Valproic acid and diazepam interaction in vivo

Predictors of valproic acid steady-state serum levels in adult and pediatric psychiatric inpatients: a comparative analysis

RATIONALE

Valproic acid (VPA) is commonly used as a second-line mood stabilizer or augmentative agent in severe mental illnesses. However, population pharmacokinetic studies specific to psychiatric populations are limited, and clinical predictors for the precision application of VPA remain undefined.

OBJECTIVES

To identify steady-state serum VPA level predictors in pediatric/adolescent and adult psychiatric inpatients.

METHODS

We analyzed data from 634 patients and 1,068 steady-state therapeutic drug monitoring (TDM) data points recorded from 2015 to 2021. Steady-state VPA levels were obtained after tapering during each hospitalization episode. Electronic patient records were screened for routine clinical parameters and co-medication. Generalized additive mixed models were employed to identify independent predictors.

RESULTS

Most TDM episodes involved patients with psychotic disorders, including schizophrenia (29.2%) and schizoaffective disorder (17.3%). Polypharmacy was common, with the most frequent combinations being VPA + quetiapine and VPA + promethazine. Age was significantly associated with VPA levels, with pediatric/adolescent patients (< 18 years) demonstrating higher dose-adjusted serum levels of VPA (β = 7.6±2.34, p < 0.001) after accounting for BMI. Women tended to have higher adjusted VPA serum levels than men (β = 5.08±1.62, p < 0.001). The formulation of VPA (Immediate-release vs. extended-release) showed no association with VPA levels. Co-administration of diazepam exhibited a dose-dependent decrease in VPA levels (F = 15.7, p < 0.001), suggesting a potential pharmacokinetic interaction.

CONCLUSIONS

This study highlights the utility of population-specific pharmacokinetic data for VPA in psychiatric populations. Age, gender, and co-administration of diazepam were identified as predictors of VPA levels. Further research is warranted to establish additional predictors and optimize the precision application of VPA in psychiatric patients.

Pharmacokinetic Interactions Between Antiseizure and Psychiatric Medications

Antiseizure medications and drugs for psychiatric diseases are frequently used in combination. In this context, pharmacokinetic interactions between these drugs may occur. The vast majority of these interactions are primarily observed at a metabolic level and result from changes in the activity of the cytochrome P450 (CYP). Carbamazepine, phenytoin, and barbiturates induce the oxidative biotransformation and can consequently reduce the plasma concentrations of tricyclic antidepressants, many typical and atypical antipsychotics and some benzodiazepines. Newer antiseizure medications show a lower potential for clinically relevant interactions with drugs for psychiatric disease. The pharmacokinetics of many antiseizure medications is not influenced by antipsychotics and anxiolytics, while some newer antidepressants, namely fluoxetine, fluvoxamine and viloxazine, may inhibit CYP enzymes leading to increased serum concentrations of some antiseizure medications, including phenytoin and carbamazepine. Clinically relevant pharmacokinetic interactions may be anticipated by knowledge of CYP enzymes involved in the biotransformation of individual medications and of the influence of the specific comedication on the activity of these CYP enzymes. As a general rule, these interactions can be managed by careful evaluation of clinical response and, when indicated, individualized dosage adjustments guided by measurement of drugs serum concentrations, especially if pharmacokinetic interactions may cause any change in seizure control or signs of toxicity. Further studies are required to improve predictions of pharmacokinetic interactions between antiseizure medications and drugs for psychiatric diseases providing practical helps for clinicians in the clinical setting.

Therapeutic Drug Monitoring of Antiepileptic Drugs in Epilepsy: A 2018 Update

BACKGROUND

Antiepileptic drugs (AEDs) are the mainstay of epilepsy treatment. Since 1989, 18 new AEDs have been licensed for clinical use and there are now 27 licensed AEDs in total for the treatment of patients with epilepsy. Furthermore, several AEDs are also used for the management of other medical conditions, for example, pain and bipolar disorder. This has led to an increasingly widespread application of therapeutic drug monitoring (TDM) of AEDs, making AEDs among the most common medications for which TDM is performed. The aim of this review is to provide an overview of the indications for AED TDM, to provide key information for each individual AED in terms of the drug's prescribing indications, key pharmacokinetic characteristics, associated drug-drug pharmacokinetic interactions, and the value and the intricacies of TDM for each AED. The concept of the reference range is discussed as well as practical issues such as choice of sample types (total versus free concentrations in blood versus saliva) and sample collection and processing.

