Nootropic drugs: Methylphenidate, modafinil and piracetam - Population use trends, occurrence in the environment, ecotoxicity and removal methods - A review.

Pharmaceuticals which originally were designed to treat people with neurological and psychiatric conditions, e.g. Alzheimer's disease or attention deficit hyperactivity disorder (ADHD), are nowadays often misused by students as a 'brain doping' substances. These substances are known as nootropic drugs, smart drugs or cognitive enhancers, as they increase memory, attention and concentration of healthy individuals. Since they are easily available illicitly, their consumption is observed to be growing. Currently, these pharmaceuticals started gaining researchers' attention, especially since they have been recently detected in wastewater, surface water and even drinking water. This review summarises the current state of knowledge on nootropic drugs in terms of their population use trends and ethics, occurrence in the environment and detection techniques, toxicity and removal methods, in example of methylphenidate, modafinil and piracetam - three most popular nootropics. It points out that the main sources of knowledge on cognitive enhancers illicit use are often inconsistent questionnaires, which are not supported by wastewater analysis to become more veracious. Simultaneously, the studies concerning toxicity and removal methods of nootropic drugs are still limited and in many cases environmentally irrelevant. Although the prescription rules has been subjected to more strict control in developed countries, regulatory frameworks with regard to their ecosystem occurrence are still lacking and should be introduced. Moreover, the use of environmentally relevant concentrations in toxicity studies should be a standard, leading to proper ecotoxicity risk assessment. Based on this review, it is recommended to routinely monitor nootropics and their metabolites in waste- and surface waters.

Reproductive toxicity after levetiracetam administration in male rats: Evidence for role of hormonal status and oxidative stress.

Levetiracetam (LEV) is an antiepileptic drug commonly used in the treatment of epilepsy because of its excellent safety profile in all age groups. It is remarkable that there are no studies evaluating the toxic effects of this drug on the male reproductive system, as it is commonly used in male patients of reproductive age. From this point of view, our aim was to evaluate the possible toxic effects of LEV on the male reproductive system. Therefore, LEV was administered to male rats orally at 50, 150, and 300 mg/kg for 70 consecutive days. At the end of this period, alterations to body and organ weights were calculated, and sperm concentration, motility, and morphology were investigated by a computer-assisted sperm analysis system. Sperm DNA damage was determined by comet assay and histopathological examination of the testes was carried out. Serum testosterone, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels were measured by ELISAs to determine the effects of hormonal status, while glutathione, superoxide dismutase, catalase, and malondialdehyde levels in the testes were measured by colorimetric assay kits to determine the role of oxidative status in potential toxicity. According to the results, sperm quality was decreased by LEV treatment in a dose-dependent manner. LEV induced significant DNA damage in the 150 and 300 mg/kg LEV-administered groups. Histopathology of the testes showed that LEV resulted in testicular injury in the 300 mg/kg LEV-administered group. Serum testosterone, FSH, and LH levels were significantly decreased in the 300 mg/kg LEV-administered group. Glutathione, superoxide dismutase, and catalase levels were significantly decreased in all experimental groups while malondialdehyde levels were significantly increased in 150 and 300 mg/kg LEV-administered groups. According to these results, it was determined that LEV administration decreased sperm quality and it was alleged that hormonal alteration and oxidative stress are potential contributors to reproductive toxicity.

Unfavorable effect of levetiracetam on cultured hippocampal neurons after hyperthermic injury.

