New anticonvulsant drugs. Focus on flunarizine, fosphenytoin, midazolam and stiripentol

Clinical applications of small-molecule GABAAR modulators for neurological disorders

Gamma-aminobutyric acid type A receptor (GABAAR) modulators are crucial in treating neurological and psychiatric disorders, including epilepsy, anxiety, insomnia, and depression. This review examines the synthetic approaches and clinical applications of representative small-molecule GABAAR modulators. Benzodiazepines, such as Diazepam, are well-known positive allosteric modulators (PAMs) that enhance GABAAR function, providing therapeutic effects but also associated with side effects like sedation and dependence. Non-benzodiazepine modulators, including Z-drugs like Zolpidem and Zaleplon, offer improved selectivity for the α1 subunit of GABAAR, reducing some of these side effects. Neurosteroids such as allopregnanolone and its synthetic analogs, including Brexanolone, have emerged as potent GABAAR modulators with applications in conditions like postpartum depression and refractory epilepsy. Advances in molecular biology and pharmacology have facilitated the development of isoform-specific modulators, potentially reducing off-target effects and enhancing therapeutic profiles. Additionally, combining GABAAR modulators with other therapeutic agents has shown promise in enhancing efficacy and minimizing side effects. This review highlights the design strategies, pharmacodynamics, clinical efficacy, and safety profiles of these compounds, emphasizing the opportunities for developing novel GABAAR modulators with improved therapeutic outcomes.

Inhibition of Radiation and Temozolomide-Induced Glioblastoma Invadopodia Activity Using Ion Channel Drugs

Simple Summary

Glioblastoma accounts for approximately 40–50% of all primary brain cancers and is a highly aggressive cancer that rapidly disseminates within the surrounding normal brain. Dynamic actin-rich protrusions known as invadopodia facilitate this invasive process. Ion channels have also been linked to a pro-invasive phenotype and may contribute to facilitating invadopodia activity in cancer cells. The aim of our study was to screen ion channel-targeting drugs for their cytotoxic efficacy and potential anti-invadopodia properties in glioblastoma cells. We demonstrated that the targeting of ion channels in glioblastoma cells can lead to a reduction in invadopodia activity and protease secretion. Importantly, the candidate drugs exhibited a significant reduction in radiation and temozolomide-induced glioblastoma cell invadopodia activity. These findings support the proposed pro-invasive role of ion channels via invadopodia in glioblastoma, which may be ideal therapeutic targets for the treatment of glioblastoma patients.

Abstract

Glioblastoma (GBM) is the most prevalent and malignant type of primary brain cancer. The rapid invasion and dissemination of tumor cells into the surrounding normal brain is a major driver of tumor recurrence, and long-term survival of GBM patients is extremely rare. Actin-rich cell membrane protrusions known as invadopodia can facilitate the highly invasive properties of GBM cells. Ion channels have been proposed to contribute to a pro-invasive phenotype in cancer cells and may also be involved in the invadopodia activity of GBM cells. GBM cell cytotoxicity screening of several ion channel drugs identified three drugs with potent cell killing efficacy: flunarizine dihydrochloride, econazole nitrate, and quinine hydrochloride dihydrate. These drugs demonstrated a reduction in GBM cell invadopodia activity and matrix metalloproteinase-2 (MMP-2) secretion. Importantly, the treatment of GBM cells with these drugs led to a significant reduction in radiation/temozolomide-induced invadopodia activity. The dual cytotoxic and anti-invasive efficacy of these agents merits further research into targeting ion channels to reduce GBM malignancy, with a potential for future clinical translation in combination with the standard therapy.

Comparison of Intravenous Anesthetic Agents for the Treatment of Refractory Status Epilepticus

Status epilepticus that cannot be controlled with first- and second-line agents is called refractory status epilepticus (RSE), a condition that is associated with significant morbidity and mortality. Most experts agree that treatment of RSE necessitates the use of continuous infusion intravenous anesthetic drugs such as midazolam, propofol, pentobarbital, thiopental, and ketamine, each of which has its own unique characteristics. This review compares the various anesthetic agents while providing an approach to their use in adult patients, along with possible associated complications.

Pharmacological considerations in the use of stiripentol for the treatment of epilepsy

INTRODUCTION

Despite the fact that more than 20 antiepileptic drugs (AEDs) are currently available, about one-third of patients still present drug resistance. Further efforts are required to develop novel and more efficacious therapeutic strategies, especially for refractory epileptic syndromes showing few and anecdotic therapeutic options.

AREAS COVERED

Stiripentol (STP) is a second generation AED that shows GABAergic activity, with immature brain selectivity, and an indirect metabolic action on co-administered AEDs. Two pivotal studies demonstrated STP efficacy in patients with Dravet syndrome with refractory partial seizures, and marketing authorization in Europe, Canada and Japan was granted thereafter. Post-marketing surveys reported a good efficacy and tolerability profile. In addition, interesting data is currently emerging regarding off-label experimentation of STP in other forms of epilepsy.

EXPERT OPINION

STP is an important addition to the limited treatment options available for patients resistant to common AEDs. The possibility to inhibit seizures through the metabolic pathway of lactate dehydrogenase and the inhibitory effects on the entry of Na(+) and Ca(2+) are the most recent findings to emerge about STP and could be proof of its neuroprotective action. Moreover, its positive effects on cognitive function, its good safety and tolerability profile and the increasing data about STP efficacy on other refractory epileptic syndromes may prove to be fertile grounds for further investigation.

