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Quantitative determination of anti-epileptic drug concentrations is of great importance in forensic toxicology cases. Although the drugs are not usually abused, they are important post-mortem cases where the question of both lack of compliance and accidental or deliberate poisoning might be raised. In addition these drugs can be relevant for driving under the influence cases. A reversed phase ultra-performance liquid chromatography-tandem mass spectrometry method has been developed for the quantitative analysis of the anti-epileptic compounds carbamazepine, carbamazepine-10,11-epoxide, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, 10-OH-carbazepine, phenobarbital, phenytoin, pregabalin, and topiramate in whole blood, using 0.1 mL sample volume with methaqualone as internal standard. Sample preparation was a simple protein precipitation with acetonitrile and methanol. The diluted supernatant was directly injected into the chromatographic system. Separation was performed on an Acquity UPLC® BEH Phenyl column with gradient elution and a mildly alkaline mobile phase. The mass spectrometric detection was performed in positive ion mode, except for phenobarbital, and multiple reaction monitoring was used for drug quantification. The limits of quantification for the different anti-epileptic drugs varied from 0.064 to 1.26 mg/L in blood, within-day and day-to-day relative standard deviations from 2.2 to 14.7% except for phenobarbital. Between-day variation for phenobarbital was 20.4% at the concentration level of 3.5 mg/L. The biases for all compounds were within ±17.5%. The recoveries ranged between 85 and 120%. The corrected matrix effects were 88-106% and 84-110% in ante-mortem and post-mortem whole blood samples, respectively., (Copyright © 2014 John Wiley & Sons, Ltd.)

The putative Major Facilitator Superfamily (MFS) transporter, SV2A, is the target for levetiracetam (LEV), which is a successful anti-epileptic drug. Furthermore, SV2A knock out mice display a severe seizure phenotype and die after a few weeks. Despite this, the mode of action of LEV is not known at the molecular level. It would be extremely desirable to understand this more fully in order to aid the design of improved anti-epileptic compounds. Since there is no structure for SV2A, homology modelling can provide insight into the ligand-binding site. However, it is not a trivial process to build such models, since SV2A has low sequence identity to those MFS transporters whose structures are known. A further level of complexity is added by the fact that it is not known which conformational state of the receptor LEV binds to, as multiple conformational states have been inferred by tomography and ligand binding assays or indeed, if binding is exclusive to a single state. Here, we explore models of both the inward and outward facing conformational states of SV2A (according to the alternating access mechanism for MFS transporters). We use a sequence conservation analysis to help guide the homology modelling process and generate the models, which we assess further with Molecular Dynamics (MD). By comparing the MD results in conjunction with docking and simulation of a LEV-analogue used in radioligand binding assays, we were able to suggest further residues that line the binding pocket. These were confirmed experimentally. In particular, mutation of D670 leads to a complete loss of binding. The results shed light on the way LEV analogues may interact with SV2A and may help with the on-going design of improved anti-epileptic compounds.

The nature of the pharmacodynamic interactions of drugs is influenced by the drugs׳ mechanisms of action. It has been hypothesized that drugs with different mechanisms are likely to interact synergistically, whereas those with similar mechanisms seem to produce additive interactions. In this review, we describe an extensive investigation of the published literature on drug combinations of anticonvulsants, the nature of the interaction of which has been evaluated by type I and II isobolographic analyses and the subthreshold method. The molecular targets of antiepileptic drugs (AEDs) include Na(+) and Ca(2+) channels, GABA type-A receptor, and glutamate receptors such as NMDA and AMPA/kainate receptors. The results of this review indicate that the nature of interactions evaluated by type I isobolographic analyses but not by the two other methods seems to be consistent with the above hypothesis. Type I isobolographic analyses may be used not only for evaluating drug combinations but also for predicting the targets of new drugs., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Background: Neonatal seizures can result in chronic epilepsy and long-term behavioral and cognitive deficits. Levetiracetam (LEV), an antiepileptic drug that binds to the synaptic vesicle protein 2A (SV2A), has been increasingly used off-label for the therapy of neonatal seizures. Preclinical data regarding the acute or long-term efficacy of LEV are lacking., Methods: We tested the anticonvulsant efficacy of LEV in a rat model of hypoxia-induced neonatal seizures. In addition, we evaluated the protective effects of postnatal day (P)10 LEV treatment on later-life kainic acid (KA)-induced seizure susceptibility and seizure-induced neuronal injury. Western blot and immunohistochemistry were used to assess the developmental regulation of SV2A in the rat and human brain., Results: LEV pretreatment at P10 significantly decreased the cumulative duration of behavioral and electrographic seizures at both 25 and 50 mg/kg. At P40, KA-induced seizures and neuronal loss were significantly diminished in rats previously treated with LEV. LEV target SV2A is present in both neonatal rat and human brain and increases steadily to adulthood., Conclusion: LEV suppressed acute seizures induced by perinatal hypoxia and diminished later-life seizure susceptibility and seizure-induced neuronal injury, providing evidence for disease modification. These results support consideration of a clinical trial of LEV in neonatal seizures.

