Early phase drug development for treatment of chronic pain--options for clinical trial and program design

Due to high prevalence and unmet medical need, chronic pain has become an important area for development of new medicines. Chronic pain disorders are heterogeneous with regard to pathophysiological mechanisms and clinical presentation. While a mechanism-based classification of pain is generally advocated, it is not yet applicable for diagnostic use. Many new analgesic drug candidates believed to act on scientifically relevant pain targets have failed to show efficacy in clinical trials. These might be true observations of inferior efficacy and/or safety. However, in part, these failures may be due to difficulties with selection of an appropriate study population and/or appropriate doses. For a new chemical entity (NCE) with a novel pharmacological mechanism, the only guidance for selection of study population and doses is often based on preclinical data. Thus, there may be considerable uncertainty in defining the population with a pain generating mechanism targeted by the NCE. Therefore, further exploration of the right population and dose may be needed in early clinical phase why alternatives to conventional trial designs may be considered. We have reviewed characteristics of three alternative design options from an early (Phase 2) drug development perspective; enriched enrolment, dose titration and adaptive dosing. The advantages and disadvantages of each type of study design were analyzed and discussed from a clinical development program perspective. It is concluded that these designs can be useful in addressing different types of issues in early development of novel analgesic drugs for chronic pain.