The U.S. Food and Drug Administration said on Thursday it is recommending an additional, earlier magnetic resonance imaging monitoring prior to the third infusion for patients with Alzheimer's disease taking Biogen's drug Leqembi.

The earlier monitoring can identify individuals with amyloid-related imaging abnormalities with edema (ARIA-E), which is characterized by brain swelling or fluid buildup.

The current prescribing information recommends MRI imaging before the fifth, seventh and 14th infusions.

The FDA said it identified six deaths early in treatment, which prompted an in-depth analysis of serious and fatal outcomes related to ARIA-E before the fifth Leqembi infusion.

Biogen did not immediately respond to a Reuters request for comment.