Pfizer Inc (NYSE: PFE) and Medivation, Inc. (NASDAQ: MDVN) announced results from the Phase 3 HORIZON trial of the investigational drug dimebon (latrepirdine*) in patients with Huntington disease. Dimebon did not achieve statistical significance for either of the co-primary endpoints, the Mini-Mental State Examination (MMSE), which measures cognition (p=0.39), or the Clinician's Interview-Based Impression of Change, plus caregiver input (CIBIC-plus), which measures global function (p=0.84).
"We are disappointed with the results of the HORIZON trial given the high unmet need in this patient population. At this point, we will discontinue development of dimebon in Huntington disease, including the ongoing open-label extension study," said David Hung, M.D., president and chief executive officer of Medivation. "We will continue our ongoing 12-month Phase 3 CONCERT trial of dimebon and its open-label extension in patients with mild-to-moderate Alzheimer's disease. We expect to report top-line data from CONCERT in the first half of 2012."
Dimebon was generally well tolerated in the HORIZON trial, consistent with findings from previous trials including over 2,000 patients, the large majority of whom were Alzheimer's disease patients.
"Huntington's is a challenging disease area, and we are also disappointed with the HORIZON results," said Pfizer's Steve Romano, M.D., senior vice president, Medicines Development Group head, Primary Care Business Unit. "The results are expected to be presented at an upcoming medical meeting."
* Latrepirdine is the generic (nonproprietary) name for dimebon.
HORIZON Study Design and Results
The double-blind, placebo-controlled Phase 3 HORIZON trial enrolled 403 patients with Huntington disease at 64 sites in North America, Europe and Australia. The trial included patients who had cognitive impairment, based on investigator judgment and verified by MMSE score. Patients were randomized to receive either 20 mg of dimebon three times daily or placebo for six months.
No statistically significant improvements were achieved for the dimebon group relative to placebo on either of the co-primary endpoints. Dimebon was generally well tolerated in the study. The overall incidence of adverse events was equivalent between the treatment groups: 69 percent in the dimebon group and 68 percent in the placebo group. Adverse events occurring in at least 5 percent of dimebon treated patients and more frequently than in placebo treated patients were chorea (8 percent vs. 4 percent), headache (6 percent vs 3 percent) and fatigue (5 percent vs 0 percent).
The trial was conducted in collaboration with the Huntington Study Group (HSG) and the European Huntington's Disease Network (EHDN). The HSG is a non-profit group of experienced clinical trial investigators from medical centers in the United States and abroad dedicated to clinical research of Huntington disease. The EHDN is a non-profit network of professionals providing an infrastructure for large scale Huntington disease clinical trials throughout Europe.
About Dimebon
Dimebon (latrepirdine) is an investigational oral medication being tested as a potential treatment for Alzheimer's disease. Dimebon is currently being studied in the Phase 3 CONCERT trial, a 12-month study evaluating dimebon in patients with mild-to-moderate Alzheimer’s disease who are taking donepezil, a commonly prescribed Alzheimer's disease medication.
About the Pfizer/Medivation Dimebon Collaboration
Medivation and Pfizer have a global collaboration to develop and commercialize dimebon for the treatment of Alzheimer's disease and Huntington disease. Under the terms of the agreement, the companies work together on the dimebon development program.