatic brain injury. However, commonly used antiepileptic drugs have multiple drug interactions, require frequent monitoring of serum levels, and are associated with adverse effects that may prompt discontinuation. In the current study, we test the hypothesis that levetiracetam, an anticonvulsant with favorable interaction and adverse event profiles, is neuroprotective in clinically relevant models of SAH and closed head injury (CHI).

METHODS

A single intravenous dose of vehicle, low-dose (18 mg/kg), or high-dose (54 mg/kg) levetiracetam was administered intravenously followed CHI. Functional assessments were performed on a daily basis, and histological assessments performed at 24 hours. In a separate series of experiments, mice were randomized to receive intravenous administration of vehicle, low-dose, or high-dose levetiracetam every 12 hours for 3 days following SAH. Functional endpoints were assessed daily, followed by measurement of MCA luminal diameter on day 3.

RESULTS

A single dose of levetiracetam improved functional and histological outcomes after CHI. This effect appeared specific for levetiracetam and was not associated with fosphenytoin treatment. Treatment with levetiracetam also improved functional outcomes and reduced vasospasm following SAH.

CONCLUSION

Levetiracetam is neuroprotective in clinically relevant animal models of SAH and CHI. Levetiracetam may be a therapeutic alternative to phenytoin following acute brain injury in the clinical setting when seizure prophylaxis is indicated.

Long-lasting antiepileptic effects of levetiracetam against epileptic seizures in the spontaneously epileptic rat (SER): differentiation of levetiracetam from conventional antiepileptic drugs

PURPOSE

Some evidence suggests that levetiracetam (LEV) possesses antiepileptogenic characteristics. The purpose of this study was to investigate the time course of seizure protection by LEV compared with that of phenytoin (PHT), phenobarbital (PB), valproate (VPA), and carbamazepine (CBZ) in the spontaneously epileptic rat (SER). The SER is a double mutant (tm/tm, zi/zi) showing both tonic convulsions and absence-like seizures.

METHODS

The effect of single (40, 80, and 160 mg/kg, i.p.) and 5-day (80 mg/kg/day, i.p.) administration of LEV on tonic convulsions and absence-like seizures in SERs were studied. Tonic convulsions induced by blowing air onto the animal's head at 5-min intervals for 30 min and spontaneous absence-like seizures characterized by 5- to 7-Hz spike-wave-like complexes in the cortical and hippocampal EEG were recorded for 30 min. In the single-administration study, observations for seizure activity were performed once before and 3 times (45, 75, and 135 min) after drug administration. In the 5-day administration study, seizure observation was performed 4 times for 30 min (once before and 3 times after drug administration) during the 5-day drug-administration period, and continued once a day until 8 days after the final administration. The antiepileptic effects of 5-day administration of conventional AEDs (PHT, PB, VPA, and CBZ) were examined by using similar methods.

RESULTS

Tonic convulsions and absence-like seizures were inhibited by a single administration of LEV at 80 and 160 mg/kg, i.p., but not significantly at 40 mg/kg, i.p. When LEV was repeatedly administered at 80 mg/kg/day, i.p., for 5 days to SERs, the inhibitory effects on seizures increased with administration time. The number of tonic convulsions and absence-like seizures were significantly reduced to 39.1% and 38.4% compared with previous values, respectively, after 5-day LEV administration. Furthermore, significant inhibition of tonic convulsions was detected <or=3 days after the final administration, and significant inhibition of absence-like seizures was still observed 8 days after the final injection of LEV. This demonstrates long-lasting seizure protection by LEV after cessation of treatment. PHT, PB, VPA, and CBZ inhibited tonic convulsions more potently compared with LEV in SERs. The maximal antiseizure effects of these drugs were reached after the initial administration, with almost the same antiseizure effects observed through day 5, despite continued drug administration. Moreover, a long-lasting treatment effect was not observed with any of these drugs except for PHT and CBZ, both of which showed moderately prolonged antiseizure effects.

CONCLUSIONS

These results show that LEV is effective in the treatment of both convulsive and absence-like seizures in SERs after single- and multiple-dose administration. Interestingly, in the 5-day administration study, it was found that the antiepileptic effects for tonic convulsions and absence-like seizures were observed both during the drug-administration period and <or=8 days after the final administration of LEV. This long-lasting effect suggests that LEV may possess an antiepileptogenic effect that it does not share with PHT, PB, VPA, and CBZ.

