Anticonvulsant drugs. An update

Anticonvulsant activity, organotypic hippocampal neuroprotection assay and in-silico sodium channel blocking potential of 2-amino-6-nitrobenzothiazole derived semicarbazones

Epilepsy is one of the dreadful neurodegenerative disorder characterized by recurrent, unprovoked seizures. Currently available antiepileptic drugs are still associated with enormous side effects resulting in search of newer, more effective and safer agents. In view of this, we have investigated anticonvulsant activity of 2-amino-6-nitrobenzothiazole derived semicarbazones (7-32) in various in-vivo animal seizure models viz. maximal electroshock (MES), subcutaneous pentylenetetrazole (scPTZ) and 6Hz psychomotor seizure model. Neurotoxicity was estimated by rotarod test. The compounds were also assessed for their neuroprotective potential from excitotoxic insult using organotypic hippocampal slice culture neuroprotection assay. Several compounds exhibited excellent anticonvulsant activity in MES and scPTZ models compared to reference drugs, phenytoin and levetiracetam. The results of kainic acid (KA) - induced neuroprotection assay indicated that compounds 26 and 24 were found to be most potent with IC₅₀ of 99.54±1.27 and 101.00±1.20μM respectively. Both the compounds attenuated KA-mediated cell death in organotypic hippocampal slice cultures. Some of the compounds were found to be good antidepressants, better than the reference drug citalopram, when analyzed in forced swim test. Since semicarbazones exhibited profile resembling phenytoin, an attempt was made to screen them against human neuronal sodium channel isoform (hNa_v1.2) by performing computational molecular docking using AutoDock 4.2. Compound 30, 1-(5-Chloro-2-oxoindolin-3-ylidene)-4-(6-nitrobenzothiazol-2-yl)semicarbazide emerged as lead candidate possessing excellent in-vivo MES activity and high binding affinity computationally, better than the reference drug phenytoin and also exhibited neuroprotection from excitotoxic insult in KA-induced neuroprotection assay (IC₅₀=126.80±1.24μM). However, some of the active compounds were neurotoxic at their anticonvulsant doses. Further optimization studies are needed to reduce toxicity and develop them as novel therapeutic agents for epilepsy.

The use of oral fluid for therapeutic drug management: clinical and forensic toxicology

One of the underlying tenets of clinical pharmacology is that only free drugs are pharmacologically active. It is thought that only free drugs can cross biological membranes to interact with a given receptor to alter its function, and that drug responses, both efficacious and toxic, are a function of unbound concentrations. The rationale for measuring drugs in oral fluid is that the free fraction of a drug in plasma reaches equilibrium with the drug in saliva. Although reports concerning the appearance of organic solutes in saliva have been in the literature for over 70 years, it has only been in the past 30 years that there has been emphasis on the appearance of drugs. Although many assumptions for drug level monitoring in saliva are made, the primary requisite for salivary monitoring to be useful is a constant or predictable relationship between the drug concentration in saliva and the drug concentration in plasma. Measurement of oral fluid drug levels for the purpose of managing patients and making dosage adjustments may be useful for select drugs or drug classes. However, it does not appear to be useful for the majority of drugs therapeutically monitored. Some work with antipsychotic medications has indicated that although the measurement of drug concentrations themselves may not be useful for dosage adjustment, the ratio of parent drug to metabolite may reflect altered metabolic status due to either pharmacogenetic variation or other clinical conditions. Furthermore, analysis of saliva may provide a cost-effective approach for the screening of large populations.

N-, alpha-, and beta-Substituted 3-Aminopropionic acids: design, syntheses and antiseizure activities

A treatment for epilepsy is proposed based on analogues of 3-aminopropionic acid (beta-alanine), a putative neurotransmitter in the central nervous system (CNS). A model three point pharmacophore was proposed based on modelling data obtained from the study of antagonists for both the glial gamma-aminobutyric acid (GABA)-uptake site and the glycine co-agonist site of N-methyl-D-aspartate (NMDA) receptor. Three series of 3-aminopropionic acids containing, N-, alpha-, and beta-substituents, were designed and synthesized to probe the position and the size of a lipophilic binding pocket within the proposed pharmacophore. These analogues were tested in vivo for both their antiseizure activities and their neurologic toxicities. Among the fourteen novel 3-aminopropionic acids synthesized, eight were found to have promising antiseizure activity. This study shows that substitution on the N-terminus confers the greatest antiseizure activity, particularly against pilocarpine-induced seizures.

