Adverse effects of established and new antiepileptic drugs: an attempted comparison

GABAergic Mechanisms Can Redress the Tilted Balance between Excitation and Inhibition in Damaged Spinal Networks

Correct operation of neuronal networks depends on the interplay between synaptic excitation and inhibition processes leading to a dynamic state termed balanced network. In the spinal cord, balanced network activity is fundamental for the expression of locomotor patterns necessary for rhythmic activation of limb extensor and flexor muscles. After spinal cord lesion, paralysis ensues often followed by spasticity. These conditions imply that, below the damaged site, the state of balanced networks has been disrupted and that restoration might be attempted by modulating the excitability of sublesional spinal neurons. Because of the widespread expression of inhibitory GABAergic neurons in the spinal cord, their role in the early and late phases of spinal cord injury deserves full attention. Thus, an early surge in extracellular GABA might be involved in the onset of spinal shock while a relative deficit of GABAergic mechanisms may be a contributor to spasticity. We discuss the role of GABA A receptors at synaptic and extrasynaptic level to modulate network excitability and to offer a pharmacological target for symptom control. In particular, it is proposed that activation of GABA A receptors with synthetic GABA agonists may downregulate motoneuron hyperexcitability (due to enhanced persistent ionic currents) and, therefore, diminish spasticity. This approach might constitute a complementary strategy to regulate network excitability after injury so that reconstruction of damaged spinal networks with new materials or cell transplants might proceed more successfully.

Fabrication and characterization of biocompatible pH responsive halloysite nanotubes grafted with sodium alginate for sustained release of phenytoin sodium

Schematic design of a new method for fabrication of biocompatible pH sensitive halloysite nanocomposites for controlled release of phenytoin sodium.

Outcome Evaluation of Gabapentin as Add-on Therapy for Partial Seizures

Objective:

The safety, tolerability, efficacy, and impact on quality of life of gabapentin (Neurontin®) as adjunctive therapy to carbamazepine (CBZ) and/or phenytoin (PHT) was assessed in epileptic patients with partial seizures.

Methods:

NEON (Neurontin Evaluation of Outcomes in Neurological Practice) was an open-label, prospective, multicentre study conducted in patients on a stable dose of CBZ and/or PHT and experiencing an average of up to 4 complex partial seizures with or without secondary generalization per month, with no seizure-free months. The treatment lasted 20 weeks. Gabapentin was started at 400 mg/day and was individually titrated to effective tolerable dose up to 2400 mg/day. Quality of life was evaluated using the QOLIE-10 questionnaire.

Results:

A total of 141 patients were enrolled at 36 sites; 114 patients were evaluable for efficacy analyses. The mean maintenance dose of gabapentin was 1600 mg/day (range = 300-3200). A decrease of 50% or more in frequency of complex partial + secondarily generalized seizures was observed in 81 (71 %) patients (p = 0.0001). Fifty two (46%) patients were seizure-free during the last 8 weeks of treatment. A significant improvement (p < 0.05) was observed in 5 of the 10 questions of the QOLIE-10, as well as in the composite QOL score (p = 0.0002). The most frequent adverse events included somnolence (16%), dizziness (9%), and asthenia (6%). Twenty-five (18%) patients prematurely discontinued the study, 16 (11%) of them due to adverse events.

Conclusion:

This study indicates that treatment with gabapentin as adjunctive therapy to standard antiepileptic drugs in this group of patients not only provides significant improvement in seizure control, but also has a positive impact on quality of life. The clinical benefits in efficacy, safety and tolerability demonstrated at 20 weeks are sustained, and no tolerance develops with gabapentin in longer term use.

