Clobazam workshop, Killarney, Eire, April 1978: [proceedings]

Clobazam for patients with Lennox-Gastaut syndrome and epilepsy

Lennox-Gastaut syndrome (LGS) is a form of childhood epileptic encephalopathy that continues to be challenging to treat and manage. The available treatments have failed to provide good control for patients with this devastating epilepsy syndrome. Clobazam is a promising antiepileptic medication, given its effectiveness and relatively low rates of adverse effects. It has been studied and used in several countries for the treatment of refractory seizures, including those that occur with LGS. Clobazam (Onfi™; Lundbeck Inc., IL, USA) has been studied in the USA to demonstrate its efficacy and safety for the treatment of seizures associated with LGS, and Phase II and III trials have recently been completed. This article will explore the use of clobazam in the treatment of LGS and present the results of Phase II and III studies, along with an overall summary of the treatment of LGS, as well as the possible role of clobazam in a treatment algorithm. We based this article on the most relevant reports with the term 'clobazam' found through a Medline search (1966-2011).

Pharmacokinetic drug interactions between clobazam and drugs metabolized by cytochrome P450 isoenzymes

STUDY OBJECTIVE

To investigate potential drug-drug interactions between clobazam and cytochrome P450 (CYP) isoenzyme substrates, inhibitors, and inducers.

DESIGN

Two, prospective, open-label, single-center, drug-drug interaction (DDI) studies and a population pharmacokinetics analysis of seven multicenter phase II-III trials.

SETTING

Clinical research unit.

PARTICIPANTS

Fifty-four healthy adult volunteers were enrolled in the two drug-drug interaction studies; 53 completed the studies. The population pharmacokinetics analysis evaluated data from 171 participants from five studies with healthy volunteers and two studies with patients with Lennox-Gastaut syndrome. Participants in these studies received clobazam and stable dosages of the following antiepileptic drugs: phenobarbital, phenytoin, carbamazepine, valproic acid, lamotrigine, felbamate, or oxcarbazepine.

INTERVENTION

In the first drug-drug interaction study, 36 participants received a single oral dose of clobazam 10 mg on day 1, followed by either ketoconazole 400 mg once/day or omeprazole 40 mg once/day on days 17-22, with a single dose of clobazam 10 mg coadministered on day 22, to study the effects of CYP3A4 or CYP2C19 inhibition, respectively, on clobazam and its active metabolite N-desmethylclobazam (N-CLB). In the second study, 18 participants received a drug cocktail consisting of caffeine 200 mg, tolbutamide 500 mg, dextromethorphan 30 mg, and midazolam 4 mg on days 1 and 19, and clobazam 40 mg/day on days 4-19, to study clobazam's effects on CYP1A2, CYP2C9, CYP2D6, and CYP3A4.

MEASUREMENTS AND MAIN RESULTS

In the first DDI study, coadministration of ketoconazole (a CYP3A4 inhibitor) and clobazam increased clobazam's area under the concentration time curve from time zero extrapolated to infinity (AUC(0-∞) ) 54% and decreased clobazam's maximum plasma concentration (C(max) ) by 15% versus administration of clobazam alone, but the combination affected these pharmacokinetic parameters for N-CLB to a lesser degree. The CYP2C19 inhibitor omeprazole increased AUC(0-∞) and C(max) of N-CLB by 36% and 15%, respectively, but did not significantly affect the pharmacokinetics of clobazam. At steady state, N-CLB has 3-4 times greater exposure than clobazam. In the second DDI study, no clinically significant drug-drug interactions were observed between clobazam 40 mg and the CYP probe substrates caffeine or tolbutamide. Exposure to midazolam and its 1-hydroxymidazolam metabolite, however, decreased by 27% and increased 4-fold, respectively. Clobazam increased dextromethorphan (CYP2D6) AUC(0-∞) by 95% and C(max) by 59%. In the population pharmacokinetics analysis, stable dosages of common antiepileptic drugs that induce CYP3A4 or CYP2C19, or inhibit CYP2C19, had negligible effects on clobazam or N-CLB. Clobazam did not affect valproic acid or lamotrigine exposures.