Synthesis of some 1-(2-naphthyl)-2-(imidazole-1-yl)ethanone oxime and oxime ether derivatives and their anticonvulsant and antimicrobial activities

In this study, oxime and oxime ether derivatives of anticonvulsant nafimidone [1-(2-naphthyl)-2-(imidozole-1-yl)ethanone] were prepared as potential anticonvulsant compounds. Nafimidone oxime was synthesized by the reaction of nafimidone and hydroxylamine hydrochloride. O-Alkylation of the oxime by various alkyl halides gave the oxime ether derivatives. Anticonvulsant activity of the compounds was determined by maximal electroshock (MES) and subcutaneous metrazole (scMet) tests in mice and rats according to procedures of the Antiepileptic Drug Development (ADD) program of the National Institutes of Health (NIH). In addition to anticonvulsant evaluation, compounds were also screened for possible antibacterial and antifungal activities because of the structural resemblance to the azole antifungals, especially to oxiconazole. All compounds were evaluated against three human pathogenic fungi and four bacteria using the microdilution method. Most of the compounds exhibited both anticonvulsant and antimicrobial activities; the O-alkyl substituted compounds (2, 3, 4 and 5) were found to be more active than the O-arylalkyl substituted compounds in both screening paradigms.

Investigation and medical management of trigeminal neuralgia by consultant oral and maxillofacial surgeons in the British Isles

Trigeminal neuralgia is an extremely painful affliction of the face that is treated by various specialists including oral and maxillofacial surgeons. Some aspects of its management remain controversial, including screening for secondary trigeminal neuralgia, and the monitoring of treatment with carbamazepine. There is, however, little information available about current practice. A postal questionnaire was sent to 254 fellows of the British Association of Oral and Maxillofacial Surgeons (BAOMS) about v arious aspects of the management of trigeminal neuralgia. One hundred and seventy nine replies (70%) were received. Orofacial and cranial nerve examinations were undertaken by the majority of surgeons, but most did not routinely arrange computed tomograp hy or magnetic resonance imaging for all patients, nor did they refer the patient to a neurologist. In contrast with current recommendations, warnings about the adverse effects of carbamazepine were given by only a few surgeons, while most routinely monitored full blood counts.

Phenytoin dosage adjustment in Saudi epileptics: utilization of steady-state pharmacokinetic parameters

We determined the Michaelis-Menten parameters (Vmax and Km) in 271 Saudi epileptic patients having generalized tonic-clonic seizures and who were treated with phenytoin (PHT) using high pressure liquid chromatography (HPLC). The patients comprised 150 (55.4%) males and 121 (44.6%) females, with a mean age of 31.7 years (SD = 18.5). The mean Vmax for subjects less than 16 years of age was 10.35 mg/kg/day (SD = 0.73, range = 3.77-17.01), while for those above 16 years, the mean value was 7.99 mg/kg/day (SD = 0.15, range = 3.68-15.95). The difference was statistically significant (P < 0.001). Vmax was positively correlated with weight (r = 0.953), but negative with age (r = -0.903). Km values ranged from 1.01-20.87 mg/litre. The adult Km mean of 6.52 mg/l (SD = 0.24) was significantly higher than the mean of 4.79 mg/l (SD = 0.40) for pediatric patients (P < 0.01), but Km was correlated neither with age nor with weight. Our results showed no difference between the predicted and observed serum PHT concentrations in both the pediatric and adult patients when the respective age group Km and Vmax values were used to adjust PHT doses. The pediatric cases, however, required 30% more PHT per kilogram of body weight than the adults for the achievement of similar serum concentrations.

Synthesis and anticonvulsant activity of 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives

A series of 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives were synthesized and evaluated for anticonvulsant activity. The compounds were assayed, intraperitoneally in mice and per os in rats, against seizures induced by maximal electroshock (MES) and pentylenetetrazole (scMet). Neurologic deficit was evaluated by the rotarod test. The compounds were prepared to determine the relationship between the 2(3H)-benzoxazolone and 2(3H)-benzothiazolone derivatives' structures and anticonvulsant activity. Several of these compounds showed significant anticonvulsant activity. Compounds 43 and 45 were the most active of the series against MES-induced seizures with ED50 values of 8.7 and 7.6 mg/kg, respectively. Compound 45 displayed good protection against MES-induced seizures and low toxicity in rats with an oral ED50 of 18.6 mg/kg and a protective index (PI = TD50/ED50) of < 26.9. In vitro receptor binding studies revealed that compounds 43 and 45 bind to sigma 1 receptors with nanomolar affinities.

