Development of tolerance to the anticonvulsant effect of diazepam in amygdala-kindled rats

The anticonvulsant long-term efficacy of diazepam was studied in amygdala-kindled rats. The drug was administered three times daily at doses of 5 mg/kg i.p. for 2 weeks in fully kindled animals. The severity of the kindled seizures was markedly reduced throughout the period of treatment, while tolerance developed to the effect of diazepam on seizure latency and duration and, less marked, on duration of amygdala afterdischarges. Concomitant determination of plasma concentrations of diazepam and its major metabolite, desmethyldiazepam, showed that diazepam increased during the 2 weeks of treatment, suggesting that the observed tolerance was not metabolic but functional in nature. After cessation of treatment, there was no clear indication for withdrawal symptoms except a significant increase in kindled seizure duration after 2 days. The data demonstrate that amygdala-kindled rats are a useful model to study the long-term efficacy of anticonvulsant drugs.     

Plasma concentrations and clinical effects after single oral doses of prazepam, clorazepate, and diazepam

In a double-blind parallel-group pharmacokinetic and pharmacodynamic study, 31 healthy volunteers received single oral doses of prazepam (10 mg), clorazepate (7.5 mg), or diazepam (5 mg). Appearance in plasma of diazepam and of desmethyldiazepam was rapid after administration of diazepam and clorazepate, respectively, with peak plasma concentrations reached within an average of 1 hour. After oral prazepam, however, desmethyldiazepam appeared in blood slowly, with the highest mean concentration at 6 hours postdosage. Clinical self-ratings of fatigue and of "feeling spacey" were significantly different among groups, with changes over baseline being more marked with clorazepate and diazepam than with prazepam. Thus, differences in absorption rate of orally administered benzodiazepines can lead to differences in the intensity of single-dose effects, despite administration of doses that are equivalent in terms of long-term anxiolytic efficacy.     

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.     

Effect of clorazepate in spasticity and rigidity: a quantitative study of reflexes and plasma concentrations

The effect on increased myotatic reflexes of desmethyldiazepam, formed from its precursor clorazepate, was assessed in a double-blind cross-over study of 27 days duration. Eight patients with spasticity or rigidity were given placebo or active substance; first in loading doses for 2 days, then 5 mg every 12 h for a total of 10 days. A wash-out period of 7 days was interposed between the 2 10-day periods. Desmethyldiazepam had a normalizing effect on the increased phasic ankle reflexes seen in spasticity, but not on the increased tonic reflex seen in rigidity. The mean concentration of desmethyldiazepam in the steady state was 1227 nmol/l (range 600-1990 nmol/l). The plasma concentration of desmethyldiazepam tended to correlate with the percent decrease in phasic reflex activity (P = 0.08, 2-tailed). A slight drowsiness in 2 patients was the only side-effect seen. In conclusion, desmethyldiazepam given as clorazepate seems to be a suitable medicament in the treatment of spasticity.     

Benzodiazepine withdrawal delirium with catatonic features. Occurrence in patients with partial seizure disorders

We report the cases of 3 patients with medically intractable seizures in whom withdrawal of treatment with a long-acting benzodiazepine (clorazepate dipotassium, 2 patients; clonazepam, 1 patient) was followed by delirium with catatoniclike features. While an increase in seizure frequency occurred during withdrawal and prior to the onset of behavioral changes, electroencephalograms did not show epileptiform activity during the delirium. We compared these 3 patients with 10 others with intractable seizures in whom antiepileptic therapy was withdrawn without subsequent behavior changes. High-dose benzodiazepine therapy and a history of viral encephalitis may be risk factors for withdrawal delirium.     

Ro 15-1788-induced seizures in rats continually exposed to diazepam for prolonged periods

Previous reports using rats have failed to demonstrate convulsions upon withdrawal from chronic benzodiazepine (BZ) treatment. We have shown earlier that rats develop tolerance to benzodiazepines following continuous exposure to low levels of diazepam (DZ) obtained by treatment with s.c. diazepam-filled silastic capsules. This report shows that intravenous infusion of the benzodiazepine antagonist Ro 15-1788 can induce seizures in rats treated for prolonged periods (4 weeks) with such diazepam-filled capsules. Precipitated seizures are also seen in rats 24 h after the cessation of chronic diazepam exposure. This procedure may provide a useful paradigm with which to study in rats the neural changes which are related to the physical dependence and withdrawal associated with prolonged exposure to the benzodiazepines.     