Clinical pharmacokinetics of new-generation antiepileptic drugs at the extremes of age: an update

Epilepsies occur across the entire age range, and their incidence peaks in the first years of life and in the elderly. Therefore, antiepileptic drugs (AEDs) are commonly used at the extremes of age. Rational prescribing in these age groups requires not only an understanding of the drugs' pharmacodynamic properties, but also careful consideration of potential age-related changes in their pharmacokinetic profile. The present article, which updates a review published in 2006 in this journal, focuses on recent findings on the pharmacokinetics of new-generation AEDs in neonates, infants, children, and the elderly. Significant new information on the pharmacokinetics of new AEDs in the perinatal period has been acquired, particularly for lamotrigine and levetiracetam. As a result of slow maturation of the enzymes involved in glucuronide conjugation, lamotrigine elimination occurs at a particularly slow rate in neonates, and becomes gradually more efficient during the first months of life. In the case of levetiracetam, elimination occurs primarily by renal excretion and is also slow at birth, but drug clearance increases rapidly thereafter and can even double within 1 week. In general, infants older than 2-3 months and children show higher drug clearance (normalized for body weight) than adults. This pattern was confirmed in recent studies that investigated the pediatric pharmacokinetics of several new AEDs, including levetiracetam, rufinamide, stiripentol, and eslicarbazepine acetate. At the other extreme of age, in the elderly, drug clearance is generally reduced compared with younger adults because of less efficient drug-metabolizing activity, decreased renal function, or both. This general pattern, described previously for several AEDs, was confirmed in recent studies on the effect of old age on the clearance of felbamate, levetiracetam, pregabalin, lacosamide, and retigabine. For those drugs which are predominantly eliminated by renal excretion, aging-related pharmacokinetic changes could be predicted by measuring creatinine clearance (CLCR). Overall, most recent findings confirm that age is a major factor influencing the pharmacokinetic profile of AEDs. However, pharmacokinetic variability at any age can be considerable, and the importance of other factors should not be disregarded. These include genetic factors, co-morbidities, and drug interactions, particularly those caused by concomitantly administered AEDs which induce or inhibit drug-metabolizing enzymes.

The 60-day temperature-dependent degradation of midazolam and Lorazepam in the prehospital environment

BACKGROUND

The choice of the optimal benzodiazepine to treat prehospital status epilepticus is unclear. Lorazepam is preferred in the emergency department, but concerns about nonrefrigerated storage limits emergency medical services (EMS) use. Midazolam is increasingly popular, but its heat stability is undocumented.

OBJECTIVE

This study evaluated temperature-dependent degradation of lorazepam and midazolam after 60 days in the EMS environment.

METHODS

Lorazepam or midazolam samples were collected prior to (n = 139) or after (n = 229) 60 days of EMS deployment during spring-summer months in 14 metropolitan areas across the United States. Medications were stored in study boxes that logged temperature every minute and were stored in EMS units per local agency policy. Mean kinetic temperature (MKT) exposure was derived for each sample. Drug concentrations were determined in a central laboratory by high-performance liquid chromatography. Concentration as a function of MKT was analyzed by linear regression.

RESULTS

Prior to deployment, measured concentrations of both benzodiazepines were 1.0 relative to labeled concentration. After 60 days, midazolam showed no degradation (mean relative concentration 1.00, 95% confidence interval [CI] 1.00-1.00) and was stable across temperature exposures (adjusted R(2) -0.008). Lorazepam experienced little degradation (mean relative concentration 0.99, 95% CI 0.98-0.99), but degradation was correlated to increasing MKT (adjusted R(2) 0.278). The difference between the temperature dependence of degradation of midazolam and lorazepam was statistically significant (T = -5.172, p < 0.001).

CONCLUSIONS

Lorazepam experiences small but statistically significant temperature-dependent degradation after 60 days in the EMS environment. Additional study is needed to evaluate whether clinically significant deterioration occurs after 60 days. Midazolam shows no degradation over this duration, even in high-heat conditions.

[Therapeutic drug monitoring of stiripentol]

Stiripentol is a third generation antiepileptic, marketed since 2007 under the name of Diacomit(®). It is indicated, always in combination, in the treatment of severe myoclonic epilepsy in infancy or Dravet syndrome. Its pharmacokinetics is not linear. It is a potent inhibitor of CYP3A4, 1A2 and 2C19 and increases the plasma concentrations of many other antiepileptic drugs. Without this being considered as a validated therapeutic range, the trough plasma concentrations at steady-state, corresponding to the usual doses are between 10 and 15 mg/L. The concentration-efficacy relationship is not established, but there is some evidence for a concentration-related toxicity. However, because of its non-linear kinetics, stiripentol should be a good candidate for therapeutic drug monitoring (TDM). Nonetheless, the current level of evidence for the advantage of TDM is "remains to be estimated".

Midazolam versus diazepam for the treatment of status epilepticus in children and young adults: a meta-analysis

BACKGROUND

Rapid treatment of status epilepticus (SE) is associated with better outcomes. Diazepam and midazolam are commonly used, but the optimal agent and administration route is unclear.

OBJECTIVES

The objective was to determine by systematic review if nonintravenous (non-IV) midazolam is as effective as diazepam, by any route, in terminating SE seizures in children and adults. Time to seizure cessation and respiratory complications was examined.

METHODS

We performed a search of PubMed, Web of Knowledge, Embase, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, American College of Physicians Journal Club, Cochrane Central Register of Controlled Trials, the Cumulative Index to Nursing and Allied Health Literature, and International Pharmaceutical Abstracts for studies published January 1, 1950, through July 4, 2009. English language quasi-experimental or randomized controlled trials comparing midazolam and diazepam as first-line treatment for SE, and meeting the Consolidated Standards of Reporting Trials (CONSORT)-based quality measures, were eligible. Two reviewers independently screened studies for inclusion and extracted outcomes data. Administration routes were stratified as non-IV (buccal, intranasal, intramuscular, rectal) or IV. Fixed-effects models generated pooled statistics.

RESULTS

Six studies with 774 subjects were included. For seizure cessation, midazolam, by any route, was superior to diazepam, by any route (relative risk [RR] = 1.52; 95% confidence interval [CI] = 1.27 to 1.82). Non-IV midazolam is as effective as IV diazepam (RR = 0.79; 95% CI = 0.19 to 3.36), and buccal midazolam is superior to rectal diazepam in achieving seizure control (RR = 1.54; 95% CI = 1.29 to 1.85). Midazolam was administered faster than diazepam (mean difference = 2.46 minutes; 95% CI = 1.52 to 3.39 minutes) and had similar times between drug administration and seizure cessation. Respiratory complications requiring intervention were similar, regardless of administration route (RR = 1.49; 95% CI = 0.25 to 8.72).