Drug management of hypertensive disorders of pregnancy

Drugs used in the acute and long-term management of hypertension in pregnancy and the preeclampsia-eclampsia syndrome have been reviewed and their therapeutic effects and maternal and fetal adverse effects have been considered. The review also focuses on recent developments in the areas of prevention and management of pre-eclampsia-eclampsia syndrome. Although a number of new drugs have emerged, as potentially useful in the management of hypertension in pregnancy and pre-eclampsia-eclampsia syndrome, some remain at the cornerstone of therapy; for example, methyldopa for long-term treatment of chronic hypertension, hydralazine or nifedipine for rapid reduction of severely elevated blood pressure, and magnesium sulphate for eclampsia. Some of these agents, especially the calcium antagonists, show promise in that their use is associated with fewer side effects. Safety for the fetus, however, has not been adequately evaluated yet. Neither aspirin nor calcium supplements appear to improve the outcome in pregnancy. Currently, the dilemma whether to treat hypertension in pregnancy and pre-eclampsia-eclampsia syndrome with old, established, cost-effective drugs or the promising newer drugs provides an interesting academic challenge.

Reappraisal of polytherapy in epilepsy: a critical review of drug load and adverse effects

PURPOSE

We reviewed the literature to determine whether an analysis of published data could clarify the relationship between antiepileptic drug (AED) polytherapy and adverse affects (AE). We highlight the problems encountered.

METHODS

We made a Medline-search for articles published between 1974 and 1994 reporting the number of AE and doses or serum levels of every AED, per patient or treatment group, and used the PDD/DDD ratio to calculate AED load per patient from doses or the OSL/AToxL ratio to do so from serum levels of individual drugs. The PDD/DDD is the sum of ratios of the actual prescribed daily doses divided by the published average therapeutic dose of each drug. The OSL/AToxL is the sum of each observed serum level divided by its average toxic level.

RESULTS

We retrieved 118 trial reports. Most had to be excluded because of incomplete reporting of concomitant medication or AE. The data of the 15 articles selected for further analysis indicate a relationship between drug load and number of AE. We noted no relationship between the number of AEDs administered and AE. In add-on studies, the difference in neurotoxicity between the active and placebo arm may be obscured if the relative increase in drug load is small, as exemplified by the study of McGuire et al..

CONCLUSIONS

Articles reporting add-on trials of new AEDs generally do not provide detailed information about the basic medication to which the new AED is added, which makes calculation of total drug load impossible. Furthermore, often only frequency of AE is reported, not severity or development of tolerance, making it difficult to judge the impact of AE. However, despite the paucity of available information, we present some evidence that toxicity in AED polytherapy may be related to total drug load, rather than to the number of drugs administered. Therefore, the present trend to reject polytherapy for fear of increased toxicity is not warranted, which removes one of the objections to initiating specific research to prove or disprove the value of AED combinations as long as the drug load is appropriate.

Hypothyroxinemia and phenytoin toxicity: a vicious circle

Phenytoin is a widely used anticonvulsant which has a relatively narrow therapeutic range of serum concentrations, 40-80 mmol/l (10-20 mg/l). Phenytoin is known to show concentration-dependent kinetics within this therapeutic range. Because of this, small changes in dose and minor alterations in hepatic metabolism of phenytoin may cause a disproportionately large affect on serum concentrations. Hypothyroidism is associated with inhibition of hepatic oxidative metabolism of many drugs. However, there is a general consensus in the literature that serum phenytoin clearance is not influenced by thyroid functional status. This report describes a 63 year-old female who developed decreased serum free T4 (8 pmol/l) and phenytoin toxicity. We identified three other similar case reports. We propose that the following vicious circle may be involved in this interaction: induction by phenytoin of hepatic enzymes involved in the metabolism of T4 and T3, decreased serum free T4 levels causing decreased activity of hepatic NADPH cytochrome P-450 reductase, a resultant decrease in hepatic P-450 IIC9 catalyzed hydroxylation of phenytoin, increased serum phenytoin concentrations and further induction of T4 and T3 hepatic metabolism.

