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

Efficacy and Tolerability of Clobazam in Adults With Drug-Refractory Epilepsy

OBJECTIVES

To evaluate the effectiveness and tolerability of clobazam as an adjunctive treatment for adults with drug-resistant epilepsy.

METHODS

We performed a single-center, retrospective chart review of patients aged ≥18 years with drug-resistant epilepsy who started clobazam between 2010 and 2018. Included patients had outpatient visits both before and ≥1 month after clobazam initiation. Epilepsy classification, seizure frequency before and after clobazam, duration of clobazam treatment, and adverse effects were analyzed.

RESULTS

A total of 417 patients met the inclusion criteria. Mean age was 37.5 years, and 54% of patients were female. Patients were on a mean of 2.4 antiepileptic drugs at the time of initiation of clobazam. Epilepsy types were focal (56.8%), Lennox-Gastaut syndrome (LGS) (21.1%), generalized (15.1%), and unclassified (7.0%). At the first follow-up visit ≥1 month after clobazam initiation, 50.3% of patients had >50% reduction in seizure frequency, and 20.5% were seizure free. Of the initial cohort, 17.1% were followed >1 year and were seizure free at last follow-up. Response rates did not differ between different epilepsy classifications. Fifty-one percent of patients experienced ≥1 side effect, most commonly lethargy/fatigue (30.7%) or mood changes (10.8%). A total of 178 (42.6%) patients discontinued clobazam, most commonly due to adverse effects (55%).

CONCLUSIONS

Clobazam is effective and safe as a long-term adjunctive therapy for adults with drug-resistant epilepsy; efficacy in off-label use is similar to that in LGS.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that clobazam is an effective treatment for adults with drug-resistant epilepsy, independent of epilepsy classification.

Determination of Clobazam and Its Major Metabolite N-desmethylclobazam in Human Plasma with High-Performance Liquid Chromatography

Clobazam (CLB) is a benzodiazepine that is used in many types of epilepsy. Although therapeutic drug monitoring (TDM) of CLB is not routine, there is evidence that TDM may be of value in conditions where pharmacokinetic alterations are suspected. Therefore, determination of both CLB and its active metabolite concentrations is essential for TDM. Herein, we present a simple and practical method for determination of CLB and N-desmethylclobazam (NDMCLB) in human plasma by high-performance liquid chromatography (HPLC). The drugs were extracted by hexane:dichloromethane (1:1, v/v) from 0.3 mL plasma. The separation was carried out with a C18 reverse phase column using a mobile phase of water:acetonitrile (57:43, v/v) pumped at 0.8 mL/min. The analytes were detected at 228 nm. The method was linear over the concentration range 20–500 ng/mL for CLB and 200–3000 ng/mL for NDMCLB. The intra-day coefficient of variation (CV) was <10% for CLB and <6% for NDMCLB, while the inter-day CV for CLB was <16%. The metabolite inter-day CV was <6%. The accuracy of intra- and inter-day assessments determined for CLB and NDMCLB was within ±10%. This paper describes a rapid, reliable, and simple method for measuring CLB and its metabolite NDMCLB in human plasma. This UV-HPLC procedure offers acceptable precision and accuracy to quantify CLB and its metabolite in human plasma.

Need of Immediate Drug Reduction after Epilepsy Surgery - A Prospective Observational Study

Background

Patients undergoing epilepsy surgery are on polytherapy. Drug tapering is usually done after 1 year in adults and after 6 months in children. Sometimes, drugs have to be altered during the perioperative period, which is more commonly seen in hemispherotomy (HS) patients. The present study was done to compare perioperative drug alterations between HS and temporal (TL) lobectomy patients.

Materials and Methods

Prospective analysis of postoperative HS and TL patients was done. Primary outcomes were drug number, dosage changes, and seizure outcome. Secondary outcome studied was a change in intelligence quotient (IQ) in the two groups.

Results

At total of 71 patients were included. Perioperative drug stopping (clobazam - CLB) was needed in 3/38 patients in the HS group, due to sedation. Dosage was reduced in 23/38 (60.52%) in HS group, and in 2/33 (6%) in TL group P < 0.001. The most common drug was CLB, with reduction in 21/27 (77.77%) patients, with a mean reduction of 41.21 ± 4.01%. Two patients required drug substitution in the HS group. About 64/71 (90.1%) patients achieved Class I outcome at a 1-year postoperative time point (TL - 90.9%, HS - 89.47%). There was no change in IQ in any of the groups.

Conclusion

Perioperative drug alteration is often needed in the HS patients as compared to TL patients. Benzodiazepines have to be reduced to maintain alertness in the HS patients. The increased sedation postoperatively can be due to decreased cortical drive over the reticular activating system, gamma-aminobutyric acid (GABA) receptor denervation hypersensitivity, or increased activity of drugs over the remaining active hemisphere.

