Takeda Pharmaceutical Co will spend as much as $856 million to secure global rights from Ovid Therapeutics Inc to an experimental drug being developed to treat rare epilepsy, the companies said on Wednesday.

Takeda will be responsible for future development and commercialization of the drug, soticlestat, worldwide and Ovid will no longer have any financial obligation, the companies said in a statement.

Ovid will receive an upfront payment of $196 million at the close of the agreement, expected by the end of March, and is eligible to receive up to an additional $660 million in milestone payments.

The Japanese drugmaker entered into a collaboration agreement in 2017 with Ovid to develop and market soticlestat, which aims to treat children and adults with Dravet Syndrome and Lennox-Gastaut syndrome.

The companies in August reported results from a mid-stage study showing soticlestat met the main goal of reduction in seizure frequency.

Jazz Pharmaceuticals Plc last month agreed to buy GW Pharmaceuticals Plc in a $7.2 bln deal for its FDA-approved drug, Epidiolex, to treat seizures associated with the two syndromes.

Takeda said it plans to start late-stage studies of soticlestat in children and young adults with the two epileptic syndromes in the second quarter.

Ovid will also receive tiered royalties beginning in the low double-digits and up to 20% on sales of the drug, Takeda said.