Introduction: Antiepileptic drugs are prescribed to patients of all ages and are commonly prescribed to patients over the age of 65. When prescribing these drugs to patients of this age bracket, treatment should be based not only on the diagnosis and seizure type but also on the propensity of the drugs for adverse effects and their drug-drug interactions., Areas Covered: This article reviews antiepileptic drugs currently used for treating the elderly and highlights the adverse effects and potential drug-drug interactions for these treatments. The article was complied through literature searches of the Cochrane database of systematic reviews, MEDLINE and SCindeks., Expert Opinion: In elderly patients who have hepatic diseases, antiepileptic drugs that are not metabolized in the liver, such as levetiracetam, are preferred; in patients with moderate and severe renal failure, carbamazepine and valproic acid are the preferred antiepileptic drugs. Phenytoin, fosphenytoin, carbamazepine, oxcarbazepine and lamotrigine should not be prescribed in elderly patients with cardiac conduction abnormalities or a history of ventricular arrhythmia. While the majority of antiepileptic drugs interact with other drugs, hepatic enzymes and plasma proteins, a few newer antiepileptic drugs are free from such interactions (e.g., gabapentin, levetiracetam and tiagabine), which make them suitable candidates for elderly patients. However, in order to make further recommendations regarding the choice and dosing regimens of antiepileptic drugs in elderly patients, more extensive clinical research in this specific population is necessary.

LEV (levetiracetam), an antiepileptic drug which possesses a unique profile in animal models of seizure and epilepsy, has as its unique binding site in brain, SV2A (synaptic vesicle protein 2A). Previous studies have used a chimaeric and site-specific mutagenesis approach to identify three residues in the putative tenth transmembrane helix of SV2A that, when mutated, alter binding of LEV and related racetam derivatives to SV2A. In the present paper, we report a combined modelling and mutagenesis study that successfully identifies another 11 residues in SV2A that appear to be involved in ligand binding. Sequence analysis and modelling of SV2A suggested residues equivalent to critical functional residues of other MFS (major facilitator superfamily) transporters. Alanine scanning of these and other SV2A residues resulted in the identification of residues affecting racetam binding, including Ile273 which differentiated between racetam analogues, when mutated to alanine. Integrating mutagenesis results with docking analysis led to the construction of a mutant in which six SV2A residues were replaced with corresponding SV2B residues. This mutant showed racetam ligand-binding affinity intermediate to the affinities observed for SV2A and SV2B.

Levetiracetam (LEV) is one of the most commonly prescribed antiepileptic drugs, but its mechanism of action is uncertain. Based on prior information that LEV binds to the vesicular protein synaptic vesicle protein 2A and reduces presynaptic neurotransmitter release, we wanted to more rigorously characterize its effect on transmitter release and explain the requirement for a prolonged incubation period for its full effect to manifest. During whole cell patch recordings from rat hippocampal pyramidal neurons in vitro, we found that LEV decreased synaptic currents in a frequency-dependent manner and reduced the readily releasable pool of vesicles. When we manipulated spontaneous activity and stimulation paradigms, we found that synaptic activity during LEV incubation alters the time at which LEV's effect appears, as well as its magnitude. We believe that synaptic activity and concomitant vesicular release allow LEV to enter recycling vesicles to reach its binding site, synaptic vesicle protein 2A. In support of this hypothesis, a vesicular "load-unload" protocol using hypertonic sucrose in the presence of LEV quickly induced LEV's effect. The effect rapidly disappeared after unloading in the absence of LEV. These findings are compatible with LEV acting at an intravesicular binding site to modulate the release of transmitter and with its most marked effect on rapidly discharging neurons. Our results identify a unique neurobiological explanation for LEV's highly selective antiepileptic effect and suggest that synaptic vesicle proteins might be appropriate targets for the development of other neuroactive drugs.

