Pfizer Inc and Medivation, Inc announced the initiation of a phase-3 trial of the investigational drug dimebon (latrepirdine) in patients with Huntington disease. The international safety and efficacy trial, known as Horizon, is designed to evaluate the potential benefits of dimebon on cognition (thinking and memory) in patients with Huntington disease. The companies also announced that the US Food and Drug Administration (FDA) has granted orphan drug designation to dimebon for the treatment of Huntington disease.

"Based on the promising results of our phase-2 trial of dimebon in Huntington disease, we are pleased to advance dimebon into late-stage clinical development," said Lynn Seely, chief medical officer for Medivation. "Huntington disease is a fatal genetic disease for which no medications are currently approved by the FDA to treat the cognitive impairment associated with the condition."

Orphan status is granted by the FDA to promote the development of products that demonstrate promise for the treatment of rare diseases affecting fewer than 200,000 Americans annually, such as Huntington disease, which affects 30,000 individuals in the United States, with another 150,000 at risk. Orphan drug designation entitles Pfizer and Medivation to a seven-year period of marketing exclusivity in the United States for dimebon if it is approved by the FDA for the treatment of Huntington disease. It also enables the companies to apply for research funding, tax credits for certain research expenses, and a waiver from the FDA's application user fee.

Latrepirdine is the proposed generic (nonproprietary) name for dimebon.

The double-blind, placebo-controlled phase-3 trial will enrol approximately 350 patients with Huntington disease at approximately 50 sites in North America, Europe and Australia. Patients will be randomized to receive either dimebon (latrepirdine) 20 mg three times daily or placebo for six months.

Dimebon (latrepirdine) is an investigational drug in phase-3 development for the treatment of Alzheimer's disease (AD) and Huntington disease (HD).