Neither dosage nor serum levels of antiepileptic drugs are predictive for efficacy and adverse effects

In order to assess whether doses or serum levels are predictive for the efficacy and adverse effects of antiepileptic drugs (AEDs), measures for exposure to drug combinations have to be used. For doses, the ratio of the observed prescribed daily dose (PDD) and the average defined daily dose (DDD) considered effective for the main indication of the drug was used. In analogy for serum levels, the OSL/ATL ratio, i.e. the ratio of the observed serum level and the average therapeutic level was used. In polypharmacy these ratios can be summed as the are normalized measures of strength. The correlations of these ratios with outcome measures were studied in 200 patients attending out-patient clinics of special centres for epilepsy; half of these patients were treated with monopharmacy and half with polypharmacy. As outcome measures the following indices were used: the index of seizures, which quantifies seizure type and frequency, the seizure activity index, the neurotoxicity score, the systemic toxicity score, and the composite index of impairments, which is the sum of the seizure activity index and the neurotoxicity score and the systemic toxicity score. When all data were pooled, the correlation coefficient between the PDD/DDD ratio and the OSL/ATL ratio was 0.77. However, when the data were examined separately for the monopharmacy and polypharmacy groups, the correlation was 0.31 for the monopharmacy group and 0.50 for the polypharmacy group. Neither the PDD/DDD ratio nor the OSL/ATL ratio correlated with the composite index of impairments or with any of the individual indices. Factors such as the difficulty of titrating the endpoint of seizure suppression and the development of tolerance to adverse drug effects may perhaps be responsible for these findings. This observational study signals the problem.

Testing human hair for carbamazepine in epileptic patients: is hair investigation suitable for drug monitoring?

Hair samples were obtained from 30 patients who had been taking carbamazepine in fixed daily doses for more than 6 months. Carbamazepine was extracted from the hair by enzymatic hydrolysis and quantified by gas chromatography-mass spectrometry. Concentrations ranged from 1.2 to 57.4 ng mg-1. The concentrations of carbamazepine were significantly correlated (P < 0.0001) with the daily dose and the correlation coefficient was 0.793. Although it had been suggested by several authors that the measurement of carbamazepine in hair might provide a better index of individual dosage history than the plasma level assays, the deviations observed in this study led to the conclusion that hair samples are not suitable for evaluating the quantity of drug consumed. However, hair testing may be useful for documenting clinical disorders by sectioning the shaft into segments corresponding to 1 month periods.

Phenytoin monitoring in status epilepticus in infants and children

Two successive protocols of phenytoin (PHT) plasma concentration monitoring were tested in 60 children with status epilepticus (SE). In each protocol, a loading dose of 15 mg/kg was injected and followed by three injections during the first 24 h. Clinical evaluation was performed at the end of the study by grouping patients into three classes according to seizure frequency during treatment: complete effect, partial effect, and no effect. In protocol 1, a complementary dose at the fourth hour was adjusted from individual plasma concentrations. Plasma concentrations at the 40th hour were within the therapeutic range in the 19 patients with complete effect (CE, mean 19 mg/L) and in the 5 patients with no effect (NE, mean 23 mg/L) whereas in the 11 patients with partial effect (PE), plasma concentrations were higher (mean 31 mg/L). In protocol 2, we added monitoring of the doses injected at the 16th and 24th hours to prevent the increase in PHT concentration noted in protocol 1. All patients but 1 were classified as either CE (13 patients) or NE (4 patients). In NE patients, average plasma concentration at the 40th hour (mean 10.5 mg/L) was lower than in CE patients (mean 15.7 mg/L). In both protocols, the NE patients were the youngest. In SE, PHT doses should be adjusted according to plasma concentrations to avoid overdosage and paradoxical inefficacy. Younger children had lower concentrations and appeared to respond less well than older children, but the etiology of SE may also play an important role.

Drugs used in the management of trigeminal neuralgia

Management of trigeminal neuralgia, a severe facial pain, remains difficult. All patients are initially treated with drugs. Since the seventeenth century more than 40 different preparations have been used; some of these, although effective, had toxic side effects. The most useful drugs at present are carbamazepine, phenytoin, baclofen, and clonazepam. A new drug, oxcarbazepine, is showing therapeutic promise. The most common reason for therapeutic failure with antineuralgic drugs is inadequate dosage. We review here the pharmacokinetics, side effects, possible drug interactions, plasma and serum therapeutic concentrations, and the available formulations of each drug. On the basis of these considerations and clinical reports describing the use of these drugs, we make dosage recommendations to enable the practitioner to individualize therapeutic regimens.