Tolerance to and Withdrawal from Anticonvulsant Action of Diazepam: Role of Nitric Oxide

Tolerance to the anticonvulsant action of diazepam as a result of central nervous system adaptation limits its use in epilepsy. In Wistar rats, diazepam 5 mg/kg ip twice daily produced tolerance to its anticonvulsant action in 6 days. Abrupt withdrawal caused hyperexcitability. Tolerance manifested as a decrease in seizure threshold to near-control values, while withdrawal hyperexcitability was evidenced by a significant decrease in seizure threshold below the control value. This effect was seen both in the "same group design" and "separate group design." L-Arginine (a donor of nitric oxide) and N(omega)-nitro-L-arginine (an inhibitor of nitric oxide synthase) were given in doses of 150 and 8 mg/kg, respectively, on Days 1, 3, and 6 along with diazepam in the same group design. Their role in preventing the development of tolerance to the anticonvulsant effect was seen on Days 1, 3, and 6. Withdrawal hyperexcitability was seen on Days 1, 2, and 4 after cessation of drug therapy. Both electroshock and pentylenetetrazole (PTZ) infusion were used as models of epilepsy, and seizure thresholds were determined. The up and down method of A. W. Kimball, W. T. Burnett, and G. D. Doherty (Radiat Res 1957;7:1-12) was used to determine the seizure threshold in cases of electroshock-induced seizures. L-Arginine, when administered with diazepam, was found to inhibit tolerance as well as withdrawal hyperexcitability. N(omega)-nitro-L-arginine did not prevent the development of tolerance or withdrawal hyperexcitability in the electroshock model, while in the PTZ model inhibition of nitric synthesis prevented withdrawal hyperexcitability but had no effect on the development of tolerance.     

Anticonvulsant effects of dipotassium clorazepate on hippocampal kindled seizures in rats

We examined the anticonvulsant properties of dipotassium clorazepate (DC) against hippocampal kindled seizures in rats. Adult male Wistar rats were subjected to kindling 1 week after the implantation of electrodes. After five stage 5 seizures were induced, the generalized convulsion triggering threshold (GST) was determined. Dipotassium clorazepate was administered intraperitoneally in rats that showed two stable stage 5 seizures induced at the GST current intensity. Dipotassium clorazepate at doses of 1 mg/kg or more produced an anticonvulsant effect, but did not readily suppress limbic seizures. Dipotassium clorazepate did not completely suppress after-discharges (AD) even at the highest dose, which was 5 mg/kg. Moreover, raised stimulus intensity failed to affect its efficacy as an anticonvulsant. The results of the present study suggest that DC has a modest anticonvulsant potency. It is reasonable to assume that its anticonvulsant efficacy is primarily due to attenuation of AD propagation rather than the raising of the seizure triggering threshold at the kindling focus.     

Convulsive and non-convulsive ethanol withdrawal behaviour in rats with lesions of the noradrenergic locus coeruleus system

The ascending noradrenergic pathways from the locus coeruleus were lesioned bilaterally in 10 rats by intracerebral 6-hydroxydopamine injections. Ten rats were sham-operated. All animals were subjected to a 4-day ethanol intoxication period using intragastric intubation. Intoxication and withdrawal assessments were performed blindly. The 6-hydroxydopamine lesions did not appear to affect tolerance to ethanol. During withdrawal, however, lesioned animals showed minor, but statistically significant changes in scores of certain non-convulsive withdrawal signs, but incidence and intensity of spontaneous and audiogenic convulsive seizures were not different between the groups.     

