Modification of polydopamine-coated Fe3O4 nanoparticles with multi-walled carbon nanotubes for magnetic-µ-dispersive solid-phase extraction of antiepileptic drugs in biological matrices.

In this study, multi-walled carbon nanotubes were coated on the surface of magnetic nanoparticles modified by polydopamine. The synthesized composite was characterized and applied to magnetic-µ-dispersive solid-phase extraction of oxcarbazepine (OXC), phenytoin (PHT), and carbamazepine (CBZ) from human plasma, urine, and cerebrospinal fluid samples prior to analysis by a high-performance liquid chromatography-photodiode array detector. The extraction parameters were investigated and the optimum condition was obtained when the variables were set to the following: sorbent type, Fe3O4@polyDA-MWCNTs (length < 2 µm); sample pH, 6; amount of sorbent, 15 mg; sorption time, 1.5 min at room temperature; type and volume of the eluent, 2.5 mL methanol; and salt content, none added. Under the optimized conditions, the calibration curves are linear in the concentration range 2-2000 ng/mL, the limits of detection are in the range 0.4-3.1 ng/mL, and the relative standard deviations and relative recoveries of plasma (spiked at 200 ng/mL) and CSF (spiked at 50 ng/mL) are in the ranges 1.4-8.2% and 92.8-96.5%, respectively. The applicability of the method was successfully confirmed by extraction and determination of OXC, PHT, and CBZ in biological matrices. Graphical abstract Magnetic multi-walled carbon nanotube core-shell composites were applied as magnetic-µ-dispersive solid-phase extraction adsorbents for determination of antiepileptic drugs in biological matrices.

Comparison of lacosamide concentrations in cerebrospinal fluid and serum in patients with epilepsy.

OBJECTIVE: This study was carried out to estimate the exposure of the central nervous system (CNS) to the antiepileptic drug (AED) lacosamide, under steady state conditions, in patients with epilepsy who take oral lacosamide alongside up to three other AEDs. METHODS: Twenty-seven serum and cerebral spinal fluid (CSF) samples were collected from 21 patients receiving lacosamide for the treatment of epilepsy (50-600 mg/day over two or three doses). This included 23 time-matched pairs of serum and CSF samples from 19 patients. The concentration of lacosamide in each sample was determined using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Linear regression was used to characterize the relationship between the CSF-to-serum ratio of lacosamide concentration and the time since dosing, the daily lacosamide dose, or the daily dose normalized by volume of distribution (Vd , approximated to total body water), and between the drug concentrations in each compartment (CSF vs. serum). RESULTS: Concentrations of lacosamide in CSF (mean ± standard deviation [SD] 7.37 ± 3.73 µg/ml, range 1.24-14.95, n = 27) and serum (mean ± SD 8.16 ± 3.82 µg/ml, range 2.29-15.45, n = 27) samples showed a good correlation over the dose range investigated. The mean CSF-to-serum ratio of lacosamide concentrations was 0.897 ± 0.193 (range 0.492-1.254, n = 23 time-matched pairs) and was independent of lacosamide dose. SIGNIFICANCE: Drug concentrations in the CSF are often used to indicate those in the brain interstitial fluid. In patients with epilepsy who follow a stable oral AED dosing regimen, lacosamide concentration in CSF is approximately 85% of that found in serum, suggesting that serum may be a valuable indicator of lacosamide concentration in the CNS.

Acute or chronic use of lacosamide does not alter its distribution between serum and cerebrospinal fluid.

