Molecular pharmacodynamics, clinical therapeutics, and pharmacokinetics of topiramate

Topiramate: A Review of Analytical Approaches for the Drug Substance, Its Impurities and Pharmaceutical Formulations

An important step during the development of high-performance liquid chromatography (HPLC) methods for quantitative analysis of drugs is choosing the appropriate detector. High sensitivity, reproducibility, stability, wide linear range, compatibility with gradient elution, non-destructive detection of the analyte and response unaffected by changes in the temperature/flow are some of the ideal characteristics of a universal HPLC detector. Topiramate is an anticonvulsant drug mainly used for the treatment of different types of seizures and prophylactic treatment of migraine. Different analytical approaches to quantify topiramate by HPLC have been described because of the lack of chromophoric moieties on its structure, such as derivatization with fluorescent moieties and UV-absorbing moieties, conductivity detection, evaporative light scattering detection, refractive index detection, chemiluminescent nitrogen detection and MS detection. Some methods for the determination of topiramate by capillary electrophoresis and gas chromatography have also been published. This systematic review provides a description of the main analytical methods presented in the literature to analyze topiramate in the drug substance and in pharmaceutical formulations. Each of these methods is briefly discussed, especially considering the detector used with HPLC. In addition, this article presents a review of the data available regarding topiramate stability, degradation products and impurities.

Pharmacotherapy for alcohol dependence: A stratified approach

Alcohol dependence is a common disorder in many societies worldwide, and remains difficult to identify and treat. It is also a risk factor for many secondary non-communicable diseases. Pharmacotherapy is one available treatment option, but appears to be underutilised in practice. Major barriers to use of medications in this area include lack of clinical guidance and questionable efficacy. However, for each medication there appears to be a subpopulation that responds positively, and understanding the moderating factors to treatment efficacy is an important research goal. Thus, this review provides a narrative regarding potential stratification techniques in pharmacological treatment of alcohol dependence, with a specific focus on typologies and pharmacogenetics. In addition, we discuss the basic background of stratified medicine and recent studies on genetic predisposition to alcohol dependence. A growing repository of data exists for both approved and non-approved pharmacotherapies, but failure to replicate findings, inadequate sample sizes, and insufficient funding has resulted in a translational gap. Implementing evidence-based stratified/personalised therapy and identifying new therapeutic agents may lead to improved clinical outcomes and reduced financial burden. Despite some promising findings to date, much work is still required.

Chronic migraine - new treatment options

Chronic migraine (CM) is defined as headache occurring more than fifteen days/month for at least three consecutive months, with headache having the clinical features of migraine without aura for at least eight days per month. Recently, new treatment options became available in chronic migraine patients. Topiramate is effective in chronic migraine, in the presence or absence of medication overuse, and/or other migraine prophylaxis. Efficacy of onabotulinumtoxin A as a preventive treatment of chronic migraine has been shown in the PREEMPT studies. Occipital nerve stimulation (ONS) is an invasive treatment for refractory chronic headaches. ONS has encouraging results in refractory chronic migraine patients in commercially funded, multi-centre randomized trials.

Effects of naltrexone plus topiramate on ethanol self-administration and tyrosine hydroxylase gene expression changes

The purpose of this study was to evaluate the effects of naltrexone (0.7 mg/kg) and/or topiramate (25 mg/kg) on ethanol consumption and the motivation to drink in an oral-operant conditioning paradigm in C57BL/6 mice. Subsequent real-time polymerase chain reaction (PCR) experiments were performed to analyze gene expression changes in tyrosine hydroxylase (TH) in the ventral tegmental area (VTA). The administration of naltrexone significantly reduced ethanol consumption and the motivation to drink during the different stages of the experiment, whereas the treatment with topiramate resulted in a much lower effect. Interestingly, the administration of naltrexone plus topiramate reduced ethanol consumption markedly compared with single-drug treatment. The water self-administration paradigm was also performed using the same drugs and no differences were found between treatment groups. Real-time PCR analyses revealed that naltrexone significantly normalized the increase of TH gene expression in the VTA induced by ethanol, whereas the administration of topiramate did not produce any significant effect. In the ethanol self-administration procedure, the combination of both drugs further reduced TH gene expression, reaching statistical significance compared with the vehicle, naltrexone or topiramate groups. Taken together, these findings indicate that the administration of naltrexone plus topiramate further reduced ethanol consumption and the motivation to drink in comparison with single-drug treatment. This action may be due, at least in part, to a greater decrease in TH gene expression in the VTA. These results suggest that the combination of both drugs deserves further exploration for the treatment of problems related to alcohol consumption.

Pharmacokinetic interactions between topiramate and pioglitazone and metformin

OBJECTIVE

To investigate potential drug-drug interactions between topiramate and metformin and pioglitazone at steady state.