CONCLUSIONS

Non-IV midazolam, compared to non-IV or IV diazepam, is safe and effective in treating SE. Comparison to lorazepam, evaluation in adults, and prospective confirmation of safety and efficacy is needed.

Interactions of stiripentol with clobazam and valproate in the mouse maximal electroshock-induced seizure model

The aim of this study was to characterize the anticonvulsant effects of stiripentol (STP) in combination with clobazam [CLB], and valproate [VPA]) in the mouse maximal electroshock (MES)-induced seizure model using the type I isobolographic analysis for parallel and non-parallel dose-response relationship curves (DRRCs). Potential adverse-effect profiles of interactions of STP with CLB and VPA at the fixed-ratio of 1:1 in the MES test with respect to motor performance, long-term memory and skeletal muscular strength were measured along with total brain antiepileptic drug concentrations. In the mouse MES model, STP administered singly had its DRRC non-parallel to that for CLB and, simultaneously, parallel to that for VPA. With type I isobolography for parallel DRRCs, the combinations of STP with VPA at three fixed-ratios of 1:3, 1:1 and 3:1 exerted sub-additive (antagonistic) interaction. Isobolography for non-parallel DRRCs revealed that the combination of STP with CLB at the fixed-ratio of 1:1 produced additive interaction. For all combinations, neither motor coordination, long-term memory nor muscular strength was affected. Total brain antiepileptic drug concentrations revealed bi-direction changes with the most profound being an 18.6-fold increase in CLB by STP and a 2.3-fold increase in STP by VPA. In conclusion, the additive interaction between STP and CLB was associated with a concurrent pharmacokinetic interaction and these data may explain the clinical efficacy seen with this combination. In contrast, the antagonism between STP and VPA was surprising since synergism is observed clinically.

Intravenous midazolam in convulsive status epilepticus in children with pharmacoresistant epilepsy

Although the efficacy of midazolam in refractory status epilepticus and as a first-line agent in children with established status epilepticus has been reported, differences in starting doses, continuation method, timing of efficacy assessment, and discontinuation pose limitations in deriving a specific protocol for midazolam use. An audit of clinical experience with a protocol of midazolam as first-line agent for impending status epilepticus (defined as a continuous, generalized, convulsive seizure lasting >5 minutes) in 76 episodes of unprovoked convulsive status epilepticus in children 1-15 years old with treatment-refractory epilepsy demonstrated that: (1) repeated bolus midazolam 0.1mg/kg (every 5 minutes, maximum 5) controlled 91% of events; (2) three bolus doses controlled 89% of the episodes, with minimal chance of response beyond that; (3) treating impending status resulted in lower doses (mean 0.17 mg/kg) than reported and infrequent utilization of additional anticonvulsants (9%); and (4) adverse events were infrequent (respiratory depression 13%, assisted ventilation 3%).

Characterization of the Anticonvulsant, Behavioral and Pharmacokinetic Interaction Profiles of Stiripentol in Combination with Clonazepam, Ethosuximide, Phenobarbital, and Valproate Using Isobolographic Analysis

PURPOSE

Isobolographic analysis was used to characterize the interactions between stiripentol (STP) and clonazepam (CZP), ethosuximide (ETS), phenobarbital (PB), and valproate (VPA) in suppressing pentylenetetrazole (PTZ)-induced clonic seizures in mice.

METHODS

The anticonvulsant and acute adverse (neurotoxic) effects of STP in combination with the various conventional antiepileptic drugs (AEDs), at fixed ratios of 1:3, 1:1, and 3:1, were evaluated in the PTZ and chimney tests in mice using the isobolographic analysis. Additionally, protective indices (PI) and benefit indices (BI) were calculated to identify their pharmacological profiles so that a ranking in relation to advantageous combination could be established. Moreover, adverse-effect paradigms were determined by use of the step-through passive avoidance task (long-term memory), threshold for the first pain reaction, grip-strength test (neuromuscular tone), and the hot plate test (acute thermal pain). Brain AED concentrations were also measured so as to ascertain any pharmacokinetic contribution to the pharmacodynamic interactions.

RESULTS

All AED combinations comprising of STP and CZP, ETS, PB, and VPA (at the fixed ratios of 1:3, 1:1 and 3:1) were additive in terms of clonic seizure suppression in the PTZ test. However, these interactions were complicated by changes in brain AED concentrations consequent to pharmacokinetic interactions. Thus STP significantly increased total brain ETS and PB concentrations, and decreased VPA concentrations, but was without effect on CZP concentrations. In contrast, PB significantly decreased and VPA increased total brain STP concentrations while CZP and ETS were without effect. Furthermore, while isobolographic analysis revealed that STP and CZP in combination, at the fixed ratios of 1:1 and 3:1, were supraadditive (synergistic; p < 0.05), the combinations of STP with CZP (1:3), ETS, PB, or VPA (at all fixed ratios of 1:3, 1:1, and 3:1) were barely additivity in terms of acute neurotoxic adverse effects in the chimney test. Additionally, none of the examined combinations of STP with conventional AEDs (CZP, ETS, PB, VPA--at their median effective doses from the PTZ-test) affected long-term memory, threshold for the first pain reaction, neuromuscular tone, and acute thermal pain.

CONCLUSIONS

Based on BI values, the combination of STP with PB at the fixed ratio of 1:3 appears to be a particularly favourable combination. In contrast, STP and CZP or ETS (at the fixed ratios of 1:1 and 3:1) were unfavorable combinations. However, these conclusions are confounded by the fact that STP is associated with significant pharmacokinetic interactions. The remaining combinations of STP with PB (1:1 and 3:1), CZP (1:3), ETS (1:3), and VPA (at all fixed ratios of 1:3, 1:1, and 3:1) do not appear to be potential favorable AED combinations.