CONCLUSION

These findings suggest no clinically meaningful drug-drug interactions between clobazam and drugs metabolized by CYP3A4, CYP2C19, CYP1A2, or CYP2C9. Concomitant use of drugs metabolized by CYP2D6 may require dosage adjustment. Clobazam may be administered safely as adjunctive therapy in patients with Lennox-Gastaut syndrome, without meaningful changes in clobazam pharmacokinetics that would require dosage adjustment.

Impact of CYP2C19 polymorphisms on the efficacy of clobazam therapy

Background: Clobazam-induced adverse reactions have been reported in cases with CYP2C19 defective allele(s). However, the relevance of the CYP2C19 genotypes to clobazam therapy remains to be clarified. Methods: The association between CYP2C19 genotypes and the antiepileptic and adverse effects of clobazam was retrospectively investigated in 110 Japanese subjects, in relation to clobazam and N-desmethylclobazam (N-clobazam) concentrations. Results: There were 41 (37.3%) homozygous extensive metabolizers (EMs), 44 (40.0%) heterozygous EMs, and 25 (22.7%) poor metabolizers (PMs). The response rate was significantly greater in PMs and heterozygous EMs than homozygous EMs with a gene–dose effect (65.2, 47.6 and 33.3%, respectively), and the adjusted odds ratio (95% CI) of PM versus homozygous EMs was 9.88 (2.47–39.56; p = 0.001). However, the genotypes did not affect the development of tolerance or adverse reactions, although the incidence of some adverse symptoms was insignificantly higher in PMs. The N-clobazam concentration (µg/ml) increased with the number of CYP2C19-defective alleles (0.92 ± 0.61, 2.14 ± 1.69 and 7.70 ± 6.04, respectively; p < 0.001), while the clobazam concentration was 1.5-fold greater in those with at least one variant. Conclusion: CYP2C19 genotype had an impact on the efficacy of clobazam, thus indicating that N-clobazam plays an important role in long-term clobazam therapy.

Efficacy of low-dose, add-on therapy of clobazam (CLB) is produced by its major metabolite, N-desmethyl-CLB

We evaluated the efficacy of low-dose, add-on therapy of CLB in adults with refractory epilepsy. 28 patients were included: 12 with temporal lobe epilepsy (TLE), 14 with extratemporal lobe epilepsy (ETLE) and 2 with symptomatic generalized epilepsy (SGE). CLB was added with the initial dose of 2.5 mg/day and increased to the optimal dose (mean, 5.6 mg/day). The mean observation period was 7.9 months. As compared with the baseline period, 14 out of 28 patients (50%) obtained an obviously good seizure control: 6 seizure free and 8 more than 50% of seizure reduction. The 14 patients comprised of 4 TLE, 8 ETLE and 2 SGE. In seizure type analysis, 26% of complex partial seizures (CPS), 64% of simple partial seizures (SPS) and 86% of generalized tonic-clonic seizures (GTC) showed a good control. Blood level of N-desmethyl-CLB in the steady state was higher in seizure-free group of 6 patients, and N-desmethyl-CLB blood level/dose per kg body weight correlated significantly to seizure control (p=0.0167). Our data show that even in low dose CLB was effective to patients with refractory epilepsy who had higher blood level of N-desmethyl-CLB.