METHODS

The present review is based on published articles and searches in PubMed and Google Scholar, last searched in March 2018, in addition to references from relevant articles.

RESULTS

In total, 171 relevant references were identified and used to prepare this review.

CONCLUSIONS

TDM provides a pragmatic approach to epilepsy care, in that bespoke dose adjustments are undertaken based on drug concentrations so as to optimize clinical outcome. For the older first-generation AEDs (carbamazepine, ethosuximide, phenobarbital, phenytoin, primidone, and valproic acid), much data have accumulated in this regard. However, this is occurring increasingly for the new AEDs (brivaracetam, eslicarbazepine acetate, felbamate, gabapentin, lacosamide, lamotrigine, levetiracetam, oxcarbazepine, perampanel, piracetam, pregabalin, rufinamide, stiripentol, sulthiame, tiagabine, topiramate, vigabatrin, and zonisamide).

In vitro changes in the proportion of protein-unbound-free propofol induced by valproate

PURPOSE

It has been reported that oral valproate (VPA) reduces the dose of propofol required for sedation. As  a potential reason for this, it is considered that VPA displaces serum protein-bound propofol and increases the proportion of protein-unbound-free propofol. To examine this hypothesis, the present in vitro study investigated the influence of VPA on the proportion of protein-unbound-free propofol in human serum samples.

METHODS

Serum samples were collected from 10 healthy volunteers, who were not taking any medication. VPA (final concentration: 0.05, 0.1 or 1 mg/mL) and propofol (final concentration: 1 or 5 µg/mL) were mixed with serum samples with normal (4.0 g/dL) or low (2.5 g/dL) albumin concentrations. Then, protein-unbound-free propofol was extracted from the samples, and its concentration was measured using high-performance liquid chromatography. We compared the proportion of protein-unbound-free propofol in each of the VPA-containing samples with that in serum samples without VPA (control).

RESULTS

In the serum samples with normal albumin concentrations, 1 mg/mL VPA significantly increased the proportion of protein-unbound-free propofol at 1 and 5 µg/mL propofol. Furthermore, in the serum samples with low albumin concentrations, the proportion of protein-unbound-free propofol was significantly increased by both 0.1 and 1 mg/mL VPA at propofol concentrations of 1 and 5 µg/mL.

CONCLUSION

VPA might increase the proportion of protein-unbound-free propofol in human serum via displacement reactions.

Challenges of managing delirium and catatonia in a medically ill patient

BACKGROUND

Untangling catatonia and delirium can be challenging. Furthermore, treatment of one syndrome can potentially worsen another.

CASE PRESENTATION

We present the case of a 71-year-old patient with a history of schizoaffective disorder, bipolar subtype, who developed catatonia and delirium with prominent psychotic symptoms, during a single hospitalization. Treatment of this patient's catatonia with benzodiazepines exacerbated delirium, while treatment of psychotic symptoms precipitated by delirium with antipsychotics led to catatonia. Catatonia and psychotic symptoms were eventually successfully managed with electroconvulsive therapy (ECT).

DISCUSSION

This case report highlights some of the treatment challenges faced when delirium and catatonia overlap in a medically ill patient. The use of benzodiazepines, valproic acid, antipsychotics, ECT and alternate medications to treat catatonia are also discussed.

Contribution of baicalin on the plasma protein binding displacement and CYP3A activity inhibition to the pharmacokinetic changes of nifedipine in rats in vivo and in vitro