Long-term follow-up of an individual with vitamin B6-dependent seizures

We report on a 31-year-old female with vitamin B6-dependent seizures whose seizure onset was in the neonatal period. Her elder brother had the same disorder and died in infancy. Administration of vitamin B6 was initiated in the postnatal period. At the age of 12 years 1 month, 2 months after withdrawal of vitamin B6, visual seizures began to occur frequently. Myoclonic seizures and occasional generalized convulsive seizures were also observed. At the same time, photoparoxysmal response and spontaneous diffuse spike-wave bursts were seen on her EEG. Myoclonic seizures were provoked by intermittent photic stimulation during the EEG. It is distinctive that visual seizures were one of the main seizure types in this patient, that her clinical course was relatively benign, and that she has normal intellectual outcome.     

Prolonged confusion following convulsions due to generalized nonconvulsive status epilepticus

Among patients with a prolonged confusional state after convulsive seizure, we diagnosed 8 cases as generalized nonconvulsive status epilepticus. Six had a history of seizures, and 2 had new onset. The convulsive seizures were generalized in 6 and focal in two. The postictal confusion lasted up to 36 hours in the most prolonged case, and a delayed response to anticonvulsant medications occurred in all cases. The clinical symptoms ranged from mild confusion to coma. Psychiatric manifestations or automatisms were rare. The presumed etiology was due to diverse causes, but a withdrawal state was the most common. EEG demonstrated continuous or nearly continuous generalized ictal discharges of variable morphology. These cases call attention to the fact that some prolonged confusional states following convulsive seizures are in fact due to persistent seizure activity that can be diagnosed by EEG.     

Excellent results with clorazepate in recalcitrant childhood epilepsies

Eleven children with severe incapacitating generalized seizures were treated with sodium valproate and clorazepate and responded with a marked decrease in seizure frequency. Three children received clorazepate alone, either because of valproate toxicity or because of parental concern over side effects. These children, 5 males and 6 females, ranged in age from 3 to 17 years. They manifested normal to severely retarded intelligence. Although valproate levels were in the therapeutic range, seizure control was inadequate. When clorazepate was added to valproate therapy a marked reduction in seizure frequency occurred within 24 hours and became optimal within 48 to 72 hours. Side effects were minimal with the exception of a nocturnal generalized tonic-clonic seizure in a single patient. Three children were withdrawn from therapy after a year because of recurrent seizures. One patient was restarted on therapy after 6 months and seizure control improved. Clorazepate may be a useful adjunct in the treatment of primary generalized seizures in children.     

Evaluation of clorazepate (Tranxene) as an anticonvulsant--a pilot study.

Desmethyldiazepam--providing the long-term anticonvulsant effect when diazepam is given orally--is conveniently administered as clorazepate (Tranxene). In this study, clorazepate was compared to phenobarbital as a secondary anticonvulsant in eight ambulatory, adult outpatients. Stable doses of phenytoin were maintained throughout. Drowsiness was present in all on phenobarbital, but there were no clorazepate-related side effects. Seizure control did not differ for each treatment. Addition of common side effects of phenytoin and phenobarbital limited the attained serum levels of each when used together. Clorazepate doses in the 0.56-mg-per-kilogram range gave desmethyldiazepam levels in the 1.0-microgram-per-milliliter range. Induction of metabolism was suggested by falling desmethyldiazepam levels despite increasing doses. Clorazepate is an effective, nontoxic secondary anticonvulsant.     

Differences between physiological and pathological convulsive thresholds in patients with epilepsy★

