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.

A simple and rapid method to collect the cerebrospinal fluid of rats and its application for the assessment of drug penetration into the central nervous system.

Many central nervous system (CNS) drug discovery programs require the successful collection of cerebrospinal fluid (CSF) for assessing CNS penetration and distribution of new chemical entities. The objective of the present investigation was to simplify the technique for collecting maximum CSF from cisterna magna of the rats. Rat was anesthetized with 5% halothane and positioned in a stereotaxic frame. The rat head was flexed downward at approximately 45 degrees , a depressible surface with the appearance of a rhomb between occipital protuberances and the spine of the atlas becomes visible. The 23 G needle was punctured into the cisterna magna for CSF collection without making any incision at this region. The blunt end of the needle was inserted into a 10 in. length of PE-50 tubing and other end of the tubing was connected to a collection syringe. The non-contaminated sample was drawn into the syringe by simple aspiration. This technique is simple and can be performed by one person. The technique has a greater than 95% success rate of CSF collection and it was free of red blood cell contamination. In addition, it yielded 100-120 microL of CSF per rat. This method is simple, effective, and easy to perform and has been successfully applied in preclinical screening of novel chemical entities in neuropharmacotherapy for CNS use. The present method is demonstrated by studying the CSF concentrations of carbamazepine and raclopride.

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.

Microdialysis sampling of carbamazepine, phenytoin and phenobarbital in subcutaneous extracellular fluid and subdural cerebrospinal fluid in humans: an in vitro and in vivo study of adsorption to the sampling device.

The purpose of the study was to determine if binding of the drugs to the sampling equipment during microdialysis would influence the results for carbamazepine, phenytoin and phenobarbital. In vitro experiments with microdialysis catheters and separate parts of catheters were performed to estimate the degree of drug binding to the dialysis equipment. A mathematical model to calculate drug binding and recovery is proposed. In vivo protein unbound carbamazepine concentrations in subcutaneous extracellular fluid at different flow rates (6 patients), unbound carbamazepine (1 patient) and unbound phenobarbital (I patient) in subdural cerebrospinal fluid and subcutaneous extracellular fluid were estimated and the in vivo data were compared to the in vitro results and data generated by the mathematical model. Binding to the soft outlet polyurethane tubing was extensive and variable for phenytoin, which precluded in vivo testing, but limited and more predictable for carbamazepine and phenobarbital. None of the three compounds bound to the hard internaltubing. Phenytoin and phenobarbital did not bind to the dialysis membrane, while a small degree of binding may be present for carbamazepine. In vivo estimates of carbamazepine protein unbound subcutaneous extracellular concentrations by microdialysis, adjusted for binding to the plastic tubing, were 81% of protein unbound plasma concentrations. In single case studies, subdural cerebrospinal fluid and subcutaneous extracellular levels of carbamazepine and phenobarbital were similar and when corrected for binding to the plastic tubings they were also close to protein unbound plasma concentrations. Microdialysis can be used for reliable estimations of protein unbound carbamazepine and possibly phenobarbital concentrations when drug binding to the plastic tubing is considered. Reliable estimation of unbound phenytoin is not possible at present.

Plasma concentration of topiramate correlates with cerebrospinal fluid concentration.

The authors examined the ratio between the plasma and the cerebrospinal fluid (CSF) concentration of topiramate in 14 adults with epilepsy. Simultaneous trough samples of venous blood and CSF were collected and analyzed as total and unbound concentrations. Concomitant levels were also analyzed of lamotrigine (n = 5) and the relevant oxcarbazepine metabolite, 10-hydroxycarbazepine (n = 3). There was a close correlation between the plasma and the CSF concentration for both the total and unbound concentration of topiramate. The median CSF/plasma ratio of total topiramate was 0.85. The free topiramate concentration in plasma was not different from the free topiramate concentration in CSF. The CSF/plasma ratios showed little variation and were independent of the plasma level for both the total and the unbound levels. The unbound fraction of topiramate was 84% in plasma and 97% in CSF. The CSF concentrations of lamotrigine and 10-hydroxycarbazepine were 50% and 61% of the plasma concentrations, respectively. For topiramate, there is a close correlation between the plasma concentration and the CSF concentration. There does not seem to be a saturable carrier mechanism restricting topiramate transport across the blood-brain barrier. The concentration of topiramate in CSF is equal to the unbound proportion of topiramate in plasma, implying that the delivery of topiramate to the brain occurs via transfer from the unbound plasma pool. Plasma is thus a relevant matrix for therapeutic drug monitoring of topiramate.