Animal models for the development of new neuropharmacological therapeutics in the status epilepticus

Status epilepticus (SE) is a major medical emergency associated with significant morbidity and mortality. SE is best defined as a continuous, generalized, convulsive seizure lasting > 5 min, or two or more seizures during which the patient does not return to baseline consciousness. The relative efficacy and safety of different drugs in the treatment of human SE should be determined in a prospective, randomized, blinded study. However, complementary animal models of SE are required to answer important questions concerning the treatment of SE because of the obvious difficulties of setting up such studies in clinical emergency conditions. This review offers an overview of the implementation and characteristics of some of the most prevalent animal models of SE currently in use. A description is also provide about how animal models of SE may facilitate the use of neurobiological techniques to successfully address critical questions in the drug treatment of SE. In particular, the experience with recently introduced drugs such as intravenous valproate will be addressed. Finally, the importance of some animal models and pharmacological approaches is explained and we discuss their impact in the development of therapeutic strategies to improve pharmacological treatment for SE is discussed.

Neuroprotection for ischemic stroke: two decades of success and failure

Alteplase (rt-PA) is the first therapy successfully developed for acute stroke therapy. The success of rt-PA spurred development of new avenues for acute stroke management. For the last two decades, a great deal of attention has been paid to neuroprotective therapies. Initial preclinical studies demonstrated numerous drugs are effective for treating acute stroke in animal models; however, subsequent clinical trials have been frustrating, and none of the agents has proven effective. The various outcomes of preclinical and clinical trials have been the subject of much discussion. In this article, we review some key neuroprotective trials and the possible reasons for their failures. By identifying the discrepancies between preclinical studies and clinical trials, we may be able to set guidelines for future effective trials.

Flunarizine: a possible adjuvant medication against soman poisoning?

Organophosphate (OP) nerve agents are amongst the most toxic chemicals. One of them, soman, can induce severe epileptic seizures and brain damage for which therapy is incomplete. The present study shows that pretreatment with flunarizine (Flu), a voltage-dependent calcium channel blocker, when used alone, does not produce any beneficial effect against the convulsions, neuropathology and lethality induced by soman. Flu was also tested in combination with atropine sulfate and diazepam. In this case, although only some results reach statistical significance, an encouraging general trend toward an improvement of the anticonvulsant, neuroprotective and antilethal capacities of this classical anti-OP two-drug regimen is constantly observed. In the light of these findings, it seems premature to definitely reject (or recommend) Flu as a possible adjuvant medication against soman poisoning. Further studies are required to determine its real potential interest.

Anticonvulsant profile of flunarizine and relation to Na(+) channel blocking effects

The present study will summarize our findings concerning the anticonvulsant properties of the Ca2+ channel blocker flunarizine in a variety of experimental models of epilepsy. Flunarizine exhibits anticonvulsant effects against tonic seizures induced by electroshock or various chemoconvulsants in mice, however, did not protect against pentylenetetrazol-induced clonic seizures. In the MES test, the efficacy of clinically established antiepileptics was increased by co-medication. In the rotarod test, a minimal "neurotoxic" dose (TD50) of 18.0 mg/kg intraperitoneally was determined. In models of complex partial seizures like the hippocampal stimulation and the amygdala kindling in rats, flunarizine showed only a moderate activity. Thus, it can be suggested that the anticonvulsant potency of flunarizine in various screening tests is lower than that of standard antiepileptics such as carbamazepine and phenytoin. Concerning the possible mode of action, whole-cell patch-clamp experiments with cultured neonatal rat cardiomyocytes showed that flunarizine depressed the fast inward Na+ current in a concentration- and frequency-dependent manner well comparable with the action of phenytoin. It is concluded that the use-dependent inhibition of voltage-dependent Na+ channels may essentially contribute to the anticonvulsant activity of flunarizine in models for generalized tonic-clonic seizures. The clinical efficacy as add-on therapy is critically discussed in view of the present data.

New antiepileptic drugs

BACKGROUND

Eight novel anticonvulsant drugs have been introduced in the United States in the past 10 years, as well as two new intravenous preparations of anticonvulsant drugs. The role of each in the treatment of patients with epilepsy is being refined as experience and research data accumulate.

REVIEW SUMMARY

Gabapentin, tiagabine, and oxcarbazepine are effective for partial seizures, whereas felbamate, lamotrigine, topiramate, levetiracetam, and zonisamide treat both partial and generalized seizure types. In general, these newer agents differ from older agents by relative lack of drug-drug interactions, and many show improved tolerability compared with phenytoin and carbamazepine. Each has distinguishing features that can prove useful in specific clinical situations. Despite limited Food and Drug Administration indications, all are useful in monotherapy under certain circumstances. Fosphenytoin avoids the adverse effects of intravenous phenytoin vehicle, and intravenous valproate represents a much needed option in patients who require rapid loading of this medication.

CONCLUSIONS

The greater number of antiseizure drugs available today makes it possible to tailor treatment to individual patient needs, allowing more patients to be free of debilitating adverse effects. Additionally, some patients can achieve complete seizure freedom even after failing one or more other antiepileptic drugs.

Treatment of refractory status epilepticus with pentobarbital, propofol, or midazolam: a systematic review

BACKGROUND

New continuous infusion antiepileptic drugs (cIV-AEDs) offer alternatives to pentobarbital for the treatment of refractory status epilepticus (RSE). However, no prospective randomized studies have evaluated the treatment of RSE. This systematic review compares the efficacy of midazolam (MDL), propofol (PRO), and pentobarbital (PTB) for terminating seizures and improving outcome in RSE patients.

METHODS

We performed a literature search of studies describing the use of MDL, PRO, or PTB for the treatment of RSE published between January 1970 and September 2001, by using MEDLINE, OVID, and manually searched bibliographies. We included peer-reviewed studies of adult patients with SE refractory to at least two standard AEDs. Main outcome measures were the frequency of immediate treatment failure (clinical or electrographic seizures occurring 1 to 6 h after starting cIV-AED therapy) and mortality according to choice of agent and titration goal (cIV-AED titration to "seizure suppression" versus "EEG background suppression").

