Clobazam: pharmacological and therapeutic profile

GABAergic Inhibition Gates Perceptual Awareness During Binocular Rivalry

Binocular rivalry is a classic experimental tool to probe the neural machinery of perceptual awareness. During rivalry, perception alternates between the two eyes, and the ebb and flow of perception is modeled to rely on the strength of inhibitory interactions between competitive neuronal populations in visual cortex. As a result, rivalry has been suggested as a noninvasive perceptual marker of inhibitory signaling in visual cortex, and its putative disturbance in psychiatric conditions, including autism. Yet, direct evidence causally implicating inhibitory signaling in the dynamics of binocular rivalry is currently lacking. We previously found that people with higher GABA levels in visual cortex, measured using magnetic resonance spectroscopy, have stronger perceptual suppression during rivalry. Here, we present direct causal tests of the impact of GABAergic inhibition on rivalry dynamics, and the contribution of specific GABA receptors to these dynamics. In a crossover pharmacological design with male and female adult participants, we found that drugs that modulate the two dominant GABA receptor types in the brain, GABA_A (clobazam) and GABA_B (arbaclofen), increase perceptual suppression during rivalry relative to a placebo. Crucially, these results could not be explained by changes in reaction times or response criteria, as determined through rivalry simulation trials, suggesting a direct and specific influence of GABA on perceptual suppression. A full replication study of the GABA_B modulator reinforces these findings. These results provide causal evidence for a link between the strength of inhibition in the brain and perceptual suppression during rivalry and have implications for psychiatric conditions including autism.SIGNIFICANCE STATEMENT How does the brain accomplish perceptual gating? Here we use a direct and causal pharmacological manipulation to present insight into the neural machinery of a classic illusion of perceptual awareness: binocular rivalry. We show that drugs that increase GABAergic inhibition in the brain, clobazam (GABA_A modulator) and arbaclofen (GABA_B modulator), increase perceptual suppression during rivalry relative to a placebo. These results present the first causal link between GABAergic inhibition and binocular rivalry in humans, complementing classic models of binocular rivalry, and have implications for our understanding of psychiatric conditions, such as autism, where binocular rivalry is posited as a behavioral marker of disruptions in inhibitory signaling in the brain.

An overview of third-generation antiseizure drugs: Clobazam, lacosamide, rufinamide, and vigabatrin

Four antiseizure drugs have been approved in the United States since 2008. Clobazam, a 1,5-benzodiazepine, was approved in October 2011 as an adjunctive therapy for Lennox-Gastaut syndrome (LGS) in patients 2 years and older. Lacosamide, an amino acid that selectively enhances the slow inactivation of voltage-gated sodium channels, was approved in October 2008 as an add-on therapy for partial onset seizures in patients 17 years and older. Rufinamide, a triazole derivative, was approved in November 2008 as an adjunctive therapy for LGS in patients 4 years and older. Vigabatrin, an irreversible inhibitor of GABA transaminase, was approved in August 2009 for the treatment of infantile spasms in children ages 1 month to 2 years and intractable complex partial seizures in adults.

Host factors affecting antiepileptic drug delivery-pharmacokinetic variability

Antiepileptic drugs (AEDs) are the mainstay in the treatment of epilepsy, one of the most common serious chronic neurological disorders. AEDs display extensive pharmacological variability between and within patients, and a major determinant of differences in response to treatment is pharmacokinetic variability. Host factors affecting AED delivery may be defined as the pharmacokinetic characteristics that determine the AED delivery to the site of action, the epileptic focus. Individual differences may occur in absorption, distribution, metabolism and excretion. These differences can be determined by genetic factors including gender and ethnicity, but the pharmacokinetics of AEDs can also be affected by age, specific physiological states in life, such as pregnancy, or pathological conditions including hepatic and renal insufficiency. Pharmacokinetic interactions with other drugs are another important source of variability in response to AEDs. Pharmacokinetic characteristics of the presently available AEDs are discussed in this review as well as their clinical implications.