The antiepileptic drug levetiracetam decreases the inositol 1,4,5-trisphosphate-dependent [Ca2+]I increase induced by ATP and bradykinin in PC12 cells

The present study explores the hypothesis that the new anti-epileptic drug levetiracetam (LEV) could interfere with the inositol 1,4,5-trisphosphate (IP(3))-dependent release of intracellular Ca(2+) initiated by G(q)-coupled receptor activation, a process that plays a role in triggering and maintaining seizures. We assessed the effect of LEV on the amplitude of [Ca(2+)](i) response to bradykinin (BK) and ATP in single Fura-2/acetoxymethyl ester-loaded PC12 rat pheochromocytoma cells, which express very high levels of LEV binding sites. LEV dose-dependently reduced the [Ca(2+)](i) increase, elicited either by 1 microM BK or by 100 microM ATP (IC(50), 0.39 +/- 0.01 microM for BK and 0.20 +/- 0.01 microM for ATP; Hill coefficients, 1.33 +/- 0.04 for BK and 1.38 +/- 0.06 for ATP). Interestingly, although the discharge of ryanodine stores by a process of calcium-induced calcium release also took place as part of the [Ca(2+)](i) response to BK, LEV inhibitory effect was mainly exerted on the IP(3)-dependent stores. In fact, the drug was still effective after the pharmacological blockade of ryanodine receptors. Furthermore, LEV did not affect Ca(2+) stored in the intracellular deposits since it did not reduce the amplitude of [Ca(2+)](i) response either to thapsigargin or to ionomycin. In conclusion, LEV inhibits Ca(2+) release from the IP(3)-sensitive stores without reducing Ca(2+) storage into these deposits. Because of the relevant implications of IP(3)-dependent Ca(2+) release in neuron excitability and epileptogenesis, this novel effect of LEV could provide a useful insight into the mechanisms underlying its antiepileptic properties.

Inhibition of multidrug transporters by verapamil or probenecid does not alter blood-brain barrier penetration of levetiracetam in rats

Overexpression of multidrug efflux transporters such as P-glycoprotein (Pgp; ABCB1) or multidrug resistance proteins (MRPs; ABCC) in the blood-brain barrier has recently been suggested to explain, at least in part, pharmacoresistance in epilepsy, which affects about 30% of all patients with this common brain disorder. The novel antiepileptic drug (AED) levetiracetam (LEV) is an effective and well tolerated drug in many patients with otherwise AED-refractory epilepsy. One explanation for the favorable efficacy of LEV in pharmacoresistant patients would be that LEV is not a substrate for Pgp or MRPs in the BBB. In the present study, we used in vivo microdialysis in rats to study whether the concentration of LEV in the extracellular fluid of the cerebral cortex can be modulated by inhibition of Pgp or MRPs, using the Pgp inhibitor verapamil and the MRP1/2 inhibitor probenecid. Local perfusion with verapamil or probenecid via the microdialysis probe did not increase the extracellular brain concentration of LEV, which is in contrast to various other AEDs which have been studied previously by the same experimental protocol in this model. The data indicate that brain uptake of LEV is not affected by Pgp or MRP1/2 which may be an important reason for its antiepileptic efficacy in patients whose seizures are poorly controlled by other AEDs.

Serum concentrations of Levetiracetam in epileptic patients: the influence of dose and co-medication

Levetiracetam (LEV) is a new antiepileptic drug approved as add-on therapy. Previous studies indicated that LEV has no relevant interactions with other antiepileptic drugs. The aim of this study was to investigate the influence of LEV dose, age, and co-medication on the serum concentration of LEV. In total, 363 samples of 297 inpatients who fulfilled the inclusion criteria (e.g., trough concentration, body weight available) were investigated. A patient was considered twice only if his co-medication had been changed. The LEV serum concentration in relation to LEV dose/body weight [level-to-dose ratio, LDR, (microgram/mL)/(mg/kg)] was calculated and compared for the most frequent drug combinations. Analysis of covariance (using age as covariate) carried out on the log-transformed data showed that co-medication had a highly significant (P < 0.001) effect on LEV serum concentrations. The median LDR of LEV was 0.32 for LEV + phenytoin, 0.32 for LEV + carbamazepine, 0.34 LEV + oxcarbazepine, 0.45 for LEV + lamotrigine, 0.46 for LEV + phenobarital, 0.52 for LEV monotherapy, 0.53 for LEV + valproic acid, and 0.54 LEV + valproic acid + lamotrigine. In co-medication with phenytoin (P < 0.001), carbamazepine (P < 0.001), and oxcarbazepine (P < 0.004), the LDR of LEV was significantly lower than it was with LEV monotherapy, whereas the LDR of LEV of patients on co-medication with valproic acid or lamotrigine did not differ significantly from the LDR of LEV of patients on LEV monotherapy (P > 0.05). Regression analysis including all 363 samples confirmed that other drugs (e.g., phenytoin, carbamazepine) lower LEV concentrations. In addition to co-medication, age had a significant effect on clearance of LEV. Children had lower LEV concentrations than adults on the same LEV dose per body weight. In contrast to other studies, our data point out that other enzyme-inducing antiepileptic drugs (e.g., phenytoin, carbamazepine) can moderately decrease LEV serum concentrations (by 20-30%). However, our observations should be confirmed by prospective pharmacokinetic studies.