Baicalin purified from the root of Radix scutellariae is widely used in clinical practices. This study aimed to evaluate the effect of baicalin on the pharmacokinetics of nifedipine, a CYP3A probe substrate, in rats in vivo and in vitro. In a randomised, three-period crossover study, significant changes in the pharmacokinetics of nifedipine (2 mg/kg) were observed after treatment with a low (0.225 g/kg) or high (0.45 g/kg) dose of baicalin in rats. In the low- and high-dose groups of baicalin-treated rats, C max of total nifedipine decreased by 40%±14% (P<0.01) and 65%±14% (P<0.01), AUC0-∞ decreased by 41%±8% (P<0.01) and 63%±7% (P<0.01), Vd increased by 85%±43% (P<0.01) and 224%±231% (P<0.01), and CL increased by 97%±78% (P<0.01) and 242%±135% (P<0.01), respectively. Plasma protein binding experiments in vivo showed that C max of unbound nifedipine significantly increased by 25%±19% (P<0.01) and 44%±29% (P<0.01), respectively, and there was a good correlation between the unbound nifedipine (%) and baicalin concentrations (P<0.01). Furthermore, in vitro results revealed that baicalin was a competitive displacer of nifedipine from plasma proteins. In vitro incubation experiments demonstrated that baicalin could also competitively inhibit CYP3A activity in rat liver microsomes in a concentration-dependent manner. In conclusion, the pharmacokinetic changes of nifedipine may be modulated by the inhibitory effects of baicalin on plasma protein binding and CYP3A-mediated metabolism.

Pharmacoepidemiologic investigation of a clonazepam-valproic acid interaction by mixed effect modeling using routine clinical pharmacokinetic data in Japanese patients

Non-linear Mixed Effects Modeling (NONMEM) was used to estimate the effects of clonazepam-valproic acid interaction on clearance values using 576 serum levels collected from 317 pediatric and adult epileptic patients (age range, 0.3-32.6 years) during their clinical routine care. Patients received the administration of clonazepam and/or valproic acid. The final model describing clonazepam clearance was CL = 144.0 TBW-0.172 1.14VPA, where CL is total body clearance (mL/kg/h); TBW is total body weight (kg); VPA = 1 for concomitant administration of valproic acid and VPA = zero otherwise. The final model describing valproic acid clearance was CL (mL/kg/h) = 17.2 TBW-0.264 DOSE0.159 0.821CZP 0.896GEN, where DOSE is the daily dose of valproic acid (mg/kg/day); CZP = 1 for concomitant administration of clonazepam and CZP = zero otherwise; GEN = 1 for female and GEN = zero otherwise. Concomitant administration of clonazepam and valproic acid resulted in a 14% increase in clonazepam clearance, and a 17.9% decrease in valproic acid clearance.

Clinically important drug interactions in epilepsy: interactions between antiepileptic drugs and other drugs

Antiepileptic drugs (AEDs) are commonly prescribed for long periods, up to a lifetime, and many patients will require treatment with other agents for the management of concomitant or intercurrent conditions. When two or more drugs are prescribed together, clinically important interactions can occur. Among old-generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone are potent inducers of hepatic enzymes, and decrease the plasma concentration of many psychotropic, immunosuppressant, antineoplastic, antimicrobial, and cardiovascular drugs, as well as oral contraceptive steroids. Most new generation AEDs do not have clinically important enzyme inducing effects. Other drugs can affect the pharmacokinetics of AEDs; examples include the stimulation of lamotrigine metabolism by oral contraceptive steroids and the inhibition of carbamazepine metabolism by certain macrolide antibiotics, antifungals, verapamil, diltiazem, and isoniazid. Careful monitoring of clinical response is recommended whenever a drug is added or removed from a patient's AED regimen.

Clinically important drug interactions in epilepsy: general features and interactions between antiepileptic drugs

There are two types of interactions between drugs, pharmacokinetic and pharmacodynamic. For antiepileptic drugs (AEDs), pharmacokinetic interactions are the most notable type, but pharmacodynamic interactions involving reciprocal potentiation of pharmacological effects at the site of action are also important. By far the most important pharmacokinetic interactions are those involving cytochrome P450 isoenzymes in hepatic metabolism. Among old generation AEDs, carbamazepine, phenytoin, phenobarbital, and primidone induce the activity of several enzymes involved in drug metabolism, leading to decreased plasma concentration and reduced pharmacological effect of drugs, which are substrates of the same enzymes (eg, tiagabine, valproic acid, lamotrigine, and topiramate). In contrast, the new AEDs gabapentin, lamotrigine, levetiracetam, tiagabine, topiramate, vigabatrin, and zonisamide do not induce the metabolism of other AEDs. Interactions involving enzyme inhibition include the increase in plasma concentrations of lamotrigine and phenobarbital caused by valproic acid. Among AEDs, the least potential interaction is associated with gabapentin and levetiracetam.