BACKGROUND: The aim of this study was to examine the viability of neurons and the putative neuroprotective effects of second-generation antiepileptic drug, levetiracetam (LEV), on cultured hippocampal neurons injured by hyperthermia. METHODS: Primary cultures of rat's hippocampal neurons at 7day in vitro (DIV) were incubated in the presence or absence of LEV in varied concentrations under hyperthermic conditions. Cultures were heated in a temperature of 40°C for 24h or in a temperature of 41°C for 6h. Flow cytometry with Annexin V/PI staining as well as fluorescent microscopy assay were used for counting and establishing neurons as viable, necrotic or apoptotic. Additionally, the release of lactate dehydrogenase (LDH) to the culture medium, as a marker of cell death, was evaluated. Assessment was performed after 9DIV and 10 DIV. RESULTS: Incubation of hippocampal cultures in hyperthermic conditions resulted in statistically significant increase in the number of injured neurons when compared with non-heated control cultures. Intensity of neuronal destruction was dependent on temperature-value. When incubation temperature 40°C was used, over 80% of the population of neurons remained viable after 10 DIV. Under higher temperature 41°C, only less than 60% of neurons were viable after 10 DIV. Both apoptotic and necrotic pathways of neuronal death induced by hyperthermia were confirmed by Annexin V/PI staining. CONCLUSIONS: LEV showed no neuroprotective effects in the current model of hyperthermia in vitro. Moreover, drug, especially when used in higher concentrations, exerted unfavorable intensification of aponecrosis of cultured hippocampal neurons.

Anti-epileptic drugs and bone loss: Phenytoin reduces pro-collagen I and alters the electrophoretic mobility of osteonectin in cultured bone cells.

Phenytoin is an antiepileptic drug used in the management of partial and tonic-clonic seizures. In previous studies we have shown that valproate, another antiepileptic drug, reduced the amount of two key bone proteins, pro-collagen I and osteonectin (SPARC, BM-40), in both skin fibroblasts and cultured osteoblast-like cells. Here we show that phenytoin also reduces pro-collagen I production in osteoblast-like cells, but does not appear to cause a decrease in osteonectin message or protein production. Instead, a 24h exposure to a clinically relevant concentration of phenytoin resulted in a dose-dependent change in electrophoretic mobility of osteonectin, which was suggestive of a change in post-translational modification status. The perturbation of these important bone proteins could be one of the mechanisms to explain the bone loss that has been reported following long-term treatment with phenytoin.

The Effect of Levetiracetam on Closure of the Midline in Early Chicken Embryos.

AIM: Genetic predisposition and some environmental factors play an important role in the development of neural tube defects. Levetiracetam is a new drug that has been approved in the treatment of partial seizures. We aimed in this study to determine the effect of levetiracetam on chick embryos. MATERIAL AND METHODS: One hundred and sixty fertile non-pathogenic Super Nick eggs were incubated for 24 hours and were divided into four groups of 40 eggs each. Levetiracetam was administered via the sub-blastodermic route. The eggs were incubated for another 24 hours. All eggs were opened at the 48th hour, and the embryos were evaluated morphologically and histopathologically. RESULTS: The effects of levetiracetam on the embryo were correlated with the dose of levetiracetam. In the light of the results, it was determined that the use of increasing doses of levetiracetam led to defects of midline closure in early chicken embryos. CONCLUSION: Levetiracetam, a new antiepileptic drug that is effective especially on calcium ion concentration, leads to defects in midline closure in embryos in a dose-dependent manner. Further studies are needed to show the mechanism of embryonic damage and the mechanisms of its teratogenous effects associated with genetic and environmental factors.

Zebrafish embryotoxicity test for developmental (neuro)toxicity: Demo case of an integrated screening approach system using anti-epileptic drugs.

To improve the predictability of the zebrafish embryotoxicity test (ZET) for developmental (neuro)toxicity screening, we used a multiple-endpoints strategy, including morphology, motor activity (MA), histopathology and kinetics. The model compounds used were antiepileptic drugs (AEDs): valproic acid (VPA), carbamazepine (CBZ), ethosuximide (ETH) and levetiracetam (LEV). For VPA, histopathology was the most sensitive parameter, showing effects already at 60µM. For CBZ, morphology and MA were the most sensitive parameters, showing effects at 180µM. For ETH, all endpoints showed similar sensitivity (6.6mM), whereas MA was the most sensitive parameter for LEV (40mM). Inclusion of kinetics did not alter the absolute ranking of the compounds, but the relative potency was changed considerably. Taking all together, this demo-case study showed that inclusion of multiple-endpoints in ZET may increase the sensitivity of the assay, contribute to the elucidation of the mode of toxic action and to a better definition of the applicability domain of ZET.