BACKGROUND： Physiological convulsive thresholds degrade when the brain is in some pathologic states; thus, a level of stimulus that cannot provoke a convulsion may evoke a seizure or epileptic seizure. OBJECTIVE： To investigate the changes that occur in the brain when the physiological convulsive threshold becomes pathological, and to determine what differences occur in pathological and physiological convulsive thresholds during the development of epilepsy. DESIGN： A randomized controlled animal experiment. SETTING： Research Institute of Epilepsy of Shanxi Medical University; Department of Neurology, The Third Hospital of Shanxi Medical University; Research Institute of Function of Shanxi Medical University. MATERIALS： Thirty-six female Wistar rats were selected for this study. The rats were obtained from the experimental animal center of Shanxi Medical University. All laboratory procedures complied with animal ethical standards. The animals were randomly divided into three groups： a strong current group, a weak current group and a control group, with 12 rats in each group. An automatic determinator of seizure threshold was made at Shanxi Medical University and Taiyuan University of Technology. Two bipolar stainless steel stimulating electrodes and an electrode connector （diameter 1.2 ram） were made at Taiyuan University of Technology. METHODS： This study was performed in the laboratory of Research Institute of the Epilepsy of Shanxi Medical University between December 2005 and August 2006. The threshold of localized seizures was measured by performing direct cortical stimulation in rats under anesthesia. After 1 week of post-operative recovery, electric stimulation was started with three different kinds of stimulation. Seizure activity was induced by a ramp-shaped single train of biphasic pulses （50 Hz, total pulse duration of 2 ms, increasing from 0 to 2 000μ A in 15 seconds）. The threshold of localized seizures （TLS） has been defined as the minimum current intensity necessary to prov     

Two successful cases of bromide therapy for refractory symptomatic localization-related epilepsy

Potassium bromide was tried for two children with daily convulsive focal motor seizures with unconsciousness and focal motor seizure status. The treatment resulted in complete cessation of the attacks. It has been reported that bromide is effective for generalized tonic-clonic seizures and not for complex partial seizures, such as convulsive focal motor seizures with unconsciousness. However, our experiences provide evidence that bromide is one of the useful therapeutic agents for intractable symptomatic localization-related epilepsy.     

Anticonvulsant efficacy of the low-affinity partial benzodiazepine receptor agonist ELB 138 in a dog seizure model and in epileptic dogs with spontaneously recurrent seizures

PURPOSE: Ataxia, sedation, amnesia, ethanol and barbiturate potentiation, loss of efficacy (tolerance), development of dependence, and the potential for drug abuse limit the clinical use of benzodiazepines (BZDs) for long-term treatment of epilepsy or anxiety. BZD ligands that are in current use act as full allosteric modulators of gamma-aminobutyric acid (GABA)-gated chloride channels and, on long-term administration, trigger a functional uncoupling between the GABAA and BZD recognition sites. Partial allosteric modulators, which have a low intrinsic activity at the BZD recognition site of the GABAA receptor, might eventually overcome the limitations of full agonists such as diazepam (DZP). METHODS: In the present study, the new low-affinity partial BZD-receptor agonist ELB 138 [former name AWD 131-138; 1-(4-chlorophenyl)-4-morpholino-imidazolin-2-one] was evaluated in a dog seizure model and in epileptic dogs with spontaneously recurrent seizures. RESULTS: ELB 138 was shown to increase potently the pentylenetetrazole (PTZ) seizure threshold in dogs. Prolonged oral administration with twice-daily dosing of ELB 138 with either 5 or 40 mg/kg over a 5-week period was not associated with loss of anticonvulsant efficacy in the PTZ dog model. To study whether physical dependence developed during long-term treatment, the BZD antagonist flumazenil was injected after 5 weeks of treatment with ELB 138. Compared with prolonged treatment with DZP, only relatively mild abstinence symptoms were precipitated in dogs treated with ELB 138, particularly at the lower dosage (5 mg/kg, b.i.d.). In a prospective trial in dogs with newly diagnosed epilepsy, ELB 138 markedly reduced seizure frequency and severity without significant difference to standard treatments (phenobarbital or primidone) but was much better tolerated than the standard drugs. In dogs with chronic epilepsy, most dogs exhibited a reduction in seizure frequency and severity during add-on treatment with ELB 138. CONCLUSIONS: The data demonstrate that the partial BZD receptor agonist ELB 138 exerts significant anticonvulsant efficacy without tolerance in a dog seizure model as well as in epileptic dogs with spontaneously recurrent seizures. These data thus substantiate that partial agonism at the BZD site of GABAA receptors offers advantages versus full agonism and constitutes a valuable approach for treatment of seizures.     