Hypersensitivity reactions to procarbazine with mechlorethamine, vincristine, and procarbazine chemotherapy in the treatment of glioma

The authors report the clinical features of hypersensitivity reactions believed to result from procarbazine in eight patients treated with mechlorethamine, vincristine, and procarbazine (MOP) for high-grade glioma. There was one instance of hypersensitivity in 7 patients treated for recurrent disease and seven instances in 16 patients treated with an adjuvant protocol using MOP directly after surgery. Maculopapular rash was seen in seven of eight, fever was seen in four of eight, and reversible abnormal liver function test results were seen in three of four patients. Pulmonary toxic effects were seen in five of eight patients and consisted of isolated interstitial pneumonitis in one, fever and infiltrate after rechallenge with procarbazine after previous rash in two, and cough accompanying rash in two. The toxic effects were mild to moderate in six patients but severe to life threatening in the two who were rechallenged after development of rash. The observed incidence of rash during adjuvant therapy was higher than that previously found by the authors for recurrent disease, and it appears to be higher than has been reported in Hodgkin's disease, lymphoma, and other solid tumors. The findings by the authors suggest that a high index of suspicion be kept for hypersensitivity reactions to procarbazine when treating primary brain tumors and that, contrary to the experience in other settings, procarbazine be stopped if rash develops.

Antiepileptic drug monitoring at the epilepsy clinic: a prospective evaluation

To assess the value of on site therapeutic drug monitoring at the epilepsy clinic, management decisions were recorded before and immediately after antiepileptic drug (AED) concentrations became available. In the first year of this prospective study, 632 [277 carbamazepine (CBZ), 170 phenytoin (PHT), 113 valproate (VPA), and 72 phenobarbital (PB)] assays were performed during 488 clinic attendances in 182 actively managed epileptic patients. The results of drug analysis led to alterations in management at 114 patients visits, i.e., 23% of those monitored. Dosage was increased in response to the circulating AED concentration in 12% of consultations and decreased in another 7.5%. Unsuspected poor compliance was uncovered in eight patients, and in three others an AED was added or discontinued on the basis of the assay result. The time of the next appointment was rearranged in 58 attendances. Only 50% of results were in the "therapeutic" ranges for the four major AEDs. Dosage was adjusted (50 up, 16 down) after 54% of low results. "Therapeutic" levels were followed by a change in AED dose (52 up, 31 down) in 26%. Only 29% of concentrations above the "therapeutic" range persuaded the doctor to alter the dosage regimen, and in 20% of these an increase in dose was recommended. On-site AED monitoring had an immediate impact on clinical decision-making in greater than 23% of consultations but in a form more subtle than the simple quest for a therapeutic result.

Behavioral changes in juvenile rats after prenatal exposure to ethosuximide

Juvenile rats 4-6 weeks old exposed prenatally at days 5-20 of gestation to ethosuximide at 10 mg/kg/dams' body weights per day were examined for behavioral abnormalities. Pinning behavior in the pups aged 4-5 weeks was significantly more frequent than that in age-matched controls. However, basal activity of open-field behavior and activity inhibited by diazepam administration in the pups aged 5-6 weeks showed no difference from the controls. The intensity of stereotyped behavior induced by apomorphine (1 mg/kg, SC) was significantly greater in the pups aged 5-6 weeks than in the controls. These results indicate that prenatal exposure to ethosuximide may cause changes in the dopaminergic neurons in the central nervous system.

Problems of drug surveillance--an international view

The importance of Post Marketing Surveillance (PMS) is stressed, both to determine the therapeutic value of the drug and its adverse effects revealed in a large population of patients. A survey of such adverse effects of anti-epileptic drugs is provided: metabolic, dose-related and idiosyncratic. Problems of monotherapy and of drug interactions are discussed, as well as questions of central nervous system toxicity and of teratogenicity.

Decreased phenytoin levels in patients receiving chemotherapy

PURPOSE AND METHODS

Seizures and unexpectedly low phenytoin levels prompted a retrospective review of phenytoin doses and serum levels in patients with primary brain tumors following the administration of cisplatin and carmustine (BCNU) chemotherapy.

RESULTS

All patients who received three or more cycles of this chemotherapeutic regimen required an increase in their maintenance phenytoin dose to maintain therapeutic phenytoin levels. The average increase in the daily phenytoin dose was 41% (range, 20% to 100%). In addition, 17 of 26 (65%) assessable chemotherapy cycles were accompanied by a greater than 20% decrease in phenytoin levels or an increase in phenytoin requirements. Significant changes in phenytoin levels occurred as early as two days after administration of chemotherapy and were seen exclusively in treatment cycles that contained cisplatin. Five additional cases were found in the literature in which serum phenytoin concentrations decreased after the administration of antineoplastic agents.

CONCLUSIONS

These observations are important to physicians treating patients who are receiving phenytoin. Serious consequences can be avoided by expecting changes in phenytoin dosage requirements after the administration of chemotherapy, monitoring serum levels frequently, and making appropriate adjustments in phenytoin dosages. Prospective evaluations are needed to confirm these observations, to define the chemotherapeutic agents that predispose patients to these alterations in phenytoin's pharmacology, and to determine if drugs other than phenytoin are affected by the administration of chemotherapy.