Pharmacokinetics of oxcarbazepine in the dog.

Oxcarbazepine has been proven to be a promising new antiepileptic drug for the treatment of human epilepsy. Unlike carbamazepine, it is not oxidatively metabolized in humans, and therefore causes almost no induction of hepatic enzymes at clinically effective dosages. Though showing similar efficacy to carbamazepine, it has been reported to cause significantly fewer side-effects. It was the purpose of the present study to determine whether oxcarbazepine might be suitable for the treatment of canine epilepsy. In single-dose experiments, 40 mg/kg oxcarbazepine as a suspension was administered to seven dogs via gastric tube. Plasma concentrations reached peak concentrations of 2.4-8.8 micrograms/mliter at about 1.5 h and declined with an elimination half-life of approximately 4 h. The corresponding concentrations of its metabolite, 10,11-dihydro-10-hydroxycarbamazepine, did not exceed 1 micrograms/mliter. During continued treatment for 8 days, doses of 30 and 50 mg/kg were administered orally in capsules to two dogs three times a day. Plasma concentrations showed a pronounced decline from day 3, and the terminal half-life decreased to 2 h and 1 h. This is considered to be the result of oxcarbazepine inducing its own metabolism. The data reveal that oxcarbazepine, compared with former results with carbamazepine, offers no advantage for the treatment of epileptic dogs.

Drogas anticonvulsivantes en suero y líquido cefalorraquideo de pacientes epilépticos: cuantificación por cromatografía líquida / Anticonvulsant drugs in serum and crebrospinal fluid of epileptical patients: liquid chromatography measurement

Se desarrolló un procedimiento de cromatografía líquida de alta presión para cuantificar simultáneamente varias drogas anticonvulsivantes en el suero y líquido cefalorraquídeo de 20 pacientes. Los coeficientes de correlación para las concentraciones en ambos líquidos decarbamazepina, fenobarbital y fenitoína fueron r=0,8588 (p<0,01), r=0,9721 (p<0,01) y r=0,9289 (p<0,01), respectivamente. Las concentraciones de cada droga en líquido cefalorraquídeo representaron porcentajes de la concentración en suero, comparables a los referidos en la literatura. Las concentraciones séricas de carbamazepina en los pacientes sin barbitúricos asociados fueron mayores que las de aquellos bajo politerapia con barbitúricos, independientemente de la dosis. La fenitoína y las concentraciones de fenobarbital en suero y líquido cefalorraquídeo. Estos resultados aqpoyan el uso de la monoterapia para tratar las epilepsias

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics (cerebrospinal fluid): hematological and biochemical characterization and kinetic evaluation using carbamazepine.

A freely moving and behaving rat model for the chronic and simultaneous study of drug pharmacokinetics (blood) and neuropharmacokinetics [cerebrospinal fluid (CSF)] is described. The blood (jugular vein) and CSF (cisterna magna) catheters employed are simple, reliable, and inexpensive. The blood catheter was made of soft and flexible Silastic tubing and sealed with heparin. The CSF catheter consisted of intersliding polythene tubing and interlocking Silastic tubing, which allowed maneuverability within the cisternal magna space and thus prolonging patency for chronic studies. Both catheters were well tolerated by the animals, and the postoperative success rate was 80%-100%; after 8 days 80%-85% of catheters were still patent. Using a sampling protocol considered suitable for kinetic studies, we determined numerous biochemical and hematological parameters and compared them with those values obtained postsurgically and in control rats. The parameter changes associated with the sampling protocol did not affect the kinetics of the commonly prescribed antiepileptic drug carbamazepine and its primary pharmacologically active metabolite carbamazepine-10, 11-epoxide. Therefore, the model can be used to study the interrelationship between drug kinetics at central and peripheral sampling sites and mechanism(s) of drug action.

