Zonisamide

There are more than 50 million epilepsy patients worldwide, of which approximately 30% are drug-resistant refractory cases, and there is an urgent clinical need for treatment options with both broad-spectrum antiepileptic effects and good tolerability. Zonisamide is a second-generation antiepileptic drug that exerts a multi-target synergistic inhibitory effect on abnormal discharge of neurons by blocking voltage-dependent sodium channels and T-type calcium channels, while inhibiting carbonic anhydrase activity. Clinically, it can be used as add-on therapy for partial seizures of epilepsy in adults and adolescents over 12 years old, and can also be used as monotherapy for the initial treatment of partial seizures. It also has a certain effect on generalized seizure types such as myoclonic seizures and absence seizures, and can also assist in improving the motor symptoms of Parkinson's disease. Due to its low burden on the liver and kidney, it is particularly suitable for elderly patients with underlying comorbidities.

In 2023, the global zonisamide market size was approximately USD 1.12 billion, with a compound annual growth rate of 6.8% in the past 5 years. The growth momentum mainly comes from the expansion of pediatric epilepsy indications and the exploration of off-label application in the field of neurology. For the domestic market, the terminal sales of public medical institutions increased from RMB 120 million in 2019 to RMB 370 million in 2023, with a compound annual growth rate of 32.5%. At present, 6 domestic enterprises have obtained approval for generic drug preparations. In the 7th batch of national centralized drug procurement in 2022, zonisamide oral regular-release dosage forms were included, and the winning bid price decreased by 71% on average compared with that before the centralized procurement, leading to a rapid increase in market penetration and a simultaneous increase in demand for upstream API.

The original developer of zonisamide is Otsuka Pharmaceutical of Japan, with the original brand name "Zonegran". The expiration date of its core compound patent in the United States is 2024, and the core European patent expired in 2021. The domestically approved dosage form of the original drug is oral tablet, with specifications of 100mg and 300mg, which has been included in the *Catalogue of Reference Preparations of Chemical Drugs* issued by the National Medical Products Administration. Up to now, there are 9 zonisamide API registration entries on the domestic API registration platform, of which 5 are in status A and can be associated with domestic preparation declarations; the approved and marketed preparations cover two dosage forms: conventional tablets and dispersible tablets, with a total of 12 approval numbers. (Data as of June 2025, please refer to the official website of CDE for the latest information)

CATO provides a full set of zonisamide impurity reference standards, covering dozens of components such as synthetic intermediates and degradation impurities. Most of the products are in stock. For in-stock products, orders placed before 16:00 will be shipped on the same day. All reference standards comply with the relevant regulatory requirements of the Chinese Pharmacopoeia and FDA, and can fully support the full-process needs of API process development, quality research and registration declaration.