Up-regulation of L-type high voltage-gated calcium channel subunits by sustained exposure to 1,4- and 1,5-benzodiazepines in cerebrocortical neurons

The aim of this study is to examine how sustained exposure to two 1,4-benzodiazepines (BZDs) with different action period, diazepam and brotizolam, and a 1,5-BZD, clobazam, affects L-type high voltage-gated calcium channel (HVCC) functions and its mechanisms using primary cultures of mouse cerebral cortical neurons. The sustained exposure to these three BZDs increased [(45)Ca2+] influx, which was due to the enhanced [(45)Ca2+] entry through L-type HVCCs but not through of Cav2.1 and Cav2.2. Increase in [(3)H]diltiazem binding after the exposure to these three BZDs was due to the increase in the binding sites of [(3)H]diltiazem. Western blot analysis showed increase of Cav1.2 and Cav1.3 in association with the increased expression of alpha2/delta1 subunit. Similar changes in [(3)H]diltiazem binding and L-type HVCC subunit expression were found in the cerebral cortex from mouse with BZD physical dependence. These results indicate that BZDs examined here have the potential to increase L-type HVCC functions mediated via the enhanced expression of not only Cav1.2 and Cav1.3 but also alpha2/delta1 subunit after their sustained exposure, which may participate in the development of physical dependence by these BZDs.

A major influence of CYP2C19 genotype on the steady-state concentration of N-desmethylclobazam

N-desmethylclobazam (N-CLB), the major metabolite of clobazam (CLB), exerts a large influence on therapeutic and adverse effects of CLB. A substantial inter-individual variability has been observed in the ratios of N-CLB concentration/CLB dose and of the N-CLB/CLB concentration. We document here a genotype-phenotype correlation between CYP2C19 polymorphisms and those ratios. Patients with two mutated CYP2C19 alleles show significantly higher ratios than those with the wild type genotype: patients with one mutated allele exhibited intermediate trait. That is, the degree of elevation in the ratios was dependent on the number of mutated alleles of CYP2C19 (gene-dose effect). The N-CLB concentration/CLB dose ratio of patients with two mutated alleles was more than six fold higher than that of wild type patients. Thus, the serum N-CLB/CLB concentration ratio may be a valuable parameter to screen for patients at risk for side effects. Such precautions may be clinically relevant in populations where the mutant allele frequency is high, such as in Asian populations ( approximately 35%). Patients co-medicated with CYP3A4 inducer showed lower CLB concentration/CLB dose ratios and higher N-CLB/CLB concentration ratios. The overall effect of CYP3A4 inducer on N-CLB metabolism, however, was small and, thus, we conclude that the CYP2C19 genotype is the major determinant of the N-CLB concentration. For this reason it is crucial for the better management of epilepsy and other chronic illnesses in general to establish the correlation of genotype of CYP enzymes and pharmacokinetics/dynamics of drugs.

Clobazam monotherapy in drug naïve adult patients with epilepsy

PURPOSE

Evaluation of the efficacy and side effects profile of Clobazam in a 24-week open-labelled trial involving 26 cases of drug naïve adult patients with epilepsy.

METHODS

The study was an open labelled unicentre trial in which only drug naïve cases with epilepsy were included. A total of 26 cases were recruited. One case was dropped because he did not complete the desired follow up. Seizure type and frequency were recorded and follow up was done at 4, 8, 12, 18 and 24 weeks after initiation of therapy. The change in seizure severity, the dose of Clobazam required and development of side effects were recorded.

RESULTS

The seizure types included GTCS (n=16), complex partial seizures (n=4), focal motor seizures with secondary generalisation (n=3) and juvenile myoclonic epilepsy (n=2). Out of 25 patients, 16 (64%) became seizure free, while five (20%) had >50% reduction in their seizure frequency. Thus, these 21 patients (84%) were considered to be well controlled. The commonest side effect seen was sedation, which was noted in 4 of the 25 patients (16%). However, in none of these four patients sedation was significant enough to warrant stoppage of therapy. Weight gain, gait ataxia, loss of short-term memory and breakthrough seizures were noted in one patient each.

CONCLUSIONS

The efficacy of Clobazam coupled with the lack of significant side effects noted in our study makes it merit consideration as monotherapy in adult patients with epilepsy.

