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CNBC Explains: New Alzheimer's drugs

Medicines in development at Biogen and Eli Lilly could be the first to slow the cognitive declines brought by Alzheimer's disease. New data will be presented Wednesday at the Alzheimer's Association International Conference in Washington, D.C. So how do they work?

The drugs take aim at the plaque buildups in the brain that characterize Alzheimer's, known as beta amyloid. Unlike currently marketed drugs Aricept and Namenda, which affect levels of certain brain chemicals and may temporarily ease symptoms of Alzheimer's, Biogen's and Lilly's drugs may be disease modifying.

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They're important because they have instilled new confidence in what's known as the amyloid hypothesis: the idea that targeting those plaque buildups will actually slow the disease.

The medicines bind to beta amyloid in slightly different ways, but both companies are treating patients in the earlier stages of Alzheimer's disease. It's thought that additional methods will be needed to help patients who have cases that are more advanced.

Other approaches include targeting tangles of proteins known as tau, and reducing the production of beta amyloid in the first place by inhibiting an enzyme known as beta secretase.

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