ABSTRACT
The clinical development of a new drug or a new treatment proceeds through three phases of testing in human subjects. Phase I trials are small studies that evaluate safety and identify a safe dose range of the treatment. Once a dose range is chosen, its therapeutic efficacy will be examined in a phase II trial. Regimens that are shown promising in phase II trials will be moved to multi-institutional phase III clinical trials for randomized comparison to standard treatments. The ultimate goal of this entire process is to translate promising discoveries in the laboratory into new medical procedures that can be used in the general clinical settings. This division of clinical trials, however, may give an oversimplified picture of the actual drug development process. Often, several phase I-II trial sequels of a drug, possibly with minor variations in the treatment schedule and patient populations, are needed before a phase III trial is warranted. This process is necessarily iterative rather than linear, as the phase I-II-III paradigm appears to suggest. In addition, the taxonomy of trials is not universal across disciplines, and may include finer divisions such as phase IA, IB, IIA, and IIB. The recent trend to combine phases of trials, the so-called combined phase I/II trials and seamless phase II/III trials, renders further refinement of the drug development process.