Interactions of clobazam with conventional antiepileptics in children

Clobazam is a 1,5-benzodiazepine effective in antiepileptic therapy of children and adults. Presently it is mainly used as adjuvant therapy for intractable seizures. Our objective was to evaluate the effect of clobazam on the apparent clearance of other antiepileptic drugs at steady state, and to determine the factors that determine the plasma levels of clobazam and its active metabolite N-desmethylclobazam. Patients were 74 children with intractable seizures who received treatment with clobazam at our institution as part of the Canadian Cooperative Clobazam Study Group during the years 1987 to 1991. Serum concentrations of clobazam, N-desmethylclobazam, and of concomitant antiepileptic drugs were monitored and prospectively collected. The effect of clobazam treatment on the apparent clearance steady state of the other antiepileptic drugs was determined by statistical comparison of the clearances of each drug before and after initiation of clobazam treatment using Wilcoxon's signed rank test. The effects of dosage, age, and concomitant antiepileptic therapy on the levels of clobazam and N-desmethylclobazam was assessed by multivariate analysis. Response to treatment and incidence of adverse effects were evaluated for each conventional antiepileptic drug to possibly identify favorable or unfavorable combinations with clobazam. Whereas the clearances of most conventional antiepileptics are not affected by cotherapy with clobazam, the apparent clearances of valproic acid and primidone are significantly reduced in the presence of clobazam. Serum concentrations of clobazam increased with dosage and age, and decreased with phenobarbital cotherapy. Serum concentrations of N-desmethylclobazam significantly correlated with clobazam serum levels, age, or clobazam dosage and were significantly increased by cotherapy with phenytoin or carbamazepine. None of the concomitantly used drugs were associated with increased or decreased rate of seizure control. Twelve patients experienced mild adverse drug effects that were not associated with particular cotherapy, clobazam dose, or plasma concentrations. When clobazam is added to a therapy regimen that includes valproic acid, the patient should be closely followed for possible adverse drug reactions caused by elevated valproic acid serum concentrations, and monitoring of valproate serum levels should be considered. When clobazam doses are gradually increased to achieve an optimal clinical effect, the interactions with phenobarbital, carbamazepine, and phenytoin do not necessitate therapeutic drug monitoring of clobazam or N-desmethylclobazam, because there is a large therapeutic window and a poor correlation between plasma concentrations and therapeutic efficacy.

Effects of clobazam and its active metabolite on GABA-activated currents in rat cerebral neurons in culture

PURPOSE

The antiepileptic effects of clobazam, a 1,5-benzodiazepine, have been well documented in animal experiments and clinical trials. However, the drug's mechanisms of antiepileptic actions are still undetermined. The purpose of this study was to learn how clobazam and its active metabolite modulate gamma-aminobutyric acid (GABA)-activated currents in rat cerebral neurons in culture.

METHODS

Whole-cell voltage-clamp recordings were performed on cultured cerebral neurons of the rat. Clobazam or its metabolite N-desmethylclobazam was dissolved in the extracellular solution and applied for 2 s by pressure ejection from a micropipette. To maintain GABA-activated currents, 2 mM Mg adenosine triphosphate (ATP) was added to the intracellular solution.

RESULTS

GABA elicited outward currents that were mediated by GABAA receptor-coupled Cl- channels. Applying clobazam with 10 microM GABA elicited enhanced outward currents. Flumazenil, an antagonist of the benzodiazepine receptor, inhibited the enhancing effect of clobazam. The enhancement ratio increased as much as 2.28-fold in a dose-dependent manner at a concentration of 3 microM clobazam. However, it started to decrease at a concentration of 10 microM clobazam. The metabolite N-desmethylclobazam was tested in the same manner, and exhibited an identical dose-dependent enhancement of GABA-activated currents.