METHODS

Two open-label studies were performed in healthy adult men and women. In Study 1, eligible participants were given metformin alone for 3 days (500 mg twice daily [BID]) followed by concomitant metformin and topiramate (titrated to 100mg BID) from days 4 to 10. In Study 2, eligible participants were randomly assigned to treatment with pioglitazone 30 mg once daily (QD) alone for 8 days followed by concomitant pioglitazone and topiramate (titrated to 96 mg BID) from days 9 to 22 (Group 1) or to topiramate (titrated to 96 mg BID) alone for 11 days followed by concomitant pioglitazone 30 mg QD and topiramate 96 mg BID from days 12 to 22 (Group 2). An analysis of variance was used to evaluate differences in pharmacokinetics with and without concomitant treatment; 90% confidence intervals (CI) for the ratio of the geometric least squares mean (LSM) estimates for maximum plasma concentration (Cmax), area under concentration-time curve for dosing interval (AUC12 or AUC24), and oral clearance (CL/F) with and without concomitant treatment were used to assess a drug interaction.

RESULTS

A comparison to historical data suggested a modest increase in topiramate oral clearance when given concomitantly with metformin. Coadministration with topiramate reduced metformin oral clearance at steady state, resulting in a modest increase in systemic metformin exposure. Geometric LSM ratios and 90% CI for metformin CL/F and AUC12 were 80% (75%, 85%) and 125% (117%, 134%), respectively. Pioglitazone had no effect on topiramate pharmacokinetics at steady state. Concomitant topiramate resulted in decreased systemic exposure to pioglitazone and its active metabolites, with geometric LSM ratios and 90% CI for AUC24 of 85.0% (75.7%, 95.6%) for pioglitazone, 40.5% (36.8%, 44.6%) for M-III, and 83.8% (76.1%, 91.2%) for M-IV, respectively. This effect appeared more pronounced in women than in men. Coadministration of topiramate with metformin or pioglitazone was generally well tolerated by healthy participants in these studies.

CONCLUSIONS

A modest increase in metformin exposure and decrease in topiramate exposure was observed at steady state following coadministration of metformin 500 mg BID and topiramate 100mg BID. The clinical significance of the observed interaction is unclear but is not likely to require a dose adjustment of either agent. Pioglitazone 30 mg QD did not affect the pharmacokinetics of topiramate at steady state, while coadministration of topiramate 96 mg BID with pioglitazone decreased steady-state systemic exposure to pioglitazone, M-III, and M-IV. While the clinical consequence of this interaction is unknown, careful attention should be given to the routine monitoring for adequate glycemic control of patients receiving this concomitant therapy. Concomitant administration of topiramate with metformin or pioglitazone was generally well tolerated and no new safety concerns were observed.

Randomized clinical trial of topiramate for levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND

The antiepileptic drug topiramate reduces levodopa-induced dyskinesia without exacerbating parkinsonism in animal models. We report a randomized, double-blind, placebo-controlled crossover trial in patients with Parkinson's disease and levodopa-induced dyskinesia.

METHODS

Fifteen patients with Parkinson's disease and stable levodopa-induced dyskinesia were enrolled into the study, of whom 13 were randomized to topiramate or placebo. The study medication was titrated to 100 mg/day over four weeks, and assessments were carried out after a further two weeks. Dyskinesia severity assessed by a blinded rater from video recordings was the primary outcome measure.

RESULTS

Seven patients (mean age 58.9 ± 12.8 years) completed the study. Patients taking topiramate vs. placebo showed a significant increase in dyskinesia severity compared to baseline (Wilcoxon signed rank test, P = 0.043). Five patients withdrew from the study whilst taking topiramate due to adverse effects.

CONCLUSIONS

Topiramate tended to worsen dyskinesia in patients with Parkinson's disease, and was poorly tolerated.

Novel, broad-spectrum anticonvulsants containing a sulfamide group: pharmacological properties of (S)-N-[(6-chloro-2,3-dihydrobenzo[1,4]dioxin-2-yl)methyl]sulfamide (JNJ-26489112)

Broad-spectrum anticonvulsants are of considerable interest as antiepileptic drugs, especially because of their potential for treating refractory patients. Such "neurostabilizers" have also been used to treat other neurological disorders, including migraine, bipolar disorder, and neuropathic pain. We synthesized a series of sulfamide derivatives (4-9, 10a-i, 11a, 11b, 12) and evaluated their anticonvulsant activity. Thus, we identified promising sulfamide 4 (JNJ-26489112) and explored its pharmacological properties. Compound 4 exhibited excellent anticonvulsant activity in rodents against audiogenic, electrically induced, and chemically induced seizures. Mechanistically, 4 inhibited voltage-gated Na(+) channels and N-type Ca(2+) channels and was effective as a K(+) channel opener. The anticonvulsant profile of 4 suggests that it may be useful for treating multiple forms of epilepsy (generalized tonic-clonic, complex partial, absence seizures), including refractory (or pharmacoresistant) epilepsy, at dose levels that confer a good safety margin. On the basis of its pharmacology and other favorable characteristics, 4 was advanced into human clinical studies.