The use of newer antiepileptic drugs in patients with renal failure

Seizures and chronic kidney disease are both common and often coexist. Treating seizures in patients with renal failure, including those on dialysis, is a challenge that is frequently encountered, especially in the inpatient setting. For the newer antiepileptic drugs, there are limited data available, so an understanding of how each drug is affected by kidney disease and dialysis is critical in order to make rational choices qualitatively (which drug) and quantitatively (dosing). Generally, newer (second-generation) antiepileptic drugs are associated with fewer systemic side effects and drug-drug interactions, so they tend to be preferred in this population. The landscape of antiepileptic drugs is constantly evolving, with new compounds being released on a regular basis. Thus, several new agents have become available since the last review of this topic (in 2006) and these are the ones discussed here. Most require dosage adjustment according to the degree of renal failure, and most require extra doses after dialysis.

Clobazam as an adjunctive therapy in treating seizures associated with Lennox-Gastaut syndrome

Lennox-Gastaut syndrome (LGS) is a devastating childhood epilepsy syndrome characterized by the occurrence of multiple types of seizures and cognitive decline. Most children suffer from frequent seizures that are refractory to current medical management. Recent clinical trials have suggested that addition of clobazam may improve the clinical outcome for some LGS patients. Although clobazam has been available for over five decades, it has only recently been approved by the US Food and Drug Administration for this indication. As a 1,5-benzodiazepine, clobazam is structurally related to the widely used 1,4-benzodiazepines, which include diazepam. Clobazam has been shown to modulate GABAergic neurotransmission by positive allosteric modulation of GABA(A) receptors, and to increase expression of transporters for both GABA and glutamate. The active metabolite n-desmethylclobazam (norclobazam) also modulates GABA(A) receptors, and the relative importance of these two compounds in the clinical effectiveness of clobazam remains an open question. Clinical trials involving clobazam as an addon therapy in a variety of pediatric epilepsy populations have found a significant improvement in seizure control. In patients with LGS, clobazam may have greatest efficacy for drop seizures. Longstanding clinical experience suggests that clobazam is a safe and well tolerated antiepileptic drug with infrequent and mild adverse effects. These results suggest that adjunctive treatment with clobazam may be a reasonable option for LGS patients, particularly those who are treatment-resistant.

[Therapeutic drug monitoring of clobazam]

Clobazam is a 1,5 benzodiazepine available in France since 1975, used in add-on with the other anticonvulsant drugs in the treatment of refractory epilepsies of child and adult and for the treatment of anxiety of adult. It is mainly metabolized in desmethylclobazam, or norclobazam, active metabolite, present in a concentration approximately eight times superior to that of the parent drug, but with an activity of the order of 20 to 40% of that of clobazam. Elimination half-life of clobazam is of 18 h while that of norclobazam is from 40 to 50 h. There is a large interindividual variability in the plasma concentrations. Furthermore, clobazam being prescribed in add-on with the other anticonvulsant drugs in resistant epilepsies, concentration-effect relationship is difficult to bring to light, since, in many studies, the patients who did not answer received the highest doses. Adverse reactions are moderated, appearing more often for the highest concentrations; also the phenomenon of tolerance seems more frequent in high concentrations. However, because of the kinetic interactions, a dosage of clobazam and norclobazam can be useful in certain cases. There is no validated therapeutic range, but the usual concentrations are in the range of 100-300 microg/L for the parent drug and about ten times more for the metabolite. The level of proof of the interest of the Therapeutic Drug Monitoring for this molecule is estimated in: rather useless.

Antiepileptic drugs--best practice guidelines for therapeutic drug monitoring: a position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies

Although no randomized studies have demonstrated a positive impact of therapeutic drug monitoring (TDM) on clinical outcome in epilepsy, evidence from nonrandomized studies and everyday clinical experience does indicate that measuring serum concentrations of old and new generation antiepileptic drugs (AEDs) can have a valuable role in guiding patient management provided that concentrations are measured with a clear indication and are interpreted critically, taking into account the whole clinical context. Situations in which AED measurements are most likely to be of benefit include (1) when a person has attained the desired clinical outcome, to establish an individual therapeutic concentration which can be used at subsequent times to assess potential causes for a change in drug response; (2) as an aid in the diagnosis of clinical toxicity; (3) to assess compliance, particularly in patients with uncontrolled seizures or breakthrough seizures; (4) to guide dosage adjustment in situations associated with increased pharmacokinetic variability (e.g., children, the elderly, patients with associated diseases, drug formulation changes); (5) when a potentially important pharmacokinetic change is anticipated (e.g., in pregnancy, or when an interacting drug is added or removed); (6) to guide dose adjustments for AEDs with dose-dependent pharmacokinetics, particularly phenytoin.