CONCLUSIONS

The antiepileptic effects of the 1,5-benzodiazepines are attributed to the enhancement of GABAergic inhibitory neurotransmission. The antiepileptic effects of clobazam are thought to depend mainly on its active metabolite N-desmethylclobazam, which is present in high concentrations in patients who receive long-term clobazam. Clobazam's enhancement of GABA-activated currents was most marked on weaker GABA currents. We therefore infer that clobazam acts more efficiently on tissues in which the release of GABA is diminished.

Clobazam in long-term epilepsy treatment: sustained responders versus those developing tolerance

Clobazam (CLB) is a structurally unique benzodiazepine (BZD) that has anticonvulsant activity in all types of refractory seizures. The main drawback to CLB, as to other BZDs, is the occurrence of tolerance. To date, there has been no way to predict which patients will develop tolerance. We compared clinical features and treatment variables between two groups of patients whose seizures were initially well controlled with CLB: patients with a sustained response and patients who developed tolerance. We retrospectively identified a group of 50 very good responders from among 173 consecutive patients with uncontrolled epilepsy treated with CLB. Very good responders were defined as patients with > 75% reduction in seizures after the addition of CLB who continued CLB treatment for at least 1 month. At a mean follow-up of 37.5 +/- 12.8 months, 25 patients continued to respond and 25 developed tolerance (mean follow-up 17.0 +/- 15.7 months). Tolerance was defined as a relapse to a level > or = 50% of pre-CLB seizure frequency after an initial very good response for a minimum period of 1 month, despite constant CLB dose and, when available, serum levels. There was no change in concomitant medication. Significant differences were noted between the two groups. The sustained response group had a shorter duration of epilepsy (mean 16.5 vs. 24.5 years, p = 0.015), a greater proportion of individuals with a known etiology for their epilepsy (48 vs. 16%, p = 0.006), and higher CLB levels (0.50 vs. 0.22 microM, p = 0.017), but no significant difference in N-desmethyl-CLB levels.(ABSTRACT TRUNCATED AT 250 WORDS)

A pharmacological evaluation of the pull-up test for muscle relaxation in rats

The pull-up test for muscle relaxation is described and validated. At testing, rats were evaluated for their ability to recover ('pull-up') from a fully inverted head-down position. Control animals rapidly regained position (median: 1 s). Known muscle relaxants increased latency to pull-up compared to controls. The test proved sensitive to the effects of barbiturates and benzodiazepines which produced graded dose-response functions. In general, results in the pull-up test corresponded with known potencies, with weaker muscle relaxants such as clobazam and oxazepam being less active. The test was relatively insensitive to non-benzodiazepine compounds (e.g., haloperidol, etomidate, morphine, fentanyl and risperidone) producing cataleptic, catatonic, neuroleptic, analgesic, sedative or hypnotic effects. In terms of ED50 values for barbiturates and benzodiazepines, the pull-up test correlated significantly with ED50s from the rotarod test, the antipentylenetetrazol test, ataxia in rats and muscle relaxation in cats. It was concluded that the pull-up test was relatively specific for muscle relaxation and provided a simple alternative to more time-consuming or equipment-intensive tests.

Isolation of clobazam-orosomucoid complexes from patients' sera

Orosomucoid, a member of the lipocalin family, may function in the in vivo transport of lipophilic compounds such as basic and neutral drugs. We describe the identification of 7-chloro-1-methyl-1,5-benzodiazepine-2,4-dione (clobazam) bound to the serum orosomucoid from individuals actively taking this tranquillizer. This suggests not only that other endogenous factors limit access to the benzodiazepine binding site on human serum albumin, but also that the differential binding of benzodiazepines and their metabolites by orosomucoid should be considered in determining therapeutic doses, particularly in the acute phase response.