Cutaneous and immunologic reactions to phenytoin

Phenytoin (diphenylhydantoin; Dilantin) is a highly effective and widely prescribed anticonvulsant and antiarrhythmic agent. Since 1938 it has been invaluable in the treatment of grand mal and psychomotor epilepsy. Hydantoin derivatives have been used medicinally for more than a half-century. In recent years dermatologists have broadened the indications for phenytoin use to include recessive dystrophic epidermolysis bullosa, linear scleroderma, and pachyonychia congenita. In spite of widespread use and popularity, it is interesting that the frequency of complications relating to drug therapy remains low, relatively speaking. Nevertheless, a broad spectrum of cutaneous and immunologic reactions to phenytoin have been reported. These range from tissue proliferative syndromes (side effects), drug hypersensitivity syndromes (allergic effects), and a possible linkage with lymphoma (idiosyncratic effects). Therapeutic and toxic reactions to this commonly prescribed drug are comprehensively reviewed, analyzed, and summarized in this monograph.

Effect of sodium valproate on carbamazepine disposition and psychomotor profile in man

1 The effect of sodium valproate (VPA; 500 mg thrice daily for 7 days) and matched placebo on the disposition and psychomotor profile of a single dose of carbamazepine (CBZ; 10 mg kg-1) was studied in eight healthy male subjects using a randomised balanced crossover design. 2 VPA alone had no effect on antipyrine clearance, urinary 6 beta-hydroxycortisol excretion and a battery of psychomotor function tests after 3 days' treatment despite achieving a mean steady-state concentration (90 +/- 6 mg 1(-1)) well within the target range (50-100 mg 1(-1)) for the drug. 3 VPA pre-treatment did not alter total CBZ area under the concentration-time curve (AUC 0-59 h) but did prolong CBZ elimination half life by 12% (P less than 0.01). AUC 0-59 h for free plasma CBZ was 13% higher (P less than 0.02) and half-life of unbound CBZ 16% longer (P less than 0.02) during VPA treatment. CBZ-10,11 epoxide (CBZ-E) levels (52%) and CBZ-E/CBZ ratios (45%) were both elevated by concurrent VPA (P less than 0.05) and free CBZ fraction was increased by 7% (P less than 0.02). 4 The sole effect of VPA on the psychomotor profile of CBZ was prolongation of card sorting time (P less than 0.05), although CBZ-related side effects were reported as more severe when VPA was also taken (P less than 0.01). 5 These data suggest that VPA displaces CBZ from plasma protein binding sites and inhibits the metabolism of both the parent drug and its epoxide.(ABSTRACT TRUNCATED AT 250 WORDS)

The risk-benefit ratio of anticonvulsant drugs

The concepts underlying the notion of a risk-benefit ratio for anticonvulsant therapy have determined the development of the drug treatment of epilepsy over many years. The risk element in the ratio arises from the various possible physical and psychological adverse effects of anticonvulsant therapy; the benefit is derived from the capacity of therapy to prevent seizures and thus reduce the disadvantages which result from having epilepsy. The physical adverse effects of anticonvulsant therapy may involve many tissues and organs. The drugs tend to depress cerebral, cerebellar and brain stem function, and may slow peripheral nerve conduction. Prolonged intake may cause hypocalcaemia and osteoporosis, folate depletion, various haematological and immunological abnormalities, and overgrowth of subcutaneous and gingival tissues. Idiopathic reactions may involve the skin, lymph nodes, liver, pancreas, kidney and thyroid, and cause electrolyte disturbances, while maternal anticonvulsant intake during pregnancy may be associated with an increased incidence of fetal malformations. Local reactions may occur at drug administration sites, and anticonvulsants may interact pharmacokinetically and pharmacodynamically with co-administered drugs. The taking of anticonvulsants sometimes has undesirable psychological effects on both the patient and his or her family. Epilepsy itself often results in adverse psychological consequences which emanate from the uncertainty and insecurity that is imposed by the unpredictable occurrence of seizures, from the limitations epilepsy sets on the patient's lifestyle and employment prospects, and from unfavourable community attitudes towards the disorder. Contemporary anticonvulsant therapy is not fully effective in all patients, but to the extent that it can control seizures it may help alleviate these emotional burdens that are a result of epilepsy. The consensus of present day medical opinion is that, in the great majority of clinical situations, the benefits of anticonvulsant therapy outweigh the disadvantages. However, to provide optimal management for individual patients, the risk-benefit ratio of therapy must be repeatedly assessed at all stages of a patient's treatment, and therapeutic decisions taken in the light of the ratio as it applies to the individual.

