By Michelle Fay Cortez March 3 (Bloomberg) — Pfizer Inc. and Medivation Inc. said Dimebon, their experimental drug for Alzheimer’s disease, failed to benefit patients in an advanced study. The trial, dubbed Connection, included almost 600 patients with mild to moderate Alzheimer’s disease from across the U.S., Europe and South America. The results counter an earlier study in Russia that found improvement in patients getting Dimebon. Medivation shares fell 68 percent in early trading. The negative results for Dimebon, a 27-year-old hay fever treatment, are the latest setback in efforts to find a way to slow the most common form of dementia in elderly people. It could have generated more than $5 billion in annual sales if it proved effective, said Raghuram Selvaraju, head of health-care research at Hapoalim Securities USA Inc., in New York. “We are surprised and disappointed,” said David Hung , chief executive officer of San Francisco-based Medivation, in a telephone interview. “We’re trying to figure out what happened in the study and decide how to move forward. This is obviously one battle in our war against Alzheimer’s disease.” Medivation plunged $27.26 to $12.99 in trading before the Nasdaq Stock Market opened. Before today, the stock had risen 6.9 percent this year, giving the company a market value of $1.35 billion. Patients on Dimebon didn’t do better than those given placebo in cognition or global functioning after six months, the two main goals of the study. It also failed to show benefits on the study’s secondary objectives, which looked at behavior, mental functioning and the patients’ ability to care for themselves. ‘Worst-Case Scenario’ “We think this was nearly the worst-case scenario, although management will talk about other ‘shots on goal,’” said Michael Yee , an analyst at RBC Capital Markets in San Francisco, in a note to investors today. He rates Medivation stock “sector perform.” The U.S. Food and Drug Administration told the companies that the original Russian study, published in the journal Lancet, would be considered a pivotal trial. Most regulators require positive results from two pivotal trials, typically in the third and final stage of human testing, to win approval. Selvaraju, who considers himself one of the most optimistic analysts on Dimebon, predicted a 40 percent chance of success for the drug before the results were released. There are four other Dimebon studies under way, evaluating the drug in addition to standard treatment in patients with mild-to-moderate and moderate-to-severe disease, Hung said. The company also is testing it in Huntington’s disease, a degenerative neurological disorder that runs in families. Pfizer’s Aricept Alzheimer’s is a progressive disease that starts with mild forgetfulness and eventually robs patients of memories and independence. It afflicts 30 million people worldwide, a number that may exceed 100 million by 2050, according to Alzheimer’s Disease International, an advocacy group based in London. Existing drugs including Aricept from New York-based Pfizer and Tokyo-based Eisai Co. , the leading therapy with $2.5 billion a year in annual sales, temporarily ease symptoms of Alzheimer’s disease. Doctors and patients are looking for novel treatments that slow the progression of the illness, allowing patients to remain in their homes and take care of themselves for longer periods of time. There hasn’t been a new drug for the disease since Namenda, from New York-based Forest Laboratories Inc., was approved in 2003. Almost a dozen drugs in mid- to late-stage testing have failed since then, according to data compiled by Bloomberg. ‘Tough Business’ “Developing treatments for Alzheimer’s disease is a tough business,” said Michael Krensavage , founder of Krensavage Asset Management in New York. “The landscape of Alzheimer’s research is littered with failure. The drugs that are available provide little clinical benefit.” Researchers have announced setbacks with experimental treatments from GlaxoSmithKline Plc, AstraZeneca Plc, Martek Biosciences Corp., Johnson & Johnson, Abbott Laboratories and Myriad Genetics Inc. in the past year. One of the most eagerly anticipated drugs, bapineuzumab from Pfizer and New Brunswick, New Jersey-based Johnson & Johnson, reduced the buildup of amyloid plaque in the brains of patients with Alzheimer’s disease, according to a study published March 1. Patients getting the drug in the trial didn’t show a clear improvement in mental function. Medivation has no products on the market and has recorded losses exceeding $150 million since 2003. Pfizer, which hasn’t brought a new drug to market that generates more than $1 billion a year since the pain pill Lyrica won U.S. clearance in 2004, has pinpointed Alzheimer’s as one of six focuses of research. Prostate-Cancer Drug Medivation also has a prostate cancer drug in development with Japan’s Astellas Pharma Inc. Information on that treatment won’t be available until the second half of 2011, according to RBC’s Yee. Pfizer has eight other compounds in development for Alzheimer’s disease. “We are committed to this area,” said Briggs Morrison , senior vice president of Pfizer’s primary-care development group, in a telephone interview. “We know it’s going to be hard and we know there’s going to occasionally be disappointments like this one. But that doesn’t in any way change our commitment to trying to come up with important treatments for Alzheimer’s disease patients.” To contact the reporter on this story: Michelle Fay Cortez in London at mcortez@bloomberg.net