Developmental outcome of levetiracetam, its major metabolite in humans, 2-pyrrolidinone N-butyric acid, and its enantiomer (R)-alpha-ethyl-oxo-pyrrolidine acetamide in a mouse model of teratogenicity

PURPOSE

The purpose of this study was to test the teratogenic potential of the antiepileptic drug (AED) levetiracetam (LEV), its major metabolite in humans, 2-pyrrolidone-N-butyric acid (PBA), and enantiomer, (R)-alpha-ethyl-oxo-pyrrolidine acetamide (REV), in a well-established mouse model.

METHODS

All compounds were administered by intraperitoneal injections once daily to SWV/Fnn mice on gestational days 8-1/2 to 12-1/2. LEV was administered at doses of 600, 1,200, and 2,000 mg/kg/day, piracetam (PIR) and PBA, at 600 and 1,200 mg/kg/day, and REV, at 600 mg/kg/day. On gestational day 18(1/2), fetuses were examined for gross external malformations and prepared for skeletal analysis by using Alizarin Red S staining.

RESULTS

No significant gross external malformations were observed in any of the study groups. Fetal weights were significantly reduced in most study groups. Resorption rates were significantly increased only in the 2,000-mg/kg/day LEV group. The overall incidence of skeletal abnormalities and specifically of hypoplastic phalanges was significantly increased in both PBA treatments and in the intermediate 1,200-mg/kg/day LEV group. In contrast to that in humans, 24-h urinary excretion analysis in mice showed that 65-100% of the LEV doses were excreted unchanged, whereas only 4% was excreted as the metabolite PBA.

CONCLUSIONS

Results of this study demonstrate that both LEV and its major metabolite in humans, PBA, do not induce major structural malformations in developing SWV/Fnn embryos and suggest that they provide a margin of reproductive safety for the pregnant epileptic population when compared with other AEDs tested in this mouse model.

Anxiolytic effects of the novel anti-epileptic drug levetiracetam in the elevated plus-maze test in the rat

There is clinical evidence of anxiolytic action of several anti-epileptic drugs. We evaluated the effects of levetiracetam (Keppra), a new generation anti-epileptic drug, in the plus-maze animal test for anxiolytic activity. Levetiracetam at 17 and 54 mg/kg intraperitoneally (i.p.) was without effect when tested in naive rats. A modified version of the test was subsequently used in which open-arm exploration was decreased by exposure of the rats to a four-open-arm maze 24 h prior to drug treatment and testing. Under these conditions of enhanced anxiety, levetiracetam, 5.4 to 54 mg/kg, dose-dependently increased open-arm exploration. Chlordiazepoxide 5 mg/kg had similar effects although buspirone 0.1 to 1.0 mg/kg was inactive. The results with levetiracetam substantiate similar findings of its anxiolytic actions against chlordiazepoxide withdrawal-induced anxiety in mice and in a modified Vogel test in rats and support a potential clinical use of this drug in anxiety states.

Treatment of epilepsy in women of reproductive age: pharmacokinetic considerations

Although epilepsy affects men and women equally, there are many women's health issues in epilepsy, especially for women of childbearing age. These issues, which include menstrual cycle influences on seizure activity (catamenial epilepsy), interactions of contraceptives with antiepileptic drugs (AEDs), pharmacokinetic changes during pregnancy, teratogenicity and the safety of breastfeeding, challenge both the woman with epilepsy and the many healthcare providers involved in her care. Although the information in the literature on women's issues in epilepsy has grown steeply in recent years, there are many examples showing that much work is yet to be done. The purpose of this article is to review these issues and describe practical considerations for women of childbearing age with epilepsy. The article addresses the established or "first-generation" AEDs (phenobarbital, phenytoin, primidone, carbamazepine, ethosuximide and valproic acid) and the "second-generation" AEDs (felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide). Although a relationship between hormones and seizure activity is present in many women, good treatment options for catamenial epilepsy remain elusive. Drug interactions between enzyme-inducing AEDs and contraceptives are well documented. Higher dosages of oral contraceptives or a second contraceptive method are suggested if women use an enzyme-inducing AED. Planned pregnancy and counselling before conception is crucial. This counselling should include, but is not limited to, folic acid supplementation, medication adherence, the risk of teratogenicity and the importance of prenatal care. AED dosage adjustments may be necessary during pregnancy and should be based on clinical symptoms, not entirely on serum drug concentrations. Many groups have turned their attention to women's issues in epilepsy and have developed clinical practice guidelines. Although the future holds promise in this area, many questions and the need for progress remain.

