Phase 0/microdosing approaches: time for mainstream application in drug development?

Phase 0 approaches - which include microdosing - evaluate subtherapeutic exposures of new drugs in first-in-human studies known as exploratory clinical trials. Recent progress extends phase 0 benefits beyond assessment of pharmacokinetics to include understanding of mechanism of action and pharmacodynamics. Phase 0 approaches have the potential to improve preclinical candidate selection and enable safer, cheaper, quicker and more informed developmental decisions. Here, we discuss phase 0 methods and applications, highlight their advantages over traditional strategies and address concerns related to extrapolation and developmental timelines. Although challenges remain, we propose that phase 0 approaches be at least considered for application in most drug development scenarios. Phase 0 approaches, including microdosing, evaluate subtherapeutic exposures to novel drugs, potentially enabling safer, cheaper and quicker first-in-human studies. Here, Burt et al. discuss the fundamentals and applications of phase 0 approaches, highlight the potential advantages of their application in drug development and address the associated limitations.