Purpose: The goals of this study are to evaluate the efficacy and tolerability of levetiracetam (LEV) as add-on therapy in children with refractory epilepsies and to determine the value of LEV blood level monitoring in this population., Methods: Sixty-nine children (39 males and 30 females) treated with LEV between 2006 and 2007 were selected. Their medical files were reviewed for LEV efficacy and tolerability. In a subgroup of children currently taking LEV, plasma concentrations were determined by high performance liquid chromatography by ultraviolet detection (HPLC-UV) method and correlated with the given dose per kilo as well as clinical response., Results: Fifty-one patients (74%) had a more than 50% reduction in seizure frequency with 16 patients (23%) becoming seizure free on LEV. Eighteen (26%) patients had a less than 50% reduction in seizure frequency. Adverse events due to LEV ranged from mild to moderate in only 18 patients (26%). The most frequently observed were drowsiness, behavioral difficulties, increase in seizure frequency and headaches. The majority (60.5%) of the responders received doses between 10 and 50mg/kg/day and had a plasma concentration (PC) between 5 and 40microg/ml. However, we found no clear correlation between PC and efficacy., Conclusion: Levetiracetam given twice a day in children with refractory epilepsy reduces seizure frequency in all types of epilepsy. In children, LEV is a broad spectrum anticonvulsant with a favourable safety profile.

Although antiepileptic drug (AED) monitoring in saliva may have some clinical applicability, it has not yet come into routine use. The correlation between levetiracetam (LEV) saliva and serum concentrations also remains unclear. To confirm LEV saliva assay as a useful, noninvasive alternative to serum measurement, we investigated the possible correlation between saliva and serum LEV concentrations. Samples of saliva and blood were collected from 30 patients with epilepsy receiving chronic therapy with LEV as monotherapy or add-on therapy, and LEV concentrations were assayed in saliva and serum. Linear regression analyses showed a close correlation between saliva and serum LEV concentrations (r2 = 0.90; P < 0.001). LEV blood and saliva concentrations were linearly related to daily drug doses (r2 = 0.78 and 0.70; P < 0.01). When data were analyzed for subgroups (patients receiving LEV in monotherapy, as add-on therapy with enzyme-inducer AEDs, and as add-on therapy with noninducer or moderate-inducer AEDs), no significant difference was found between saliva and serum LEV concentrations among groups. These preliminary results indicate that LEV, like other AEDs, can be measured in saliva as an alternative to blood-based assays. Saliva LEV collection and assay is a valid noninvasive, more convenient alternative to serum measurement.

Purpose: Although levetiracetam undergoes minimum metabolism, B-esterases have been identified in whole blood that are capable of metabolising levetiracetam. The present study was designed to ascertain any variability in levetiracetam blood concentrations that could be attributed to in situ metabolism and which could impact on the utility of such concentration measurements in guiding therapeutic management., Methods: Blood samples were collected from 40 patients that were prescribed levetiracetam. Sera (Groups 1 and 2) or whole blood (Groups 3 and 4) were compared. Paraoxan, an inhibitor of B-esterase activity, was added to samples assigned to Groups 2 and 4. Samples within each group were assigned to Time 0 (frozen within 30 min of sample collection), Time 2 days and Time 7 days (samples kept at ambient temperature for 2 and 7 days)., Results: For serum samples, mean levetiracetam concentrations at Time 2 days and Time 7 days were indistinguishable from Time 0, regardless of whether B-esterase activity was inhibited on not. In contrast, for whole blood, in the absence of B-esterase inhibition, mean levetiracetam concentrations declined over time (11% and 29%; 2 and 7 days) compared to baseline values. In the presence of B-esterase inhibitor, mean levetiracetam concentrations at 2 days were indistinguishable from baseline values, although at 7 days values declined by 4%., Conclusions: If therapeutic monitoring of levetiracetam is to be undertaken, serum should be the matrix of choice and that whole blood should be separated as soon as possible after patient sampling so as to minimize in situ levetiracetam metabolism which could result in spuriously low concentrations and substantial intrapatient variability.