Levetiracetam in the treatment of paroxysmal kinesiogenic choreoathetosis

Anticonvulsants are frequently used in the treatment of paroxysmal kinesiogenic choreoathetosis (PKC). Although they are often extremely effective in eliminating paroxysmal movements, short- and long-term side-effects may limit their use in young patients. Levetiracetam (Keppra), a novel antiepileptic drug approved for the treatment of partial seizures is well tolerated in patients with epilepsy. We report on the use of levetiracetam in the treatment of PKC. Levetiracetam was effective in eliminating paroxysmal events and should be considered as an alternative to standard antiepileptic medications in this disorder.

Effects of the novel antiepileptic drug levetiracetam on spontaneous recurrent seizures in the rat pilocarpine model of temporal lobe epilepsy

PURPOSE

Animal models in which seizures are elicited by chemical or electrical means are commonly used for identification and preclinical testing of novel antiepileptic drugs (AEDs). Such models have been successful in discovering all the new AEDs. However, despite the high efficacy of AEDs against elicited seizures in rodent models, a significant proportion of epilepsy patients with spontaneous recurrent seizures is resistant to these drugs. It is not known whether drug testing in rodent models with spontaneous recurrent seizures would yield a more predictive result with respect to AED efficacy in the clinic. This led us to test one of the novel AEDs, levetiracetam (LEV), in a rat model of temporal lobe epilepsy (TLE) with spontaneous recurrent seizures.

METHODS

Wistar rats were subjected to pilocarpine-induced status epilepticus and recorded for spontaneous recurrent seizures in the months after pilocarpine treatment. A group of rats with frequent spontaneous seizures was used for the drug trial with LEV. The experimental protocol for drug testing in these rats was as follows. For 2 weeks, rats received subcutaneous implantation of osmotic minipumps filled with saline (predrug control period), followed by a 2-week period with implantation of LEV-filled minipumps (drug period), after which pumps were replaced by drug-free pumps for 2 weeks (postdrug control period). The LEV concentration in the pumps during the drug period was adjusted to give daily doses resulting in the maximal plasma concentration range determined previously in patients with TLE during prolonged treatment with LEV. During the 6 weeks of the experiment in epileptic rats, seizures were recorded by video monitoring.

RESULTS

Average seizure frequency during the pre- and postdrug control period in a group of eight epileptic rats was 21 and 25 seizures. This was reduced to an average seizure frequency of 8 seizures during the 2 weeks of treatment with LEV. However, the individual response of rats to LEV varied markedly from complete seizure control to no effect at all, although plasma drug levels were within the therapeutic range in all rats. When seizure frequency was separately calculated for the first and second week of treatment, the significant anticonvulsant effect determined in the first week was partially diminished in the second week, suggesting that tolerance may have developed in some of the rats.

CONCLUSIONS

The data demonstrate that interesting results can be obtained by drug testing in epileptic rats, giving a more realistic prediction of clinical efficacy than results from drug testing in animal models with elicited seizures. Thus, although drug trials in rats with spontaneous recurrent seizures are laborious and time-consuming, such trials should be added to the preclinical characterization of novel AEDs.

Using the new antiepilepsy drugs in children

New epilepsy treatment options are becoming available to physicians and may help provide safe and effective seizure management in patients for whom traditional drug therapies have been unsuccessful. Presented here is a brief discussion on the screening models used to test drugs for efficacy against various seizure types and the mechanisms of action and pharmacology of antiepilepsy drugs. This is followed by a more detailed review of the clinical pharmacology of the latest three antiepilepsy drugs introduced to the United States: levetiracetam, oxcarbazepine, and zonisamide. All three appear to have advantages over some traditional antiepilepsy drugs and with more clinical experience may replace them in certain seizure types or epilepsy syndromes.

