Medivation has received a letter from the FDA regarding its investigational new drug (IND) application to begin human testing of Dimebon for Huntington's disease.

The letter confirmed the information initially communicated by the FDA that additional rat toxicology data are required before human clinical trials can begin. The FDA expressed the concern that the dose levels of Dimebon used in one of Medivation's rat toxicology studies did not result in sufficient toxicity to define a maximum tolerated dose. This information might provide additional guidance to physicians regarding the potential toxicities of Dimebon in humans.