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.

The effects of levetiracetam on neural tube development in the early stage of chick embryos.

AIM: This study aimed to investigate the effects of a new generation antiepileptic agent, levetiracetam, on the neural tube development in a chick embryo model that corresponds to the first month of vertebral development in mammals. MATERIAL AND METHODS: Forty-five Atabey® breed fertilized chicken eggs with no specific pathogens were randomly divided into 5 groups. All of the eggs were incubated at 37.8±2°C and 60±5 % relative humidity in an incubator. Group A was control group. The other eggs were applied physiological saline and drugs at a volume of 10 µL by the in ovo method at the 28th hour of the incubation period. Group B was given distilled water; Group C, physiological saline; Group D, Levetiracetam (L8668) at a dose equivalent to the treatment dose for humans (10 mg/ kg), and Group E, Levetiracetam (L8668) at a dose of 10 times the treatment dose. The embryos in all of the groups were removed from the shells at the 48th hour and morphologically and histologically evaluated. RESULTS: Of the 45 embryos incubated, neural tubes of 41 were closed and the embryos displayed normal development. CONCLUSION: Levetiracetam, at a dose equivalent to human treatment dose and 10 times the treatment dose, was shown not to cause neural tube defects in chick embryos.

Early valproic acid exposure alters functional organization in the primary visual cortex.

Epilepsy is one of the most common neurologic disorders and affects 0.5 to 1% of pregnant women. The use of antiepileptic drugs, which is usually continued throughout pregnancy, can cause in offspring mild to severe sensory deficits. Neuronal selectivity to stimulus orientation is a basic functional property of the visual cortex that is crucial for perception of shapes and borders. Here we investigate the effects of early exposure to valproic acid (Val) and levetiracetam (Lev), commonly used antiepileptic drugs, on the development of cortical neuron orientation selectivity and organization of cortical orientation columns. Ferrets pups were exposed to Val (200mg/kg), Lev (100mg/kg) or saline every other day between postnatal day (P) 10 and P30, a period roughly equivalent to the third trimester of human gestation. Optical imaging of intrinsic signals or single-unit recordings were examined at P42-P84, when orientation selectivity in the ferret cortex has reached a mature state. Optical imaging of intrinsic signals revealed decreased contrast of orientation maps in Val- but not Lev- or saline-treated animals. Moreover, single-unit recordings revealed that early Val treatment also reduced orientation selectivity at the cellular level. These findings indicate that Val exposure during a brief period of development disrupts cortical processing of sensory information at a later age and suggest a neurobiological substrate for some types of sensory deficits in fetal anticonvulsant syndrome.

Zebrafish (Danio rerio) embryos as a model for testing proteratogens.

Zebrafish embryos have been shown to be a useful model for the detection of direct acting teratogens. This communication presents a protocol for a 3-day in vitro zebrafish embryo teratogenicity assay and describes results obtained for 10 proteratogens: 2-acetylaminofluorene, benzo[a]pyrene, aflatoxin B(1), carbamazepine, phenytoin, trimethadione, cyclophosphamide, ifosfamide, tegafur and thio-TEPA. The selection of the test substances accounts for differences in structure, origin, metabolism and water solubility. Apart from 2-acetylaminofluorene, which mainly produces lethal effects, all proteratogens tested were teratogenic in zebrafish embryos exposed for 3 days. The test substances and/or the substance class produced characteristic patterns of fingerprint endpoints. Several substances produced effects that could be identified already at 1 dpf (days post fertilization), whereas the effects of others could only be identified unambiguously after hatching at ≥ 3 dpf. The LC50 and EC50 values were used to calculate the teratogenicity index (TI) for the different substances, and the EC20 values were related to human plasma concentrations. Results lead to the conclusion that zebrafish embryos are able to activate proteratogenic substances without addition of an exogenous metabolic activation system. Moreover, the teratogenic effects were observed at concentrations relevant to human exposure data. Along with other findings, our results indicate that zebrafish embryos are a useful alternative method for traditional teratogenicity testing with mammalian species.