Systematic review of clobazam use in patients with status epilepticus

Clobazam (CLB) is a commonly used oral antiepileptic drug (AED) that has been shown to be effective in various forms of epilepsy. Given its distinct 1,5‐benzodiazepine structure, rapid absorption, minimal drug interactions, and favorable safety profile, CLB displays unique properties when compared to other commonly used benzodiazepines. Recent evidence has shown that CLB may demonstrate therapeutic efficacy in status epilepticus (SE). The objective of this systematic review was to summarize the available evidence pertaining to the efficacy of CLB use in SE. An electronic literature search of Medline (1946 to November 6, 2017), Embase (1974 to November 6, 2017), and the Cochrane Library (1999 to November 6, 2017) databases was performed to identify reports of CLB use in SE. After screening and full text review, a total of 15 articles were included: 8 retrospective studies, 2 case series, and 5 case reports. Efficacy rates for CLB have varied among reports. Overall, based on the retrospective studies, a total of 76 patients with SE have been reported. CLB was introduced within 2–4 days from SE onset and has been reported to contribute to remission in 36 patients (47%). CLB maintenance dose ranged from 10 to 60 mg/day. However, the results need to be interpreted carefully because SE patients are a heterogeneous group with different etiologies and disease severities, and the response to CLB might vary in different patient population or seizure types. In conclusion, there is not sufficient evidence to determine the safety and efficacy of clobazam in the setting of SE. However, the current limited evidence combined with the unique characteristics of CLB suggest that the drug might be considered as an add‐on option in SE patients, with a suggested dosage range of 10–60 mg/day. Prospective studies are needed to fully establish the role of CLB in the management of SE.

Deconstructing tolerance with clobazam: Post hoc analyses from an open-label extension study

Objective:

To evaluate potential development of tolerance to adjunctive clobazam in patients with Lennox-Gastaut syndrome.

Methods:

Eligible patients enrolled in open-label extension study OV-1004, which continued until clobazam was commercially available in the United States or for a maximum of 2 years outside the United States. Enrolled patients started at 0.5 mg·kg⁻¹·d⁻¹ clobazam, not to exceed 40 mg/d. After 48 hours, dosages could be adjusted up to 2.0 mg·kg⁻¹·d⁻¹ (maximum 80 mg/d) on the basis of efficacy and tolerability. Post hoc analyses evaluated mean dosages and drop-seizure rates for the first 2 years of the open-label extension based on responder categories and baseline seizure quartiles in OV-1012. Individual patient listings were reviewed for dosage increases ≥40% and increasing seizure rates.

Results:

Data from 200 patients were included. For patients free of drop seizures, there was no notable change in dosage over 24 months. For responder groups still exhibiting drop seizures, dosages were increased. Weekly drop-seizure rates for 100% and ≥75% responders demonstrated a consistent response over time. Few patients had a dosage increase ≥40% associated with an increase in seizure rates.

Conclusions:

Two-year findings suggest that the majority of patients do not develop tolerance to the antiseizure actions of clobazam. Observed dosage increases may reflect best efforts to achieve seizure freedom. It is possible that the clinical development of tolerance to clobazam has been overstated.

ClinicalTrials.gov identifier:

NCT00518713 and NCT01160770.

Classification of evidence:

This study provides Class III evidence that the majority of patients do not develop tolerance to clobazam over 2 years of treatment.

Correlating blood and urinary concentrations of clobazam doses in Japanese children and adolescents with intractable epilepsy

Clobazam (CLB) is an antiepileptic drug that is metabolized to the major metabolite N-desmethylclobazam (N-CLB). Our aim was to evaluate the utility of corrected urinary concentrations of CLB and N-CLB in Japanese children and adolescents with epilepsy. Blood and urinary concentrations of CLB and N-CLB were evaluated in 42 patients. The urinary and peak blood concentrations were measured 2-3 h after the last dose. The ratio of the blood and urinary creatinine concentrations was used to calculate the corrected urinary concentrations. A moderate correlation was found between the CLB dose and the CLB serum concentration, but this correlation was not found for N-CLB. Patients were dichotomized based on two regression lines, which were detected by statistical analyses with a cumulative distribution function: the lower ratio group (CLB/N-CLB < 0.275) and the higher ratio group (≥0.275). Moderate correlations were observed between the CLB dose and the serum concentration or the corrected value of CLB for the lower ratio group, and moderate to strong correlations were observed for the higher ratio group. The corrected urinary concentration of CLB correlates to the CLB dose when stratified by the CLB/N-CLB ratio and may prove practical for clinical estimation of the CLB serum concentration.

Mutations in the Na(+)/citrate cotransporter NaCT (SLC13A5) in pediatric patients with epilepsy and developmental delay

Mutations in the SLC13A5 gene that codes for the Na(+)/citrate cotransporter, NaCT, are associated with early onset epilepsy, developmental delay and tooth dysplasia in children. In the present study we identify additional SLC13A5 mutations in nine epilepsy patients from six families. To better characterize the syndrome, families with affected children answered questions about the scope of illness and treatment strategies. There are currently no effective treatments, but some anti-epileptic drugs targeting the GABA system reduce seizure frequency. Acetazolamide, a carbonic anhydrase inhibitor and atypical anti-seizure medication decreases seizures in 4 patients. In contrast to previous reports, the ketogenic diet and fasting produce worsening of symptoms. The effects of the mutations on NaCT transport function and protein expression were examined by transient transfections of COS-7 cells. There was no transport activity from any of the mutant transporters, although some of the mutant transporter proteins were present on the plasma membrane. The structural model of NaCT suggests that these mutations can affect helix packing or substrate binding. We tested various treatments, including chemical chaperones and low temperatures, but none improve transport function in the NaCT mutants. Interestingly, coexpression of NaCT and the mutants results in decreased protein expression and activity of the wild-type transporter, indicating functional interaction. In conclusion, our study has identified additional SLC13A5 mutations in patients with chronic epilepsy starting in the neonatal period, with the mutations producing inactive Na(+)/citrate transporters.