Benzodiazepines in epilepsy: pharmacology and pharmacokinetics

Benzodiazepines (BZDs) remain important agents in the management of epilepsy. They are drugs of first choice for status epilepticus and seizures associated with post-anoxic insult and are also frequently used in the treatment of febrile, acute repetitive and alcohol withdrawal seizures. Clinical advantages of these drugs include rapid onset of action, high efficacy rates and minimal toxicity. Benzodiazepines are used in a variety of clinical situations because they have a broad spectrum of clinical activity and can be administered via several routes. Potential shortcomings of BZDs include tolerance, withdrawal symptoms, adverse events, such as cognitive impairment and sedation, and drug interactions. Benzodiazepines differ in their pharmacologic effects and pharmacokinetic profiles, which dictate how the drugs are used. Among the approximately 35 BZDs available, a select few are used for the management of seizures and epilepsy: clobazam, clonazepam, clorazepate, diazepam, lorazepam and midazolam. Among these BZDs, clorazepate has a unique profile that includes a long half-life of its active metabolite and slow onset of tolerance. Additionally, the pharmacokinetic characteristics of clorazepate (particularly the sustained-release formulation) could theoretically help minimize adverse events. However, larger, controlled studies of clorazepate are needed to further examine its role in the treatment of patients with epilepsy.

Properties of antiepileptic drugs in the treatment of idiopathic generalized epilepsies

Although valproate is considered to be the drug of first choice for the treatment of idiopathic generalized epilepsies (IGEs), other antiepileptic drugs (AEDs), both old (ethosuximide, clobazam, and clonazepam) and new (lamotrigine, levetiracetam, topiramate, and zonisamide) are also available. These AEDs do not appear to have a common mechanism of action in that both inhibitory gamma-aminobutyric acid (GABA; e.g., clobazam, clonazepam, and valproate) and excitatory glutamate (e.g., lamotrigine and topiramate) mechanisms are involved. Ethosuximide primarily acts by blocking T-type voltage-gated calcium channels in thalamic neurones while topiramate and zonisamide have multiple mechanisms of action. In contrast, levetiracetam is unique in that it may act via a specific binding site in the brain. In terms of their pharmacokinetic characteristics, all eight AEDs are rapidly absorbed after oral ingestion with peak blood concentration being achieved within 1-4 hours. Bioavailability is 100% with the exception clonazepam (90%) and topiramate (81-95%). Plasma protein binding is variable with valproate (90%), clobazam (85%) and clonazepam (86%) showing substantial binding, lamotrigine (55%) and zonisamide (50%) intermediate binding, and levetiracetam (0%), ethosuximide (0%) and topiramate (10%) being minimally bound. However, the binding by zonisamide is complicated by its binding to erythrocytes as well as albumin. All AEDs, with the exception of lamotrigine and levetiracetam, undergo elimination as a result of extensive metabolism by hepatic cytochrome P450 enzymes, which are highly amenable to induction and inhibition by other drugs and therefore susceptible to pharmacokinetic interactions. Lamotrigine metabolism is via hepatic glucuronidation, a process that is also susceptible to induction and inhibition by concurrent drugs. Levetiracetam is minimally metabolized (by hydrolysis in blood), is excreted predominantly unchanged in urine, and to date has not been associated with any clinically significant pharmacokinetic interactions. Using a semiquantitative pharmacokinetic rating system, based on 16 pharmacokinetic characteristics, a direct comparison between AEDs is possible. Thus valproic acid, regarded as the drug of first choice in the treatment of IGEs, rates lowest with respect to favorable pharmacokinetic characteristics, mostly because of its nonlinear pharmacokinetics, extensive hepatic metabolism, and its high propensity to interact both with other AEDs and non-AEDs. Levetiracetam rates highest with topiramate in second place.