Concurrent monitoring of central carbamazepine and transmitter amine metabolism and motor activity in individual unrestrained rats using repetitive withdrawal of cerebrospinal fluid.

A method for repeated withdrawal of cerebrospinal fluid (CSF) from the cisterna magna was used in a pharmacokinetic and behavioural study of conscious, freely-moving rats, given the antiepileptic drug carbamazepine (35 mg/kg i.p.). Pharmacokinetic constants (i.e. time to peak concentration, peak concentration, area under the curve and t 1/2) for the drug and its primary metabolite carbamazepine-10,11-epoxide and also concentrations of acidic metabolites of 5-hydroxytryptamine and dopamine were obtained for the CSF of individual rats. A pharmacodynamic constant, the effective concentration of drug in CSF for 50% inhibition of motor activity was also determined for each animal. The above data provides good indices of the corresponding values for carbamazepine and its metabolite in brain insofar as a separate experiment showed good correlations between CSF and brain for concentrations of both the drug and its metabolite. Carbamazepine appeared to be largely responsible for the depression of motor activity as the metabolite, at the levels attained, seemed to have little effect. The changes in motor activity were not associated with altered concentrations of the metabolites of 5-hydroxytryptamine or dopamine in the CSF. While the investigation did not reveal major advantages in monitoring the drug under study in CSF rather than in serum it illustrates the potential of the CSF method as a simple way to obtain neuropharmacokinetic and neuropharmacodynamic profiles of the action of drugs in individual rats.

Carbamazepine and its -10,11-epoxide metabolite in plasma and CSF. Relationship to antidepressant response.

Levels of carbamazepine and its -10,11-epoxide metabolite were measured in plasma and CSF of affectively ill patients treated only with carbamazepine for an average of 33 days at an average dosage of 1,055 mg/day. The CSF levels of carbamazepine were 2.06 micrograms/mL (ie, 31% of plasma levels, which equaled 6.55 micrograms/mL); CSF -10,11-epoxide concentrations averaged 0.91 micrograms/mL in 18 subjects (63% of those found in plasma). Carbamazepine levels in plasma or CSF were not related to degree of antidepressant or antimanic response. In contrast, concentrations of the -10,11-epoxide metabolite were correlated with the degree of antidepressant response. This preliminary study suggests the possibility that the -10,11-epoxide metabolite of carbamazepine may be related to the degree of clinical efficacy in affectively ill patients and may thus possess active psychotropic properties in man in addition to its reported anticonvulsant effects in animals.

Brain uptake of carbamazepine in the cat.

Carbamazepine (CBZ) was determined by EMIT assay in plasma, cerebrospinal fluid (CSF), and brain samples of cats after administration of the drug (40 mg/kg, i.p.). Plasma and CSF levels increase in a parallel manner from time 0 to 90 min after completion of injection, indicating a passive transport from one body fluid to the other. Brain levels reach a steady state at 15 min, with no significant difference being found between the concentrations at 15, 30, 60, and 90 min postinjection; this indicates that substantial early binding occurs in the brain. Since peak CSF concentrations occur at 90 min, concomitant with those for plasma, while brain levels are already high at 15 min, it is likely that CBZ enters the two compartments by independent mechanisms.

Antiepileptic drug distribution in cerebral cortex, ammon's horn, and amygdala in man.