UV-photoconversion of ethosuximide from a longevity-promoting compound to a potent toxin

The anticonvulsant ethosuximide has been previously shown to increase life span and promote healthspan in the nematode Caenorhabditis elegans at millimolar concentrations. Here we report that following exposure to ultraviolet irradiation at 254 nm, ethosuximide is converted into a compound that displays toxicity toward C. elegans. This effect is specific for ethosuximide, as the structurally related compounds trimethadione and succinimide do not show similar toxicities following UV exposure. Killing by UV-irradiated ethosuximide is not attenuated in chemosensory mutants that are resistant to toxicity associated with high doses of non-irradiated ethosuximide. Non-irradiated ethosuximide extends life span at 15°C or 20°C, but not at 25°C, while irradiated ethosuximide shows similar toxicity at all three temperatures. Dietary restriction by bacterial deprivation does not protect against toxicity from irradiated ethosuximide, while non-irradiated ethosuximide further extends the long life spans of restricted animals. These data support the model that ethosuximide extends life span by a mechanism that is, at least partially, distinct from dietary restriction by bacterial deprivation and demonstrates an unexpected photochemical conversion of ethosuximide into a toxic compound by UV light.

Safety, Tolerability, and Pharmacokinetic Profile of BIA 2-093, a Novel Putative Antiepileptic, in a Rising Multiple-Dose Study in Young Healthy Humans

This was a double-blind, randomized, placebo-controlled study to investigate rising oral doses of BIA 2-093 (S-(-)-10-acetoxy-10,11-dihydro-5H-dibenz/b,f/azepine-5-carboxamide), a putative new antiepileptic drug. Within each of 4 dosage groups of 8 healthy male adult subjects, 2 subjects were randomized to receive placebo, and the remaining 6 subjects were randomized to receive BIA 2-093 (200 mg bid, 400 mg qd, 800 mg qd, and 1200 mg qd) for 8 days. Concentrations of BIA 2-093 in plasma or urine were generally not measurable. Median maximum plasma concentrations of the major metabolite (licarbazepine, (+/-)-10,11-dihydro-10-hydroxy-5H-dibenz/b,f/azepine-5-carboxamide) were attained (t(max)) at 2 to 3 h postdose; thereafter, plasma concentrations declined with a mean apparent terminal half-life of 9 to 13 h following repeated dosing. The extent of systemic exposure to licarbazepine increased in an approximately dose-proportional manner following single and repeated administration. Licarbazepine accumulated in plasma following repeated administration of BIA 2-093; the mean extent of accumulation (R(O), calculated from AUC(0-tau) (day 8)/AUC(0-tau) (day 1)) was 3.0 after repeated, twice-daily dosing and 1.4 to 1.7 after once-daily dosing. Steady-state plasma licarbazepine concentrations were attained at 4 to 5 days of once- or twice-daily dosing, consistent with an effective half-life on the order of 20 to 24 h. The mean renal clearance of licarbazepine from plasma was approximately 20 to 30 mL/min, which is low compared with the glomerular filtration rate. The total amount of licarbazepine recovered in urine was approximately 20% within 12 h postdose and 40% within 24 h postdose. All adverse events were mild in severity, except for 1 case of somnolence of moderate severity, which occurred in a subject receiving 1200 mg BIA 2-093. The incidence of adverse events was similar between all treatment groups, including placebo. There were no serious adverse events. In conclusion, BIA 2-093 was well tolerated and appeared to be rapidly and extensively metabolized to licarbazepine following single and repeated administration to healthy young subjects.

Characteristics of selected second-generation antiepileptic drugs used in dogs

A significant number of cases of clinical canine epilepsy remain difficult to control in spite of the applied treatment. At the same time, the range of antiepileptic drugs is increasingly wide, which allows efficient treatment. In the present paper we describe the pharmacodynamics and pharmacokinetics of the newer antiepileptic drugs which were licensed after 1990 but are still not widely used in veterinary medicine. The pharmacokinetic profiles of six of these drugs were tested on dogs. The results of experimental studies suggest that second generation antiepileptic drugs may be applied in mono- as well as in poli- treatment of canine epilepsy because of the larger safety margin and more advantageous pharmacokinetic parameters. Knowledge of the drugs' pharmacokinetics allows its proper clinical appliance, which, in turn, gives the chance to improve the efficiency of pharmacotherapy of canine epilepsy.