RESULTS

Twenty-eight studies describing a total of 193 patients fulfilled our selection criteria: MDL (n = 54), PRO (n = 33), and PTB (n = 106). Forty-eight percent of patients died, and mortality was not significantly associated with the choice of agent or titration goal. PTB was usually titrated to EEG background suppression by using intermittent EEG monitoring, whereas MDL and PRO were more often titrated to seizure suppression with continuous EEG monitoring. Compared with treatment with MDL or PRO, PTB treatment was associated with a lower frequency of short-term treatment failure (8 vs. 23%; p < 0.01), breakthrough seizures (12 vs. 42%; p < 0.001), and changes to a different cIV-AED (3 vs. 21%; p < 0.001), and a higher frequency of hypotension (systolic blood pressure <100 mm Hg; 77 vs. 34%; p < 0.001). Compared with seizure suppression (n = 59), titration of treatment to EEG background suppression (n = 87) was associated with a lower frequency of breakthrough seizures (4 vs. 53%; p < 0.001) and a higher frequency of hypotension (76 vs. 29%; p < 0.001).

CONCLUSIONS

Despite the inherent limitations of a systematic review, our results suggest that treatment with PTB, or any cIV-AED infusion to attain EEG background suppression, may be more effective than other strategies for treating RSE. However, these interventions also were associated with an increased frequency of hypotension, and no effect on mortality was seen. A prospective randomized trial comparing different agents and titration goals for RSE with obligatory continuous EEG monitoring is needed.

Clinical review: status epilepticus

Status epilepticus (SE) has an annual incidence exceeding 100,000 cases in the United States alone, of which more than 20% result in death. Thus, increased awareness of presentation, etiologies, and treatment of SE is essential in the practice of critical care medicine. This review discusses current definitions of SE, as well as its clinical presentation and classification. The recent literature on epidemiology is reviewed, including morbidity and mortality data. An overview of the systemic pathophysiologic effects of SE is presented. Finally, significant studies on the treatment of acute SE and refractory SE are reviewed, including the use of anticonvulsants, such as benzodiazepines, and other drugs.

Treatment of epilepsy in the multiply handicapped

The medical management of epilepsy in the multi-handicapped patient requires careful evaluation, classification, and pharmacologic treatment. It is estimated that 20-40% of patients with mental retardation and cerebral palsy have epilepsy. This review reports the clinical trial data and personal experience related to the use of newer AEDs in the chronic management of epilepsy syndromes in children and adults, as well as information available on the treatment of seizures in individuals with mental retardation and associated handicaps. Furthermore, clusters of seizures, prolonged seizures and status epilepticus are more commonly seen in the multiply handicapped and mentally retarded population and require special attention. The new antiepileptic drugs felbamate, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin and zonisamide show specific advantage in some multiply handicapped patients, be it for seizure control or medication tolerance. Furthermore, new modalities of treatment for prolonged seizures allow better efficacy both outside of hospital and within hospital facilities. The treatment of epilepsy in multi-handicapped and retarded adults and children has significantly advanced in the past few years, and much of this improvement can be attributed to improved knowledge and monitoring of new antiepileptic drugs. Conventional anticonvulsants remain first line therapy for most clinicians, but newer AEDs must broaden the therapeutic option and do allow improved therapy for some multiply handicapped patients.

Management approaches to prolonged seizures and status epilepticus

Status epilepticus (SE) treatment should proceed on four fronts: termination of SE, prevention of recurrence, management of potential precipitating causes, and management of SE complications and underlying conditions. The intensity of the treatment should reflect the risk to the patient from SE, and drugs likely to depress respiration and blood pressure should initially be avoided. The Veterans Administration cooperative trial showed that when treating overt SE, first-line treatment success rates were: lorazepam 64.9%; phenobarbital 58.2%; diazepam/phenytoin 55.8%; and phenytoin alone 43.6%. The aggregate response rate to second-line agents for patients who did not respond to first-line agents was 7.0%, and it was 2.3% for third-line agents, raising the question of the efficacy of a second and third drug. The recommended treatment for generalized convulsive SE is to begin with lorazepam. As a second-line agent, phenytoin or fosphenytoin, is still recommended if SE control is not achieved within 5 to 7 min. Fosphenytoin achieves a free phenytoin level of about 2 micro/mL in 15 min, as opposed to 25 min with phenytoin itself. Moreover, fosphenytoin is safer and, despite higher cost, it may be cost-effective. High-dose barbiturates, high-dose benzodiazepines, and propofol are employed for major treatment for refractory SE. Patients at this stage should undergo continuous electroencephalogram monitoring. Once SE is controlled, prevention of seizure recurrence should be individualized to each patient. The major complications of generalized convulsive SE (GCSE), rhabdomyolysis and hyperthermia, should be watched for and treated.

Inhibition of mouse mast cell proliferation and proinflammatory mediator release by benzodiazepines

Mast cell (MC) activation may occur in vitro and in vivo following stimulation with various immunologic or nonimmunologic agents. Such activation leads to the release of several biological mediators, including vasoactive amines, nitric oxide and cytokines, which account for the adverse effects observed during allergic reactions. While high affinity binding sites for benzodiazepines (BZDs) have been reported on MC, the effects of the ligation of these receptors on the proliferation of, and the mediator release from, these cells are poorly documented. In the present work, we have examined the effects of midazolam and of diazepam on the proliferation of mucosal (MMC)-like and of serosal (CTMC)-like mouse MC. In addition, we have studied the effects of these BZDs on beta-hexosaminidase, TNF-alpha and nitrite release induced from mouse mast cells through IgE receptor activation. We demonstrated that each of the two BZDs studied inhibited the proliferation of MMC- and CTMC-like elements in a dose-dependent fashion (10 to 100 microM). Furthermore, the BZDs inhibited the IgE-mediated release of beta-hexosaminidase, TNF-alpha and nitrites from MMC- or CTMC-like cells. Altogether, these data provide new insights into the pharmacological regulation of MC activation and may lead to the discovery of new and potent antiallergic compounds.