Free drug concentration monitoring in clinical practice. Rationale and current status

Recent advances in techniques to determine free drug concentrations have lead to a substantial increase in the monitoring of this parameter in clinical practice. The majority of drug binding to macromolecules in serum can be accounted for by association with albumin and alpha 1-acid glycoprotein. Albumin is the primary binding protein for acidic drugs, while binding to alpha 1-acid glycoprotein is more commonly observed with basic lipophilic agents. Alterations in the concentrations of either of these macromolecules can result in significant changes in free fraction. Diseases such as cirrhosis, nephrotic syndrome and malnourishment can result in hypoalbuminaemia. Burn injury, cancer, chronic pain syndrome, myocardial infarction, inflammatory diseases and trauma are all associated with elevations in the concentration of alpha 1-acid glycoprotein. Treatment with a number of drugs has also been shown to increase alpha 1-acid glycoprotein serum concentrations. A wide variety of biological fluids have been examined for their ability to provide an estimation of free drug concentration at receptor sites. The most useful fluid for estimating free drug concentrations appears to be plasma or serum, with subsequent treatment of the sample to separate free and bound drug by an appropriate technique. The two most widely used methods are equilibrium dialysis and ultrafiltration. Of these two, ultrafiltration has the greatest utility clinically because it is rapid and relatively simple. The major difficulty associated with this method involves the binding of drug to the ultrafilters, but significant progress has been made in solving this problem. Several authors have endorsed the routine use of free drug concentration monitoring. Data examining the clinical usefulness of free drug concentration monitoring for phenytoin, carbamazepine, valproic acid, disopyramide and lignocaine (lidocaine) are reviewed. While available evidence suggests that free concentrations may correlate with clinical effects better than total drug concentrations, there are insufficient data to justify the recommendation of the routine use of free drug concentration monitoring for any of these agents at present.

Aging variabilities of level-dose relationship in antiepileptic monopharmacy--with reference to drug interaction between mono- and bipharmacy

The influences of age, dose and comedication on the dose-level relationship were investigated using the ratio of plasma level to dose per body weight (microgram/ml/mg/kg/day) as an index in patients who had received the therapeutic doses of antiepileptic drug(s) for a long term. Samples of the blood concentrations were taken from 1,922 patients ranging in age from one to 40: 1,567 measured values were obtained under medication with phenobarbital (PB), phenytoin (PHT), carbamazepine (CBZ) or valproate (VPA) alone, and 2,201 under medication with any two of the above-mentioned antiepileptic drugs. With regard to PB, PHT, CBZ and VPA, when used alone, the L/D ratio was the lowest in the youngest age group, increased toward the latter half of teens, reached a peak at about age 20 and slightly decreased in the rest between the 20s and 30s. The age when the L/D ratio changes with aging is consistent with the age when the body weight of children obviously increases. As a result, during such a term, the fairly constant blood concentration can be maintained without overtly changing the daily dose. In the same age group given a single antiepileptic drug, the L/D ratio for PHT steeply increased at the dose of 4 in adults or 5 mg/kg/day in children, while the ratio rather decreased for CBZ and VPA. Clinical considerations should be paid to the fact that there was a non-linear relationship between the dose and the plasma concentration not only of PHT but of CBZ and VPA, and that the turning points were all within the range of therapeutic doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Valproic acid pharmacokinetics in children: III. Very high dosage requirements

Nine children were studied who required very high doses of valproic acid (VPA) (63.6-105 mg/kg/day) in order to achieve VPA serum concentrations between 50-100 micrograms/ml. These nine children had poorly controlled seizures and were receiving other antiepileptic drugs at the time of this study. The children with very high dose requirements were significantly lighter, shorter, and had less body surface area than the control group. Of the pharmacokinetic parameters studied, total and intrinsic clearance, distribution volume, and valproic acid free fraction were significantly increased in the very high dose group. In three patients who were investigated after co-medications were eliminated, clearances and dosage requirements decreased by more than 50%. We concluded that very high VPA dosages are sometimes required to achieve therapeutic serum drug concentrations and that this therapy occasionally improves seizure control. There were no adverse effects of very high dose therapy that required dosage reduction.