Significant correlations in the concentrations of phenobarbital, phenytoin, and carbamazepine in the brain, plasma, and cerebrospinal fluid were found in 12 surgically treated epileptic patients. These findings confirm the clinical reliability of monitoring anticonvulsant drug plasma levels as part of the routine management of epilepsy. Phenobarbital, phenytoin, and carbamazepine are uniformly distributed in the gray and white matter in different brain areas (except for a higher concentration of phenobarbital in the rhinencephalic structures in comparison with the corresponding temporal neocortex) and in normal and scar tissue. In these 12 patients, all of whom were medically resistant, molar cortex concentration of phenobarbital and phenytoin was at "therapeutic" levels or even higher. These data suggest that in therapy-resistant patients, despite cerebral drug concentrations of the same therapeutic level as, or higher than, those present in medically controlled patients, anticonvulsant drugs are pharmacologically ineffective.

Pharmacokinetics of carbamazepine in the dog.

1. The pharmacokinetics of carbamazepine was studied in dogs after oral administration of two pharmaceutical preparations. Adsorption was rapid, however, the drug was much better absorbed from a liquid preparation than from tablets. Plasma concentrations declined with an elimination half-life of 1.5 hr. Carbamazepine-10,11-epoxide, which is equipotent with carbamazepine as an anticonvulsant, was rapidly formed and reached plasma concentrations higher than those of the mother compound. The concentrations of the epoxide remained high as long as plasma concentrations of carbamazepine were above 2--4 nmole/ml, then they fell with an average half-life of 2.2 hr. 2. During continued treatment with daily doses of 0.34--0.38 mmole/kg carbamazepine, plasma concentrations showed a pronounced and progressive decline from Day 2 which is considered as the result of induction of microsomal liver enzymes. 3. Carbamazepine and the epoxide pass into CSF at a rate comparable to that of phenobarbital or barbital and primidone, respectively. 4. Binding to serum proteins was about 70% for carbamazepine and 40% for the epoxide in dog serum; slightly higher values were found for human serum.

Carbamazepine and its 10,11-epoxide in children and adults with epilepsy.

The plasma concentrations of carbamazepine and its 10,11-epoxide were measured in 37 children and 13 adults with epilepsy during maintenance therapy. The children formed relatively more of the epoxy metabolite than adults. The daily dose, expressed as mg/kg or mg/m2, showed a statistically significant correlation with blood level in children, but not in adults. The cerebrospinal fluid concentrations of carbamazepine and carbamazepine-10,11-epoxide in nine children were 33 and 41 per cent, respectively, of the concomitant plasma level.

CSF concentrations and serum protein binding of carbamazepine and carbamazepine-10,11-epoxide in epileptic patients.

Serum and CSF samples of patients receiving chronic carbamazepine treatment were analysed. Daily fluctuations in serum levels of carbamazepine and carbamazepine-10,11-epoxide did not appear to be related to the dosage schedule, but some patients tended to have lower fluctuations when the carbamazepine was given more frequently. The epoxide/carbamazepine serum ratios varied greatly from patient to patient, and also fluctuated during the day for the same patient. Carbamazepine and carbamazepine-10,11-epoxide were present in CSF in concentrations ranging from 19 to 34% and 26 to 71% of the serum concentrations, respectively. There was a significant relationship between the free fraction of both drugs evaluated in vivo and the CSF/serum ratios. The need for a careful evaluation of the possible clinical effect of the epoxide is stressed.

Anticonvulsant level in saliva, serum, and cerebrospinal fluid.

Levels of four anticonvulsant drugs were measured simultaneously in saliva, spinal fluid, and dialyzed serum, i.e., free drug in serum. The level of diphenylhydantoin and possibly of carbamazepine was the same in the three body fluids. The leves of phenobarbital was the same in spinal fluid and dialyzed serum, but was lower in saliva. The level of primidone was different in each body fluid. The technique is simple (flow of saliva stimulated when the subject chews candle was or Teflon) and will be useful to determine the level of free diphenylhydantoin and carbamazepine, which is more closely related to intoxication or drug failure than is the total level of drug.