Neuropharmacology of zonisamide, a new antiepileptic drug

Structural insights into a novel anticancer sulfonamide chalcone

Natural products have stood out due to their wide range of biological activities.

Effects of zonisamide in the treatment of alcohol dependence

OBJECTIVE

Anticonvulsant drugs have been used in the treatment of alcohol dependence. The purpose of the present study was to evaluate tolerance and safety of zonisamide in a sample of patients presenting alcohol dependence.

METHODS

Open-label zonisamide was examined in 22 outpatients with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition alcohol dependence. Zonisamide was started at a dose of 50 mg/d and titrated to a maximun dose of 300 mg/d. Subjects received a baseline evaluation including Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition and the Severity of Alcohol Dependence Scale. Alcohol craving and alcohol consumption were assessed at weeks 2, 4, 6, 8, 10, and 12. The concentration of γ-glutamyltransferase was used as an indirect measure of alcohol consumption.

RESULTS

Significant improvement was observed in visual analog scale for craving severity scores, weekly drink consumption, and γ-glutamyltransferase. Zonisamide was well tolerated, with only a dropout due to adverse events.

CONCLUSIONS

Zonisamide is safe and well tolerated in this sample and associated with improvement in alcohol craving and alcohol consumption. A placebo-controlled study would be of interest.

Novel anticonvulsant drugs

Principles of complex mechanisms of action of anticonvulsants including latest reports concerning new antiepileptic drugs (AED) are considered. Different aspects of new anticonvulsant drugs (2nd generation) from preclinical and clinical testing, pharmacokinetics, and mono or combination therapy in children and adults are summarized. In the following condensed synopsis pharmacological and clinical characteristics of gabapentin (GBP), lamotrigine (LTG), levetiracetam (LEV), oxcarbazepine (OXC), pregabalin (PGB) and tiagabine (TGB) as well as topiramate (TPM) and zonisamide (ZNS) are discussed. In addition to the mechanisms of action, pharmacokinetics, interactions, indications and dosages as well as side effects are considered. Important data concerning the effect and tolerability of anticonvulsant drugs can be obtained from controlled studies. In comparison to drugs of the first generation (phenobarbital [PB], primidon [PRD], phenytoin [PHT], carbamazepine [CBZ] and valproic acid [VPA]) the potential for interactions and side effects due to enzyme induction or inhibition is reduced by most of the anticonvulsant drugs of the second generation. New anticonvulsant drugs increase the spectrum of treatment and represent further steps with regard to the optimization of an individual therapy of the epilepsies.

Efficacy, pharmacology, and adverse effects of antiepileptic drugs

This article discusses the factors involved in the appropriate selection of anticonvulsant medications. The clinical use of commonly used traditional antiepileptic drugs and the newly marketed antiepileptic drugs is discussed. This includes the specific indications for use, adverse effects, and dosing of each drug. Drug interactions, mechanisms of action, and pharmacological properties of each drug is also reviewed.

The anticonvulsant zonisamide scavenges free radicals

Zonisamide (ZNS) is effective in animal models of epilepsy and epileptic patients. The free radical scavenging activities of ZNS were analyzed by using electron spin resonance. ZNS, in the mmolar range, scavenged hydroxyl and nitric oxide radicals in a dose-dependent manner. This suggests that the mechanism of antiepileptic effect of ZNS may involve protection of neurons from free radical damage and stabilization of neuronal membranes.

Zonisamide as a neuroprotective agent in an adult gerbil model of global forebrain ischemia: a histological, in vivo microdialysis and behavioral study

Brief periods of global cerebral ischemia are known to produce characteristic patterns of neuronal injury both in human studies and in experimental animal models. Ischemic damage to vulnerable areas such as the CA1 sector of the hippocampus is thought to result from excitotoxic amino acid neurotransmission. The objective of this study was to determine the ability of a novel sodium channel blocking compound, zonisamide, to reduce neuronal damage by preventing the ischemia-associated accumulation of extracellular glutamate. Using a gerbil model, animals were subjected to 5 min ischemic insults. Both pre- and post-ischemic drug administration (zonisamide 150 mg/kg) were studied. Histological brain sections were prepared using a silver stain at 7 and 28 days post ischemia. The animals sacrificed at 28 days also underwent behavioral testing using a modified Morris water maze. In vivo microdialysis was performed on a separate group of animals in order to determine the patterns of ischemia-induced glutamate accumulation in the CA1 sector of the hippocampus. Pyramidal cell damage scores in the CA1 region of the hippocampus were significantly reduced in animals pre-treated with zonisamide compared to saline-treated controls, both at 7 days (drug pre-treated: 0.812 +/- 0.28, n = 8; controls: 1.625 +/- 0.24, n = 8; *P < 0.05) and 28 (drug pre-treated: 0.833 +/- 0.22, n = 12; controls: 1.955 +/- 0.26, n = 11; **P < 0.01) days post ischemia. However, animals receiving zonisamide post-treatment did not display significant differences from controls. Behavioral studies also showed significant preservation of function in drug-treated animals. Microdialysis studies confirmed a reduction in glutamate release in drug-treated animals compared to saline-treated controls. Our data suggest that zonisamide is effective in reducing neuronal damage by a mechanism involving decreased ischemia-induced extracellular glutamate accumulation and interruption of excitotoxic pathways.