In vitro evaluation of valproic acid as an inhibitor of human cytochrome P450 isoforms: preferential inhibition of cytochrome P450 2C9 (CYP2C9)

AIMS

To evaluate the potency and specificity of valproic acid as an inhibitor of the activity of different human CYP isoforms in liver microsomes.

METHODS

Using pooled human liver microsomes, the effects of valproic acid on seven CYP isoform specific marker reactions were measured: phenacetin O-deethylase (CYP1A2), coumarin 7-hydroxylase (CYP2A6), tolbutamide hydroxylase (CYP2C9), S-mephenytoin 4'-hydroxylase (CYP2C19), dextromethorphan O-demethylase (CYP2D6), chlorzoxazone 6-hydroxylase (CYP2E1) and midazolam 1'-hydroxylase (CYP3A4).

RESULTS

Valproic acid competitively inhibited CYP2C9 activity with a Ki value of 600 microM. In addition, valproic acid slightly inhibited CYP2C19 activity (Ki = 8553 microM, mixed inhibition) and CYP3A4 activity (Ki = 7975 microM, competitive inhibition). The inhibition of CYP2A6 activity by valproic acid was time-, concentration- and NADPH-dependent (KI = 9150 microM, Kinact=0.048 min(-1)), consistent with mechanism-based inhibition of CYP2A6. However, minimal inhibition of CYP1A2, CYP2D6 and CYP2E1 activities was observed.

CONCLUSIONS

Valproic acid inhibits the activity of CYP2C9 at clinically relevant concentrations in human liver microsomes. Inhibition of CYP2C9 can explain some of the effects of valproic acid on the pharmacokinetics of other drugs, such as phenytoin. Co-administration of high doses of valproic acid with drugs that are primarily metabolized by CYP2C9 may result in significant drug interactions.

Pharmacokinetic interactions between antiepileptic drugs. Clinical considerations

Antiepileptic drug interactions represent a common clinical problem which has been compounded by the introduction of many new compounds in recent years. Most pharmacokinetic interactions involve the modification of drug metabolism; the propensity of antiepileptic drugs to interact depends on their metabolic characteristics and action on drug metabolic enzymes. Phenobarbital, phenytoin, primidone and carbamazepine are potent inducers of cytochrome P450 (CYP), epoxide hydrolase and uridine diphosphate glucuronosyltransferase (UDPGT) enzyme systems; oxcarbazepine is a weak inducer of CYP enzymes, probably acting on a few specific isoforms only. All stimulate the rate of metabolism and the clearance of the drugs which are catabolised by the induced enzymes. Valproic acid (valproate sodium) inhibits to different extents many hepatic enzyme system activities involved in drug metabolism and is able to significantly displace drugs from plasma albumin. Felbamate is an inhibitor of some specific CYP isoforms and mitochondrial beta-oxidation, whereas it is a weak inducer of other enzyme systems. Topiramate is an inducer of specific CYP isoforms and an inhibitor of other isoforms. Ethosuximide, vigabatrin, lamotrigine, gabapentin and possibly zonisamide and tiagabine have no significant effect on hepatic drug metabolism. Apart from vigabatrin and gabapentin, which are mainly eliminated unchanged by the renal route, all other antiepileptic drugs are metabolised wholly or in part by hepatic enzymes and their disposition may be altered by metabolic changes. Some interactions are clinically unremarkable and some need only careful clinical monitoring, but others require prompt dosage adjustment. From a practical point of view, if valproic acid is added to lamotrigine or phenobarbital therapy, or if felbamate is added to phenobarbital, phenytoin or valproic acid therapy, a significant rise in plasma concentrations of the first drug is expected with a corresponding increase in clinical effects. In these cases a concomitant reduction of the dosage of the first drug is recommended to avoid toxicity. Conversely, if a strong inducer is added to carbamazepine, lamotrigine, valproic acid or ethosuximide monotherapy, a significant decrease in their plasma concentrations is expected within days or weeks, with a possible reduction in efficacy. In these cases a dosage increase of the first drug may be required.

Phenobarbitone to gabapentin: a guide to 82 years of anti-epileptic drug pharmacokinetic interactions

With the introduction of three new anti-epileptic drugs (AEDs) in the UK during the past 4 years as adjunctive add-on therapy, the possibility of AED pharmacokinetic interactions has become a relevant consideration. This review highlights the current status of AED interactions with particular emphasis on those interactions that are likely to be frequently experienced or whose outcome is potentially clinically significant.