'Possessed': acute confusional migraine in an adolescent, prevented by topiramate

Acute confusional migraine (ACM) is recognized as a rare, but highly disabling migraine equivalent, mostly reported in children and adolescents. Herein we describe the case of a 12-year-old girl admitted to hospital for an acute confusional state and severe psychomotor agitation, associated with a pulsating headache and nausea, which turned out to be a manifestation of ACM. The girl was discharged on topiramate prophylaxis, titrated up to 75 mg/die; no recurrence of confusional and/or headache episodes has been reported over the last 14 months to date. Due to the rarity of this clinical entity, only anecdotal reports about acute and prophylactic treatment of ACM are available in the literature. The case reported herein suggests that topiramate seems to be effective in ACM prophylaxis, although a longer observation period in our patient and more cases are needed to confirm any long-term clinical benefit.

Pregabalin- and topiramate-mediated regulation of cognitive and motor impulsivity in DBA/2 mice

BACKGROUND AND PURPOSE

Impulsivity is a core symptom in many neuropsychiatric disorders. The main objective of this study was to evaluate the effects of topiramate and pregabalin on the modulation of different impulsivity dimensions in DBA/2 mice.

EXPERIMENTAL APPROACH

The effects of acute and chronic administration of pregabalin (10, 20 and 40 mg·kg(-1) ) and topiramate (12.5, 25 and 50 mg·kg(-1) ) were evaluated in the light-dark box (LDB), hole board test (HBT) and delayed reinforcement task (DRT). α(2A) -Adrenoceptor, D(2) -receptor and TH gene expression were evaluated by real-time PCR in the prefrontal cortex (PFC), accumbens (ACC) and ventral tegmental area (VTA), respectively.

KEY RESULTS

Acute pregabalin administration showed a clear anxiolytic-like effect (LDB) but did not modify novelty-seeking behaviour (HBT). In contrast, topiramate produced an anxiolytic effect only at the highest dose, whereas it reduced novelty seeking at all doses tested. In the DRT, acute pregabalin had no effect, whereas topiramate only reduced motor impulsivity. Chronically, pregabalin significantly increased motor impulsivity and topiramate diminished cognitive impulsivity. Pregabalin decreased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and increased TH in the VTA. In contrast, chronic administration of topiramate increased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and also increased TH in the VTA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the usefulness of pregabalin in impulsivity-related disorders is related to its anxiolytic properties, whereas topiramate modulates impulsivity. These differences could be linked to their opposite effects on α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively.

Neurological perspectives on voltage-gated sodium channels

The activity of voltage-gated sodium channels has long been linked to disorders of neuronal excitability such as epilepsy and chronic pain. Recent genetic studies have now expanded the role of sodium channels in health and disease, to include autism, migraine, multiple sclerosis, cancer as well as muscle and immune system disorders. Transgenic mouse models have proved useful in understanding the physiological role of individual sodium channels, and there has been significant progress in the development of subtype selective inhibitors of sodium channels. This review will outline the functions and roles of specific sodium channels in electrical signalling and disease, focusing on neurological aspects. We also discuss recent advances in the development of selective sodium channel inhibitors.

Effects of selenium and topiramate on cytosolic Ca(2+) influx and oxidative stress in neuronal PC12 cells

It has been widely suggested that selenium (Se) deficiency play an important role in the pathophysiology of epilepsy. It has been reported that Se provides protection against the neuronal damage in patients and animals with epilepsy by restoring the antioxidant defense mechanism. The neuroprotective effects of topiramate (TPM) have been reported in several studies but the putative mechanism of action remains elusive. We investigated effects of Se and TPM in neuronal PC12 cell by evaluating Ca(2+) mobilization, lipid peroxidation and antioxidant levels. PC12 cells were divided into eight groups namely control, TPM, Se, H(2)O(2), TPM + H(2)O(2), Se + H(2)O(2), Se + TPM and Se + TPM + H(2)O(2). The toxic doses and times of H(2)O(2), TPM and Se were determined by cell viability assay which is used to evaluate cell viability. Cells were incubated with 0.01 mM TPM for 5 h and 500 nM Se for 10 h. Then, the cells were exposed to 0.1 mM H(2)O(2) for 10 h before analysis. The cells in all groups except control, TPM and Se were exposed to H(2)O(2) for 15 min before analysis. Cytosolic Ca(2+) release and lipid peroxidation levels were higher in H(2)O(2) group than in control, Se and TPM combination groups although their levels were decreased by incubation of Se and TPM combination. However, there is no difference on Ca(2+) release in TPM group. Glutathione peroxidase activity, reduced glutathione and vitamin C levels in the cells were lower in H(2)O(2) group than in control, Se and TPM groups although their values were higher in the cells incubated with Se and TPM groups than in H(2)O(2) groups. In conclusion, these results indicate that Se induced protective effects on oxidative stress in PC12 cells by modulating cytosolic Ca(2+) influx and antioxidant levels. TPM modulated also lipid peroxidation and glutathione and vitamin C concentrations in the cell system.