Benefit of combination therapy in epilepsy: a review of the preclinical evidence with levetiracetam.

Levetiracetam (Keppra) is an antiepileptic drug (AED) characterized by a novel mechanism of action, unique profile of activity in seizure models, and broad-spectrum clinical efficacy. The present report critically reviews several preclinical studies focused on combination therapy with levetiracetam and other anticonvulsants in various seizure and epilepsy models. Administration of levetiracetam together with many different clinically used AEDs or other anticonvulsants generally enhances their protective activity and, among existing AEDs, this was particularly prevalent with valproate. The protective activity of other AEDs was also enhanced by levetiracetam, which seems to be a universal finding that is independent of seizure model or drug combination studied. However, particularly strong enhancement was observed when levetiracetam was combined with agents either enhancing GABAergic or reducing glutamatergic neurotransmission. Importantly, these combinations were not associated with exacerbation of side effects or pharmacokinetic interactions. Based on the available preclinical data, it appears that combination treatment with levetiracetam and other anticonvulsants provides additional therapeutic benefit that may be attributed to its novel and distinct mechanism of action. Moreover, combinations of levetiracetam with clinically used AEDs that enhance GABAergic inhibition may be considered for rational polytherapy, which is often necessary in drug-resistant patients.

Antiepileptic drugs and brain maturation: fetal exposure to lamotrigine generates cortical malformations in rats.

Intake of antiepileptic drugs (AEDs) during pregnancy can provoke severe and subtle fetal malformations associated with deleterious sequelae, reflecting the need for experimental investigations on the comparative teratogenic potential of these agents. We recently reported that prenatal exposure to vigabatrin and valproate, two AEDs which act through GABAergic mechanisms, induces hippocampal and cortical dysplasias in rodents. We have now investigated the effects of phenobarbital (PB, 30 mg/kg day) i.p.), a drug also endowed with GABAergic effects, and the new generation AEDs lamotrigine (LTG, 5-20mg/kg/day i.p.), topiramate (TPM, 10mg/kg/day i.p.), and levetiracetam (LEV, 50mg/kg/day i.p.) on brain development. Prenatal exposure to LTG induced hippocampal and cortical malformations in a dose-dependent manner, at maternal plasma concentrations within the clinically occurring range. These abnormalities were not observed after exposure to PB, TP and LEV. These observations raise concerns about potential clinical correlates and call for detailed comparative investigations on the consequences of AED use during pregnancy.

Developmental toxic effects of N-ethyl-2-pyrrolidone administered orally to rats.

The developmental toxicity of N-ethyl-2-pyrrolidone (NEP) was studied in Sprague-Dawley rats after oral administration. Pregnant rats were given NEP at doses of 0 (distilled water), 50, 250, 500 and 750 mg kg(-1) day(-1), by gavage (5 ml kg(-1)), on gestational days (GD) 6-20. Maternal toxicity, as evidenced by reduction in body weight gain and food consumption, was observed in all NEP groups at the beginning of treatment (GD 6-9). The incidence of resorptions was significantly increased at 500 mg kg(-1) day(-1), and reached 83% at 750 mg kg(-1) day(-1). There was a dose-related decrease in fetal weight, which was significantly lower than control at 250 mg kg(-1) day(-1) and higher doses. The incidence of malformed fetuses per litter and the number of litters with malformed fetuses were significantly increased at 500 and 750 mg kg(-1) day(-1). Malformations mainly consisted of edema, anal atresia with absent tail, cardiovascular defects and fused cervical arches. Ossification of skull bones and sternebrae was significantly reduced at 500 and 750 mg kg(-1) day(-1). The incidence of supernumerary ribs was significantly elevated at 250 mg kg(-1) day(-1) and higher doses. In conclusion, NEP administered by gavage is embryotoxic and teratogenic at maternal toxic doses.