Monitoring of concentrations of clobazam and norclobazam in serum and saliva of children with epilepsy

Clobazam was added to the previous antiepileptic drug therapy of 90 children suffering from drug resistant epilepsy. Ten patients became seizure free, although four of these later developed tolerance. Thirty-three patients experienced a decrease in seizure frequency, and 24 of these, too, developed tolerance. Forty-four patients showed no change in seizure frequency, and three experienced an increase. The best results were experienced by patients with myoclonic seizures, whereas patients with complex partial seizures usually developed tolerance. The concentrations of clobazam and its active metabolite norclobazam were measured in 251 serum and 57 saliva samples. The group of seizure-free patients had the lowest clobazam and norclobazam concentrations; tolerance was associated with the highest concentrations. Beneficial side effects were associated with low, and adverse effects with high, concentrations of norclobazam. The concentrations of clobazam and norclobazam in saliva correlated with concentrations in serum. Monitoring of serum and salivary concentrations of clobazam and norclobazam is of limited value only, and no therapeutic target range can be given.

HPLC method for simultaneous determination of clobazam and N-desmethylclobazam in human serum, rat serum and rat brain homogenates

A method for simultaneous determination of clobazam (CBZ) and its active metabolite N-desmethylclobazam (DCBZ) in various biological samples by RP-HPLC with UV detection is described. The determination of both CBZ and DCBZ is performed without derivatization. The internal standard is diazepam. The method is rapid and simple with sensitivity limits of 10 ng/mL for both CBZ and DCBZ and is suitable for routine analysis as well as for animal studies.

Clobazam in therapy-resistant patients with partial epilepsy: a double-blind placebo-controlled crossover study

Clobazam was compared with placebo as antiepileptic adjunct medication in 129 therapy-resistant epileptic patients who were mainly suffering from complex partial seizures. The study was performed in five European countries according to a double-blind crossover design lasting 7 months. Two treatment periods of 3 months (1 month adjustment and 2 months maintenance medication) were separated by one medication switch-over month. The difference in seizure reduction between clobazam and placebo was significant (p less than 0.05). Nineteen percent of patients receiving clobazam became seizure-free during the maintenance dose period. In contrast, freedom from seizures was not observed in any placebo patient. Electroencephalogram (EEG) signs, mood ratings, and global impressions also indicated therapeutic effects of clobazam in epilepsy. The most frequent adverse reactions to clobazam were drowsiness and dizziness. However, the sedative effects of clobazam seemed to be less pronounced in comparison with other benzodiazepines. The study gives evidence of the therapeutic value of clobazam as adjunct medication in therapy-resistant partial seizures. The use of clobazam as monotherapy and long-term treatment, as well as the particular seizure response pattern to clobazam, has to be further investigated.

N-desmethylclobazam: a possible alternative to clobazam in the treatment of refractory epilepsy?

The development of anticonvulsant tolerance during 10 days treatment with either clobazam or its principal metabolite, N-desmethylclobazam (NDMC), was compared in mice using an i.v. infusion of pentylenetetrazole as the convulsive stimulus. Subsequently the anticonvulsant activity of NDMC was assessed in patients with refractory epilepsy. In mice, a highly significant tolerance (P less than 0.001) developed to clobazam (10 mg kg-1 twice daily). During the same period, there was no significant change (P greater than 0.05) in the protection afforded by NDMC (40 or 80 mg kg-1 twice daily) although some reduction in anticonvulsant activity was apparent. NDMC (30 mg once daily) was given to nine patients with frequent complex partial and/or grand mal seizures who had become tolerant to the anticonvulsant effect of clobazam. Seven of the patients had been free from benzodiazepine therapy for at least 2 weeks, while the other two patients were switched directly from clobazam. Eight of the nine patients showed a favourable response to NDMC. In the seven who had been given a holiday from clobazam the response to NDMC was similar to the initial response to clobazam and was achieved at plasma NDMC concentrations in the same range as those seen during clobazam administration (1000-3000 ng ml-1). It is concluded that NDMC is active as an anticonvulsant in man and there is evidence from the animal studies to suggest that it may be preferable to clobazam.

