Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Epilepsy is common in the elderly. The incidence of epilepsy is age-dependent, with a peak during the first year of life and higher incidence in those older than 75 years. Cerebrovascular disease is a common cause of epilepsy in the elderly. Drug treatment of the elderly is a challenge because of pharmacokinetic changes with aging, including impaired drug protein binding or displacement of drug from protein binding sites, potentially causing drug toxicity as a result of increased free drug concentrations. With aging, hepatic mass and blood flow decline along with renal function. Established anticonvulsant drugs have adverse effects and drug interactions that can make treating the elderly difficult. Newly available anticonvulsants cause fewer drug-drug interactions and less toxicity. Gabapentin is not metabolised, is not bound to protein, and has a favourable adverse effect profile and thus may be useful in the treatment of elderly patients. Lamotrigine reduced seizures between 20 and 30% in trials. Dose response was between 300mg per day and 500mg per day. This drug was well tolerated in open-label trials. Rash occurred in younger patients. Oxcarbazepine is rapidly absorbed and is converted to a monohydroxy derivative. Use with hepatic enzyme-inducing drugs necessitates an increase in dose. This drug may be substituted for carbamazepine. Hyponatraemia has been reported and monitoring is suggested. Topiramate blocks voltage-dependent sustained repetitive firing and has an effect on the gamma-aminobutyric acid (GABA) receptors. It affects glutamate responses and inhibits carbonic anhydrase. Topiramate has a dose response pattern up to 400mg per day. Cognitive effects limits its use in some patients. Nephrolithiasis has occurred with this drug. Tiagabine blocks GABA transporter proteins. Clearance is rapid and metabolism complete. Hepatic dysfunction prolongs clearance. The use of tiagabine has not been reported in the elderly. Zonisamide is rapidly absorbed and protein binding is 50%. Plasma half-life is 55 hours but is reduced to about 30 hours by hepatic enzyme-inducing drugs. Responder rate is 45%. Adverse effects include drowsiness, altered thinking and nephrolithiasis. Treatment of the elderly requires obligatory polypharmacy with potential drug interactions. Changes in body physiology alter absorption, binding, metabolism and elimination of drugs. Concomitant illness and sensitivity to drug effects narrow the therapeutic range and complicate pharmacokinetics in elderly patients. Newer anticonvulsant drugs have advantages that may outweigh risks and have therapeutic profiles that may aid in the treatment of this special population of patients.
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PMID:Choice and use of newer anticonvulsant drugs in older patients. 1120 Mar 5

Of the 9 new anticonvulsants that have been marketed recently in the UK or US, a number appear to have either adverse or beneficial effects on behaviour. There is now a considerable database of information, in terms of the number of patients treated and/or the number of published reports, on vigabatrin, lamotrigine, gabapentin and topiramate. Oxcarbazepine has been available in some centres for several years and there is extensive experience with the drug in Scandinavia. It appears that the profile of adverse and beneficial effects is similar to that of carbamazepine. Behavioural effects have probably been greatest with vigabatrin, with psychosis, depression and other behavioural problems recorded, but the use of this drug has been limited because of the concern about visual field constriction. The cognitive and behavioural effects of topiramate have caused concern, but these may be much less of a problem if lower starting dosages and escalation rates are used. Psychosis and depression have been associated with topiramate, as they have with another carbonic anhydrase inhibiting drug, zonisamide. Although zonisamide has been used for many years in Japan and Korea, experience elsewhere with this drug is currently very limited. Gabapentin seems to be less associated with adverse behavioural effects than some of the other new anticonvulsant drugs. The reports of behavioural disturbance with gabapentin in children may be related to dose escalation. Behavioural disturbance as a direct result of lamotrigine seems to be uncommon, although indirect effects on behaviour, through the so-called 'release phenomenon' from improved seizure control and consequent ability to misbehave, can occur. Positive behavioural effects have been described with several of the new anticonvulsants, particularly gabapentin, lamotrigine and oxcarbazepine; all of these drugs may have mood-levelling effects that could be of value in treating affective disorders. The information on tiagabine and levetiracetam is too limited to allow any firm conclusions to be drawn with regard to positive or negative behavioural effects. When interpreting reports of behavioural changes with anticonvulsants, it is important to avoid attributing the effect to the drug when one or more of the other multiple causes of behavioural disturbance in people with epilepsy may be responsible or when an indirect effect such as 'forced normalisation' may be the cause. Many of the published studies are retrospective and unblinded rather than double-blind, placebo-controlled, prospective trials, implying that much of the data must be interpreted with caution at this stage.
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PMID:Behavioural effects of the new anticonvulsants. 1144 24