Clobazam for Refractory Childhood Seizure Disorders - A Valuable Supplementary Drug

Clobazam is a new benzodiazepine recently introduced in Canada on an experimental basis. We report our experience with 27 children (average age 9.1 years) with severe intractable seizure disorders. All had mixed seizures (41% focal plus generalized, 59% mixed generalized) and 93% were mentally retarded. Eighty-five percent had multiple daily seizures and all had been on an average of 6 other anticonvulsants in the past. Forty-one percent of our patients responded to clobazam with a reduction of greater than 75% in seizure frequency and 15% had no further seizures. Tolerance to clobazam which could not be overcome by dose increases developed in 26% of patients. Fortyfour percent of non-responders had exacerbations of their seizures shortly after starting clobazam, however 43% of these patients had reductions in comedications simultaneously. Side effects of clobazam in responders were minimal. We conclude that clobazam shows sufficient promise to warrant further trials in more benign seizure disorders in children.

Efficacy, safety, and tolerability of imepitoin in dogs with newly diagnosed epilepsy in a randomized controlled clinical study with long-term follow up

BACKGROUND

Imepitoin is a novel antiepileptic drug for the treatment of canine idiopathic epilepsy. The present study was conducted to demonstrate superior antiepileptic activity of a high dose of 30 mg/kg BID over a low dose of 1 mg/kg BID of imepitoin during 12 weeks of treatment under double blind conditions in a field population of dogs with previously untreated epilepsy. In a consecutive 12 weeks open label follow up (phase 2), all animals received 30 mg/kg BID, to evaluate the persistence of the antiepileptic activity, and to evaluate the effect of a dose step up to 30 mg/kg in the former low-dose animals.

RESULTS

A treatment with 30 mg/kg BID resulted in a significantly greater reduction in monthly seizure frequency relative to baseline data as compared to the 1 mg/kg dose. Both generalized and partial seizures but not cluster seizures were significantly less frequent in the high dose group. The antiepileptic activity was maintained during study phase 2 in the high dose group. An increase to 30 mg/kg BID in the low- dose animals resulted in a significant reduction in generalized and partial seizures, but not cluster seizures. At the end of study phase 2, 32.1 and 46.8 % of dogs of the former high and former low-dose groups respectively, remained free of generalized tonic-clonic seizures. Imepitoin was well tolerated. The frequency of dogs with any adverse drug reactions was higher in the 30 mg/kg BID dose (59 % vs. 41 %, p = 0.041), and the main target organ was the central nervous system (CNS). The occurrence of CNS related adverse reactions was transient and findings were mostly restricted to the first weeks of treatment. No hepatic enzyme increase and no other organ toxicity were observed.

CONCLUSION

The administration of imepitoin twice daily at a dose of 30 mg/kg results in significant and persistent antiepileptic effects in patients with newly diagnosed epilepsy and generalized tonic-clonic seizures, as observed over a study period of up to 6 months. Imepitoin was well tolerated. Most CNS related adverse drug reactions were transient. Both the antiepileptic activity and the safety profile make the drug suitable for long-term clinical use.

Comprehensive overview: efficacy, tolerability, and cost-effectiveness of clobazam in Lennox-Gastaut syndrome

Clobazam is the newest medication approved by the US Food and Drug Administration (FDA) for the treatment of Lennox–Gastaut syndrome (LGS) in patients at least 2 years of age, although the medication has been available in countries around the world to treat epilepsy and anxiety disorders for many years. Though classified as a benzodiazepine, the drug differs structurally from other drugs in the class as it possesses nitrogen atoms at the 1 and 5 positions within the heterocyclic ring rather than at the 1 and 4 positions. This difference and the classification of clobazam as a partial agonist are believed to be responsible for the decreased incidence of sedative effects compared to other benzodiazepines. Adverse events associated with clobazam use in clinical trials have generally been mild to moderate in nature. Data from an open-label extension trial have confirmed that clobazam is efficacious for the treatment of seizures associated with LGS, particularly atonic seizures (drop seizures), over the long term. Tolerance to the drug’s antiepileptic effects does not seem to be a common occurrence. The drug has proven to be a cost-effective option for therapy, particularly due to its ability to decrease the number of seizures that require medical treatment. Clobazam represents a welcome addition to the treatment options for LGS.

