The evaluation of disease modifying therapies in Alzheimer's disease: a regulatory viewpoint.

Several drugs have received marketing approval in this country for the treatment of dementia of the Alzheimer's type. Their approval has been based on clinical trial designs that do not permit a distinction to be made between an effect of the drug on the symptoms of that disease, and an effect on the pathophysiological mechanisms that underlie that disorder. The latter effect has been referred to as 'disease-modifying.'In recent years there has been considerable interest in developing disease-modifying treatments for Alzheimer's disease (AD), using either specific clinical designs, or surrogate markers, such as brain imaging modalities. This paper outlines the regulatory framework governing how the Food and Drug Administration addresses new drug claims, the current basis for approving drugs for the treatment of AD, clinical trial designs that have been proposed as a means of demonstrating disease-modifying effects, a general and regulatory background to the use of surrogate markers in drug development, and, finally, views about the possible role of surrogate markers, especially brain imaging, as outcome measures in clinical trials intended to produce disease-modifying effects in Alzheimer's Disease.