Antiepileptic drugs. A review of clinically significant drug interactions

Approximately 20 to 30% of patients with active intractable epilepsy are commonly treated with polytherapy antiepileptic drug regimens, and these patients may experience complicated drug interactions. Furthermore, because of the long term nature of treatment, the possibility of drug interactions with drugs used for the treatment of concomitant disease is high. Classically, clinically significant drug interactions, both pharmacokinetic and pharmacodynamic, have been considered to be detrimental to the patient, necessitating dosage adjustment. However, this need not always be the case. With the introduction of new drugs (e.g. vigabatrin and lamotrigine) with known mechanisms of action, the possibility exists that these can be used synergistically. The most commonly observed clinically significant pharmacokinetic interactions can be attributed to interactions at the metabolic and serum protein binding levels. The best known examples relate to induction (e.g. phenobarbital, phenytoin, carbamazepine and primidone) or inhibition [e.g. valproic acid (sodium valproate)] of hepatic monoxygenase enzymes. The extent and direction of interactions between the different antiepileptic drugs are varied and unpredictable. Interactions in which the metabolism of phenobarbital, phenytoin or carbamazepine is inhibited are particularly important since these are commonly associated with toxicity. Some inhibitory drugs include macrolide antibiotics, chloramphenicol, cimetidine, isoniazid and numerous sulphonamides. A reduction in efficacy of antibiotic, cardiovascular, corticosteroid, oral anticoagulant and oral contraceptive drugs occurs during combination therapy with enzyme-inducing antiepileptic drugs. Discontinuation of the enzyme inducer or inhibitor will influence the concentrations of the remaining drug(s) and may necessitate dosage readjustment.

Differential effects of valproic acid and enzyme-inducing anticonvulsants on nimodipine pharmacokinetics in epileptic patients

1. The single dose pharmacokinetics of orally administered nimodipine (60 mg) were investigated in normal subjects and in two groups of epileptic patients receiving chronic treatment with hepatic microsomal enzyme-inducing anticonvulsants (carbamazepine, phenobarbitone or phenytoin) and sodium valproate, respectively. 2. Compared with the values found in the control group, mean areas under the plasma nimodipine concentration curve were lowered by about seven-fold (P less than 0.01) in patients taking enzyme-inducing anticonvulsants and increased by about 50% (P less than 0.05) in patients taking sodium valproate. 3. Nimodipine half-lives were shorter in enzyme-induced patients than in controls (3.9 +/- 2.0 h vs 9.1 +/- 3.4 h, means +/- s.d., P less than 0.01), but this difference could be artifactual since in the patients drug concentrations declined rapidly below the limit of assay, thus preventing identification of a possible slower terminal phase. In valproate-treated patients, half-lives (8.2 +/- 1.8 h) were similar to those found in controls.

Evaluation of the pharmacokinetic interaction between diazepam and ACC-9653 (a phenytoin prodrug) in healthy male volunteers

The protein binding and pharmacokinetics of diazepam, ACC-9653 (a phenytoin prodrug), and phenytoin were evaluated in nine healthy male volunteers following administration of diazepam and ACC-9653, alone or concomitantly, in a randomized crossover design. No significant differences were observed in the fraction unbound or pharmacokinetic parameters of ACC-9653, phenytoin, or diazepam when ACC-9653 was administered alone compared to concomitant administration with diazepam. The phenytoin fraction unbound increased significantly with increased concentrations of ACC-9653, indicating displacement of phenytoin from its binding sites by ACC-9653. ACC-9653 also demonstrated concentration dependent binding. The lack of a significant pharmacokinetic drug interaction between ACC-9653 and diazepam suggests that these drugs may be safely administered together, although this conclusion should be confirmed in the intended patient population.