Clobazam: A Safe, Efficacious, and Newly Rediscovered Therapeutic for Epilepsy

Clobazam is an oral 1,5-benzodiazepine used worldwide for the treatment of many types of epilepsies, although it is currently only approved for Lennox-Gastaut syndrome in the USA. This anticonvulsant and anxiolytic therapeutic has repeatedly demonstrated great efficacy and a high safety profile in refractory epilepsy as well as in a few monotherapy trials in both children and adults. Clobazam allosterically activates the GABAA receptor, and it binds less to subunits that mediate sedative effects than other benzodiazepines. It acts quickly, maintaining a therapeutic effect for a long duration due to its active metabolite, N-desmethylclobazam. Dosage is between 5 mg and 40 mg a day, depending on patient weight, efficacy, and tolerability. Efficacy tolerance has not been a problem in the best studies. Clobazam has provided many benefits to epileptic patients. It should be used by clinicians early as an adjuvant therapy in the treatment of refractory epilepsy and even considered as monotherapy in a broad spectrum of epilepsy syndromes.

Long-term use of clobazam in Lennox-Gastaut syndrome: experience in a single tertiary epilepsy center

OBJECTIVE

Clobazam (CLB) is a 1,5-benzodiazepine, which is known to be effective for treating refractory partial epilepsy. We have evaluated the long-term efficacy and tolerability of CLB as an add-on therapy in patients with Lennox-Gastaut syndrome (LGS).

METHODS

Forty-six patients with LGS who had received CLB add-on therapy were enrolled in this study. We retrospectively reviewed their clinical characteristics, including type of seizures, use of CLB, efficacy, adverse events, and retention rate.

RESULTS

The mean±SD dose of CLB was 0.70±0.37 mg/kg per day (range, 0.16-1.60 mg/kg per day). After 1 month on CLB, 15 patients (32.6%) became seizure-free and 10 patients (21.7%) had 50% or greater seizure reduction. Response to CLB was not significantly associated with age, sex, or etiology (symptomatic or not). Five (10.8%) of 46 patients maintained seizure remission for more than 12 months. Tolerance developed in 48.0% of initial responders, and the 3-year retention rate by the Kaplan-Meier method was 76.6%. Seven patients (15.2%) reported adverse events, including somnolence and behavioral change, but only one discontinued CLB.

CONCLUSIONS

Clobazam add-on therapy was effective and very tolerable in patients with LGS.

Clobazam: a newly approved but well-established drug for the treatment of intractable epilepsy syndromes

Clobazam, a 1,5-benzodiazepine, was introduced in the 1970s as an anxiolytic and antiepileptic drug. Despite worldwide usage, it was only recently approved in the United States (seizures associated with Lennox-Gastaut syndrome). This article reviews historical and recent data to help practitioners better understand clobazam's clinical properties and usage. In many clinical trials, open-label studies, and retrospective reviews, clobazam was generally associated with ≥50% seizure reduction for more than half of Lennox-Gastaut syndrome patients, with approximately 10% achieving freedom from drop attacks. Efficacy is persistent, with little evidence for development of tolerance. Clobazam's safety profile appears to be similar to that of other benzodiazepines, but with substantially decreased sedation and increased psychomotor performance. Studies suggest clobazam acts through potentiation of gamma-aminobutyric acid type A receptors in a manner similar to other benzodiazepines. However, clobazam appears to display greater selectivity for receptors responsible for anticonvulsant activity than for those involved in sedation.

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).

[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.

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.

Experimental and clinical evidence for loss of effect (tolerance) during prolonged treatment with antiepileptic drugs

Development of tolerance (i.e., the reduction in response to a drug after repeated administration) is an adaptive response of the body to prolonged exposure to the drug, and tolerance to antiepileptic drugs (AEDs) is no exception. Tolerance develops to some drug effects much more rapidly than to others. The extent of tolerance depends on the drug and individual (genetic?) factors. Tolerance may lead to attenuation of side effects but also to loss of efficacy of AEDs and is reversible after discontinuation of drug treatment. Different experimental approaches are used to study tolerance in laboratory animals. Development of tolerance depends on the experimental model, drug, drug dosage, and duration of treatment, so that a battery of experimental protocols is needed to evaluate fully whether tolerance to effect occurs. Two major types of tolerance are known. Pharmacokinetic (metabolic) tolerance, due to induction of AED-metabolizing enzymes has been shown for most first-generation AEDs, and is easy to overcome by increasing dosage. Pharmacodynamic (functional) tolerance is due to "adaptation" of AED targets (e.g., by loss of receptor sensitivity) and has been shown experimentally for all AEDs that lose activity during prolonged treatment. Functional tolerance may lead to complete loss of AED activity and cross-tolerance to other AEDs. Convincing experimental evidence indicates that almost all first-, second-, and third-generation AEDs lose their antiepileptic activity during prolonged treatment, although to a different extent. Because of diverse confounding factors, detecting tolerance in patients with epilepsy is more difficult but can be done with careful assessment of decline during long-term individual patient response. After excluding confounding factors, tolerance to antiepileptic effect for most modern and old AEDs can be shown in small subgroups of responders by assessing individual or group response. Development of tolerance to the antiepileptic activity of an AED may be an important reason for failure of drug treatment. Knowledge of tolerance to AED effects as a mechanism of drug resistance in previous responders is important for patients, physicians, and scientists.

