1,2-Benzoxazol-3-ylmethanesulfonimidic acid

161-163 °C

161 - 163 °C

At concentrations between 1.0 and 7.0 μg/mL, zonisamide is approximately 40% bound to human plasma proteins. The concentration of zonisamide is 8-fold higher in red blood cells than in plasma due to its ability to bind extensively to erythrocytes. The presence of therapeutic concentrations of phenytoin, phenobarbital, or carbamazepine does not affect zonisamide protein binding.

By stopping the spread of seizure discharges, zonisamide prevents the extensor component of tonic convulsion, restricts the spread of focal seizures and prevents the propagation of seizures from the cortex to subcortical structures. In animal models, zonisamide was effective against tonic extension seizures but ineffective against clonic seizures. It also increased the threshold for generalized seizures and reduced the duration of cortical focal seizures. Aside from its antiepileptic effects, zonisamide is capable of activating neuroprotective mechanisms. It inhibits nitric oxide synthase and ​​reduces ischemia-induced memory impairment and lipid peroxidation. The use of zonisamide may lead to potentially fatal reactions. Severe reactions such as Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, and aplastic anemia have been reported in patients treated with sulfonamides such as zonisamide. Zonisamide may also lead to the development of serious hematological events, drug reaction with eosinophilia and systemic symptoms (DRESS) and multi-organ hypersensitivity, acute myopia and secondary angle closure glaucoma, as well as suicidal behaviour and ideation. Zonisamide is a carbonic anhydrase inhibitor, which may lead to metabolic acidosis in patients treated with this drug. Its therapeutic effects due to this pharmacological action are unknown.

The mechanism of action by which zonisamide controls seizures has not been fully established. However, its antiepileptic properties may be due to its effects on sodium and calcium channels. Zonisamide blocks sodium channels and reduces voltage-dependent, transient inward currents, stabilizing neuronal membranes and suppressing neuronal hypersynchronization. It affects T-type calcium currents, but has no effect on L-type calcium currents. Zonisamide suppresses synaptically-driven electrical activity by altering the synthesis, release, and degradation of neurotransmitters, such as glutamate, gamma-aminobutyric acid (GABA), dopamine, serotonin (5-hydroxytryptamine [5-HT]), and acetylcholine. Furthermore, it binds to the GABA/benzodiazepine receptor ionophore complex without producing changes in chloride flux. _In vitro_ studies have suggested that zonisamide does not affect postsynaptic GABA or glutamate responses, nor the neuronal or glial uptake of [³H]-GABA.