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

The 1,4-benzodiazepines have a recognised place in the treatment of epilepsy. Thus, diazepam, clonazepam, and, more recently, lorazepam are used intravenously for status epilepticus. Oral clonazepam has proved useful as adjunctive therapy in generalised absence seizures, myoclonic seizures, and partial seizures. Oral nitrazepam is well known for its use in the treatment of infantile spasms with hypsarrhythmia and in the myoclonic epilepsies of childhood. Clobazam, a 1,5-benzodiazepine, has been shown in controlled studies to be superior to placebo, and in open studies it has produced an overall reduction in seizure frequency of 65%. The main indication for its use is as oral adjunctive therapy in refractory epilepsy. It has a rapid onset of action, is well tolerated, and many studies indicate it has a psychotropic action and produces minimal or no cognitive impairment. The most common side-effect reported was sedation, while the overall incidence of side-effects in the open studies was 38%. In all studies reviewed, 4% of patients had to be withdrawn because of adverse reactions. In general, there are no significant interactions with other anticonvulsants, although changes in a few have been described. Withdrawal seizures can occur and require gradual termination of clobazam. The main disadvantage of clobazam is the development of tolerance, which develops in approximately 36% of patients, and there is no way of predicting in which patients or when the phenomenon is likely to occur. A dose of 20 to 30 mg at night is recommended, possibly commencing at 10 mg.

Antiepileptic drug toxicity: definition and mechanism of action

A detailed review of the adverse reactions of anticonvulsants is given, focusing on the definitions of drug toxicity, sources of information, patterns of drug utilization, pharmacokinetic variables and different mechanisms of action. The information available in the literature provides a wide spectrum of drug toxicity with no attempt at a practical definition of the reported events. This favors uncertainty among practising physicians, who are led to use the individual items with different attitudes. Suggestions are given for the evaluation, prevention and treatment of anticonvulsant drug toxicity.

Double-blind, placebo-controlled study of vigabatrin (gamma-vinyl GABA) in drug-resistant epilepsy

Vigabatrin (GVG) (3 g/day) and placebo were compared as an add-on to standard therapy in therapy-resistant epileptic patients using a double-blind crossover design with randomized treatment allocation. Twenty-three patients entered the trial, with four dropping out due to either increased seizure frequency following the cross-over from GVG to placebo (n = 1), intolerance to GVG therapy (n = 2), or poor seizure record (n = 1). Of the 19 patients who completed the study, 17 had partial seizures, eight of whom had secondary generalization and two who had primary generalized seizures. Compared with placebo, GVG was associated with a significant reduction in seizure frequency (p less than 0.01), with 11 of 19 patients experiencing greater than 50% reduction in weekly seizure occurrence, two showing a 25-50% reduction, four unchanged, and two showing an increase in seizures. Global efficacy ratings were greater in the GVG period for 15 patients (p less than 0.05) compared with one in whom there was no period difference and two in whom ratings were higher in the placebo period. Fourteen of the 19 patients indicated a preference for the GVG period. Adverse effects observed during GVG treatment were generally mild and consisted of drowsiness, confusion, nausea, irritability, and constipation. No clinically significant alterations in laboratory test results were observed. No treatment-related changes in plasma concentrations of concomitant antiepileptic drugs were noted. These results confirm the antiepileptic efficacy of oral GVG in refractory epileptics.

Effects of antiepileptic drugs on concentration of serum proteins and immunoglobulins of epileptic patients

Serum of normal volunteers and serum of epileptic patients receiving either a single drug or combined antiepileptic therapy with Phenytoin (Phen); Carbamazepine (Cbz); Primidone (Prim); Phenobarbital (Phb) were examined and showed: No differences with regard to total proteins, albumins and A/G ratio. The alpha 1-globulin fraction increased to 4.4% with Phen/Cbz (P less than 0.001) and decreased to 1.7% with Phen/Prim = (P less than 0.001). The alpha 2-globulins corresponded to 7.2% (P less than 0.001) with Phen/Prim and 15.5% (P less than 0.001) with Phen/Phb treatments. beta-Globulins decreased to 7.1% (P less than 0.05) when received Phen/Phb treatment. Low concentrations of serum gamma-Globulins were found in Phb (P less than 0.001), Prim (P less than 0.001, Phen (P less than 0.001) treated patients. However, with Cbz, Phen/Phb, Phen/Prim this electrophoretic fraction remained within the upper range of normal. IgA of patients treated with Phen showed a mean of 60 mg/dl. Those patients with Phen serum levels below or above 12-20 micrograms/ml remained normal. Prim and Phb treatment also decreased IgA. IgD was normal in patients treated with Phen/Prim. Alterations of immune humoral responses to all antiepileptic drugs were found.

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).