Clobazam as a New Antiepileptic Drug and Clorazepate Dipotassium as an Alternative Antiepileptic Drug in Japan

PURPOSE

To confirm the efficacy and to clarify the problems of clobazam (CLB) as a new antiepileptic drug (AED) and clorazepate (CLP) as an alternative AED in Japan.

METHODS

CLB and CLP were added on or replaced with conventional AEDs in 55 and 170 patients with refractory epilepsies, respectively. Short-term efficacy was studied after at least 2 months of CLB administration and at least 4 weeks of CLP administration. Long-term efficacy was examined in 31 cases with CLB for > or =6 months and in 86 cases with CLP for > or =6 months. CLB was initiated at 0.15-0.40 mg/kg and increased by 0.1-0.2 mg/kg every 1-2 weeks up to 0.28-1.25 mg/kg. CLP was started at 0.3-0.7 mg/kg and increased by 0.2-0.3 mg/kg every 1-2 weeks up to 2.5 mg/kg. Tolerance was examined in 42 cases with CLB for > or =3 months and 112 cases with CLP for > or =4 weeks.

RESULTS

CLB was effective, defined as > or =50% reduction in seizure frequency, in 71% of the short-term subjects and 81% of the long-term subjects. Short-term efficacy was better in symptomatic localization-related epilepsies, but long-term efficacy did not differ according to seizure classification. Short-term efficacy was not different by seizure types or EEG findings. CLP was effective in 70% of the short-term subjects and 80% of the long-term subjects. CLP was more effective in patients with localization-related epilepsies or in patients with partial seizures or focal epileptiform discharges on EEG. Adverse effects developed in 47% of CLB cases and 31% of CLP cases, but the incidence was reduced by lower initial doses and slow dose titration. Tolerance occurred in 24% of CLB cases and 48% of CLP cases, half within 3-4 months after the initiation of CLB and half by 2 months after the start of CLP. Upon rechallenge, 70% of CLB-tolerant cases and 50% of CLP-tolerant cases responded to each drug again by increasing or maintaining the dosage.

CONCLUSIONS

Excellent efficacy of CLB and excellent and prolonged efficacy of CLP for refractory epilepsies were confirmed. Frequent tolerance and adverse effects were major problems, but were manageable.

Use of clobazam for the treatment of refractory complex partial seizures

Clobazam (CLB) add-on therapy was attempted in 183 patients with intractable complex partial seizures in whom conventional benzodiazepines had been successfully discontinued before initiation of CLB. Although complete remission was initially achieved in 61, tolerance developed in almost half (49.2%) within the first 3 months, whereas 23 out of 31 patients (74.2%) who remained seizure free for the first 3 months continued to be so over the next 3 months. CLB add-on therapy proved to be significantly more effective when concurrent GTC occurred more often than yearly. In the current series, no frank psychotic episodes were elicited among the 61 patients who achieved complete suppression of long-standing complex partial seizures, which was in agreement with previous studies. From these results, we believe that CLB is an effective, safe, and inexpensive medication for add-on therapy in difficult to treat focal epilepsies, especially without concurrent use of conventional benzodiazepine compounds.

Effect of lamotrigine on the Ca(2+)-sensing cation current in cultured hippocampal neurons

Concentrations of extracellular calcium ([Ca(2+)](e)) in the CNS decrease substantially during seizure activity. We have demonstrated previously that decreases in [Ca(2+)](e) activate a novel calcium-sensing nonselective cation (csNSC) channel in hippocampal neurons. Activation of csNSC channels is responsible for a sustained membrane depolarization and increased neuronal excitability. Our study has suggested that the csNSC channel is likely involved in generating and maintaining seizure activities. In the present study, the effects of anti-epileptic agent lamotrigine (LTG) on csNSC channels were studied in cultured mouse hippocampal neurons using patch-clamp techniques. At a holding potential of -60 mV, a slow inward current through csNSC channels was activated by a step reduction of [Ca(2+)](e) from 1.5 to 0.2 mM. LTG decreased the amplitude of csNSC currents dose dependently with an IC(50) of 171 +/- 25.8 (SE) microM. The effect of LTG was independent of membrane potential. In the presence of 300 microM LTG, the amplitude of csNSC current was decreased by 31 +/- 3% at -60 mV and 29 +/- 2.9% at +40 mV (P > 0.05). LTG depressed csNSC current without affecting the potency of Ca(2+) block of the current (IC(50) for Ca(2+) block of csNSC currents in the absence of LTG: 145 +/- 18 microM; in the presence of 300 microM LTG: 136 +/- 10 microM. n = 5, P > 0.05). In current-clamp recordings, activation of csNSC channel by reducing the [Ca(2+)](e) caused a sustained membrane depolarization and an increase in the frequency of spontaneous firing of action potentials. LTG (300 microM) significantly inhibited csNSC channel-mediated membrane depolarization and the excitation of neurons. Fura-2 ratiometric Ca(2+) imaging experiment showed that LTG also inhibited the increase in intracellular Ca(2+) concentration induced by csNSC channel activation. The effect of LTG on csNSC channels may partially contribute to its broad spectrum of anti-epileptic actions.