Zonisamide. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in epilepsy

Zonisamide is a 1,2 benzisoxazole derivative and the first agent of this chemical class to be developed as an antiepileptic drug. It has shown activity in various animal models of epilepsy, and although a detailed mode of action awaits clarification it appears to block the propagation/spread of seizure discharges and to suppress the epileptogenic focus. Clinical experience with zonisamide in Japan has documented its efficacy in the treatment of partial seizures (partial-onset generalised tonic-clonic, simple partial and/or complex partial seizures), and to a more variable extent, generalised tonic-clonic, generalised tonic (mainly seen in symptomatic generalised epilepsies including Lennox-Gastaut Syndrome) and compound/combination seizures (including those refractory to treatment with other antiepileptic drugs). Other generalised seizure types have also responded to therapy with zonisamide, although only small patient numbers were studied. Zonisamide has demonstrated efficacy equivalent to that of carbamazepine in patients with (mainly) partial seizures, and to that of valproic acid in a small study of children (n = 32) with generalised seizures. Animal studies suggest that zonisamide possesses a more favourable therapeutic index than most other antiepileptic drugs. However, clinical trials conducted to date, have not confirmed any overt tolerability advantage. Indeed, whereas the recommended therapeutic plasma zonisamide concentration is 20 mg/L, clinical investigations have associated adverse events with plasma zonisamide concentrations of > 30 mg/L, suggesting the usefulness of therapeutic drug monitoring. Moreover, although plasma concentrations of zonisamide are empirically regarded to be proportional to therapeutic doses in patients in Japan, nonlinear pharmacokinetics have been reported for this drug in patients in the US and may further complicate its use in this patient population. Additional pharmacokinetic studies will help to establish the change in pharmacokinetic profile that occurs with dosage titration in patients outside Japan. Among 700 patients treated with zonisamide in Europe/US, a high incidence of renal calculi (1.9%) has been noted, however, the causal relationship to zonisamide is disputed. Indeed, although urinary lithiasis has also been recorded for patients in Japan, the aetiology, incidence and spontaneous regression of this condition suggest that it is not a serious problem for this patient population. Until this difference is clarified, it is likely that zonisamide will find its greatest use in the treatment of patients in Japan. Like many other established antiepileptic drugs, available data suggest the propensity for zonisamide to alter the pharmacokinetic profile of other anticonvulsant agents, although severe interactions appear to be unlikely.(ABSTRACT TRUNCATED AT 400 WORDS)

Zonisamide blocks T-type calcium channel in cultured neurons of rat cerebral cortex

We investigated the effect of zonisamide, a new antiepileptic drug, on voltage-dependent Ca2+ currents in cultured neurons of rat cerebral cortex. Whole-cell voltage-clamp recordings demonstrated at least two distinct voltage-dependent Ca2+ currents: (1) a low-threshold, rapidly inactivating component, T-type Ca2+ current, which is sensitive to 100 microM Ni2+, and (2) a high-threshold, slowly inactivating (long-lasting) component, L-type Ca2+ current. Zonisamide, a new anticonvulsant effective against maximal electroshock (MES) seizures in mice reduced T-type Ca2+ current in a dose-dependent manner. The mean percentage of reduction was 59.5 +/- 7.2% at 500 microM, but zonisamide had no effect on L-type Ca2+ current. A methylated analog of zonisamide, which is ineffective against MES seizures in mice, was tested at a concentration of 500 microM, and reduced neither T-type nor L-type Ca2+ current. These findings suggest that the effects of zonisamide against MES seizures might occur through the reduction of T-type Ca2+ current. Because drugs that are effective against MES seizures are thought to prevent seizure discharge spread, T-type Ca2+ channels could underlie a cellular mechanism of spreading activity in epileptic seizures.