A case of sudden unexpected death in epilepsy 3 years after the onset of acute encephalitis with refractory, repetitive partial seizures

Acute encephalitis with refractory, repetitive partial seizures (AERRPS) is a peculiar form of encephalitis mainly affecting children. Although not usually lethal, we report a case of sudden unexpected death in epilepsy (SUDEP) 3 years after the onset of AERRPS. A 6-year-old boy was admitted to our hospital because of fever and extremely refractory partial and secondary generalized seizures with delirium and psychiatric change. The seizures were highly resistant to anticonvulsants and suppressed only by large dose intravenous administration of midazolam. Seven months after the onset, the seizures were ameliorated by treatment with potassium bromide and clorazepate. After the acute phase, the patient developed complex partial seizures that tended to present with cyanosis. At the age of 10, he was found lying prone in respiratory arrest with facial pallor. Although he regained cardiac function after being taken to our emergency room, the patient died 12 days later. Six SUDEP cases after the onset of AERRPS, including this one, have been reported to date. Since epilepsy following AERRPS is one of the risk factors of SUDEP, clinicians should consider SUDEP to be a rare but high risk syndrome in AERRPS-afflicted children.     

Increases in NMDAR1 mRNA Levels are Involved in the Generation of Local Afterdischarges in Amygdaloid-Kindled Rats

Purpose : The Noda epileptic rat (NER), which was found in a colony of Crj:Wistar rats, shows spontaneous tonicxlonic convulsions at a frequency of approximately once per 30 h. However, weekly applied acoustic priming consistently induces tonic-clonic convulsion with sound stimuli. When NERs were given sound stimuli (95 dB, 8 kHz, 30 s) weekly from age 3 weeks, the percentage of animals with audiogenic seizures increased with age and was 100% after age 9 weeks. The audiogenic-response score to quantify the intensity of seizure responses also increased with age. Frontal cortical and hippocampal electroencephalograms (EEGs) showed low-voltage spike-and-wave complexes during tonic convulsions, which evolved into high-amplitude spike- or polyspike-and-wave complexes during clonic convulsion. Immediately after cessation of the seizures, the EEG showed a flattening or diffuse slowing. To elucidate the development of the seizure induction by acoustic priming, we examined the epileptiform discharges in the in-terictal EEG as a function of age.
Methods : The acoustic priming was applied to NERs from age 7 to 35 weeks. Cortical and hippocampal EEGs were recorded weekly during the interictal stage for 15 min after a 15-min habituation by using implanted electrodes.
Results : Sporadic spikes were observed predominantly in the hippocampus with age, although they were rarely synchronized in the cortex. Hippocampal spikes were observed in two (33.3%) of six animals at age 7–10 weeks, 23 (82.4%) of 28 animals at age 11–15 weeks, 12 (85.7%) of 14 animals at age 16–19 weeks, and 21 (100%) of 21 animals at age >20 weeks. This development of abnormal hippocampal discharges with acoustic priming was in line with the development of convulsive seizures.
Conclusions : Development of hippocampal excitation induced by acoustic priming is thought to lead to the induction of convulsive seizures in the NERs.     

Efficacy of Standard Anticonvulsants in Monkey Model with Spontaneous Motor Seizures

Monkeys were rendered chronically epileptic by injection of alumina gel into the pre- and postcentral gyrus. To test the validity of this primate model, the effects of diphenylhydantoin (DPH), phenobarbital, and primidone on spontaneous seizures evaluated for 8 months with a Latin-Squar experimental design. All three drugs were effective, the frequency of seizures being reduced by at least one-half during 6 weeks with treatment as compared with 6 weeks without. In most monkeys the frequency and severity of seizures were correlated to the number of interictal spikes in the EEG, and were inversely related to the level of drug in plasma. During withdrawal of phenobarbital and primidone, epileptic activity increased over that during control periods. Side effects were minimal with all three drugs. Patterns of behavior, although they differed from one monkey to the next, exhibited trends specific to each drug but particularly DPH. The seizures of some animals seemed to be related to the sleep-waking cycle.