Midazolam and pentobarbital for refractory status epilepticus

Status epilepticus, a serious, life-threatening emergency characterized by prolonged seizure activity, occurs most commonly in pediatric patients. Although initial therapies with agents such as diazepam, phenytoin, or phenobarbital generally terminate seizure activity within 30-60 minutes, patients with refractory status epilepticus (RSE) lasting longer require additional intervention. High-dose pentobarbital has been the most commonly prescribed agent for the management of RSE in children; however, midazolam has emerged as a new treatment option. This review compares the use of midazolam with pentobarbital in published reports of pediatric RSE. Both drugs effectively terminated refractory seizure activity, although pentobarbital use was complicated by hypotension, delayed recovery, pneumonia, and other adverse effects. Midazolam use was effective and well tolerated, affirming its value in pediatric RSE management.

Pharmacological interaction of the calcium channel blockers verapamil and flunarizine with the opioid system

We evaluated the opioid antinociceptive mechanism of the calcium channel blockers verapamil and flunarizine in groups of mice with the hotplate test. Both produced a naloxone-sensitive dose-dependent analgesia. The antinociceptive effect of both was reversed by beta-FNA, (mu1 and mu2 antagonists), and both enhanced the antinociceptive activity of morphine, implying a role for mu receptors. Furthermore, since the analgesic effect of flunarizine, but not verapamil, was reversed by naloxonazine (mu1 antagonist), we suggest that the mu1 subtype is involved in flunarizine analgesia, but not in verapamil analgesia. Studies with the selective delta opioid agonist DPDPE and the selective antagonists naltrindole indicated that the antinociceptive activity of verapamil is also mediated by delta receptor agonistic activity (primarily following i.c.v. administration); flunarizine, by contrast, exhibited antagonistic activity at this receptor. Verapamil amplified the antinociceptive activity of kappa1 (U50,488H) and kappa3 (nalorphine) agonists, but its known analgesic activity was inhibited only partially by the kappa1 antagonist Nor-BNI, indicating partial involvement of kappa1 receptor. Flunarizine, however, demonstrated antagonistic activity at both kappa1 and kappa3 receptors, with more prominent inhibitory activity at the latter one. These findings suggest that verapamil and flunarizine elicit analgesia at both the spinal and supraspinal levels. Verapamil's analgesia was explained by agonistic activity at the mu, delta and may also be kappa3 receptor subtypes. Flunarizine exhibited a mixed agonistic-antagonistic opioid activity as shown by its agonistic activity at the mu1 receptor and antagonistic activity at delta, kappa1 and kappa3 receptor subtypes.

Use of midazolam in the treatment of refractory status epilepticus

Status epilepticus is an epileptic seizure that lasts at least 30 minutes or is repeated at sufficiently brief intervals to produce a continued epileptic condition lasting a total of 30 minutes without the patient fully regaining consciousness. Various combinations of anticonvulsant agents, including benzodiazepines, phenytoin, and phenobarbital, have been used to manage this condition. However, at least 9% of patients with generalized convulsive status epilepticus do not respond to conventional first-line agents, and additional intervention is required. Refractory status epilepticus refers to sustained seizures that do not respond to initial drug therapy and persist longer than 60 minutes. Reports on the response to first- and second-line agents suggest that the incidence of refractory status epilepticus is between 2000 and 6000 cases per year in the United States. Refractory status epilepticus is a major medical and neurologic emergency that requires immediate treatment to avoid significant morbidity and mortality. The anticonvulsive agent midazolam has proved to be effective, well tolerated, and fast acting when used to treat refractory status epilepticus in both adults and children. Its pharmacodynamic effects can be seen within 1 to 5 minutes of administration, and its anticonvulsive effects are apparent as early as 5 to 15 minutes after administration. This article reviews the pharmacology of midazolam and recent clinical reports on the drug's tolerability and effectiveness in the treatment of patients with refractory status epilepticus.

Electrophysiological effects of felbamate

Felbamate is a broad spectrum antiepileptic drug recently introduced into clinical practice for controlling seizures in patients affected by Lennox-Gastaut epilepsy, complex partial seizures or otherwise intractable epilepsies. However, the cellular mechanisms by which the drug exerts its anticonvulsant actions are not fully understood. The aim of the present article is to outline the possible mechanisms of action of felbamate as suggested by findings obtained with electrophysiological approaches.

Phenytoin blocks the reversal of a classically conditioned discriminative eyeblink response in rabbits

PURPOSE

Cognitive deficits associated with chronic treatment with phenytoin (PHT) have been reported. PHT blocks transfer from a signaled appetitive bar press to an active avoidance response in rats. We investigated the effects of PHT and the prodrug fosphenytoin in rabbits required to learn a discrimination and reversal of a classical eyeblink conditioning paradigm.

METHODS

Before drug treatment was started, rabbits were trained to produce a discriminated eyeblink response. PHT (n = 7) was administered centrally or the prodrug fosphenytoin (n = 2) was given systemically. Control animals were similarly treated centrally with either saline (n = 3) or no drug treatment (n = 13). Rabbits were then challenged with a stimulus reversal while being maintained on the respective drug.

RESULTS

On the first day of reversal training, control animals typically displayed high response rates to both tones, followed by a reduction in responsiveness to the new conditioned stimulus (CS-) in the ensuing days. In contrast, PHT-treated animals failed to suppress responsiveness to the new CS-.

CONCLUSIONS

The response patterns observed are similar to those observed in rabbits with hippocampal ablations, leading us to suggest that the adverse effects of phenytoin may be due to actions in the hippocampus.

