Both focus on beta-amyloid, a protein that is suspected of causing Alzheimer's. It accumulates into the characteristic clogs called plaques that distinguish the brains of people who have died from Alzheimer's.
More than 15 million people globally have Alzheimer's.
In one study at Georgetown University Medical Center in Washington, 58 people with mild to moderate Alzheimer's disease took a drug called Alzhemed or a placebo for three months, then for an additional 21 months.
Alzhemed, made by Montreal, Canada-based Neurochem Inc., is a pill just beginning Phase III trials, the final stage before a company seeks approval from regulators for a new drug.
The study, reported at a meeting of Alzheimer's experts in in Philadelphia, found a significant drop in the level of beta-amyloid among patients who took the drug and no change among those taking the placebo.
The researchers also found Alzhemed in cerebral spinal fluid, which indicates it was finding its way to the brain where it is needed. The drug reduced the levels of beta-amyloid in the spinal fluid and was generally safe and well tolerated, the researchers found.
Among patients who began the trial with mild Alzheimer's, there was no further cognitive decline after 12 months of taking the drug, said Dr Paul Aisen, who leads the study.
Alzheimer's begins with mild memory loss but can quickly progress to destroy learning, memory and patients' ability to care for themselves. There is no cure and it is always fatal
There are now 26 patients who have taken the drug for 16 months, and 19 who have taken it for 20 months, Aisen told a news conference. He said the trial will now be expanded.
"It will be a large, long trial that will provide a definitive answer on the efficacy of Alzhemed in inhibiting Alzheimer's," Aisen said.
In another study, Eli Lilly & Co is trying to prevent beta-amyloid from forming in the first place.
A trial of 37 healthy adults aged over 45 found blood levels of beta-amyloid were reduced after they took LY450139, an experimental drug designed to interfere with the formation enzymes called secretases, which generate beta-amyloid.
The trial found reduced levels of beta-amyloid in the blood after the drug was administered. Higher doses produced a greater reduction.
Although the drug was detected in cerebral spinal fluid, it did not reduce concentration of beta-amyloid in the fluid.
Researchers need to know the most effective dose before starting a larger trial, said Dr Eric Siemers of Eli Lilly.
Alzheimer's begins with mild memory loss but can quickly progress to destroy learning, memory and patients' ability to care for themselves. There is no cure and it is always fatal.