OBJECTIVE: The site of action for antiepileptic drugs (AEDs) is within the brain; however, cerebrospinal fluid (CSF) concentration is highly variable. Lacosamide (LCM) is approved by the U.S. Food and Drug Administration (FDA) for treatment of partial-onset seizures in adults, and has linear pharmacokinetics in serum. Penetration across the blood-brain barrier (BBB) is unknown. This study aims to provide additional insights into the pharmacokinetics of LCM. METHODS: Thirty adults undergoing craniotomy for treatment of intractable epilepsy or brain tumor were recruited and were either taking LCM long term (group 1, n = 15), or were LCM naive, receiving LCM as prophylaxis for surgery (group 2, n = 15). All patients received one intravenous (IV) dose (15 min infusion) immediately prior to craniotomy. CSF and arterial blood were collected simultaneously following craniotomy. LCM concentrations were measured in serum and CSF. RESULTS: LCM concentration differences between groups 1 and 2 for both CSF and serum were statistically significant (p ≤ 0.0005), but there was no statistically significant difference in CSF/serum ratios (group 1 = 0.726 ± 0.231; group 2 = 0.556 ±0.241; p = 0.0585). LCM concentration in serum correlated positively with CSF concentration in group 1 (Pearson r = 0.8527, p < 0.0001). The time interval between the end of dose delivery and sample collection correlated positively with the CSF/serum ratio for the drug-naive group (Pearson r = 0.6525; p = 0.0084). Treatment with other AEDs did not affect LCM distribution between serum and CSF. SIGNIFICANCE: Although chronic dosing resulted in higher LCM concentrations in serum and CSF compared to drug-naive patients, the CSF/serum ratio was not affected by LCM pretreatment. These data suggest that LCM serum concentration may reliably predict CSF concentration.

Steady-state plasma and cerebrospinal fluid pharmacokinetics and tolerability of eslicarbazepine acetate and oxcarbazepine in healthy volunteers.

PURPOSE: To evaluate the pharmacokinetics and tolerability of once-daily eslicarbazepine acetate (ESL) and twice-daily oxcarbazepine (OXC) and their metabolites in cerebrospinal fluid (CSF) and plasma following repeated oral administration. METHODS: Single-center, open-label, randomized, parallel-group study in healthy volunteers. Volunteers in ESL group (n = 7) received 600 mg on days 1-3 and 1,200 mg on days 4-9, once daily. Volunteers in the OXC group (n = 7) received 300 mg on days 1-3 and 600 mg on days 4-9, twice daily. Plasma and CSF sampling was performed following the last dose. KEY FINDINGS: Eslicarbazepine was the major drug entity in plasma and CSF, accounting for, respectively, 93.84% and 91.96% of total exposure in the ESL group and 78.06% and 76.42% in the OXC group. The extent of exposure to drug entities R-licarbazepine and oxcarbazepine was approximately four-fold higher with OXC as compared with ESL. There was relatively little fluctuation from peak-to-trough (ratio) in the CSF for both eslicarbazepine (ESL = 1.5; OXC = 1.2) and R-licarbazepine (ESL = 1.2; OXC = 1.2). In contrast, oxcarbazepine showed larger differences between peak and trough (ESL = 3.1; OXC = 6.4). A total of 84 and 24 treatment-emergent adverse events (TEAEs) were reported with OXC and ESL, respectively. SIGNIFICANCE: In comparison to OXC, administration of ESL resulted in more eslicarbazepine, less R-licarbazepine, and less oxcarbazepine in plasma and CSF, which may correlate with the tolerability profile reported with ESL. The smaller peak-to-trough fluctuation of eslicarbazepine in CSF (a measure of sustained delivery to the brain) than in plasma supports once-daily dosing of ESL.

Antiepileptic drugs abolish ictal but not interictal epileptiform discharges in vitro.

PURPOSE: We established the effects of the antiepileptic drugs (AEDs) carbamazepine (CBZ), topiramate (TPM), and valproic acid (VPA) on the epileptiform activity induced by 4-aminopyridine (4AP) in the rat entorhinal cortex (EC) in an in vitro brain slice preparation. METHODS: Brain slices were obtained from Sprague-Dawley rats (200-250 g). Field and intracellular recordings were made from the EC during bath application of 4AP (50 microm). AEDs, and in some experiments, picrotoxin were bath applied concomitantly. RESULTS: Prolonged (>3 s), ictal-like epileptiform events were abolished by CBZ (50 microm), TPM (50 microm), and VPA (1 mm), whereas shorter (<3 s) interictal-like discharges continued to occur, even at concentrations up to 4-fold as high. gamma-Aminobutyric acid (GABA)(A)-receptor antagonism changed the 4AP-induced activity into recurrent interictal-like events that were not affected by CBZ or TPM, even at the highest concentrations. To establish whether these findings reflected the temporal features of the epileptiform discharges, we tested CBZ and TPM on 4AP-induced epileptiform activity driven by stimuli delivered at 100-, 10-, and 5-s intervals; these AEDs reduced ictal-like responses to stimuli at 100-s intervals at nearly therapeutic concentrations, but did not influence shorter interictal-like events elicited by stimuli delivered every 10 or 5 s. CONCLUSIONS: We conclude that the AED ability to control epileptiform synchronization in vitro depends mainly on activity-dependent characteristics such as discharge duration. Our data are in keeping with clinical evidence indicating that interictal activity is unaffected by AED levels that are effective to stop seizures.