Pharmacokinetics of a single oral dose of clobazam in patients with liver disease

The pharmacokinetic effect of a single oral in dose of 20 mg clobazam was studied in 15 patients with liver disease and in 6 healthy volunteers. Plasma concentrations of clobazam and its main metabolite, norclobazam, were measured by gas liquid chromatography. Clobazam was rapidly absorbed. Peak plasma concentrations were 350 +/- 63 ng/ml at 1.7 +/- 0.8 hr in healthy volunteers, 239 +/- 70 ng/ml at 3 +/- 1.9 hr in patients with viral hepatitis and 240 +/- 113 ng/ml at 2.5 +/- 1.5 hr in patients with cirrhosis. Total distribution volume was 173 +/- 88 l and 168 +/- 71 l in patients with viral hepatitis and cirrhosis respectively, and 81 +/- 20 l in volunteers. Corresponding half-life values were 47 +/- 18 hr and 51 +/- 21 hr in patients and 22 +/- 6.3 hr in volunteers. The difference between patients was not significant, whereas the difference between patients and volunteers was significant.

Effects of age and antiepileptic drugs on plasma levels and kinetics of clobazam and N-desmethylclobazam

The authors monitored the plasma levels of clobazam (CLO) and its principal metabolite, N-desmethylclobazam (NCLO) during chronic treatment of more than 400 epileptic patients receiving different co-medications, such as phenytoin (PH), carbamazepine (CBZ), sodium valproate (VPA) and phenobarbital (PB). This study investigated the influence of age and antiepileptic drugs on plasma levels of CLO and NCLO. Plasma concentrations measured 3 hr after morning administration of CLO varied from 30 to 700 [formula; see text] for CLO, and from 160 to 7000 [formula; see text] for NCLO. Plasma levels of CLO were higher in patients aged 20-30 years. NCLO concentrations increased with age up to 20 years. Coadministered antiepileptic compounds significantly decreased maximal plasma levels of CLO. Moreover, PH and CBZ a significantly increased the plasma levels of NCLO. Results on the influence of CBZ on CLO kinetics were confirmed in a group of ten patients receiving PB and VPA and later PB, VPA and CBZ as CLO associated drugs. The influence of VPA on the pharmacokinetics parameters of CLO was also evaluated in a patient in the latter group.

A comparison of the anticonvulsant effects of 1,4- and 1,5-benzodiazepines in the amygdala-kindled rat and their effects on motor function

Studies suggest that the 1,5-benzodiazepine clobazam possesses a favorable anticonvulsant profile due to its minimal neurotoxicity. The anticonvulsant and motor impairment effects of clobazam and 2 1,4-benzodiazepine, diazepam and clonazepam, were compared by dose-response analysis in amygdala-kindled rats and on 3 tests of motor function: gross motor impairment, a vertical screen test, and muscle tone. All drugs produced a significant, dose-dependent decrease in the duration of both behavioral and electrographic kindled seizure measures. Forelimb clonus suppression was the most sensitive measure of anticonvulsant drug effect. The order of potency for all effects was clonazepam greater than diazepam greater than clobazam. ED50s for the benzodiazepines' effects on motor impairment were compared to their ability to protect rats from forelimb clonus. Different spectrums of action for the various benzodiazepines were found depending on the comparison measure. Clonazepam had the most favorable ratio of potency for anticonvulsant vs. motor impairment activity when ataxia rating was the comparison measure. Diazepam had the most advantageous profile when the more sensitive screen test was used for comparison. Clobazam was not found to have a superior spectrum of action when compared across these measures. The results emphasize the importance of dose-response analyses and the consideration of behavioral measures used to assess beneficial and adverse effects of anticonvulsants.

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.

