FDA: Rare Diseases: Common Issues in Drug Development

This guidance assists sponsors of drug and biological products intended to treat or prevent rare diseases in conducting more efficient and successful development programs through a discussion of selected issues commonly encountered in rare disease drug development. Although similar issues are encountered in other drug development programs, they are frequently more difficult to address in the context of a rare disease with which there is often little medical experience. These issues are also more acute with increasing rarity of the disorder. A rare disease is defined by the Orphan Drug Act of 1983 as a disorder or condition that affects less than 200,000 persons in the United States. Most rare diseases, however, affect far fewer persons.