Topiramate is a recently developed antiepileptic medication that is becoming more widely prescribed because of its efficacy in treating refractory seizures. Urologists should be aware that this medication can cause metabolic acidosis in patients secondary to inhibition of carbonic anhydrase. In addition, a distal tubular acidification defect may result, thus impairing the normal compensatory drop in urine pH. These factors can lead to the development of calcium phosphate nephrolithiasis. We report the first two cases of topiramate-induced nephrolithiasis in the urologic literature.
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PMID:Topiramate-induced nephrolithiasis. 1204 5

Intracellular and extracellular pH are known to influence neuronal activity and may play a role in seizure termination. In the pyramidal cell layer of the CA1 region of the hippocampus in the urethane anesthetized adult rat, there is an initial alkalinization in response to stimulus trains administered to the contralateral CA3 region. This is followed by an acidification that peaks after termination of the afterdischarge. Initial experiments demonstrated that the peak level of acidification correlated with the duration of the afterdischarge, but that the peak level of alkalinization did not. The effects of several antiepileptic drugs on the initial alkalinization were determined. Systemic administration of acetazolamide (50 mg/kg, n=4) and topiramate (45 mg/kg, n=7) and local administration of benzolamide (n=3), all of which inhibit carbonic anhydrase, decreased the initial alkalinization that occurs during the stimulus train. Diazepam (3 mg/kg, n=5) and phenobarbital (60 mg/kg, n=6), agonists at the GABA(A) receptor complex, increased the initial alkalinization, while sodium channel blockers phenytoin (80 mg/kg, n=5) and carbamazepine (50 mg/kg, n=5) had no significant effect. The data suggest that the alkalinization in CA1 in vivo is predominantly regulated through activity of the GABA(A) receptor, rather than through activation of glutamatergic receptors. The change in alkalinization does not appear to be related to the mechanism of the antiepileptic effect of the drugs that were tested.
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PMID:Effects of antiepileptic drugs on extracellular pH regulation in the hippocampal CA1 region in vivo. 1204 2

Limited data exist on overdose with new antiepileptic drugs. We reviewed the medical records of two patients who took a topiramate overdose as a suicide attempt. We recorded their medical and seizure histories, concomitant antiepileptic medications, neurologic examination, and laboratory findings at the time of presentation following the overdose. We also recorded their progress and the evolution of laboratory abnormalities. Both patients progressed to coma and had generalized convulsive status epilepticus, requiring intubation and treatment with benzodiazepines. Both patients recovered within 2 days but had a non-anion-gap metabolic acidosis that persisted for 5-6 days. Physicians should carefully monitor patients treated with topiramate who develop signs of clinical depression. The non-anion-gap metabolic acidosis observed may be due to inhibition of renal cortical carbonic anhydrase.
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PMID:Topiramate Overdose: Clinical and Laboratory Features. 1260 21

A 6-year-old boy with partial complex seizures developed recurrent episodes of hyperthermia 2 months after topiramate was introduced into his antiepilepsy drug regimen. Further investigation revealed that the febrile episodes were related to environmental temperature and physical activity. A pilocarpine iontophoresis sweat test showed that the amount of sweat produced by the child was 5% that of age-matched controls. Topiramate discontinuation resulted in the disappearance of febrile episodes and normalization of sweat quantity in repeat sweat testing. Based on this observation and the previous data on zonisamide and isolated case reports on topiramate-related hyperthermia and the effect on sweat production, topiramate was suspected of causing oligohydrosis. A pilot study was carried out involving 13 additional children and young adults (age range 1-37 years) receiving topiramate. All patients were directly questioned regarding symptoms of decreased sweating and heat intolerance, went through a pilocarpine iontophoresis sweat test, and were compared with 14 age-matched controls who went through the sweat test for unrelated reasons. Nine of the patients were found to have reduced sweat quantity on the pilocarpine iontophoresis sweat test (including index case) (mean 0.089 g/30 minutes, SD 0.082; age-matched control: mean 0.21 g/30 minutes, SD 0.06). Eight of them were children (below 16 years). However, only three patients revealed symptoms related to heat intolerance. Topiramate is most likely responsible for decreased sweat production as detected by a pilocarpine iontophoresis sweat test. The effect seems to be more significant in children than in adults. There is a discrepancy between test results and clinical symptoms. Interestingly, oligohydrosis was found to be a relatively common side effect of zonisamide. Both zonisamide and topiramate share a carbonic anhydrase inhibitor activity. The significance of oligohydrosis in hot climates should not be underestimated. Its extent, the role of sweat test prediction, and clinical significance during topiramate treatment should be further estimated.
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PMID:Oligohydrosis and hyperthermia: pilot study of a novel topiramate adverse effect. 1276 Apr 27