Topiramate as an adjunctive treatment in patients with refractory status epilepticus: an observational cohort study

BACKGROUND

Refractory status epilepticus (RSE) is the most severe manifestation of status epilepticus (SE), often requiring intensive care and therapeutic coma. It is associated with prolonged intensive care unit (ICU) and hospital stays, as well as increased morbidity and mortality. Treatment involves both intravenous anaesthetics and antiepileptic drugs (AEDs) that can be administrated intravenously, by nasogastric tube or by percutaneous endoscopic gastrostomy. Experience with some of the newer AEDs for the treatment of RSE is restricted and higher-class evidence regarding tolerability and efficacy is lacking. Topiramate is a potent broad-spectrum AED with several modes of action, including blockade of the ionotropic glutamatergic AMPA receptor, which is likely to be an important mechanism for the treatment of SE. While there is no commercially available intravenous formulation, topiramate can be administered enterally, which may make it suitable for the treatment of RSE.

OBJECTIVE

The objective of this study was to evaluate the tolerability, safety profile and efficacy of adjunctive and enterally administered topiramate in patients with RSE.

METHODS

A medical chart review was performed of all consecutive patients treated for RSE between August 2004 and December 2011 at the ICU of the University Hospital Basel (Basel, Switzerland).

RESULTS

113 (43%) of all consecutive 268 patients with SE developed RSE. Of those, 35 (31%) were treated with topiramate. Median age was 60.5 years. Topiramate was used as an add-on treatment after 1-6 (median 4) prior administered AEDs had failed. It was introduced after a median of 2 (range 2-23) days for a duration of 1-24 (median 3) days. The response rate after topiramate administration as the third AED was 86% (6/7 patients), and remained stable at 67% after administration as the fourth, fifth, sixth or seventh AED when the groups of successfully and probably successfully treated patients were pooled. Overall, RSE was terminated in 71% of patients within 72 hours after first administration of topiramate, in 9% of patients, within 24 hours (none in the 800 mg/day group; 9% in the 400-799 mg/day group; and 11% in the <400 mg/day group). Mortality was 31% and was not strictly dependent on failure to terminate RSE, but also on the underlying aetiology of RSE. There were no serious or fatal adverse events directly attributable to topiramate. Adverse effects included slight hyperchloremic acidosis and hyperammonemia (all associated with co-medication with valproic acid).

CONCLUSION

Treatment with enterally administered topiramate was feasible, well tolerated and had a good safety profile in patients with RSE in this observational, single-centre, cohort study. Refractory SE was terminated in the majority of patients within 3 days after initiation of topiramate. Prospective studies are warranted to further evaluate topiramate for the treatment of RSE.

Phentermine plus topiramate for the treatment of obesity

A novel combination therapy is currently being investigated for the treatment of obesity. Phentermine plus topiramate has shown efficacy in both Phase II and III trials as compared with either drug used alone. With average 2-year weight loss as high as 10.5% and reduction of up to 76% in the incidence of progression of Type II diabetes, combination phentermine plus topiramate may provide significant benefit in conjunction with behavioral modification in the management of obesity. However, as with any new pharmacologic treatment option, the risk/benefit profile needs to be carefully assessed.

The effect of topiramate plasma concentration on linguistic behavior, verbal recall and working memory

This is the first study of the effect of topiramate on linguistic behavior and verbal recall using a computational linguistics system for automated language and speech analysis to detect and quantify drug-induced changes in speech recorded during discourse-level tasks. Healthy volunteers were administered a single, 100-mg oral dose of topiramate in two double-blind, randomized, placebo-controlled, crossover studies. Subjects' topiramate plasma levels ranged from 0.23 to 2.81 μg/mL. We found a significant association between topiramate levels and impairment on measures of verbal fluency elicited during a picture description task, correct number of words recalled on a paragraph recall test, and reaction time recorded during a working memory task. Using the tools of clinical pharmacology and computational linguistics, we elucidated the relationship between the determinants of a drug's disposition as reflected in plasma concentrations and their impact on cognitive functioning as reflected in spoken language discourse.

Elevated sweat chloride concentration in children without cystic fibrosis who are receiving topiramate therapy

BACKGROUND

Topiramate, which is used as an anticonvulsant and for migraine prophylaxis in children, causes oligohydrosis as a side-effect, but its effect on sweat chloride concentrations has not been studied systematically.

METHODS

Twenty-one children receiving topiramate and 20 healthy controls with no signs or symptoms of pulmonary or gastrointestinal disease and a negative family history for cystic fibrosis (CF) underwent bilateral pilocarpine iontophoresis and sweat collection via Macroduct® system.

