To obtain approval from the Food and Drug Administration (FDA) or an equivalent agency outside the United States to market and sell a new drug or biologic product for use in humans, a series of clinical studies must be performed. These clinical studies exist in four phases. Each phase has specific and differing requirements for patient types, goals, inclusion/exclusion criteria, design features, and expected outcomes. Combined, they build the patient care database for safety and efficacy that hopefully will lead to product approval.

The time frame for these clinical studies often is called "clinical development" and requires about 5 years. In the past, there were clear boundaries between the four fairly standardized phases of clinical drug development. However, the phases have become less well defined as questions previously addressed in one phase are being addressed in both earlier and later phases. In part, this new approach is designed to accelerate the acquisition of information needed for approval and successful marketing of a new drug and for collection of full and sufficient safety information as early as possible. The information that follows is designed to provide an overview of the types of studies used during clinical drug development.

Under usual circumstances, the studies progress from those designed to evaluate single and multiple dose toxicity by using a small number of normal subjects (phase 1), to define dose-response relationships and additional toxicity using a larger number of subjects with disease (phase 2), and to determine efficacy and safety with the dose(s) of interest using several thousand subjects with disease (phase 3). This chapter will address all the types of clinical studies listed in the outline above. The phase 3 studies need to provide sufficient information for a successful New Drug Application (NDA) or approval of a new biologic, that is, sufficient proof of efficacy and safety for the targeted indication.

Before receiving approval, plans are made to initiate additional studies, which are to be done during and after marketing the product. These include large, simple, clinical trials (phase 4 studies) designed to more closely resemble what occurs outside the rigid double-blind, randomized, placebo-controlled clinical trial, such as pharmacoeconomic and phar-macogenetic studies, drug-interaction studies, comparator studies, studies in special populations, and studies that primarily examine quality of life. These studies display well the need for more much information through clinical research after product approval and expand our understanding of how products will be used and perform in patients.

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