Calcium channels in neurological disease

Channels involved in the influx and intracellular mobilization of calcium have been implicated as targets of diverse genetic and immune-mediated neurological diseases. These include the L-type voltage-gated calcium channel of skeletal muscle (hypokalemic periodic paralysis), the neuronal P/Q-type voltage-gated calcium channel (familial hemiplegic migraine, episodic ataxia type 2, spinocerebellar ataxia 6, and Lambert-Eaton myasthenic syndrome), and the skeletal muscle ryanodine receptor (malignant hyperthermia and central core disease). The discovery of these and other calcium channelopathies should help to clarify how different mutations affect channel function and how altered channel function produces disease, and may lead to new treatments for these conditions.

Status epilepticus in children and adults

Status epilepticus (SE) in children and adults is one of the most common neurology problems confronting the intensivist. Recognition of SE is usually straightforward, but may be complicated by the effects of other diseases or therapies. Emergent treatment is necessary to prevent further brain damage. This article reviews protocols for standard treatments of SE patients and includes recommendations for the management of refractory SE.

Recent advances in the pharmacotherapy of epilepsy

The therapeutic options for the treatment of epilepsy have expanded during the 1990s. Since 1993, four novel agents (felbamate, gabapentin, lamotrigine, and topiramate) have been approved by the US Food and Drug Administration, primarily for adjunctive treatment of partial seizures. In addition, a water-soluble pro-drug of phenytoin, fosphenytoin, and a sustained-release preparation of carbamazepine have been introduced. The novel anticonvulsants represent a potential improvement for patients whose seizures are incompletely controlled or who experience significant adverse effects with older anticonvulsants. Felbamate, lamotrigine, and topiramate appear to have a broad spectrum of action in seizure control, but felbamate use is limited by the potential for serious adverse effects. Gabapentin, lamotrigine, and topiramate are all well tolerated. Gabapentin has no known drug interactions, whereas lamotrigine and topiramate have limited interactions compared with older agents. The sustained-release preparation of carbamazepine may decrease the incidence of adverse effects and increase patient compliance. Fosphenytoin offers a safer method for intravenous administration of phenytoin and the added flexibility of intramuscular administration. Taken together, these recent advances in treatment may bring about improved efficacy and decreased adverse effects for many patients with epilepsy.

The new generation of antiepileptic drugs: advantages and disadvantages

1. After a hiatus of over 20 years, several new antiepileptic drugs (vigabatrin, lamotrigine, gabapentin, oxcarbazepine, topiramate, felbamate, zonisamide and tiagabine) have reached or approached the registration phase. 2. Compared with older agents, many new drugs exhibit simpler pharmacokinetics. This is especially true for vigabatrin and gabapentin, which are renally eliminated and have a low interaction potential. 3. Unlike most of the older agents, vigabatrin, lamotrigine, gabapentin and tiagabine are devoid of significant enzyme inducing or inhibiting properties. Topiramate, oxcarbazepine and felbamate may induce the metabolism of steroid oral contraceptives. In addition, felbamate also acts as a metabolic inhibitor. 4. To date, the efficacy of new drugs has been evaluated extensively only under add-on conditions in patients with partial seizures (with or without secondary generalization) refractory to conventional treatment. However, there is evidence that lamotrigine, zonisamide, felbamate and, possibly, topiramate may also be effective in generalized epilepsies. 5. In placebo-controlled studies, typically between 15 and 40% of patients with difficult-to-treat partial epilepsy have shown an improvement (defined as a 50% or greater decrease in seizure frequency) after addition of a new drug. Only a small minority of these patients achieved complete seizure control. 6. Compared with older agents, some of the new drugs may have a better tolerability profile. Felbamate, however, has been associated with a high risk of aplastic anaemia and hepatotoxicity. 7. At present, the main use of the new agents is in patients refractory to first-line drugs such as carbamazepine or valproate, and further studies are required to characterize their activity spectrum as well as their potential value in monotherapy. In most patients, new drugs cannot be recommended for first-line use until evidence is obtained that potential advantages in tolerability or ease of use outweigh the drawback of their high cost.

Bioavailability and anticonvulsant activity of 2-cyanoguanidinophenytoin, a structural analogue of phenytoin

Phenytoin is extensively used in Europe and the United States for the treatment of generalized tonic clonic seizures (grand mal). However, the efficacy is lowered by the erratic bioavailability after oral administration. The current study was conducted in order to investigate the physicochemical properties, the bioavailability, and the anticonvulsant activity of cyanoguanidinophenytoin (CNG-DPH), a structural analogue of phenytoin, which was obtained by the replacement of the urea moiety by a cyanoguanidine moiety. CNG-DPH was prepared under homogeneous Biltz conditions and under heterogeneous phase-transfer conditions. CNG-DPH is poorly water soluble and has a pKa of 5.3. At pH 7.4, log P was 1.16, from which a pH-independent log P of 3 can be calculated. Pharmacokinetic parameters were obtained after oral administration of CNG-DPH to rats and were compared to those of phenytoin after administration of an equimolar amount. AUC, tmax, and Cmax were significantly increased compared to those of phenytoin. The anticonvulsant profile was similar to the profile of phenytoin. CNG-DPH was active in the maximal electroshock seizure test, albeit 7-fold less active than phenytoin. The analogue did not protect animals against convulsions induced by chemicals such as pentylenetetrazole, picrotoxin, N-methyl-aspartate, strychnine, and bicuculline. It is concluded that while the bioisosteric exchange of the urea moiety of the molecule with the cyanoguanidine moiety dramatically changed the physicochemical and pharmacokinetic parameters compared to those of phenytoin, the concomitant change of the affinity toward molecular targets reduced the pharmacological activity and the therapeutic efficacy of the compound.