RESULTS

Adequate samples (>15 µl volume) were obtained from 17/19 topiramate subjects (89%), and 19/20 (95%) controls. The mean sweat chloride concentration was 37.7 ± 18.8 mmol/L for patients receiving topiramate, and 15.9 ± 6.9 mmol/L for controls (p = 0.0001). The mean sweat volume was 29.1 ± 17.4 µl for patients receiving topiramate, and 41.2 ± 17.5 µl for controls (p = 0.037). Overall 8/17 (47%) of patients on topiramate with a measurable sweat chloride had either an intermediate (>40 mmol/L but <60 mmol/L) or elevated (>60 mmol/L) sweat chloride test result, while 0/19 control subjects had elevated sweat chloride (p = 0.0008). Further analysis of the in vitro activity of topiramate on cultured human bronchial epithelial cells in modified Ussing chambers showed no differences in chloride conductance measured in cells exposed to 10 or 50 µg/ml of topiramate when compared to non-exposed cells.

CONCLUSIONS

This is the first report of a medication affecting sweat chloride values and shows that topiramate therapy can cause elevated sweat chloride concentrations in the absence of clinical manifestations of CF.

The psychopharmacology of aggressive behavior: a translational approach: part 2: clinical studies using atypical antipsychotics, anticonvulsants, and lithium

Patients experiencing mental disorders are at an elevated risk for developing aggressive behavior. In the past 10 years, the psychopharmacological treatment of aggression has changed dramatically owing to the introduction of atypical antipsychotics on the market and the increased use of anticonvulsants and lithium in the treatment of aggressive patients.This review (second of 2 parts) uses a translational medicine approach to examine the neurobiology of aggression, discussing the major neurotransmitter systems implicated in its pathogenesis (serotonin, glutamate, norepinephrine, dopamine, and γ-aminobutyric acid) and the neuropharmacological rationale for using atypical antipsychotics, anticonvulsants, and lithium in the therapeutics of aggressive behavior. A critical review of all clinical trials using atypical antipsychotics (aripiprazole, clozapine, loxapine, olanzapine, quetiapine, risperidone, ziprasidone, and amisulpride), anticonvulsants (topiramate, valproate, lamotrigine, and gabapentin), and lithium are presented. Given the complex, multifaceted nature of aggression, a multifunctional combined therapy, targeting different receptors, seems to be the best strategy for treating aggressive behavior. This therapeutic strategy is supported by translational studies and a few human studies, even if additional randomized, double-blind, clinical trials are needed to confirm the clinical efficacy of this framework.

Topiramate treatment is neuroprotective and reduces oligodendrocyte loss after cervical spinal cord injury

Excess glutamate release and associated neurotoxicity contributes to cell death after spinal cord injury (SCI). Indeed, delayed administration of glutamate receptor antagonists after SCI in rodents improves tissue sparing and functional recovery. Despite their therapeutic potential, most glutamate receptor antagonists have detrimental side effects and have largely failed clinical trials. Topiramate is an AMPA-specific, glutamate receptor antagonists that is FDA-approved to treat CNS disorders. In the current study we tested whether topiramate treatment is neuroprotective after cervical contusion injury in rats. We report that topiramate, delivered 15-minutes after SCI, increases tissue sparing and preserves oligodendrocytes and neurons when compared to vehicle treatment. In addition, topiramate is more effective than the AMPA-receptor antagonist, NBQX. To the best of our knowledge, this is the first report documenting a neuroprotective effect of topiramate treatment after spinal cord injury.

Synergistic antidyskinetic effects of topiramate and amantadine in animal models of Parkinson's disease

L-Dopa-induced dyskinesia in patients with Parkinson's disease can be alleviated by amantadine, an antagonist at N-methyl-D-aspartate glutamate receptors. The antiepileptic drug topiramate, which blocks α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, has also been shown to reduce dyskinesia. The purpose of this study was to examine the behavioral pharmacology of topiramate alone and in combination with amantadine in animal models of PD and L-dopa-induced dyskinesia. The effects of topiramate (5-20 mg/kg) and amantadine (5-20 mg/kg) on abnormal involuntary movements (the rat homologue of dyskinesia) and Rotarod performance were assessed alone and in combination in the 6-hydroxydopamine-lesioned rat following chronic L-dopa treatment. Dyskinesia, parkinsonian disability, and "on-time" were assessed in the MPTP-lesioned nonhuman primate following administration of topiramate (5-20 mg/kg) and amantadine (0.1-1.0 mg/kg) alone and in combination. Topiramate and amantadine dose-dependently reduced dyskinesia in the 6-hydroxydopamine-lesioned rat, whereas topiramate reduced Rotarod performance; there was no effect on parkinsonian disability in the MPTP-lesioned nonhuman primate, in which both drugs reduced dyskinesia. Topiramate and amantadine exhibited differential antidyskinetic effects on dyskinesia elicited by the dopamine D1 receptor agonist SKF 38393 (2 mg/kg). Subthreshold doses of both drugs in combination had a synergistic effect on dyskinesia in the 6-hydroxydopamine-lesioned rat, with no worsening of motor performance; this effect was confirmed in the MPTP-lesioned nonhuman primate, with a selective reduction in "bad on-time." These data confirm the antidyskinetic potential of topiramate and suggest that combination with low-dose amantadine may allow better reduction of dyskinesia with no adverse motor effects.