Benzodiazepines in the home treatment of acute seizures

Prompt home treatment of dangerous seizures or upsetting relapses can prevent the effects of prolonged seizures and offer patients and their families an alternative to emergency medical treatment. The choice of benzodiazepine and route of administration should be based on patients' clinical presentation and acceptance. The challenge for the practitioner is to select the patients for whom home use of benzodiazepines will be appropriate, safe, and cost-effective.

Vigabatrin versus ACTH as first-line treatment for infantile spasms: a randomized, prospective study

PURPOSE

To compare the efficacy and tolerability of vigabatrin (VGB) and adrenocorticotrophic hormone (ACTH) as first-line therapy in infantile spasms.

METHODS

Forty-two infants (22 males, 20 females) aged 2-9 months with newly diagnosed infantile spasms, were included in the trial. Patients were randomized to receive VGB 100-150 mg/kg/day or Depot ACTH 10 IU/day. The alternative drug was given if spasms were not controlled within 20 days or in cases of intolerance to initial therapy. Twenty-three patients (7 cryptogenic, 16 symptomatic) received VGB as first-line therapy; 19 patients (8 cryptogenic, 11 symptomatic) received ACTH as the first drug.

RESULTS

Cessation of spasms was observed in 11 (48%) of the patients randomized to VGB and in 14 (74%) of those randomized to ACTH. Response to VGB was observed within 1-14 days, but two-thirds of patients (7/11) responded within 3 days. In the group treated with VGB, side effects such as drowsiness, hypotonia and irritability were observed in 13% of patients, compared with 37% in the group treated with ACTH. VGB was more effective than ACTH as treatment for cerebral malformations or tuberous sclerosis, whereas ACTH proved more effective in perinatal hypoxic/ischemic injury. The efficacy of the two drugs was similar in cryptogenic cases. Disappearance of interictal EEG abnormalities occurred sooner in patients randomized to ACTH than in those who received VGB as initial therapy. During the second phase, the alternative drug was given to the resistant patients. Spasms ceased in 2 of 5 patients treated with VGB and in 11 of 12 patients treated with ACTH. After 3 months, relapses of spasms were observed in 6 patients treated with ACTH and in 1 treated with VGB. VGB produced a therapeutic response in nearly half the patients receiving this drug.

CONCLUSIONS

Our data lend further support to the view that VGB may be considered a first-choice drug in the treatment of IS.

Prognosis and clinical features of intractable epilepsy: a prospective study

Of the epileptic patients who were treated for > or = 5 years until the end of 1990 and had more than four seizures in 1990, 63 patients had been treated without interruption until the end of 1995. We analyzed their clinical courses from 1990 to 1995 prospectively. More than half the subjects were diagnosed with temporal lobe epilepsy. Twenty cases had presumed etiology, and 32 had neuropsychiatric complications. Of the subjects whose seizures were not controlled with conventional antiepileptic drugs (AED), 11 cases demonstrated significant improvement when new AED; that is, lamotrigine, vigabatrin, clobazam, topiramate, tiagabine or CGP33101 were added. However, 10 patients did not respond to new AED. Presumed etiology, neuropsychiatric complications, multiple epileptic foci in EEG and abnormalities on head CT or MRI were characteristics of the patients whose seizures were resistant to new AED.

Established antiepileptic drugs

Despite the recent entry into the market-place of a range of new pharmacological treatments for epilepsy, most patients still receive the standard antiepileptic drugs. This review considers the clinical place and practical use of these agents. Detailed consideration is given to carbamazepine, phenytoin, sodium valproate, phenobarbital and ethosuximide, with lesser emphasis on primidone, clobazam and clonazepam. Individualization of therapy, polypharmacy, refractory epilepsy, therapeutic drug monitoring, pregnancy, withdrawing treatment, epilepsy prophylaxis and referral to an epilepsy centre are also discussed. The paper concludes with a statement of 12 basic rules in prescribing established antiepileptic drugs.

Tolerance to anticonvulsant effects of some benzodiazepines in genetically epilepsy prone rats

The development of tolerance to the anticonvulsant effects of clonazepam, clobazam, and diazepam were studied in genetically epilepsy-prone rats following intraperitoneal (IP) or oral administration. The anticonvulsant effects were evaluated on seizures evoked by means of auditory stimulation (109 dB, 12-16 kHz). All compounds showed 60 min after IP injection antiseizure activity with ED50 against clonus of 0.24 mumol kg-1 for clonazepam, 0.72 mumol kg-1 for diazepam, and 3.9 mumol kg-1 for clobazam. After 120 min of oral administration the ED50 against clonus of 2.37 mumol kg-1 for clonazepam, 15.8 mumol kg-1 for diazepam, and 30 mumol kg-1 for clobazam. The dose chosen for the chronic treatment were 2.5 mumol kg-1 for clonazepam, 15 mumol kg-1 for diazepam, and 30 mumol kg-1 for clobazam. The animals were treated three times daily for 4 or 6 weeks. Auditory stimulation was administered 60 min after drug IP injection on various days. During treatment, tolerance was observed as a loss of drug anticonvulsant effects. No changes of occurrence of audiogenic seizures was observed in rats treated with vehicle. Tolerance to the anticonvulsant activity developed most rapidly during clobazam treatment, less rapidly following diazepam treatment, and most slowly during clonazepam treatment. Sixty minutes after IP injection on various days of chronic treatment the motor impairment induced by these benzodiazepines was also studied by means of a rotarod apparatus. The tolerance to the motor impairment developed more rapidly than the anticonvulsant effects. The response to auditory stimulation to benzodiazepines was stopped 24 and 48 h after chronic treatment with these compounds, showing no residual drug effects and that rats were still tolerant. The genetically epilepsy-prone rats is a reliable and sensitive model for studying long-term effects of anticonvulsant drugs.