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 and multiple dose kinetics of clobazam, and clinical effects during multiple dosage

Sixteen healthy volunteers, aged 19 to 62 years, took a single 20-mg oral dose of clobazam and the serum concentrations of clobazam and desmethylclobazam were measured for the following 7 days. The mean kinetic variables for clobazam were: volume of distribution 1.31/kg, elimination half-life 24h, total clearance 0.47 ml/min/kg. 13 of the volunteers then took clobazam 5 mg twice daily for 22 consecutive days. Serum concentrations were measured during and after this period. Both clobazam and desmethylclobazam showed slow and extensive accumulation, their steady-state kinetics being entirely consistent with those observed after single doses. Elimination of both compounds after termination of treatment was equally slow. Clinical self-rating of morning sedation indicated a significant increase over baseline in subjective perception of sedation during the treatment period, and this effect persisted into the washout period. However, sedation did not increase in parallel with accumulating levels of clobazam and desmethylclobazam, probably due to functional adaptation or tolerance.

Clobazam kinetics in the elderly

1 The effects of age and sex on the disposition of clobazam (CBZ), a 1.5-benzodiazepine derivative, were evaluated in a series of 29 healthy volunteers aged 18 to 72 years, who ingested single 20 mg oral doses. CBZ kinetics were determined from multiple plasma concentrations measured during 7 days after the dose. 2 CBZ was rapidly absorbed, with peak levels reached an average of 1.5 h after dosing (range 0.5--2.5 h). Mean absorption half-life was 19.7 min. Absorption kinetics were not influenced by age of sex. 3 Elimination half-life ranged from 11 to 77 h, and was significantly longer in elderly v young males (48 v 17 h, P less than 0.01). In women, half-life also increased with age, but differences between young and elderly women were less striking (31 v 49 h, P less than 0.05). 4 Volume of distribution (Vd) was influenced by age and sex. Vd became larger with age regardless of sex, and within each age group was larger in women than in men. Total clearance was unrelated to age in women, but declined significantly with age in men (P less than 0.01). 5 The mean free fraction for CBZ in plasma was 11.5% (range 8.6--15.0%), and tended to increase with age, partly due to a significant age-related decline in plasma albumin concentration (r = -0.68, P less than 0.001). Correction of Vd and clearance for individual differences in binding did not alter their relation to age and sex. 6 As in the case of other benzodiazepines biotransformed by oxidative pathways, the capacity for N-demethylation of CBZ declines with age in men, but age has a minimal effect on CBZ clearance in women.

Clobazam: a review of its pharmacological properties and therapeutic use in anxiety

Clobazam1 is a 1,5-benzodiazepine with antianxiety and anticonvulsant properties, advocated for the treatment of primary anxiety and that associated with organic or functional disorders. Clobazam itself has a half-life of 18 hours, but that of the principal metabolite, N-desmethylclobazam, is about 50 hours. Although the metabolite is pharmacologically less active than the parent drug, steady-state plasma concentrations of the metabolite are 8 times higher than those of the unchanged drug. Therapeutic trials indicate that the antianxiety effect of clobazam 30 to 80 mg daily is comparable with that of half its dose of diazepam. Clobazam has minimal muscle relaxant and hypnotic activity. Although subjective drowsiness has occurred with similar frequency with clobazam and diazepam in some studies, clobazam causes less objectively measured sedation or psychomotor impairment in experimental studies. Results of studies of vigilance and psychomotor performance during therapeutic use in patients are less conclusive, but clobazam may be useful in anxious patients who experience such impairment with other benzodiazepines.

Single daily dose treatment of anxiety with clobazam: a double-blind study versus normal multiple-dose treatment with diazepam

A double-blind trial was carried out in 45 anxious out-patients to compare the effectiveness and tolerance of clobazam and diazepam. The severity of each patient's symptoms was assessed before, during and at the end of the trial period using the Hamilton Anxiety Rating Scale, and a note kept of any side-effects. The results showed that a single daily dose of 20 mg clobazam was equally as effective as 5 mg diazepam 3-times daily. Clobazam, however, produced considerably fewer side-effects than diazepam, especially drowsiness.