By Manas Mishra

(Reuters) – The U.S. Food and Drug Administration on Monday refused to fully review the marketing application for Zogenix Inc’s treatment for seizures associated with Dravet syndrome, a rare form of childhood epilepsy.

Shares of the California-based drug developer plunged nearly 30 percent to $36.50 after it disclosed the FDA’s “refusal to file” letter, which investors could consider as a potential delay in getting approval for the drug.

Zogenix’s drug, to be branded as Fintepla, uses a low-dose, liquid solution of fenfluramine, which was used in an obesity drug combination that was withdrawn from the market due to evidence of heart valve damage.

The FDA, after a preliminary review, cited a lack of certain non-clinical studies to assess the chronic administration of fenfluramine and due to an incorrect dataset. The regulator had not yet asked for any additional clinical trials, Zogenix said, adding that it plans to meet with the FDA soon.

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Zogenix has already filed an application for approval from the European regulator and a decision is awaited by 2020.

Current treatment options for Dravet syndrome, which affects an estimated 20,000 patients in the United States, are limited to a combination of seizure medication and drugs to prevent emergencies.

Shares of GW Pharmaceuticals Plc, which last July gained approval for its cannabis-based drug to treat the disorder, were up 4 percent at $174.30 after the bell.

(Reporting by Manas Mishra in Bengaluru; Editing by Shounak Dasgupta and James Emmanuel)