Abstract
The evaluation of new drug entities with specific modes of action may be hampered by rigid diagnostic classification systems and patient selection processes that do not focus on the anticipated symptomatic, behavioral, and functional outcomes to be achieved. Patients enrolled in central nervous system (CNS) clinical trials may present with a heterogeneous group of symptoms representing several syndromes or subtypes, subsumed under the same diagnosis in the DSM-IV classification system. As a result, enrolled patients may not have the valid illness characteristics of interest to the particular study. We propose that clinical drug development needs to focus on the primary nosological entity likely to be affected by a new drug entity's mode of action. Ideally, a valid patient will have the acute primary symptoms that the novel drug is supposed to influence. In this article, we propose operational criteria to delineate a more symptom-specific and ecologically valid approach to the identification of the valid patient for clinical trials.