Pharmacokinetic interactions of the new antiepileptic drugs

Therapy with traditional antiepileptic drugs is associated with a wide range of pharmacokinetic drug-drug interactions. In particular, enzyme induction, enzyme inhibition and displacement from protein binding may result in important changes in serum concentrations of antiepileptics. Relevant interactions have also been described for some new antiepileptics. Felbamate increases serum concentrations of phenytoin, phenobarbital and valproic acid (sodium valproate). On the other hand, it reduces concentrations of carbamazepine and increases concentrations of its metabolite carbamazepine-10,11-epoxide. Concentrations of felbamate itself are reduced by phenytoin and carbamazepine. Concentrations of lamotrigine are considerably increased by valproic acid and decreased by phenytoin, carbamazepine and phenobarbital (phenobarbitone). Vigabatrin reduces serum concentrations of phenytoin by approximately 20%. On the other hand, some new antiepileptics have the important advantage of not interfering with the metabolism of other antiepileptics; this is the case for gabapentin, lamotrigine and oxcarbazepine. Furthermore, the pharmacokinetics of gabapentin, oxcarbazepine and vigabatrin are independent of concomitant drugs. These aspects are especially important as, until now, new antiepileptics have been most often utilised as add-on therapy.

The clinical pharmacokinetics of the newer antiepileptic drugs. Focus on topiramate, zonisamide and tiagabine

Following the introduction of felbamate, gabapentin, lamotrigine, oxcarbazepine and vigabatrin in the early 1990s, other new antiepileptic drugs have been advancing in clinical development. Those most extensively evaluated to date include topiramate, zonisamide and tiagabine. Topiramate, licensed recently in the UK, acts multifactorially through the blockade of sodium channels and kainate/AMPA receptors, enhancement of gamma-aminobutyric acid (GABA)ergic transmission and inhibition of carbonic anhydrase. It is well absorbed from the gastrointestinal tract and negligibly bound to plasma proteins. When used as a monotherapy, topiramate is eliminated primarily in the urine in an unchanged form with a half-life of 20 to 30 hours; elimination is faster in patients receiving concurrent medication with enzyme-inducing anticonvulsants, in whom the extent of biotransformation becomes more prominent. Zonisamide, which has been commercially available in Japan for some years, also has a multifactorial mode of action, possibly involving the blockade of sodium channels, T-type calcium channels and inhibition of carbonic anhydrase. It is rapidly absorbed, 50% bound to plasma proteins and is eliminated predominantly by biotransformation; zonisamide has a half-life of 50 to 70 hours in monotherapy patients, or 25 to 35 hours in patients comedicated with enzyme-inducing anticonvulsants. Tiagabine, a nipecotic acid derivative which inhibits GABA reuptake, is rapidly and completely absorbed after oral intake. It is highly (96%) bound to plasma proteins and it is eliminated primarily by cytochrome P450 3A-mediated oxidation, with a half-life of about 7 hours in healthy volunteers. Tiagabine metabolism is also enhanced by concurrent medication with enzyme-inducing anticonvulsants, resulting in a need to use dosages larger than those required in monotherapy or valproic acid (sodium valproate)-treated patients. Additional investigational antiepileptic agents included in this article are rufinamide (CGP 33101), fosphenytoin, levetiracetam, losigamone, remacemide and stiripentol. All these drugs have undergone early characterisation with respect to pharmacokinetic features and interaction potential.

Status epilepticus and acute repetitive seizures in children, adolescents, and young adults: etiology, outcome, and treatment

Status epilepticus (SE) is one of the most common neurologic emergencies in children, adolescents, and young adults. SE may be due to acute neurologic conditions such as meningitis, encephalitis, or stroke, complicated febrile seizures, intractable epilepsy, degenerative diseases, intoxication, or may be the first manifestation of epilepsy. Initial treatment of convulsive SE is usually with an intravenous benzodiazepine (BZD) [lorazepam (LZP) or diazepam (DZP)], phenobarbital (PB), or phenytoin (PHT). LZP is less likely to cause respiratory depression than DZP and is therefore preferred. Sequelae and risk for recurrence of SE are primarily related to the underlying cause. Refractory SE (RSE) is most often symptomatic of an acute neurologic condition or neurodegenerative disease. Treatment for RSE is difficult, usually requiring intensive support of vital functions. Reported treatments for RSE include very high dose PB, continuous infusions of pentobarbital or BZDs (DZP, midazolam), lidocaine, inhalation anesthesia, and propofol. Outcome is related to underlying cause. Nonconvulsive SE may present as confusion or may mimic psychiatric illness. Response to BZDs is usually rapid but may not be sustained. Rapid initiation of oral or rectal valproate may be useful. Epilepsia partialis continua (EPC) is almost always due to an acute or chronic destructive lesion. Surgical treatment may be the only effective modality in some children with EPC. Acute treatment of breakthrough seizures and clusters of seizures at home with rectal BZDs (usually DZP, 0.2-0.5 mg/kg) may prevent progression to SE in some children and adolescents and reduce the need for visits to emergency facilities.

Flunarizine of limited value in children with intractable epilepsy

Fourteen ambulatory children and adolescents with intractable epilepsy were studied in an open phase II study to investigate the pharmacokinetics and pharmacodynamics of flunarizine as an add-on treatment. Flunarizine was given in increasing doses starting with 0.1-0.3 mg/kg/day until effect was observed or a steady-state plasma concentration of 50-60 ng/ml was reached. Treatment was continued for 3 months at steady state. Pharmacokinetics were determined during the immediate posttreatment period. Positive antiepileptic effect (> or = 50% reduction in seizure frequency) was observed in 4 of 14 patients (29%; 95% CI: 52-5). Independently of antiepileptic effect, 10 of 14 parents (71.4%; 95% CI: 95-48) observed positive cognitive effects. In all patients treatment was withdrawn due to either lack of effect or weight gain. Flunarizine was rapidly absorbed; mean time of peak concentration (Tmax) was 2.7 hours (range: 1-8). The mean terminal half-life was 23.2 days (range: 7-48), the total plasma clearance of flunarizine per fraction of the dose absorbed (CLp/F) was 0.28 ml/min/kg (range: 0.07-042), and the volume of distribution of flunarizine per fraction of the dose absorbed (Vd/F) was 187 L/kg (range: 99-348). We conclude that flunarizine (0.1-0.3 mg/kg/day) seems to be of limited antiepileptic value in children with intractable epilepsy. The pharmacokinetic profile of flunarizine complicates its clinical use.