Fluconazole-induced intoxication with phenytoin in a patient with ultra-high activity of CYP2C9.

PURPOSE: The cytochrome P450 enzyme CYP2C9 metabolizes several important drugs, such as warfarin and oral antidiabetic drugs. The enzyme is polymorphic, and all known alleles, for example, CYP2C9*2 and*3, give decreased activity. Ultra-high activity of the enzyme has not yet been reported. METHODS: We present a patient with Behçet's disease who required treatment with high doses of phenytoin. When fluconazole, a potent inhibitor of CYP2C9, was added to the treatment regimen, the patient developed ataxia, tremor, fatigue, slurred speech and somnolence, indicating phenytoin intoxication. On suspicion of ultra-high activity of CYP2C9, a phenotyping test for CYP2C9 with losartan was performed. RESULTS: The patient was shown to have a higher activity of CYP2C9 than any of the 190 healthy Swedish Caucasians used as controls. CONCLUSIONS: Our finding of an ultrarapid metabolism of losartan and phenytoin may apply to other CYP2C9 substrates, where inhibition of CYP2C9 may cause severe adverse drug reactions.

Endogenous anticonvulsant substance in rat cerebrospinal fluid after a generalized seizure.

Cerebrospinal fluid taken from rats subjected to electroshock-induced seizures and injected into the cerebral ventricles of rats that had not been shocked increased the seizure threshold of the recipients. The anticonvulsant activity of the donor cerebrospinal fluid was antagonized by opioid antagonists and enhanced by peptidase inhibitors. These results suggest the existence of an endogenous anticonvulsant substance in rat cerebrospinal fluid, possibly opioid in nature, which is activated as a consequence of a seizure and which may play a critical role in postseizure inhibition.

Pharmacokinetics of a commercially available product and a compounded formulation of extended-release levetiracetam after oral administration of a single dose in cats.

OBJECTIVE: To compare pharmacokinetics of levetiracetam in serum and CSF of cats after oral administration of extended-release (ER) levetiracetam. ANIMALS: 9 healthy cats. PROCEDURES: Cats received 1 dose of a commercially available ER levetiracetam product (500 mg, PO). Thirteen blood and 10 CSF samples were collected over a 24-hour period for pharmacokinetic analysis. After 1 week, cats received 1 dose of a compounded ER levetiracetam formulation (500 mg, PO), and samples were obtained at the same times for analysis. RESULTS: CSF concentrations of levetiracetam closely paralleled serum concentrations. There were significant differences between the commercially available product and the compounded formulation for mean ± SD serum maximum concentration (Cmax; 126 ± 33 µg/mL and 169 ± 51 µg/mL, respectively), Cmax corrected for dose (0.83 ± 0.10 µg/mL/mg and 1.10 ± 0.28 µg/mL/mg, respectively), and time to Cmax (5.1 ± 1.6 hours and 3.1 ± 1.5 hours, respectively). Half-life for the commercially available product and compounded formulation of ER levetiracetam was 4.3 ± 2.0 hours and 5.0 ± 1.6 hours, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The commercially available product and compounded formulation of ER levetiracetam both maintained concentrations in healthy cats 12 hours after oral administration that have been found to be therapeutic in humans (ie, 5 µg/mL). Results of this study supported dosing intervals of 12 hours, and potentially 24 hours, for oral administration of ER levetiracetam to cats. Monitoring of serum concentrations of levetiracetam can be used as an accurate representation of levetiracetam concentrations in CSF of cats.

Status epilepticus in encephalitis: a study of clinical findings, magnetic resonance imaging, and response to antiepileptic drugs.