Current status of the 1,4- and 1,5-benzodiazepines in the treatment of epilepsy: the place of clobazam

The 1,4-benzodiazepines have a recognised place in the treatment of epilepsy. Thus, diazepam, clonazepam, and, more recently, lorazepam are used intravenously for status epilepticus. Oral clonazepam has proved useful as adjunctive therapy in generalised absence seizures, myoclonic seizures, and partial seizures. Oral nitrazepam is well known for its use in the treatment of infantile spasms with hypsarrhythmia and in the myoclonic epilepsies of childhood. Clobazam, a 1,5-benzodiazepine, has been shown in controlled studies to be superior to placebo, and in open studies it has produced an overall reduction in seizure frequency of 65%. The main indication for its use is as oral adjunctive therapy in refractory epilepsy. It has a rapid onset of action, is well tolerated, and many studies indicate it has a psychotropic action and produces minimal or no cognitive impairment. The most common side-effect reported was sedation, while the overall incidence of side-effects in the open studies was 38%. In all studies reviewed, 4% of patients had to be withdrawn because of adverse reactions. In general, there are no significant interactions with other anticonvulsants, although changes in a few have been described. Withdrawal seizures can occur and require gradual termination of clobazam. The main disadvantage of clobazam is the development of tolerance, which develops in approximately 36% of patients, and there is no way of predicting in which patients or when the phenomenon is likely to occur. A dose of 20 to 30 mg at night is recommended, possibly commencing at 10 mg.

Determination of clobazam, N-desmethylclobazam and their hydroxy metabolites in plasma and urine by high-performance liquid chromatography

Owing to the pharmacological and clinical importance of the determination of plasma and urine levels of the hydroxy metabolites of clobazam and N-desmethylclobazam in healthy volunteers and in epileptic patients, a high-performance liquid chromatographic (HPLC) method was developed that permits the determination of all these compounds in the same plasma or urine sample. The method involved ether extraction at pH 13 with diazepam as internal standard for the measurement of clobazam and N-desmethylcobazam, followed by ether extraction at pH 9 with nitrazepam as internal standard for the measurement of the hydroxy derivatives. The limit of detection was about 10-20 ng/ml for each of these compounds. Applications to patients were limited by chromatographic interferences between the hydroxy metabolites and some medications currently associated with clobazam in the treatment of epilepsy. The only interference in clobazam and N-desmethylclobazam analysis was from N-desmethyldiazepam. Despite these inconveniences, this HPLC procedure appears to be the only available method for the simultaneous quantification of clobazam and its three main metabolites.

Differences between the tolerance characteristics of two anticonvulsant benzodiazepines

Clobazam (10 mg/kg) and clonazepam (0.25 mg/kg) were administered to mice twice daily by the intraperitoneal route. The development of tolerance to their anticonvulsant effect was compared using a slow intravenous infusion of pentylenetetrazole as the convulsant stimulus. Tolerance to clonazepam developed gradually throughout a 72 h study and did not become significant until the fifth dose. In contrast, tolerance to clobazam occurred extremely rapidly, after only one dose; it was manifested as a single step and no further significant change in protection was observed. Recovery from benzodiazepine tolerance was also studied and seen to occur rapidly with both these compounds; following cessation of dosing, protection was restored to initial levels within 36-48 h.

Single dose pharmacokinetic study of clobazam in normal volunteers and epileptic patients

The pharmacokinetics of clobazam were studied in six healthy volunteers and six age and sex matched enzyme-induced epileptic patients. In the epileptic patients the area under the plasma concentration-time curve for clobazam was significantly smaller and the area under the plasma concentration-time curve for N-desmethylclobazam was significantly greater than in the healthy volunteers. Plasma N-desmethylclobazam concentrations were found to be much higher than those of clobazam in the epileptic patients, raising the possibility that the antiepileptic properties of clobazam are to be attributed more to its metabolite than the parent drug.

