(Reuters) - The U.S. Food and Drug Administration has approved monthly maintenance dosing for Japan's Eisai and partner Biogen (NASDAQ: BIIB )'s Alzheimer's drug Leqembi, the companies said on Monday.

The drug received standard U.S. approval in 2023 after showing it slowed cognitive decline in patients with the brain-wasting disease but growth has been slow, in part because its administration is time-consuming and it requires regular MRIs and screenings.

Patients can switch to a monthly dose after having received an intravenous infusion of the drug every two weeks for 18 months, the companies said in a joint statement. They can also continue to dose once every two weeks.

Leqembi clears sticky deposits of a protein called amyloid beta in the brain, believed to be a hallmark of Alzheimer's disease. Patients receive the drug at an infusion center in almost an hour-long process.

The companies said that modeling simulations of trial data predicted that maintenance dosing would maintain benefits of the therapy.

A rival drug from Eli Lilly (NYSE: LLY ), Kisunla, was approved in July and is given by infusion once a month. Patients stop taking the treatment once brain scans no longer show amyloid plaques.

Both drugs have safety warnings regarding the potential for brain swelling and bleeds. Patients are recommended to undergo monitoring with scans.

Eisai has a collaboration agreement with BioArctic on the drug.