Levetiracetam (Lev) is a new antiepileptic drug with a distinct mechanism of action, shown in regulatory trials to be effective. These controlled trials do not always predict how useful a drug will be in day to day clinical practice. Retention rates can provide a better indication of efficacy and tolerability in everyday use. Patients attending a tertiary referral centre for epilepsy and who received Lev in the first 2 years of its marketing were assessed (n = 811) to determine continuation rates of treatment with this drug. At the last follow up, 65% of patients were still taking Lev, and the estimated 3 year retention rate was 58%. In total, 11% attained seizure freedom of at least 6 months. Patients taking greater numbers of concurrent antiepileptic drugs (AEDs) were more likely to discontinue Lev, and those reaching higher maximum daily dosages were less likely to discontinue Lev. The retention rate for Lev compares favourably with that of other new AEDs.

The novel antiepileptic drug levetiracetam ((2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA possesses a specific binding site in brain, which has very recently been identified as the synaptic vesicle protein SV 2 A. The aim of this study was to evaluate the presence of a levetiracetam binding site in the spinal cord and compare its properties to that in rat brain. We used [(3)H]ucb 30889 ((2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide), a levetiracetam analogue, to perform binding assays, photoaffinity labelling and autoradiography experiments, and revealed the presence of SV 2 A by Western-blot analysis. [(3)H]ucb 30889 binding kinetics at 4 degrees C were biphasic and saturation binding curves were compatible with the labelling of a homogenous population of binding sites with a K(d) similar to that in brain. Competition curves with ligands known to interact with levetiracetam binding sites and photolabelling experiments indicated that [(3)H]ucb 30889 labels the same 90 kDa protein in both spinal cord and brain. Levetiracetam binding site was localised in the grey matter of the spinal cord and its expression was not modified in a model of neuropathic pain. This study demonstrates the presence of a specific levetiracetam binding site in the rat spinal cord, which is similar to that found in rat brain.

Seizures may occur after orthotopic liver transplantation. Antiepileptic drugs (AEDs) are used to treat these seizures, but the immunosuppressant regimen also may be altered. Levetiracetam is an attractive treatment because of its efficacy, lack of hepatic enzyme induction, and its rapid attainment of serum levels. Treatment with levetiracetam is efficacious, and levetiracetam-treated patients require significantly lower doses of immunosuppressant medications to achieve an equivalent antirejection effect.

Here, we show that the synaptic vesicle protein SV2A is the brain binding site of levetiracetam (LEV), a new antiepileptic drug with a unique activity profile in animal models of seizure and epilepsy. The LEV-binding site is enriched in synaptic vesicles, and photoaffinity labeling of purified synaptic vesicles confirms that it has an apparent molecular mass of approximately 90 kDa. Brain membranes and purified synaptic vesicles from mice lacking SV2A do not bind a tritiated LEV derivative, indicating that SV2A is necessary for LEV binding. LEV and related compounds bind to SV2A expressed in fibroblasts, indicating that SV2A is sufficient for LEV binding. No binding was observed to the related isoforms SV2B and SV2C. Furthermore, there is a high degree of correlation between binding affinities of a series of LEV derivatives to SV2A in fibroblasts and to the LEV-binding site in brain. Finally, there is a strong correlation between the affinity of a compound for SV2A and its ability to protect against seizures in an audiogenic mouse animal model of epilepsy. These experimental results suggest that SV2A is the binding site of LEV in the brain and that LEV acts by modulating the function of SV2A, supporting previous indications that LEV possesses a mechanism of action distinct from that of other antiepileptic drugs. Further, these results indicate that proteins involved in vesicle exocytosis, and SV2 in particular, are promising targets for the development of new CNS drug therapies.