Plasma concentrations of clobazam and its N-desmethyl metabolite; protection against pentetrazol-induced convulsions in mice

The anticonvulsant effects of acute administration of clobazam and its principal metabolite N-desmethylclobazam were studied in mice. Pentetrazol, given by slow intravenous infusion 1 or 2 h after the anticonvulsant dose, was used as the convulsant stimulus. Log dose response relationships for both clobazam and N-desmethylclobazam appeared linear, but there was no correlation between plasma concentrations of clobazam and protection. However, correlation between plasma concentrations of N-desmethylclobazam and protection was significant in both cases.

The pull-up test in rats: a simple method for evaluating muscle relaxation

A test for muscle relaxation in rats is described. The pull-up test is performed by holding an inverted rat by its hind legs. The time taken by the rat to pull itself up and grasp the hand of the experimenter is used as the test parameter. It is simple and quick and separates muscle relaxation from sedation, catalepsy, and catatonia.

Development of tolerance to the anticonvulsant effects of clobazam

The anticonvulsant properties of the 1,5-benzodiazepine clobazam were studied in mice during and after chronic treatment at two different dose levels. Pentylenetetrazol given by slow intravenous infusion was used as the convulsant stimulus. Tolerance to the anticonvulsant effects was observed; this was rapid in onset and could be overcome by increasing the dose of clobazam.

Antileptazol activity and kinetic of CP 1414 S (7-nitro-2-amino-5-phenyl-3-H-,1,5-benzodiazepine-4-one) in the rat and mouse

The antileptazol effect of CP 1414 S (7-nitro-2-amino-3-phenyl-3H-1,5-benzodiazepine-4-one) a newly developed 1,5 benzodiazepine, lasts longer in mice than in rats. After intraperitoneal injection (10 mg/kg) brain levels of the drug were higher and persisted for longer in the mouse than in the rat. Although it cannot be excluded tht possible metabolites of CP 1414 S may contribute to the anticonvulsant effect of CP 1414 S, in both species the protective effect correlates well with the brain concentrations of the drug.

Antiepileptic effects of clobazam in children

Many benzodiazepines used as anticonvulsants have nitrogen radicals in positions 1 and 4. Clobazam has nitrogen radicals in positions 1 and 5. We studied the antiepileptic effect of clobazam in 36 patients with intractable epilepsies in childhood. Their ages were 1 year 1 month to 16 years 5 months (mean 8 years). The mean initial dose was 0.33 mg/kg of daily doses and increased up to 0.71 mg/kg. Nine cases (primary generalized epilepsy 2/2, secondary generalized epilepsy 7/29) were completely free from seizures, and another 9 (secondary generalized epilepsy 8/29, partial epilepsy 1/5) experienced a decrease of 50% or more in seizure frequency. Seizure frequency did not change in 16, and increased in the other 2 (secondary generalized epilepsy 2/29). The antiepileptic effects were observed on the first day to 10th day after clobazam treatment. There were recurrences of seizures in 4 out of 9 patients with complete control of seizures, 1 month alter in 3 and 10 months later in one. Mean serum clobazam level of 7 improved cases was 73 ng/ml and that of 3 cases with no response was 94 ng/ml. Although mild clinical side effects such as drowsiness were observed transiently in 17 cases, no abnormality was found in laboratory investigations performed.

Electron-capture GLC determination of clobazam and desmethylclobazam in plasma

Electron-capture GLC was utilized for simultaneous quantitation of clobazam, a 1,5-benzodiazepine derivative, and its active metabolite, desmethylclobazam, in human plasma and serum. After addition of diazepam as the internal standard, samples were extracted into benzene--isopentanol. The organic extracts were evaporated to dryness, reconstituted, and subjected to chromatographic analysis without derivatization or cleanup. All three compounds were resolved completely and had favorable chromatographic properties using an OV-101 liquid phase. The limits of detection are 3--5 ng/ml for clobazam and 5--10 ng/ml for desmethylclobazam. Relative standard deviations for identical samples do not exceed 6%. The application of the method to a clinical pharmacokinetic study is demonstrated.