This study evaluates clinical findings, magnetic resonance imaging (MRI), and response to antiepileptic drugs (AEDs) in encephalitis patients with status epilepticus (SE). Encephalitis patients with SE were included and they were grouped into herpes (HSE), Japanese (JE), dengue, and nonspecific encephalitis on the basis of virological studies. The demographic and clinical details, including SE type and duration, were noted. Cranial MRI and cerebrospinal fluid (CSF) were carried out. Response to first, second, and third AEDs were noted and the patients not responding to the second AED were considered refractory SE. The relationships of the mortality and the refractoriness of SE with various clinical findings, MRI, CSF, and the type of encephalitis were evaluated. Thirty SE patients with encephalitis aged 1 to 64 years were included. Nine patients had JE, 4 HSE, 1 dengue, and 16 nonspecific encephalitis. Generalized convulsive SE was present in 26 and nonconvulsive SE in 4 patients. The mean duration of SE was 21 (0.83 to 72) h. MRI was abnormal in 20 patients. A 46.7% of patients responded to the first AED and 36.7% remained refractory to the second AED. In 26.7% patients, the seizure continued even after the third AED. The response to AED was not related to the clinical, MRI, and laboratory variables. Nine patients died and the mortality was related to gender and Glasgow Coma Scale (GCS) score. In encephalitis with SE, 46.7% patients responded to the fist AED and 36.7% remained refractory to the second AED. One third of patients of died, which was related to the depth of coma.

Development and validation of a high performance liquid chromatographic method for the determination of oxcarbazepine and its main metabolites in human plasma and cerebrospinal fluid and its application to pharmacokinetic study.

An isocratic reversed-phase HPLC-UV procedure for the determination of oxcarbazepine and its main metabolites 10-hydroxy-10,11-dihydrocarbamazepine and 10,11-dihydroxy-trans-10,11-dihydrocarbamazepine in human plasma and cerebrospinal fluid has been developed and validated. After addition of bromazepam as internal standard, the analytes were isolated from plasma and cerebrospinal fluid by liquid-liquid extraction. Separation was achieved on a X-TERRA C18 column using a mobile phase composed of 20 mM KH(2)PO(4), acetonitrile, and n-octylamine (76:24:0.05, v/v/v) at 40 degrees C and detected at 237 nm. The described assay was validated in terms of linearity, accuracy, precision, recovery and lower limit of quantification according to the FDA validation guidelines. Calibration curves were linear with a coefficient of variation (r) greater than 0.998. Accuracy ranged from 92.3% to 106.0% and precision was between 2.3% and 8.2%. The method has been applied to plasma and cerebrospinal fluid samples obtained from patients treated with oxcarbazepine, both in monotherapy and adjunctive therapy.

The pharmacokinetics of vigabatrin in rat blood and cerebrospinal fluid.

PURPOSE: Data on the blood pharmacokinetics of vigabatrin, an antiepileptic drug with a unique and novel mechanism of action, in the rat are sparse. Additionally, little is known of the kinetics of vigabatrin in the central cerebrospinal fluid (CSF) compartment. We therefore investigated the rate of penetration into and the inter-relationship between serum and CSF compartments following systemic administration of vigabatrin in the rat. METHODS: Sprague-Dawley rats were implanted with a jugular vein catheter and a cisterna magna catheter for blood and CSF sampling, respectively. Vigabatrin was administered by intraperitonial injection at three different doses (250, 500 and 1000mg/kg) and blood and CSF collected at timed intervals up to 8h. Vigabatrin concentrations in sera and CSF were determined by high performance liquid chromatography. RESULTS: Vigabatrin concentrations in blood and CSF rose linearly and dose-dependently and the time to maximum concentration (Tmax) was 0.4 and 1.0h, respectively. Vigabatrin is not protein bound in serum and its elimination from serum (mean t1/2 values, 1.1-1.4 h) is rapid and dose-independent. The efflux of vigabatrin from CSF was significantly slower than that seen for serum (mean t1/2 values, 2.2-3.3h). CONCLUSIONS: The kinetics of vigabatrin are linear with rapid entry into CSF. However, although vigabatrin CSF kinetics parallel that seen in serum, CSF vigabatrin concentrations represent only 2% of concentrations seen in serum and do not reflect free drug concentrations in serum.

Comparison of drug concentrations in postmortem cerebrospinal fluid and blood specimens.