1: The pharmacokinetics and metabolism of 14C-levetiracetam, a new anti-epileptic agent, in mouse, rat, rabbit and dog after a single oral dose were investigated. Moreover, the in vitro hydrolysis of levetiracetam to its major carboxylic metabolite by rat tissue homogenates was investigated to identify tissues involved in the production of the metabolite. Data are also presented on the induction of the enzyme(s) involved in levetiracetam hydrolysis in the rat. 2: Levetiracetam was rapidly and almost completely absorbed. The unchanged drug accounted for a very high percentage of plasma radioactivity. Levetiracetam did not bind to plasma proteins. Although brain radioactivity concentrations were lower than those of whole blood at early time points, brain-to-blood ratios increased over time. The predominant route of elimination of total 14C was excretion via urine, accounting for about 81, 93, 87 and 89% of the dose in the mouse, rat, rabbit and dog, respectively. Consequently, levetiracetam was poorly metabolized. It was submitted in vivo to hydrolysis and/or oxidation. Hydrolysis of the amide function of levetiracetam produced the corresponding acid. However, levetiracetam could also be oxidized at positions 3 and 4 of the 2-oxopyrrolidine ring. Finally, the compound and the corresponding acid metabolite could be oxidized at position 5 of the 2-oxopyrrolidine ring and then hydrolysed with the opening of the ring. 3: All the investigated rat tissues (liver, kidney, lung, brain, small intestine mucosa) had the potential to produce the acid metabolite. By contrast, the acid was undetectable following incubation of levetiracetam with buffer alone or heat-denaturated liver fractions. 4: No marked species or sex differences were observed in the absorption, disposition and metabolism of levetiracetam. 5:The hydrolysis of levetiracetam is carried out by an enzymatic process characterized by a broad tissue distribution. In the rat, the enzyme system hydrolysing levetiracetam is not induced by phenobarbital, at least under the experimental conditions used herein, whereas the enzyme system(s) involved in the other metabolic pathways is induced., (Copyright 2004 Taylor and Francis Ltd.)

(S)-alpha-ethyl-2-oxopyrrolidine acetamide 2 (levetiracetam, Keppra, UCB S.A.), a structural analogue of piracetam, has recently been approved as an add-on treatment of refractory partial onset seizures in adults. This drug appears to combine significant efficacy and high tolerability due to a unique mechanism of action. The latter relates to a brain-specific binding site for 2 (LBS for levetiracetam binding site) that probably plays a major role in its antiepileptic properties. Using this novel molecular target, we initiated a drug-discovery program searching for ligands with significant affinity to LBS with the aim to characterize their therapeutic potential in epilepsy and other central nervous system diseases. We systematically investigated the various positions of the pyrrolidone acetamide scaffold. We found that (i) the carboxamide moiety on 2 is essential for affinity; (ii) among 100 different side chains, the preferred substitution alpha to the carboxamide is an ethyl group with the (S)-configuration; (iii) the 2-oxopyrrolidine ring is preferred over piperidine analogues or acyclic compounds; (iv) substitution of positions 3 or 5 of the lactam ring decreases the LBS affinity; and (v) 4-substitution of the lactam ring by small hydrophobic groups improves the in vitro and in vivo potency. Six interesting candidates substituted in the 4-position have been shown to be more potent antiseizure agents in vivo than 2. Further pharmacological studies from our group led to the selection of (2S)-2-[(4R)-2-oxo-4-propylpyrrolidin-1-yl]butanamide 83alpha (ucb 34714) as the most interesting candidate. It is approximately 10 times more potent than 2 as an antiseizure agent in audiogenic seizure-prone mice. A clinical phase I program has been successfully concluded and 83alpha will commence several phase II trials during 2003.

The absorption, disposition and metabolism of levetiracetam, a new antiepileptic drug, have been investigated after a single oral dose of the (14)C-labelled molecule administered to male healthy volunteers. As chiral inversion can occur during drug metabolism, the chiral inversion of levetiracetam and/or of its major metabolite produced by hydrolysis (the corresponding acid) was also investigated. Finally, the in vitro hydrolysis of levetiracetam to its major metabolite and the inhibition of this reaction in human blood have been studied. Levetiracetam was very rapidly absorbed in man, with the peak plasma concentration of the unchanged drug occurring at 0.25-0.50 h. The unchanged drug accounted for a very high percentage of plasma radioactivity (97-82%) at all the times measured, i.e. until 48 h after administration. The apparent volume of distribution of the compound was close (0.55-0.62 l/kg) to the volume of total body water. Total body clearance (0.80-0.97 ml/min/kg) was much lower than the nominal hepatic blood flow. The plasma elimination half-life of the unchanged drug varied between 7.4 h and 7.9 h. Plasma to blood ratio of total radioactivity concentrations was 1.1-1.3, showing that radioactivity concentrations were similar in blood cells and plasma. The balance of excretion was very high in all four volunteers. The predominant route of excretion was via urine, accounting for a mean of 95% of the administered dose after 4 days. Two major radioactive components were present in urine, the unchanged drug and the acid obtained by hydrolysis, accounting for 66% and 24% of the dose after 48 h, respectively. Hydrolysis of levetiracetam in human blood followed Michaelis-Menten kinetics with Km and V(max) values of 435 microM and 129 pmol/min/ml blood, respectively. Among the inhibitory agents investigated in this study, only paraoxon inhibited levetiracetam hydrolysis (92% inhibition at 100 microM). Oxidative metabolism occurred in man, although it accounted for no more than 2.5% of the dose. There was no evidence of chiral inversion.