[Fulminant liver failure in a patient on carbamazepine and levetiracetam treatment associated with status epilepticus]. / Fulminantes Leberversagen unter Therapie mit Carbamazepin und Levetiracetam nach einer Anfallserie.

A 22-year-old female with a history of developmental delay and seizures successfully treated with carbamazepine and levetiracetam developed fulminant hepatic failure and subsequently died. She had been admitted to the hospital following secondary generalized seizures of 35 min duration. A circulatory shock as well as intoxication was taken into consideration during the clinical course. Autopsy failed to reveal a macroscopically discernible cause of death. Significant findings on microscopic examination included acute tubular necrosis in the kidneys, pre-existing marked accumulation of neutral lipid within the hepatocytes as well as hyperacute liver damage with evidence of almost complete hepatocyte necrosis. Carbamazepine and levetiracetam were simultaneously determined from blood and tissues such as liver, lungs, muscle and kidneys by LC-MS/MS following addition of lamotrigine as an internal standard and liquid-liquid extraction. Validation data are given for levetiracetam. Both carbamazepine and levetiracetam were present in blood at concentrations within or below the therapeutic range, respectively. Moreover, tissue concentrations suggested long-term administration of anticonvulsant drugs, which is in accordance with the medical history. After excessive drug concentrations could be ruled out, the metabolic consequences of a prolonged carbamazepine therapy to cause severe hepatic injury in the present case are discussed. A mechanism of injury to the hepatocytes may be membrane damage by either an increased production of free radicals and/or a decreased free radical scavenging capacity. Following ischemia with reperfusion and during hyperthermia, large amounts of free radicals are formed. Induction of the mixed oxidase activity during longterm administration of carbamazepine may also increase production of free radicals, leaving the hepatic cell more vulnerable to oxidative injury.

Levetiracetam selectively potentiates the acute neurotoxic effects of topiramate and carbamazepine in the rotarod test in mice.

The effect of levetiracetam (LEV) on the acute neurotoxic profiles of various antiepileptic drugs (carbamazepine [CBZ], phenytoin [PHT], phenobarbital [PB], valproate [VPA], lamotrigine [LTG], topiramate [TPM], oxcarbazepine [OXC], and felbamate [FBM]) was evaluated in the rotarod test, allowing the determination of median toxic doses (TD50 values) with respect to impairment of motor coordination in mice. The TD50 of LEV administered singly was 1601 mg/kg. Whilst LEV at 150 mg/kg, being its TID50 (a dose increasing the electroconvulsive threshold by 50%), was without effect with regards to motor coordination impairment associated with PHT, PB, VPA, LTG, OXC, and FBM, it significantly enhanced that associated with CBZ and TPM co-administration. Thus LEV (150 mg/kg) significantly decreased the TD50 of CBZ from 53.6 to 37.3 mg/kg (P<0.01) and that of TPM from 423 to 246 mg/kg (P<0.01). In addition LEV (75 mg/kg) significantly decreased the TD50 of TPM from 423 to 278 (P<0.01). That concurrent measurement of total brain LEV, CBZ, and TPM concentrations showed that concentrations were not significantly different when AEDs were administered singly compared to when they were administered in combination would suggest that there is no pharmacokinetic interaction between these AEDs. Thus, the observed potentialization of the acute neurotoxic effects of CBZ and TPM by LEV is the consequence of a pharmacodynamic interaction. These data support both experimental and clinical published data advocating that LEV may interact with some AEDs by pharmacodynamic mechanisms.