Zonisamide is an antiepileptic drug developed and first marketed in Japan in 1989. Cases of oligohydrosis, characterized by deficient production and secretion of sweat, were reported in children treated with zonisamide in Japan during development and in the postmarketing period. Zonisamide was approved in the United States in March 2000 for adjunctive treatment of partial seizures in adults. Searching the Food and Drug Administration's Adverse Events Reporting System, we identified six domestic cases of zonisamide-associated oligohydrosis and/or fever, all in patients </= 18 years of age. The calculated reporting rate was 13 cases per 10,000 pediatric-years of exposure, approximately 10-fold the reporting rate in Japan. A possible risk factor for the development of oligohydrosis in these cases was pediatric age, leading to exposure to elevated zonisamide blood levels relative to patient size. Although the mechanism for zonisamide-associated oligohydrosis has not been fully elucidated, the drug may mediate its effect on eccrine sweat glands by inhibiting carbonic anhydrase, thereby influencing pH dynamics, hydrogen ion concentration, and available calcium transients. Awareness of zonisamide-associated oligohydrosis may prevent morbidity, especially in the pediatric population.
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PMID:Oligohydrosis and fever in pediatric patients treated with zonisamide. 1277 Jun 70

Experimental and theoretical evidence indicates that GABAergic neurotransmission is fundamental for the synchronization of neuronal activity. In particular, the role of GABA in epileptiform activity has received increased attention due to, among others, the fact that the GABA-mediated potentials can be depolarizing, and hence excitatory, in some circumstances. Evidence is presented here that bicarbonate efflux via GABAA receptors in interneurons and pyramidal cells of the CA1 hippocampal area contribute to depolarizing GABAA-mediated potentials in an in vitro nonpharmacological seizure-like model of status epilepticus. Seizure-like and interictal activity was evoked in rat horizontal hippocampal slices using a superfusing solution with low magnesium concentration (0.5-0.9 mm). Whole-cell recordings from stratum oriens-alveus interneurons and CA1 pyramidal cells revealed that, during epileptiform activity, some GABAA-mediated potentials were depolarizing, and were suppressed by the carbonic anhydrase inhibitor ethoxyzolamide as well as by the GABAA-receptor antagonist bicuculline. These observations indicate that the depolarizing potentials observed during epileptiform activity reflect both glutamatergic and GABAA-receptor-mediated activity, and adds further support for the important role of GABAergic interneurons in promoting long-range synchronization.
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PMID:Bicarbonate-dependent depolarizing potentials in pyramidal cells and interneurons during epileptiform activity. 1295 33

Topiramate is an antiepileptic drug that has a broad spectrum of antiseizure effects, which appear to be the result of several neurostabilising pharmacological mechanisms. These include blockade of ion channels, potentiation of GABA neuroinhibition and glutamate receptor antagonism at non-NMDA receptors, as well as mild inhibition of carbonic anhydrase. Topiramate monotherapy dose dependently reduced the number of patients who met seizure related exit criteria in children (aged > or =6 years) and adults with epilepsy. This effect was also observed in patients who had previously experienced partial onset seizures and for those who had experienced generalised tonic clonic seizures. Six-month and 1-year seizure-free rates were dose-dependently reduced. In epilepsy, topiramate monotherapy 100 or 200 mg/day was as effective as carbamazepine 600 mg/day or valproate 1250 mg/day as measured by time to study exit for any reason, time to first seizure and percentage of patients seizure-free in the final 6 months of treatment (mean treatment duration 244 days). Adverse events associated with topiramate monotherapy that were dosage related included paraesthesia, weight loss and diarrhoea. Renal calculi were also reported in both fully published trials.
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PMID:Topiramate: as monotherapy in newly diagnosed epilepsy. 1453 52

Zonisamide is a synthetic 1,2-benzisoxazole-3-methanesulfonamide with anticonvulsant properties. The sulfamoyl group on zonisamide was expected to suppress seizures in a manner similar to another sulfonamide analogue, acetazolamide, through inhibition of carbonic anhydrase. However, this does not appear to be the primary mechanism of action since zonisamide requires much higher doses than acetazolamide to achieve equivalent titration in vivo. Studies with cultured neurons indicate that zonisamide blocks repetitive firing of voltage-sensitive sodium channels and reduces voltage-sensitive T-type calcium currents without affecting L-type calcium currents. Its dual mechanism of action may explain its efficacy in patients resistant to other antiepileptic drugs (AEDs). Zonisamide has a pharmacokinetic profile favorable for clinical use. It is rapidly and completely absorbed and has a long half-life (63-69h in healthy volunteers) which allows twice-daily, or even once-daily, dosing. Zonisamide is not highly bound to plasma proteins. Consequently, it does not affect protein binding of other highly protein-bound AEDs. Furthermore, zonisamide does not induce its own metabolism and does not induce liver enzymes. However, since zonisamide is metabolized by cytochrome P450, liver enzyme-inducing AEDs will increase zonisamide clearance, and dosage adjustments may be necessary when it is used in combination with certain AEDs.
Seizure 2004 Dec
PMID:Zonisamide: chemistry, mechanism of action, and pharmacokinetics. 1551 91


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