Levetiracetam (2S-(2-oxo-1-pyrrolidinyl)butanamide, KEPPRA, a novel antiepileptic drug, has been shown to bind to a specific binding site located in brain (levetiracetam binding site [Eur. J. Pharmacol. 286 (1995) 137]). However, [3H]levetiracetam displayed only micromolar affinity for these sites making it an unsuitable probe for further characterization. The present study describes the binding properties of an analogue of levetiracetam: [3H]ucb 30889, (2S)-2-[4-(3-azidophenyl)-2-oxopyrrolidin-1-yl]butanamide. [3H]ucb 30889 binds reversibly to specific binding sites in rat brain. Kinetics at 4 degrees C were biphasic with half-times of association and dissociation of, respectively, 3 and 4 min for the fast component and 47 and 61 min for the slow component. [3H]ucb 30889 saturation binding curves were compatible with the labelling of a homogenous population of binding sites having a B(max) of 4496+/-790 fmol/mg protein (mean+/-S.D., n=5) and a K(d) of 62+/-20 nM (mean+/-S.D., n=5), a 20-fold increase in affinity compared to [3H]levetiracetam. Competition binding curves with ligands known to interact with levetiracetam binding sites and tissue distribution restricted to the brain indicated that [3H]ucb 30889 and [3H]levetiracetam bind to the same site. Although levetiracetam binding sites and GABA(A) (gamma-aminobutyric acid) receptors share some ligands such as pentobarbital and pentylenetetrazol, experiments performed with [35S]TBPS (tert-butyl-bicyclo[2.2.2]phosporothionate), a probe for the GABA(A) Cl(-) channel do not support the hypothesis that levetiracetam binding sites are part of the GABA(A) receptor complex. Preliminary autoradiography studies in rat brain revealed that [3H]ucb 30889 labels specific sites in all brain regions and that this binding is concentration-dependently displaced by levetiracetam.

Levetiracetam is the latest in a series of nine new antiepileptic drugs (AEDs) to be licensed for clinical use. Its present license is for use as adjunctive therapy for the treatment of patients with partial seizures with or without secondary generalization that are refractory to other established first line AEDs. Pharmacokinetic studies of levetiracetam have been conducted in healthy volunteers, in patients of all ages with epilepsy, and in certain special populations. Results of these studies indicate that levetiracetam has a very favorable pharmacokinetic profile, characterized by excellent oral absorption and bioavailability (> 95%) and a mean elimination half-life in adults, children and the elderly of 7, 6 and 10.5 h, respectively. Levetiracetam is not bound to plasma proteins and is not metabolized in the liver, so it is not expected to be associated with significant pharmacokinetic interactions. Indeed, to the best of the author's knowledge, no clinically relevant pharmacokinetic interactions with levetiracetam have yet been identified. However, pharmacodynamic interactions with carbamazepine and topiramate have been highlighted. As levetiracetam is primarily excreted unchanged in urine, dosage adjustments are necessary for patients with moderate-to-severe renal impairment. Overall, the pharmacokinetic characteristics of levetiracetam can be considered highly desirable.