Chronic Cellular Hyperexcitability in Elderly Epileptic Rats with Spontaneous Seizures Induced by Kainic Acid Status Epilepticus while Young Adults

Emerging data indicate that age-related brain changes alter seizure susceptibility, seizure-associated neurodegeneration, and responsiveness to AEDs. The present study assessed long-term animal survival in the Kainic Acid (KA) model along with in-vivo spontaneous seizure frequency, cellular hyperexcitability in CA1 in-vitro and in-vivo in subiculum, and responsiveness of in-vitro CA1 hyperexcitability to topiramate. Sprague-Dawley male rats were given KA to induce convulsive status epilepticus (KA-SE) at 2-3 months of age. The one-month mortality after KA-SE was 27%. One-month survivor rats had 37% sudden unexplained late mortality after KA-SE as compared to none in saline controls during their second year of life. In-vivo seizure frequency was examined prior to terminal experiments. The diurnal average seizure frequency in the KA-SE group at age 2 years was 1.06 ± 0.24 seizures/hour while no seizures were observed in the saline age-matched controls (p<0.001). In-vitro recordings of CA1 pyramidal neurons revealed that depolarizing current injection from -60 mV evoked an increased number of action potentials in the aged KA-SE group compared to controls (p<0.002). Topiramate exhibited dose-dependent inhibition of action potential firing evoked by current injections into CA1 pyramidal neurons of KA-SE rats. In subiculum, KA-SE rats had frequent interictal spikes associated with high frequency oscillations while only rare spontaneous EPSPs were recorded in saline controls. Our experiments revealed that the hippocampal formation of aged epileptic rats shares features of hyperexcitability previously described in young adult epileptic rats using the KA model.

Topiramate: safety and efficacy of its use in the prevention and treatment of migraine

Migraine headaches are typically episodic in nature and may affect nearly 10% of the population. In addition to treatment, prevention of subsequent episodes or progression to a chronic migraine state is an important therapeutic area. Topiramate is a centrally acting medication approved for both the prevention of seizures and migraine headache. At this time, the exact mechanism of how topiramate assists in migraine prevention is unknown. Several large randomized, controlled trials have aided in establishing topiramate's role in migraine prevention. Despite a favorable pharmacokinetic and adverse effect profile established in clinical trials, several additional studies, case reports and toxicology reports have demonstrated topiramate as a cause of cognitive and behavioural changes. The use of topiramate in migraine prevention can improve a patient's quality of life and is a cost-effective option for migraine prevention.

Phentermine and topiramate for the management of obesity: a review

Obesity is now a major public health concern worldwide with increasing prevalence and a growing list of comorbidities and complications. The morbidity, mortality and reduced productivity associated with obesity and its complications result in a major burden to health care costs. Obesity is a complex chronic medical syndrome often with multiple different etiologic factors in individual patients. The long term successful management of obesity remains particularly challenging and invariably requires a multifaceted approach including lifestyle and behavioral modification, increased physical activity, and adjunctive pharmacotherapy. Bariatric surgery remains a last resort though at present it has the best results for achieving sustained robust weight loss. Obesity pharmacotherapy has been very limited in its role for long term obesity management because of the past history of several failed agents as well as the fact that presently available agents are few, and generally utilized as monotherapy. The recent FDA approval of the fixed drug combination of phentermine and extended release topiramate (topiramate-ER) (trade name Qsymia™) marks the first FDA approved combination pharmacotherapeutic agent for obesity since the Phen-Fen combination of the 1990s. This review details the history and clinical trial basis for the use of both phentermine and topiramate in obesity therapeutics as well as the results of clinical trials of their combination for obesity treatment in humans. The initial clinical approval trials offer evidence that this fixed drug combination offers synergistic potential for effective, robust and sustained weight loss with mean weight loss of at least 10% of baseline achieved and sustained for up to 2 years in over 50% of subjects treated. It is anticipated that this agent will be the first in a new trend of multi-agent combination therapy for the chronic adjunctive management of obesity.

Neurologic bases for comorbidity of balance disorders, anxiety disorders and migraine: neurotherapeutic implications

The comorbidity among balance disorders, anxiety disorders and migraine has been studied extensively from clinical and basic research perspectives. From a neurological perspective, the comorbid symptoms are viewed as the product of sensorimotor, interoceptive and cognitive adaptations that are produced by afferent interoceptive information processing, a vestibulo-parabrachial nucleus network, a cerebral cortical network (including the insula, orbitofrontal cortex, prefrontal cortex and anterior cingulate cortex), a raphe nuclear-vestibular network, a coeruleo-vestibular network and a raphe-locus coeruleus loop. As these pathways overlap extensively with pathways implicated in the generation, perception and regulation of emotions and affective states, the comorbid disorders and effective treatment modalities can be viewed within the contexts of neurological and psychopharmacological sites of action of current therapies.