The relationship among side effects associated with anti-epileptic medications in those with intellectual disability

Seizures are fairly common in those with intellectual disabilities. In order to treat these seizures, antiepileptic drugs (AEDs) are often used and in many cases are effective. However, these medications often create a variety of associated side effects. In order to monitor these side effects, measures such as the SEIZES-B have been used. While many side effects have been found to occur with the use of AEDs, research has not explored if certain side effects are more likely to co-occur. For the current study, 281 people with intellectual disability were administered the SEIZES-B to monitor side effects associated with AEDs. Correlations between side effect subscales were then computed. Several subscales were found to be significantly correlated: hepatic disturbance with dermatological changes and cognitive disturbance; respiratory disturbance with dermatological changes, sedation, and electrolyte disturbance; and cognitive disturbance with sedation and dermatological disturbance. Possible implications of these findings are discussed.

Difficulties in Treatment and Management of Epilepsy and Challenges in New Drug Development

Epilepsy is a serious neurological disorder that affects around 50 million people worldwide. Almost 30% of epileptic patients suffer from pharmacoresistance, which is associated with social isolation, dependent behaviour, low marriage rates, unemployment, psychological issues and reduced quality of life. Currently available antiepileptic drugs have a limited efficacy, and their negative properties limit their use and cause difficulties in patient management. Antiepileptic drugs can provide only symptomatic relief as these drugs suppress seizures but do not have ability to cure epileptogenesis. The long term use of antiepileptic drugs is limited due to their adverse effects, withdrawal symptoms, deleterious interactions with other drugs and economic burden, especially in developing countries. Furthermore, some of the available antiepileptic drugs may even potentiate certain type of seizures. Several in vivo and in vitro animal models have been proposed and many new antiepileptic drugs have been marketed recently, but large numbers of patients are still pharmacoresistant. This review will highlight the difficulties in treatment and management of epilepsy and the limitations of available antiepileptic drugs and animal seizure models.

Psychological well-being of people with epilepsy in Norway

The subjective well-being of people with epilepsy has been studied extensively, but only sparingly in Norway. In 2005, members of the Norwegian Epilepsy Association responded to a short version of the Hopkins Symptom Check List ("psychological distress") and to a version of the Self-Anchoring Striving Scale, also termed the Cantril Ladder ("life satisfaction"). In this article, the relationships between responses to the two questionnaires (the two outcome variables) and seizure frequency, medication side effects, comorbidity, and surgery, as well as demographic variables such as age, sex, marital status, occupational status, education, and place of residence, are addressed. The analyses demonstrate clear effects of seizure frequency (P<0.001) and medication side effects (P<0.001) on both outcome variables. People with no comorbidity (no additional diagnoses) reported less psychological distress (P<0.001) and greater satisfaction with life (P<0.05) than those who reported additional diagnoses. The factor having the strongest impact on the psychological well-being of these people was medication side effects.

Ethosuximide: from bench to bedside

Ethosuximide, 2-ethyl-2-methylsuccinimide, has been used extensively for "petit mal" seizures and it is a valuable agent in studies of absence epilepsy. In the treatment of epilepsy, ethosuximide has a narrow therapeutic profile. It is the drug of choice in the monotherapy or combination therapy of children with generalized absence (petit mal) epilepsy. Commonly observed side effects of ethosuximide are dose dependent and involve the gastrointestinal tract and central nervous system. Ethosuximide has been associated with a wide variety of idiosyncratic reactions and with hematopoietic adverse effects. Typical absence seizures are generated as a result of complex interactions between the thalamus and the cerebral cortex. This thalamocortical circuitry is under the control of several specific inhibitory and excitatory systems arising from the forebrain and brainstem. Corticothalamic rhythms are believed to be involved in the generation of spike-and-wave discharges that are the characteristic electroencephalographic signs of absence seizures. The spontaneous pacemaker oscillatory activity of thalamocortical circuitry involves low threshold T-type Ca2+ currents in the thalamus, and ethosuximide is presumed to reduce these low threshold T-type Ca2+ currents in thalamic neurons. Ethosuximide also decreases the persistent Na+ and Ca2+ -activated K+ currents in thalamic and layer V cortical pyramidal neurons. In addition, there is evidence that in a genetic absence epilepsy rat model ethosuximide reduces cortical gamma-aminobutyric acid (GABA) levels. Also, elevated glutamate levels in the primary motor cortex of rats with absence epilepsy (but not in normal animals) are reduced by ethosuximide.