Purpose: The new antiepileptic drug, levetiracetam (LEV, ucb LO59), is a chiral molecule with one asymmetric carbon atom whose anticonvulsant activity is highly enantioselective. The purpose of this study was to evaluate and compare the pharmacokinetics (PK) of LEV [(S)-alpha-ethyl-2-oxo-pyrrolidine acetamide] and its enantiomer (R)-alpha-ethyl-2-oxo-pyrrolidine acetamide (REV) after i.v. administration to dogs. This is the first time that the pharmacokinetics of both enantiomers has been evaluated., Methods: Optically pure LEV and REV were synthesized, and 20 mg/kg of individual enantiomers was administered intravenously to six dogs. Plasma and urine samples were collected until 24 h, and the concentrations of LEV and REV were determined by an enantioselective assay. The levels of 2-pyrrolidone-N-butyric acid, an acid metabolite of LEV and REV, were determined by high-performance liquid chromatography (HPLC). The data were used for PK analysis of LEV and REV., Results: LEV and REV had similar mean +/- SD values for clearance; 1.5 +/- 0.3 ml/min/kg and volume of distribution; 0.5 +/- 0.1 L/kg. The half-life (t1/2) and mean residence time (MRT) of REV (t1/2, 4.3 +/- 0.8 h, and MRT, 6.0 +/- 1.1 h) were, however, significantly longer than those of LEV (t1/2, 3.6 +/- 0.8 h, and MRT, 5.0 +/- 1.2 h). The renal clearance and fraction excreted unchanged for LEV and REV were significantly different., Conclusions: In addition to the enantioselective pharmacodynamics, alpha-ethyl-2-oxo-pyrrolidine acetamide has enantioselective PK. The enantioselectivity was observed in renal clearance. Because REV has more favorable PK in dogs than LEV, the higher antiepileptic potency of LEV is more likely due to intrinsic pharmacodynamic activity rather than to enantioselective PK.

Major considerations in the acceptance and impact of new antiepileptic drugs include their pharmacokinetics and their potential for interaction with other drugs. The pharmacokinetics of levetiracetam, a newly approved add-on antiepileptic agent for partial-onset seizures in adults, has been evaluated in 27 phase I and II studies. Consistent findings in these studies include rapid and complete oral absorption, linear dose kinetics, a minimal degree of protein binding, and predominantly renal excretion. Because of the lack of hepatic metabolism and low protein binding, the risk of interaction with other drugs is considered low.

Each antiepileptic drug has a characteristic pharmacokinetic profile, and the unique properties of each must be considered when selecting the optimal agent for a particular patient. Detailed pharmacologic data are obtained during the preapproval evaluation of a drug, particularly in early phase studies in healthy volunteers. Each drug is then evaluated in the target population in later phase trials and in certain populations, such as children and individuals with various types of organ failure. Key considerations are bioavailability, protein binding, metabolism and elimination, and drug interactions. Important pharmacokinetic considerations in the selection and use of these drugs are presented in this review, with examples from currently available drugs.

Unlabelled: Levetiracetam, the S-enantiomer of alpha-ethyl-2-oxo-1-pyrollidine acetamide, is approved for use as adjunctive therapy in adult patients with partial onset seizures. Oral levetiracetam 1000, 2000 and 3000 mg/day administered as adjunctive therapy for up to 18 weeks significantly increased responder rates and reduced seizure frequency compared with placebo in 3 well designed pivotal trials in adults with treatment-refractory partial seizures with or without secondary generalisation. Levetiracetam 3000 mg/day also significantly increased the number of seizure-free patients, but the effects of levetiracetam 1000 and 2000 mg/day on this end-point were unclear. Effects on seizure severity were not assessed in these trials. Although not yet approved as monotherapy or for use in paediatric patients, efficacy was observed with levetiracetam 3000 mg/day as monotherapy in adult patients with refractory partial seizures with or without secondary generalisation and with the 10 to 40 mg/kg/day dosage as adjunctive therapy in children with refractory partial seizures. However, these data are limited. Oral levetiracetam 1000, 2000 and 3000 mg/day as adjunctive therapy is generally well tolerated with an overall incidence of adverse events similar to that observed with placebo. The most commonly reported events in individual clinical trials were CNS-related and included somnolence, asthenia, headache and dizziness. Levetiracetam administered as adjunctive therapy does not appear to interact with other anticonvulsant drugs, and no clinically relevant interactions were observed between levetiracetam and digoxin, warfarin or probenecid; oral contraceptive protective efficacy was also not affected by levetiracetam., Conclusions: Levetiracetam is a new anticonvulsant agent with a favourable tolerability profile and a low potential for drug interactions. It has shown efficacy as adjunctive therapy in patients with treatment-refractory partial onset seizures with or without secondary generalisation in clinical trials. Direct comparative trials with other anticonvulsant agents are not yet available, but placebo-controlled clinical evidence to date suggests that levetiracetam (1000, 2000 and 3000 mg/day) is a useful option as adjunctive therapy in patients with this subtype of epilepsy.

