(Reuters) - Eisai ( ESALF ) and Biogen have launched their Alzheimer's treatment Leqembi in China, the third country after the United States and Japan, the companies said on Friday.

Leqembi, which works by removing a toxic protein called beta amyloid from the brain, is the first Alzheimer's treatment proven to alter the course of the fatal, brain-wasting disease.

The drug will first be launched in the private market at 2,508 yuan ($345.04) for a 200 mg vial, the companies said in a statement.

Eisai ( ESALF ) has also collaborated with a major Chinese medical insurance firm to plan partial coverage of the drug cost, the companies said without naming the insurer.

China approved the treatment in January after a standard approval from the U.S. Food and Drug Administration last July.

More convenient Alzheimer's blood tests expected to be ready by 2025 could help Eisai ( ESALF ) reach a bigger share of China's estimated 17 million people with early-stage disease, a company spokesperson had told Reuters after approval in China.

($1 = 7.2688 Chinese yuan)

(Reporting by Surbhi Misra in Bengaluru; Editing by Subhranshu Sahu)