TOKYO (Kyodo) -- Japanese pharmaceutical company Eisai Co. and U.S. firm Biogen Inc. said Monday that a jointly developed Alzheimer's drug has been approved for continuous use for people with early stages of the disease by U.S. regulators.

With the green light from the U.S. Food and Drug Administration, the intravenous dosing of the drug, known chemically as lecanemab and branded Leqembi, could be reduced to every four weeks after 18 months of dosing every two weeks, potentially decreasing the patients' burden of needing to go to hospital for treatment.

The companies aim to introduce injectable drugs in the United States that can be administered at home in the future. They did not comment on possible future developments in Japan.

The drug utilizes an antibody that targets a protein called amyloid beta. The plaque-like protein, which accumulates inside the brain and destroys nerve cells, is considered the cause of the disease.

Last year, a team of Eisai and others presented an estimate at a conference in the United States that amyloid beta increases by 30 percent over the following two and a half years if treatment is stopped after 18 months, but that this increase can be prevented if the treatment is continued with the pace of dosage halved.

Meanwhile, it is speculated that treatment from a similar drug called donanemab, developed by U.S. firm Eli Lilly and Co. and approved for use in the United States and Japan, can be ended once the amyloid beta has been sufficiently eliminated from the brain, with the long-term cost-effectiveness of both drugs coming under scrutiny.