The adverse effects of antiepileptic drugs in children

Efficacy of antiepileptic drugs (AEDs) are often equivalent, hence selection of an AED is often determined by the adverse effects (AEs). The development of neurocognitive AEs is almost inevitable with use of AEDs, especially in high-risk groups. Teratogenesis with major or minor malformations is of great concern during the first trimester of pregnancy, but an increasing body of information suggests that potential neurocognitive developmental delay may also occur with use of AEDs in the latter part of pregnancy. Decreased bone mineral density has been found in adults and children receiving both enzyme-inducing AEDs and valproate, an enzyme-inhibiting drug. AEDs may influence the lipid profile, body weight, reproductive, hormonal and other endocrine functions, and sleep architecture. There are age-specific AEs related to pharmacokinetic differences that have been highlighted in this review with emphasis on the pediatric population. A classification of AEs using different parameters is also included.

Algorithm for neuropathic pain treatment: an evidence based proposal

New studies of the treatment of neuropathic pain have increased the need for an updated review of randomized, double-blind, placebo-controlled trials to support an evidence based algorithm to treat neuropathic pain conditions. Available studies were identified using a MEDLINE and EMBASE search. One hundred and five studies were included. Numbers needed to treat (NNT) and numbers needed to harm (NNH) were used to compare efficacy and safety of the treatments in different neuropathic pain syndromes. The quality of each trial was assessed. Tricyclic antidepressants and the anticonvulsants gabapentin and pregabalin were the most frequently studied drug classes. In peripheral neuropathic pain, the lowest NNT was for tricyclic antidepressants, followed by opioids and the anticonvulsants gabapentin and pregabalin. For central neuropathic pain there is limited data. NNT and NNH are currently the best way to assess relative efficacy and safety, but the need for dichotomous data, which may have to be estimated retrospectively for old trials, and the methodological complexity of pooling data from small cross-over and large parallel group trials, remain as limitations.

Isobolographic and subthreshold methods in the detection of interactions between oxcarbazepine and conventional antiepileptics--a comparative study

Until now, a character of interactions among the antiepileptic drugs (AEDs), in some experimental models of epilepsy, has been determined alternatively with subthreshold and isobolographic methods. In order to elicit the precise and adequate method for evaluating two drug interactions, the comparative study was performed in the maximal electroshock-induced seizure test in mice. In this experimental model, the exact types of interactions among oxcarbazepine (OXC) and conventional AEDs (diphenylhydantoin, phenobarbital, valproate, carbamazepine, and clonazepam) were determined with both methods. Results from the subthreshold method showed a considerable reduction of ED(50) values of clonazepam, diphenylhydantoin and valproate (after administration of OXC at the highest subthreshold dose of 2.5 mg/kg), whilst ED(50)s of carbamazepine or phenobarbital were almost unchanged when OXC (2.5 mg/kg) was co-administered with these AEDs. Results from the 2-dimensional (2-D) isobolographic analysis of interactions for a 50% anticonvulsant effect, for three fixed drug dose ratio combinations of 1:2, 1:1, and 2:1, indicate antagonism between OXC and diphenylhydantoin as regards their anticonvulsant (protective) activity. Furthermore, the interactions between OXC and clonazepam occurred either antagonistic (for the fixed-ratios of 1:4 and 1:3) or synergistic (for the fixed-ratio combinations of 1:1 and 2:1) depending on the proportions of used drugs. Remaining interactions between OXC and carbamazepine, OXC and valproate, or OXC and phenobarbital (for the fixed-ratios of 1:3, 1:1, and 3:1) were isobolographically additive for a 50% anticonvulsant effect tested. The 3-dimensional (3-D) isobolographic analysis of interactions between OXC and CZP revealed that the dual character of interactions (antagonistic and synergistic) observed for a 50% anticonvulsant effect (ED(50)) was also present for additional drug-dose effects tested, i.e. ED(16) and ED(84). The 3-D isobologram for the combination of OXC with CZP clearly visualized either synergy or antagonism between the drugs in combinations.Distinct differences resulting from two experimental methods prove evidently the superiority of isobolographic analysis over the subthreshold method. The former clearly and adequately detects the exact types of interactions between two AEDs, becoming a potent and powerful paradigm for further studies evaluating the character of interactions among AEDs.