Selective blockade of N-type calcium channels by levetiracetam

PURPOSE

We investigated the effect of the new antiepileptic drug (AED) levetiracetam (LEV) on different types of high-voltage-activated (HVA) Ca2+ channels in freshly isolated CA1 hippocampal neurons of rats.

METHODS

Patch-clamp recordings of HVA Ca2+ channel activity were obtained from isolated hippocampal CA1 neurons. LEV was applied by gravity flow from a pipette placed near the cell, and solution changes were made by electromicrovalves. Ca2+ channel blockers were used for separation of the channel subtypes.

RESULTS

The currents were measured in controls and after application of 1-200 microM LEV. LEV irreversibly inhibited the HVA calcium current by approximately 18% on the average. With a prepulse stimulation protocol, which can eliminate direct inhibition of Ca2+ channels by G proteins, we found that G proteins were not involved in the pathways underlying the LEV inhibitory effect. This suggested that the inhibitory effect arises from a direct action of LEV on the channel molecule. The blocking mechanism of LEV was not related to changes in steady-state activation or inactivation of Ca2+ channels. LEV also did not influence the rundown of the HVA Ca2+ current during experimental protocols lasting approximately 10 min. Finally, LEV at the highest concentration used (200 microM) did not influence the activity of L-, P- or Q-type Ca2+ channels in CA1 neurons, while selectively influencing the activity of N-type calcium channels. The maximal effect on these channels separated from other channel types was approximately 37%.

CONCLUSIONS

Our results provide evidence that LEV selectively inhibits N-type Ca2+ channels of CA1 pyramidal hippocampal neurons. These data suggest the existence of a subtype of N-type channels sensitive to LEV, which might be involved in the molecular basis of its antiepileptic action.

Clinical pharmacology and therapeutic use of the new antiepileptic drugs

Although older generation antiepileptic drugs (AEDs) such as carbamazepine, phenytoin and valproic acid continue to be widely used in the treatment of epilepsy, these drugs have important shortcomings such as a highly variable and nonlinear pharmacokinetics, a narrow therapeutic index, suboptimal response rates, and a propensity to cause significant adverse effects and drug interactions. In an attempt to overcome these problems, a new generation of AEDs has been introduced in the last decade. Compared with older agents, some of these drugs offer appreciable advantages in terms of less variable kinetics and, particularly in the case of gabapentin, levetiracetam and vigabatrin, a lower interaction potential. Lamotrigine, topiramate, zonisamide and felbamate protect against partial seizures and a variety of generalized seizure types, vigabatrin is effective against partial seizures (with or without secondary generalization) and infantile spasms, while the use of oxcarbazepine, tiagabine and gabapentin is mainly restricted to patients with partial epilepsy (and, in the case of oxcarbazepine, also primarily generalized tonic-clonic seizures). Levetiracetam, the latest AED to be introduced, has been found to be effective in partial seizures, but its potentially broader efficacy spectrum remains to be determined in clinical studies. Currently, the main use of new generation AEDs is in the adjunctive therapy of patients refractory to older agents. However, due to advantages in terms of tolerability and ease of use, some of these drugs are increasingly used for first-line management in certain subgroups of patients. Due to serious toxicity risks, felbamate and vigabatrin should be prescribed only in patients refractory to other drugs. In the case of vigabatrin, however, first line use may be justified in infants with spasms.

Vagus nerve stimulation for refractory epilepsy

Vagus nerve stimulation (VNS) is a neurophysiological treatment for patients with medically or surgically refractory epilepsy. Since the first human implant in 1989, more than 10 000 patients have been treated with VNS. Two randomized controlled studies have shown a statistically significant decrease in seizure frequency during a 12-week treatment period versus a baseline period when 'high stimulation' mode was compared with 'low stimulation' mode. The efficacy appears to increase over time. In general, one third of the patients show a >50% reduction of seizure frequency; one third show a 30-50% seizure reduction, and one third of patients show no response. Few patients become seizure-free. Side effects during stimulation are mainly voice alteration, coughing, throat paraesthesia and discomfort. When studied on a long-term basis, VNS is an efficacious, safe and cost-effective treatment not only in adults but also in children and the elderly. The precise mechanism of action remains to be elucidated. In recent years much progress has been made through neurophysiological, neuroanatomical, neurochemical and cerebral blood flow studies in animals and patients treated with VNS. Further elucidation of the mechanism of action of VNS may increase its clinical efficacy and our general understanding of some physiopathological aspects of epilepsy. Finally, VNS may become an alternative treatment for other conditions such as depression and pain.