Sulthiame but not levetiracetam exerts neurotoxic effect in the developing rat brain.

Antiepileptic drugs (AEDs) used to treat seizures in pregnant women, infants, and young children can cause cognitive impairment. One mechanism implicated in the development of neurocognitive deficits is a pathologic enhancement of physiologically occurring apoptotic neuronal death in the developing brain. We investigated whether the newer antiepileptic drug levetiracetam (LEV) and the older antiepileptic drug sulthiame (SUL) have neurotoxic properties in the developing rat brain. SUL significantly enhanced neuronal death in the brains of rat pups ages 0 to 7 days at doses of 100 mg/kg and above, whereas LEV did not show this neurotoxic effect. Dosages of both drugs used in the context of this study comply with an effective anticonvulsant dose range applied in rodent seizure models. Thus, LEV is an AED which lacks neurotoxicity in the developing rat brain and should be considered in the treatment of epilepsy in pregnant women, infants, and toddlers once general safety issues have been properly addressed.

[Functional-behavioral profile of new cyclic GABA analogs in acute toxicity tests]. / Funktsional'no-povedencheskii profil' deistviia tsiklicheskikh analogov GAMK pri izuchenii ostroi toksichnosti.

The properties of karphedone and phepyrone--new phenyl derivatives of pyrrolidone possessing nootropic activity--were studied in the course of the acute toxicity tests on rats. The drug effects were evaluated in terms of their integral influence on the state and behavior of test animals. The real therapeutic range and the profit/risk ratio of karphedone were comparable with those of the reference drug pyracetam and exceeded by a factor of 1.3 the corresponding values for phepyrone (irrespective of the LD50 values). The results give grounds for the further preclinical investigation of karphedone.

[Preclinical prognosis of pyracetam and picamilon safety based on acute toxicity data]. / Doklinicheskii prognoz bezopasnosti piratsetama i pikamilona na osnove pokazatelei ostroi toksichnosti.

A comparative acute toxicity test of the nootropic drugs piracetam and picamilon was performed on rats. The study was based on the principles of integral evaluation of the drug effect upon the functional and behavioral state of animals. It was found that the conventional therapeutic index does not coincide with the actual therapeutic activity range. Piracetam and picamilon, while exhibiting significantly different toxicity, are characterized by approximately equal ranges of the therapeutic activity.

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.

Levetiracetam: the preclinical profile of a new class of antiepileptic drugs?

Levetiracetam is a new antiepileptic drug (AED) devoid of anticonvulsant activity in the two classic screening models for AEDs, the maximal electroshock and pentylenetetrazol seizure tests in both mice and rats. This contrasts a potent seizure suppression in genetic and kindled mice and rats and against chemoconvulsants inducing partial seizures in rats. The highly selective action in "epileptic" animals distinguishes levetiracetam from classic and other new AEDs that have nearly equipotent effects in normal and "epileptic" animals. Levetiracetam induces minor behavioral alterations in normal and in kindled mice and rats. This results in an unusually high safety margin in animal models reflecting both partial and primary generalized epilepsy. Furthermore, experiments in the kindling model suggest that levetiracetam may possess antiepileptogenic properties due to a potent ability to prevent the development of kindling in mice and rats at doses devoid of adverse effects. Electrophysiologic recordings from different experimental models suggest that levetiracetam exerts a selective action against abnormal patterns of neuronal activity, which probably explains its selective protection in epileptic animals and its unique tolerability. This effect appears to derive from one or more novel mechanisms of action that do not involve a conventional interaction with traditional drug targets implicated in the modulation of inhibitory and excitatory neurotransmission. Instead, ligand-binding assays have disclosed a brain-specific binding site for levetiracetam. These studies reveal a unique preclinical profile of levetiracetam, distinct from that of all known AEDs, suggesting that levetiracetam could represent the first agent in a new class of AEDs.