UPDATE 1-Merck starts new trial to test Alzheimer's drug

Dec 3 (Reuters) - Merck & Co Inc has started a new trial of its experimental Alzheimer's drug, the first mid-stage clinical trial of a promising new class of oral medicines that has the potential to shut down the production of a protein that many researchers believe is the primary cause of the disease.

The drugmaker said on Monday it had started the trial to evaluate the safety and effectiveness of the drug, MK-8931, in patients with mild-to-moderate Alzheimer's disease.

The Phase II trial, which will compare the drug with a placebo, is a global, multi-center study that includes a group of 200 patients to test safety.

The study is expected eventually enroll up to 1,700 patients in the main Phase III group.

The drug is the first of its kind to advance to this stage of clinical research.

Eli Lilly and Co is considered the frontrunner in Alzheimer's research after its drug solanezumab was shown in August to slow down cognitive declines in patients with mild symptoms of Alzheimer's disease. However, the drug failed its overall goal of delaying cognitive and physical decline in patients with mild to moderate Alzheimer's.

The start of Merck's new trial of MK-8931 could put the company on an equal footing with Lilly in the race for the first approved drug to delay the progress of the disease.

The Lilly drug is administered intravenously, while the Merck drug is taken orally.