Increasing the success rate for Alzheimer's disease drug discovery and development.

This paper responds to the fact that over 200 Alzheimer's disease (AD) drug candidates have failed to date and draws on searches of the literature for studies of error effects in drug developments and the authors' published works. In the same period, basic knowledge of AD pathology has greatly expanded providing both potential therapeutic targets and rationales for modifications in strategies for testing AD drug candidates. Current opinion generally holds that AD drug candidates have failed because they address pathology that is already too advanced. Less attention is paid to numerous reported methodological weaknesses capable of biasing AD clinical trials and drug developments and thus invalidating conclusions to be reached about the drugs being tested. The costs of quality controls possibly needed to better insure validity in AD drug developments raises concerns that progress toward success in AD drug development may be hindered by the costs of intervening against current methodological barriers to the successful completions of AD drug developments.