Interactions between oxcarbazepine and conventional antiepileptic drugs in the maximal electroshock test in mice: an isobolographic analysis

PURPOSE

The aim of this study was to determine the types of interactions between oxcarbazepine (OCBZ) and conventional antiepileptic drugs (AEDs) against maximal electroshock-induced seizures (MES test) in mice, by using a method of isobolographic analysis.

METHODS

Adverse effects of combinations were evaluated in the chimney test (motor performance), also using the isobolographic method, which allowed determination of the median toxic dose (TD50) values for individual combinations; thus the protective indices could be determined.

RESULTS

OCBZ and phenytoin (PHT) at the fixed-ratio combination of 1:1 were significantly infraadditive (antagonistic) with respect to the antiseizure protection against MES and simultaneously additive in terms of side effects in the chimney test. Interestingly, combinations between OCBZ and clonazepam (CZP) in the MES test proved antagonistic or synergistic, depending on the proportion of both AEDs in the mixture. Low doses of OCBZ with high doses of CZP exerted antagonism. Conversely, high doses of OCBZ combined with low doses of CZP resulted in a synergistic interaction. Remaining combinations between OCBZ and phenobarbital, valproate, or carbamazepine were purely additive, either as regards the anticonvulsant activity against MES or in terms of motor impairment in the chimney test.

CONCLUSIONS

The results of this study indicate that interaction of OCBZ and CZP at fixed-ratio combination of 1:1 might be profitable from a clinical point of view. Conversely, combinations of OCBZ with PHT may not be clinically efficient.

Antagonists of GLU(K5)-containing kainate receptors prevent pilocarpine-induced limbic seizures

Developments in the molecular biology and pharmacology of GLU(K5), a subtype of the kainate class of ionotropic glutamate receptors, have enabled insights into the roles of this subunit in synaptic transmission and plasticity. However, little is known about the possible functions of GLU(K5)-containing kainate receptors in pathological conditions. We report here that, in hippocampal slices, selective antagonists of GLU(K5)-containing kainate receptors prevented development of epileptiform activity--evoked by the muscarinic agonist, pilocarpine--and inhibited the activity when it was pre-established. In conscious rats, these GLU(K5) antagonists prevented and interrupted limbic seizures induced by intra-hippocampal pilocarpine perfusion, and attenuated accompanying rises in extracellular L-glutamate and GABA. This anticonvulsant activity occurred without overt side effects. GLU(K5) antagonism also prevented epileptiform activity induced by electrical stimulation, both in vitro and in vivo. Therefore, we propose that subtype-selective GLU(K5) kainate receptor antagonists offer a potential new therapy for epilepsy.

Adjunctive agents in the management of chronic pain

Chronic pain syndromes include cancer-related pain, postherpetic neuralgia, painful diabetic neuropathy, and central poststroke pain and are common in the elderly. Adjunctive (or adjuvant) analgesics, defined as drugs that do not contain acetaminophen and those not classified as nonsteroidal antiinflammatory or opioid agents, play a role in the management of chronic pain. The term "adjunctive" (or "adjuvant") is a misnomer as several of these agents may constitute first-line therapy for many chronic pain syndromes. Tricyclic antidepressants have formed the backbone of therapy for chronic neuropathic pain for years. However, the difficulty with using agents of this class, due to their clinically significant adverse-event potential, has led to the evaluation of other agents, most notably, the antiepileptic drugs. The most useful are gabapentin, carbamazepine, and lamotrigine. In selected patients, baclofen, mexiletine, and clonidine may be useful as well. Cancer-related pain may respond substantially to corticosteroids, and pain associated with bone metastases to parenteral bisphosphonates and strontium. Practitioners should consider these alternative agents when treating chronic pain.