The concentration of drugs and metabolites in cerebrospinal fluid (CSF) and blood were determined in 282 autopsied cases using liquid-liquid extraction techniques and gas chromatographic analyses. All drugs were confirmed in one matrix by gas chromatography-mass spectrometry. CSF/blood ratios were used to compare the two biological fluids. Classes of drugs evaluated in this study included: benzodiazepines, anticonvulsants, sedatives, opioids, antidepressants, anesthetics, and antihistamines. The majority of the drugs tested were readily detected in CSF specimens. The average CSF/blood ratio for most drugs was in the range of 0.05-0.50. Interpretation of these results is difficult because protein binding, half-life, hydrophobic properties, and pKa of a drug, in addition to survival time after drug use, influence the CSF/blood ratio. While CSF specimens do provide a viable alternative testing matrix when blood specimens are not available, they should not be used to estimate blood drug concentrations.

In vitro responsiveness of human-drug-resistant tissue to antiepileptic drugs: insights into the mechanisms of pharmacoresistance.

Pharmacoresistance in epileptic patients may be ascribed to at least two, not mutually exclusive, mechanisms: a pharmacokinetic mechanism and a decreased sensitivity or availability of targets to antiepileptic drugs (AEDs; i.e., carbamazepine and phenytoin (CBZ, PHT)). Brain:plasma drug concentration ratios were determined intraoperatively during lobectomies performed to alleviate drug-resistant seizures. The brain:plasma ratio of CBZ was 1.48 when therapeutic serum levels (15-34 microM) were achieved. When concentrations of CBZ found in multiple-drug-resistant brain were directly applied to human cortical slices from drug-resistant patients made hyperexcitable and hypersynchronous by Mg(2+)-free media, bursting frequency was not significantly affected and overall excitability was reduced by 40%. Similar results were obtained for PHT. At higher AED concentrations (60-200 microM), a dose-dependent decrease of bursting frequency and amplitude was observed. Slices from drug-resistant epileptic patients made hypersynchronous/hyperexcitable by elevated potassium or inhibition of GABA-A receptors behaved similarly. Of note is the response of slices from human multiple-drug-resistant brain, which was greater than in rodent cortex from naive animals. Taken together, our results support the hypothesis that multiple drug resistance to AEDs involves cerebrovascular changes that impede the achievement of appropriate drug levels in the central nervous system.

Comparison of serum, cerebrospinal fluid and brain extracellular fluid pharmacokinetics of lamotrigine.

We investigated the rate of penetration into and the intra-relationship between the serum, cerebrospinal fluid (CSF) and regional brain extracellular fluid (bECF) compartments following systemic administration of lamotrigine in rat. The serum pharmacokinetics were biphasic with an initial distribution phase, (half-life approximately 3 h), and then a prolonged elimination phase of over 30 h. The serum pharmacokinetics were linear over the range 10 - 40 mg kg(-1). Using direct sampling of CSF with concomitant serum sampling, the calculated penetration half-time into CSF was 0.42+/-0.15 h. At equilibrium, the CSF to total serum concentration ratio (0.61+/-0.02) was greater than the free to total serum concentration (0.39+/-0.01). Using in vivo recovery corrected microdialysis sampling in frontal cortex and hippocampus with concomitant serum sampling, the calculated penetration half-time of lamotrigine into bECF, 0.51+/-0.11 h, was similar to that for CSF and was not area or dose dependent. At equilibrium, the bECF to total serum concentration ratio (0.40+/-0.04) was similar to the free to total serum concentration (0.39+/-0.01), and did not differ between hippocampus and frontal cortex. The species specific serum kinetics can explain the prolonged action of lamotrigine in rat seizure models. Lamotrigine has a relatively slow penetration into both CSF and bECF compartments compared with antiepileptic drugs used in acute seizures. Furthermore, the free serum drug concentration is not the sole contributor to the CSF compartment, and the CSF concentration is an overestimate of the bECF concentration of lamotrigine.

Antiepileptic drug pharmacokinetics and neuropharmacokinetics in individual rats by repetitive withdrawal of blood and cerebrospinal fluid: milacemide.