Levetiracetam and its carboxylic metabolite (AcL) were tested for their potential inhibitory effect on 11 different drug metabolizing enzyme activities using human liver microsomes. The following specific assays were investigated: testosterone 6beta-hydroxylation [cytochrome P-450 3A4 (CYP3A4)], coumarin hydroxylation (CYP2A6), (R)-warfarin hydroxylation (CYP1A2), (S)-mephenytoin hydroxylation (CYP2C19), p-nitrophenol hydroxylation (CYP2E1) tolbutamide hydroxylation (CYP2C9), dextromethorphan O-demethylation (CYP2D6), epoxide hydrolase and UDP-glucuronyltransferase (UGT) toward paracetamol (UGT1*6), ethinyloestradiol (UGT1*1), p-nitrophenol (UGT(pl 6.2)), and valproic acid. None of these activities were affected by levetiracetam or AcL added at concentrations up to 1 mM. Additionally, primary cultures of rat hepatocytes were used to assess a potential inducing effect of levetiracetam on CYPs. Phenobarbital (2 mM), beta-naphtoflavone (40 microM), dexamethasone (1 microM), and phenytoin (up to 300 microM) were tested as positive controls. When added to cells for 48 h, all the positive controls increased 7-ethoxycoumarin O-deethylase activity demonstrating the inducibility of CYPs in the present culture conditions. By contrast, levetiracetam did not affect the activity up to 1 mM. The highest levetiracetam concentrations examined in the above in vitro studies are well in excess of those measured in the plasma of patients receiving therapeutic doses. It is thus concluded that levetiracetam is unlikely to produce pharmacokinetic interactions through inhibition of CYPs, UGTs, and epoxide hydrolase. Furthermore, based on the in vitro assays with rat hepatocytes, it could be speculated that levetiracetam does not act as a CYP inducer.

Levetiracetam ((S)-alpha-ethyl-2-oxo-pyrrolidine acetamide, ucb L059) is a novel potential antiepileptic agent presently in clinical development with unknown mechanism of action. The finding that its anticonvulsant activity is highly stereoselective (Gower et al., 1992) led us to investigate the presence of specific binding sites for [3H]levetiracetam in rat central nervous system (CNS). Binding assays, performed on crude membranes, revealed the existence of a reversible, saturable and stereoselective specific binding site. Results obtained in hippocampal membranes suggest that [3H]levetiracetam labels a single class of binding sites (nH = 0.92 +/- 0.06) with modest affinity (Kd = 780 +/- 115 nM) and with a high binding capacity (Bmax = 9.1 +/- 1.2 pmol/mg protein). Similar Kd and Bmax values were obtained in other brain regions (cortex, cerebellum and striatum). ucb L060, the (R) enantiomer of levetiracetam, displayed about 1000 times less affinity for these sites. The binding of [3H]levetiracetam is confined to the synaptic plasma membranes in the central nervous system since no specific binding was observed in a range of peripheral tissues including heart, kidneys, spleen, pancreas, adrenals, lungs and liver. The commonly used antiepileptic drugs carbamazepine, phenytoin, valproate, phenobarbital and clonazepam, as well as the convulsant agent t-butylbicyclophosphorothionate (TBPS), picrotoxin and bicuculline did not displace [3H]levetiracetam binding. However, ethosuximide (pKi = 3.5 +/- 0.1), pentobarbital (pKi = 3.8 +/- 0.1), pentylenetetrazole (pKi = 4.1 +/- 0.1) and bemegride (pKi = 5.0 +/- 0.1) competed with [3H]levetiracetam with pKi values comparable to active drug concentrations observed in vivo. Structurally related compounds, including piracetam and aniracetam, also displaced [3H]levetiracetam binding. (S) Stereoisomer homologues of levetiracetam demonstrated a rank order of affinity for [3H]levetiracetam binding in correlation with their anticonvulsant activity in the audiogenic mouse test (r2 = 0.84, n = 12, P < 0.0001). These results support a possible role of this binding site in the anticonvulsant activity of levetiracetam and substantiate the singular pharmacological profile of this compound. This site remains however to be further characterised.