Metabolism of two new antiepileptic drugs and their principal metabolites S(+)- and R(-)-10,11-dihydro-10-hydroxy carbamazepine

BIA 2-093 and BIA 2-059 are two stereoisomers under development as new antiepileptic drugs. They act as prodrugs for the corresponding hydroxy derivatives (S(+)- or R(-)-10,11-dihydro-10-hydroxy carbamazepine, respectively) which are known to be the active metabolites of the antiepileptic drug oxcarbazepine (OXC). The purpose of this study was to define the metabolic pathway especially in terms of stereoselectivity, and to estimate the possibility of racemization in humans. For in vivo studies, the rat, mouse and rabbit were chosen as models in order to cover a broad spectrum of metabolic activity. In addition, incubations with liver microsomes from these three species plus dog and monkey were compared to results obtained with human liver microsomes. It was found that both drugs were almost instantly hydrolysed to the corresponding 10-hydroxy compounds in mice, rats and rabbits. Mice and rabbits were not able to oxidize the 10-hydroxy compounds to OXC in significant amounts. In the rat, BIA 2-093 also gave origin to OXC, whereas BIA 2-059 resulted in the formation of OXC and the trans-diol metabolite in equal amounts. It could be shown that the rat is able to reduce the formed OXC in liver to S(+)-10-hydroxy metabolite, resulting in a loss of enantiomeric purity after treatment with BIA 2-059 rather than in the case of BIA 2-093. Human liver microsomes hydrolysed BIA 2-093 and BIA 2-059 to their corresponding 10-hydroxy compounds and to OXC in a very small extent with BIA 2-093 only. Therefore, BIA 2-093 and BIA 2-059 seem to be preferable drugs over OXC since they most likely exhibit a 'cleaner' metabolism. From a therapeutic point of view BIA 2-059 would be less appropriate than BIA 2-093 for the purpose of treating epileptic patients due to its propensity to undergo inactivation to the trans-diol.

New drugs for epilepsy

Seizure freedom with no side-effects is the aim of treatment, and new antiepileptic drugs have not lived up to expectations; only a few patients with chronic epilepsy have been rendered seizure-free. These treatments have side-effects but their safety profile may be better than older alternatives, although chronic effects have not yet been established. This article reviews newly marketed antiepileptic drugs. It concentrates on shortcomings of current antiepileptic treatment and on the way drugs are developed. A new approach to treatment is long overdue. The development of rational antiepileptic treatments should be strongly encouraged. More clinically relevant paradigms need to be developed and incorporated into clinical trial programmes as these are presently biased in their designs towards regulatory issues.

New visions in the pharmacology of anticonvulsion

Seizures are resistant to treatment with currently available anticonvulsant drugs in about 1 out of 3 patients with epilepsy. Thus, there is a need for new, more effective anticonvulsant drugs for intractable epilepsy. Furthermore, because of the inadequacy of the currently available anticonvulsant armamentarium with respect to safety, newly developed drugs should be less toxic than existing drugs. Previous and current strategies for development of novel anticonvulsants with improved efficacy or safety are critically discussed in this review. 'Old drugs' (or 'first generation' drugs), which were developed and introduced between 1910 and 1970, are compared with new anticonvulsants both in terms of clinical efficacy and safety and in terms of mechanisms of action. The new drugs are referred to as 'second generation' drugs, i.e. anticonvulsants which have been introduced into clinical practice in recent years, or 'third generation' drugs, i.e. compounds in the pipeline of development. In spite of some 30 years of 'modern' neuroscientific epilepsy research, most novel, clinically effective second generation anticonvulsants have been found by screening (i.e. serendipity) or structural variation of known drugs and not by rational strategies based on knowledge of processes involved in generation of seizures or in development of epilepsy. An exception are only the GABA (gamma-aminobutyrate)-mimetic drugs vigabatrin and tiagabine and, to some extent, gabapentin, which have been developed by a rational strategy, i.e. the 'GABA hypothesis' of epilepsy. The fact that preclinical seizure models used for identification and development of novel drugs have been originally validated by old drugs, i.e. conventional anticonvulsants, may explain that several of the new drugs possess mechanisms which do not differ from those of the standard drugs. This may also explain that none of the new drugs seems to offer any marked advantage towards the old, first generation drugs with respect to the ultimate goal of drug treatment of epilepsy, i.e. complete control of seizures, although some of the second generation drugs may have benefits in terms of side effects and tolerability. It is to be hoped that the various novel currently used or planned strategies for drug development produce more effective and safe anticonvulsants than previous strategies. This goal can only be achieved by strengthening our understanding of the fundamental pathophysiology of seizure expression and epileptogenesis as theoretical substrates for new pharmacological strategies, and by devising and refining laboratory models for studying new agents obtained by such strategies.