1. The kinetics and metabolism of milacemide have been studied in an animal model which allows the simultaneous investigation of the temporal inter-relationships of drugs and metabolites in blood (pharmacokinetics) and cerebrospinal fluid (CSF, neuropharmacokinetics) in individual freely moving rats. 2. Milacemide dose-dependently increased CSF glycine and glycinamide (intermediary metabolite) concentrations. This confirms that milacemide is a CNS glycine prodrug. 3. Pretreatment with L-deprenyl (2 mg kg-1), a specific inhibitor of monoamine oxidase type B (MAO-B), almost completely prevented the formation of glycinamide and increased milacemide accumulation in CSF. Tmax and t1/2 were significantly increased and Cmax and AUC values were decreased for glycinamide compared to controls. Pretreatment with clorgyline (5 mg kg-1), a specific inhibitor of MAO-type A, only moderately decreased glycinamide Cmax and AUC values. 4. After milacemide administration (100, 200 and 400 mg kg-1, i.p.) serum and CSF milacemide concentrations rose linearly and dose-dependently. Serum glycinamide concentrations exhibited small dose-dependent rises but these were not linearly related. In contrast, CSF glycinamide concentrations rose linearly and dose-dependently with Cmax values 2.5, 3.2 and 4.1 times greater than the corresponding values for serum glycinamide after giving 100, 200 and 400 mg kg-1 respectively of milacemide. 5. Serum glycine concentrations were unaffected but CSF concentrations increased dose-dependently and these were significant at the higher milacemide doses (200 and 400 mg kg-1). Animals given 400 mg kg-1 milacemide had glycine values which were still significantly elevated 7 h later. 6. In conclusion, serum milacemide rapidly enters and equilibrates with the CNS compartment where it is metabolised primarily by MAO-B to glycinamide and finally to glycine. Metabolism in the peripheral compartment is negligible.

Characterization of opioid peptide-like anticonvulsant activity in rat cerebrospinal fluid.

The biochemical and pharmacological properties of an endogenous anticonvulsant substance(s) found in rat cerebrospinal fluid (CSF) following seizures are described. CSF taken from donor rats following a single maximal electroshock (MES) seizure caused significant elevations in seizure thresholds in naive recipient rats when intracerebroventricularly injected 15 min prior to exposure to the volatile convulsant flurothyl. Anticonvulsant activity was antagonized by pre-injection in recipients of high doses of naloxone or the selective delta-opioid receptor antagonist ICI 174,864. The anticonvulsant activity was also lost when the CSF was exposed to heat (90 degrees C) or immobilized trypsin. Although unaffected by the peptidase inhibitors thiorphan and bestatin, the anticonvulsant activity was significantly potentiated by a combination of aprotinin and bacitracin. Ultrafiltration of CSF revealed that the anticonvulsant activity passed through membranes with a 10,000 molecular weight cut-off, but was retained by membranes with a 5000 molecular weight cut-off. CSF removed from rats following MES had significantly increased concentrations of beta-endorphin-like, but not dynorphin A, Leu- or Met-enkephalin-like immunoreactivities relative to CSF from sham-treated rats. However, significant increases in Met-enkephalin-like immunoreactivity were measured following exposure of the CSF to the proteolytic enzymes trypsin and carboxypeptidase B, suggesting the seizure-induced presence of a higher molecular weight form of Met-enkephalin not recognized immunologically prior to enzyme exposure. These data reconfirm the anticonvulsant actions of postseizure CSF, and indicate that these effects require mediation through delta-opioid receptors in the recipient rat. These data additionally argue against these effects being mediated by Met-enkephalin, Leu-enkephalin or dynorphin A in the CSF, and suggest instead that anticonvulsant effects are attributable to a heat- and trypsin-sensitive opioid peptide(s) with a molecular weight approximately in the range of 5000-10,000 Da.

On the mechanism of antiepileptic peptides appearance in the cerebrospinal fluid.

Intraventricular injection of cerebrospinal fluid obtained from cats with electroshock seizures resulted in suppression of generalized picrotoxin-induced seizures in rats. Antiepileptic action of cerebrospinal fluid was abolished by partial bilateral midbrain destruction that included the region of colliculi superii. Electrical stimulation of cerebellum in cats with such destructions caused the appearance of a pronase-sensitive antiepileptic substances in cerebrospinal fluid.