Topiramate-antagonism of L-glutamate-induced paroxysms in planarians

We recently reported that NMDA (N-methyl-D-aspartate) and AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) induce concentration-dependent paroxysms in planarians (Dugesia dorotocephala). Since the postulated mechanisms of action of the sulfamate-substituted monosaccharide antiepileptic drug topiramate include inhibition of glutamate-activated ion channels, we tested the hypothesis that topiramate would inhibit glutamate-induced paroxysms in our model. We demonstrate that: (1) L-glutamate (1-10 mM), but not D-glutamate, induced dose-related paroxysms, and that (2) topiramate dose-relatedly (0.3-3 mM) inhibited L-glutamate-induced paroxysms. These results provide further evidence of a topiramate-sensitive glutamate receptor-mediated activity in this model.

New drugs in migraine treatment and prophylaxis: telcagepant and topiramate

Although the triptan drugs provide effective relief from migraine for many patients, a substantial number of affected individuals are unresponsive to these compounds, and such therapy can also lead to a range of adverse effects. Telcagepant represents a new class of antimigraine drug-the calcitonin gene-related peptide receptor blockers. This compound exerts its effects by blocking receptors for the calcitonin-gene-related peptide at several sites in the trigeminal and central nervous systems, resulting in pain relief. Telcagepant does not cause vasoconstriction, a major limitation in the use of triptans. Comparisons with triptans in clinical trials for acute treatment of migraine attacks revealed clinical effects similar to those of triptans but better than those of placebo. Telcagepant might provide hope for those who have a poor response to, or are unable to use, older drugs. In patients who need prophylaxis because of frequent attacks of migraine, topiramate is a first-line drug for migraine prevention in many countries; it is generally safe and reasonably well tolerated. Data suggest that topiramate could aid reversion of chronic migraine to episodic migraine.

Pharmacokinetic interaction study between eslicarbazepine acetate and topiramate in healthy subjects

OBJECTIVE

Combination therapy is frequently required in the management of epilepsy. The primary objective of this study was to investigate the pharmacokinetic interaction between eslicarbazepine acetate (ESL) 1200 mg once daily and topiramate (TPM) 200 mg once daily in healthy subjects.

METHODS

Multiple-dose, open-label, one-sequence study in two parallel groups of 16 healthy male volunteers. After an 8-day treatment with ESL (Group A) or TPM (Group B), ESL and TPM were co-administered for 19 days. A bioequivalence approach based on a within-subject comparison was used to investigate a potential drug-drug interaction. End/start of treatment geometric mean ratios (GMR, %) and 90% confidence intervals (90% CI) were calculated for maximum plasma concentration (C(max)) and area under the plasma concentration-time curve over the dosing interval at steady-state (AUC(ss)) of eslicarbazepine (ESL major active metabolite), R-licarbazepine (ESL minor active metabolite) and TPM at Day 8 and Day 27.

RESULTS

In Group A, eslicarbazepine GMR (90% CI) was 86.79% (81.06%; 92.94%) for C(max) and 92.70% (89.21%; 96.32%) for AUC(ss). In Group B, TPM GMR (90% CI) was 81.50% (77.48%; 85.89%) for C(max) and 81.81% (79.69%; 84.00%) for AUC(ss). The 90% CI of eslicarbazepine C(max) and AUC(ss) fell within the pre-specified bioequivalence range (80.00%; 125.00%), allowing it to be concluded that the extent of systemic exposure to eslicarbazepine was unaffected by the concomitant administration of TPM. The 90% CI for topiramate AUC(ss) was borderline in relation to the pre-specified bioequivalence range and topiramate C(max) fell outside the pre-specified bioequivalence range. Therefore, the extent of systemic exposure to TPM following co-administration with ESL was not formally bioequivalent to the extent of systemic exposure to TPM when TPM was administered alone. However, there was no difference between TPM elimination half-life following TPM co-administered with ESL and TPM administered alone (24.0 and 24.3 h, respectively). The bioavailability of R-licarbazepine was essentially bioequivalent. Two subjects discontinued due to adverse events. No clinical interaction appeared to be present in terms of adverse events when both drugs were given concomitantly.

CONCLUSION

Concomitant administration of eslicarbazepine acetate 1200 mg once daily and topiramate 200 mg once daily showed no significant change in exposure to eslicarbazepine but an 18% decrease in exposure to topiramate, most likely caused by a reduced bioavailability of topiramate. No dose adjustment is required.

Review of topiramate for the treatment of epilepsy in elderly patients

Individuals over 65 years of age experience the new onset of seizures at a prevalence rate of roughly twice that of younger adults. Differences in physiology, need of concomitant medications, and liability for cognitive deficits in this population, make the choice of anticonvulsant drugs especially important. This paper reviews topiramate (TPM), a treatment for many types of seizures, with the above risks in mind. In particular, we discuss efficacy and pharmacokinetics with emphasis on the older patient, and adverse events in both the younger and older adult. With most studies of TPM-induced cognitive deficits having been performed in younger adults and volunteers, we discuss the implications for the older adult. Even in studies of younger individuals, up to 50% discontinue TPM because of intolerable cognitive deficits. Most studies find specific declines in working memory and verbal fluency. In conclusion, we give recommendations for use of this antiepileptic drug in this population.