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.

Effectiveness and tolerance of clobazam in temporal lobe epilepsy

INTRODUCTION

The main objective of this retrospective study was the further exploration of the loss of efficiency of the clobazam therapy (CLOB tolerance) in resistant temporal lobe epilepsy (TLE).

MATERIAL AND METHODS

For up to 42 months we closely followed the state of 55 TLE patients placed on CLOB as an add-on therapy. Also, we sought for a connection between CLOB tolerance and clinical characteristics.

RESULTS

By the end of the 1st month 71% of the patients were seizure-free; 20% improved; 3% relapsed totally and 6% did not respond at all. After 24 months 15% were seizure-free, 11% maintained the original improved state, 36% relapsed totally and 32% partially--which remained unchanged thereafter. Long-term efficiency was in inverse proportion to the pretreatment interictal spike activity. No significant cross-tolerance was noted between CLOB and clonazepam.

CONCLUSION

Although the problem of CLOB tolerance is hardly overestimated, the use of CLOB in the treatment of TLE deserves consideration--despite the possibilities new drugs offer.

Lack of anticonvulsant tolerance and benzodiazepine receptor down regulation with imidazenil in rats

1. Development of anticonvulsant tolerance and benzodiazepine (BZD) receptor down-regulation has been reported to occur upon chronic administration of conventional BZDs. We compared the effect of chronic treatment with imidazenil, a new BZD partial agonist, and diazepam in rats. 2. After acute administration, imidazenil was more potent though less effective than diazepam in protecting from bicuculline-induced seizure. The time-course analysis of two peak equieffective doses of imidazenil (2.5 mumol kg-1 p.o.) and diazepam (35 mumol kg-1, p.o.) showed a longer lasting action of the former drug. 3. The anticonvulsant efficacy of diazepam (35 mumol kg-1, p.o.) was reduced in rats given chronic diazepam (35 mumol kg-1 p.o., 3 times a day for 8-15 days). No tolerance to imidazenil (2.5 mumol kg-1, p.o.) was apparent after 130-day administration with imidazenil (2.5 mumol kg-1, p.o., 3 times a day). 4. Plasma levels of imidazenil and diazepam, assessed 30 min after administration, were not changed in chronically treated animals. 5. In rats made tolerant to diazepam, the maximum number of [3H]-flumazenil binding sites were reduced in both cerebral cortex (-36%) and cerebellum (-42%). No changes in [3H]-flumazenil binding were found in chronic imidazenil-treated rats. 6. Specific [3H]-flumazenil binding in vivo was decreased in the forebrain of chronic diazepam- but not of chronic imidazenil-treated animals. 7. These data indicate that imidazenil possesses a very low tolerance potential to its anticonvulsant activity and does not affect BZD receptor density even after prolonged administration.

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)

Clobazam for intractable pediatric epilepsy

We report our experience with add-on clobazam therapy over a 5-year period in 63 children with refractory epilepsy. The mean duration of epilepsy was 6.7 years. Children were followed for 15 to 64 months. Of 63 children, 57 were developmentally delayed, and 54 had a symptomatic/cryptogenic epilepsy. Forty-one percent became either seizure free or had a greater than 90% reduction in seizure frequency. Seizure frequency was reduced 50% to 90% in another 24%. The average daily dose of clobazam was 0.8 mg/kg. Thirty-five percent had the medication withdrawn for persistent or unacceptable side effects or the development of tolerance (seven patients). Side effects included severe aggressive outbursts, hyperactivity, insomnia, and depression with suicidal ideation. Clobazam is a useful add-on medication for 65% of children with epilepsy. Clinical utility may be limited by behavioral side effects in some patients.

Clobazam for treatment of intractable epilepsy: a critical assessment

Clobazam (CLB), a 1,5-benzodiazepine, is a remarkably effective add-on drug for individual patients with refractory partial epilepsy. CLB has an excellent safety record. As with all benzodiazepines used for treating epilepsy, sedation and withdrawal effects, together with the development of tolerance, limit its usefulness. Recent efforts to prevent or reverse tolerance with intermittent administration of CLB or periodic injection of a benzodiazepine antagonist, flumazenil, are encouraging and justify further investigations.