Effects of vagus nerve stimulation on amino acids and other metabolites in the CSF of patients with partial seizures.

Electrical stimulation of the vagus nerve (VNS) is a new method for the treatment of patients with medically intractable epilepsy. Sixteen patients, ten of whom participated in a larger multicenter double-blind trial on the efficacy of VNS in epilepsy, and six who participated in pilot studies, consented to participate in the present study. Ten patients received HIGH stimulation and six patients LOW stimulation for the 3-month trial. Cerebrospinal fluid (CSF) samples (16 ml) were collected both before and after 3 months of VNS. Amino acid and neurotransmitter metabolites were analyzed. Four patients responded to VS with more than a 25% seizure reduction after 3 months. Mean and median concentrations of phosphoethanolamine (PEA) increased in responders and decreased in nonresponders. Free GABA increased in both groups but more so in the nonresponders. After 9 months of VS (6-9 months on HIGH stimulation) 4 of 15 patients had more than 40% seizure reduction. There were significant correlations between seizure reduction and increases in asparagine, phenylalanine, PEA, alanine and tryptophan concentrations. Comparison between patients with HIGH or LOW stimulation showed a significant increase in ethanolamine (EA) in the HIGH group and a decrease in glutamine in the LOW group. All patients regardless of response or stimulation intensity showed significantly increased total and free GABA levels. A decrease in CSF aspartate was marginally significant. Other trends were decreases in glutamate and increases in 5-hydroxyindoleacetic acid. Chronic VNS appears to have an effect on various amino acids pools in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiepileptic drug pharmacokinetics and neuropharmacokinetics in individual rats by repetitive withdrawal of blood and cerebrospinal fluid: phenytoin.

The temporal pharmacokinetic (blood) and neuropharmacokinetic (cerebrospinal fluid, CSF) interrelationship of phenytoin was studied after acute and during chronic (up to 5 days) intraperitoneal administration of phenytoin (30, 50 or 100 mg/kg) using a new freely behaving rat model. After administration, phenytoin rapidly appeared in both serum (Tmax mean range 0.15-0.38 h) and CSF (Tmax mean range 0.9-1.4 h), suggesting ready penetration of the blood-brain barrier. However, transport across the blood-brain barrier may be rate limiting since whilst phenytoin concentrations rose dose dependently in serum, CSF concentrations did not. Further, the divergence between the blood and CSF compartments increased with chronic dosing. Cmax, AUC and t1/2 values for serum increased non-linearly, suggestive of accumulation kinetics. Based on these data, high initial phenytoin blood concentrations are essential if phenytoin entry into the brain is to be facilitated, and this may be important in studies of phenytoin in animal models of status epilepticus.

Blood and cerebrospinal fluid pharmacokinetics of the novel anticonvulsant levetiracetam (ucb L059) in the rat.

The temporal pharmacokinetic interrelationship of levetiracetam in blood and cerebrospinal fluid (CSF) was studied after acute intraperitoneal administration of levetiracetam (20, 40 and 80 mg/kg), using an animal model that permits concurrent blood and CSF sampling in freely moving rats. After administration, levetiracetam rapidly appeared in both serum (time to maximum concentration (Tmax) mean range 0.25 0.50 h) and CSF (Tmax mean range 1.33-1.92 h), suggesting ready penetration of the blood brain barrier. Both serum and CSF levetiracetam concentrations rose essentially linearly and dose-dependently, suggesting that transport across the blood-brain barrier is not rate limiting over the levetiracetam concentration range observed in the present study. However, while apparent elimination half-life (t1/2) values for both serum and CSF were dose-independent (mean value range 1.8-2.8 and 4.4-4.9 h, respectively), t1/2 values for CSF were significantly larger. As the serum free/total serum levetiracetam concentration ratio (free fraction) was 1.01+/-0.02 (mean+/-S.E.M.), it can be concluded that levetiracetam is not protein bound. Furthermore, the free fraction was indistinguishable from that of the CSF/serum levetiracetam concentration ratio at equilibrium. It can be concluded that the kinetics of levetiracetam, in the rat, is simple and, thus, dosing strategies in studies designed to elucidate its mechanism of action should be straightforward.