How chronically administered valproate increases chlordiazepoxide transfer through the blood-brain barrier

Sodium valproate (VPA) is a drug widely used in the treatment of epileptics often in association with benzodiazepines. Recent animal studies have shown that the addition of valproate increases diazepam levels in the cortex and the cerebellum (Hariton et al, 1985). The aim of our study was to determine the effect of VPA on the transfer of benzodiazepines through the blood-brain barrier. They were investigated using the intracarotid injection technique in rats as described by Oldendorf (1971). Our results show that the 14C-chlordiazepoxide brain extraction is significantly higher in rats on prolonged valproate treatment than in controls. With regard to plasma protein binding effects on chlordiazepoxide transport, our data indicate that a fraction of the protein-bound chlordiazepoxide could transfer from the intracapillary space to the brain tissue space because of enhanced drug dissociation from albumin in the brain microcirculation (Kd in vitro = 74.1 microM; Kd in vivo = 793.7 microM). Two distinct mechanisms can be deduced from this study: 1) chlordiazepoxide is displaced from HSA by valproate, 2) in addition, this fatty acid could increase drug permeation through the blood brain barrier (PS/F (chlordiazepoxide) = 0.60 in controls, PS/F (chlordiazepoxide) = 0.97 in treated rats). On the contrary, the washout of the benzodiazepine from the rat brain does not seem to be modified by the addition of valproate.

Effect of sodium valproate on midazolam distribution

The displacement of midazolam, a new water-soluble, short acting benzodiazepine, from its plasma binding sites by sodium valproate, has been studied in man. An increase of its free fraction (ranging from 2.71 to 5.35%) in plasma from epileptic patients receiving sodium valproate was observed. A similar situation was created in rabbits by pretreatment with sodium valproate (600 mg kg-1 day-1) and posterior hypnosis with midazolam. Due to the interaction, sodium valproate-pretreated rabbits showed an increase in midazolam brain levels (130.91 micrograms g-1 in cortex vs 84.55 micrograms g-1 in control animals). Therefore, it seems likely that displacement of midazolam by sodium valproate in epileptic patients could lead to an increase of the midazolam response.

Valproate: an updated review

Valproate in all its aspects is comprehensively surveyed. Previous reviews covering various aspects such as mechanism of action, clinical pharmacology, clinical efficacy in epilepsy, febrile convulsions and other neurological disorders, side effects, teratogenicity and intoxications are discussed and updated (161 references).

An update on sodium valproate

Sodium valproate has been in clinical use for the treatment of epilepsy in Great Britain since 1973 and in the United States since 1978. It is chemically quite different from the existing antiepileptic drugs. Although most authorities concentrate on its modification of GABAergic inhibitory transmission in the central nervous system, its mechanism of action remains obscure. It has been shown to be an effective antiepileptic drug in a wide variety of seizure types, but clinically, its major use to date has been in generalized seizures. It is particularly effective in photosensitive epilepsy and myoclonus. Most adverse reactions to sodium valproate are mild and reversible, but with increasing experience, the drug's rare, idiosyncratic, adverse effects are becoming apparent, particularly hepatotoxicity and teratogenicity. The role of therapeutic drug monitoring in the management of patients taking sodium valproate is controversial.

Anticonvulsant drugs. An update

A considerable amount of information is now available concerning the clinical pharmacology of the anticonvulsant drugs. Some of the more important data are reviewed in this article. In recent years, valproic acid (or sodium valproate) has found a place as a major anticonvulsant agent, while older drugs such as troxidone and sulthiame seem to be disappearing from use. Although much information is available, the essential mechanisms of action of the anticonvulsant drugs are still not understood, either at a molecular or at an electrophysiological level. The pharmacokinetics of the anticonvulsants in common use are now reasonably well documented, though some minor questions are still to be answered. Numerous interactions between anticonvulsants and endogenous substances or other drugs administered concurrently (including other anticonvulsants) have been recorded, but much work still needs to be done to elucidate the frequency and mechanisms of the various interactions. Many adverse effects of the anticonvulsants are known, but further unwanted effects of long-established drugs continue to emerge from time to time, including the still somewhat controversial matter of anticonvulsant-related dysmorphogenesis. The use of valproic acid and its sodium salt has been associated with a worrying incidence of serious liver and pancreatic toxicity. Adequate basic data are now available to put the clinical use of anticonvulsants on a rational basis, but much work remains to be done in this area. In particular, the question of 'therapeutic ranges' of plasma concentrations of the various drugs needs to be reinvestigated in a rigorous statistical fashion, and in relation to different clinical types of epilepsy. The usefulness of monitoring free rather than total drug concentrations also needs further investigation. The ultimate test of the validity of all background scientific pharmacological information about anticonvulsants is its usefulness in the treatment of patients with epilepsy.