Voltage-gated sodium channels as therapeutic targets in epilepsy and other neurological disorders

Voltage-gated sodium channels (VGSCs) are key mediators of intrinsic neuronal and muscle excitability. Abnormal VGSC activity is central to the pathophysiology of epileptic seizures, and many of the most widely used antiepileptic drugs, including phenytoin, carbamazepine, and lamotrigine, are inhibitors of VGSC function. These antiepileptic drugs might also be efficacious in the treatment of other nervous system disorders, such as migraine, multiple sclerosis, neurodegenerative diseases, and neuropathic pain. In this Review, we summarise the structure and function of VGSCs and their involvement in the pathophysiology of several neurological disorders. We also describe the biophysical and molecular bases for the mechanisms of action of antiepileptic VGSC blockers and discuss the efficacy of these drugs in the treatment of epileptic and non-epileptic disorders. Overall, clinical and experimental data indicate that these drugs are efficacious for a range of diseases, and that the development of drugs with enhanced selectivity for specific VGSC isoforms might be an effective and novel approach for the treatment of several neurological diseases.

Pharmacologic therapies for obesity

This article examines the transitions in pharmacological therapy for obesity. It reviews the current options approved by the Food and Drug Administration and several drugs approved for other indications that can be used to treat obesity as well. Because weight regulation is complex and redundant systems protect against perceived starvation, optimal treatment of obesity in individual patients will likely require different combinations of behavioral, nutritional, pharmacologic, endoscopic, and surgical therapies.

Evidences for pharmacokinetic interaction of riluzole and topiramate with pilocarpine in pilocarpine-induced seizures in rats

In this study we investigated the effectiveness of two antiepileptic drugs: riluzole and topiramate against pilocarpine-induced seizures, which are considered to be a model of intractable epilepsy commonly used to investigate the antiepileptic effect of drugs and mechanisms of epileptogenesis. Seizures and status epilepticus were induced by pilocarpine in adult male Wistar rats. Riluzole (1-4mg/kg) administered intraperitoneally before pilocarpine dose-dependently protected rats against seizures with the anticonvulsant ED(50) value (50% effective anticonvulsant dose) of 1.8 (1.3-2.6)mg/kg. In contrast, riluzole at 8 and 12mg/kg administered after the onset of pilocarpine-induced seizures affected neither status epilepticus nor mortality of rats. Topiramate significantly enhanced convulsive action of pilocarpine, lowering the convulsant CD(50) value (50% effective convulsant dose) of pilocarpine from 350.8 (329.2-373.8) to 246.4 (218.6-278.2)mg/kg. Riluzole (4mg/kg) lowered plasma and brain concentration of pilocarpine administered at a dose of 400mg/kg from 168.0+/-8.6 to 75.3+/-19.9microg/ml and from 193.7+/-6.6 to 97.0+/-26.1microg/g, respectively. Topiramate (200mg/kg) increased plasma and brain concentration of pilocarpine administered at a dose of 300mg/kg from 78.1+/-2.9 to 106.0+/-6.8microg/ml and from 138.4+/-5.0 to 155.2+/-5.1microg/g, respectively. It seems that both anticonvulsant effect exerted by riluzole and proconvulsant effect exerted by topiramate in pilocarpine model of seizures are due to a pharmacokinetic interaction. Therefore, we postulate that the concentration of pilocarpine should be measured routinely whenever the anticonvulsant effect of drugs is determined in the pilocarpine model of seizures.

Topiramate in migraine progression

Increasing evidence shows that migraine, typically considered as an episodic disease, is a chronic and, in some patients, progressive disorder. Among neuromodulators used for migraine prevention, topiramate has a high level of evidence-based efficacy. Through its wide range of mechanisms of action topiramate increases the activation threshold resulting in neuronal stabilization and thereby reducing cortical neurons hyperexcitability, which is believed to be an important electrophysiological feature underlying the pathogenesis of epilepsy and migraine. Recent studies show that migraineurs have subclinical structural brain changes and persistent alteration of pain perception, in some cases correlated with the duration of the disease and the frequency of attacks that might play a role in the transformation of episodic migraine to chronic forms. An early and prolonged preventive treatment might reduce the risk of such transformation. Recent evidence suggests that topiramate, by reducing migraine frequency and use of acute medication, may prevent the negative progression of migraine. Furthermore, two recently completed multicenter, randomised, placebo-controlled trials have shown that treatment with topiramate 100 mg/day is effective and well tolerated in patients already progressed to chronic migraine and difficult to treat conditions associated with medication-overuse. Topiramate seems to be a preventive treatment, which might be able to act at different levels of the migraine cycle: reduction of frequency in episodic migraine, prevention, and treatment of chronic migraine.