Central and peripheral benzodiazepine receptors in rat brain and platelets: effects of treatment with diazepam and clobazam

Tolerance to the effects of benzodiazepines (BZ) may be mediated by changes in benzodiazepine receptors (BZRs). Peripheral BZRs (in brain and platelets) and central BZRs (in brain) were measured in rats following intraperitoneal administration of diazepam and clobazam each for 4 and 12 days. BZRs were measured by binding assays using [3H] PK 11195 (peripheral) and [3H] flunitrazepam (central) as radioligands. Diazepam, but not clobazam, increased peripheral BZR numbers in platelets (both P < 0.005), but not in brain, after 4 and 12 days' treatment compared with appropriate controls. Neither drug altered central BZR affinities or numbers in rat brain. BZ effects on peripheral BZRs in platelets cannot be extrapolated to predict changes in brain receptors, either peripheral or central.

Peripheral benzodiazepine receptors in platelets of epileptic patients

Tolerance to the anticonvulsant effect of benzodiazepines is likely to involve changes at the central benzodiazepine-GABA receptor complex. Peripheral benzodiazepine receptors (pBZRs), which can be measured in platelets, may also be involved. Using a binding assay with [3H]-PK 11195 as radioligand, pBZRs were assayed in platelets of patients taking a variety of antiepileptic drugs (AEDs). Comparisons were made with untreated patients. pBZR receptor density (mean +/- s.e. mean) was increased vs controls (8083 +/- 557 fmol mg-1 protein) in the platelets of patients taking a polypharmacy regime including the benzodiazepine clobazam (12661 +/- 1011 fmol mg-1 protein, P < 0.005) and also in those receiving sodium valproate as monotherapy (15003 +/- 1756 fmol mg-1 protein, P < 0.01). The significance of these findings is unclear, but the use of a specific pBZR antagonist may be a promising avenue for investigating the mechanism of BZ tolerance and its prevention.

Lack of effect of concomitant clobazam on interictal 123I-iomazenil SPECT

Single photon emission computed tomography (SPECT) is being increasingly used as an adjunctive technique in the localisation of epileptogenic foci prior to surgery. Fourteen patients (five male, nine female; mean age 31 years) with refractory complex partial seizures, all of whom had abnormal 99Tc HM-PAO SPECT scans, were imaged again using the benzodiazepine receptor ligand 123I-iomazenil. Eleven of these patients displayed the same abnormality on both scans. The magnitude of the deficit, however, was slightly greater (P < 0.05) on the iomazenil scan compared with the HM-PAO study. These 11 patients were then randomised into two groups. Group 1 (n = 7) received clobazam 20 mg/day for a minimum of 7 days before a second iomazenil study was performed. Patients in group 2 (n = 4) underwent a second iomazenil scan at the same time interval as those in group 1, but without the additional clobazam. The resultant scans were reported blind to treatment. There were no qualitative or quantitative differences between the first and second iomazenil studies in either group. Patients can be imaged using 123I-iomazenil without withdrawing clobazam therapy. From this preliminary study, there seems little advantage in using iomazenil in place of HM-PAO to delineate the extent of the zone of epileptogenesis. Whether iomazenil SPECT will prove to be more sensitive in identifying the site of the epileptic focus remains to be determined.

[Clobazam use in refractory epilepsies in children]

We present the study of 20 pediatric patients with difficult controlled epilepsy in which we used clobazam as adjuvant anticonvulsant therapy between January 1986 and July 1990 at the outpatients neuropediatric facility of the Hospital General Base Cayetano Heredia and the private practice, with 6 to 45 months follow up. The mean age for the onset of the epilepsy was 22 months and the most frequent kind was the generalized epilepsy syndrome both secondary and idiopathic. It was obtained a significant decrease of seizures in 60% of the patients with a complete control in 35% of the total. It was found the best outcome in secondary generalized epilepsies Lennox-Gastaut and West types. It was found tolerance phenomenon in 25%, and psychotropic effect in three patients. We suggest the use of this 1,5 benzodiazepine drug in difficult controlled epilepsies in children of our region.

Repeated anticonvulsant testing: contingent tolerance to diazepam and clobazam in kindled rats

The acute anticonvulsant efficacy of diazepam (1.5 mg/kg, i.p.) was evaluated by repeated test injection in kindled rats subcutaneously implanted with diazepam-filled or empty silastic tubes for 3 weeks. Tolerance developed to acute test injections in both diazepam- and sham-implanted rats. Tolerance developed to a lesser extent in another group of diazepam-implanted rats which did not receive acute intermittent anticonvulsant tests. The hypothesis that contingent tolerance had developed to the anticonvulsant actions of benzodiazepines (diazepam, 1.5 mg/kg, i.p. and clobazam, 10 mg/kg, i.p.) in kindled rats given acute intermittent injections was investigated using a 'before-after' design. Significant contingent tolerance developed in rats which received intermittent benzodiazepine treatment before, but not after, amygdala stimulation. Tolerance developed to different extents depending on the seizure measure evaluated (forelimb clonus duration, amygdala afterdischarge duration, motor seizure latency and duration, and seizure stage). Contingent tolerance to both benzodiazepines developed at a similar rate. The findings suggest that contingent tolerance may contribute a sizeable component to the overall functional benzodiazepine tolerance measured in long-term anticonvulsant drug studies in kindled rats. Several questions regarding contingent tolerance phenomena are posed and the implications of these findings for studies using repeated anticonvulsant testing are discussed.

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.