Describe the Different Phases of Drug Development

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The Answer is Drug development to support a viable marketing application advances in somewhat overlapping phases. Nonclinical (also called preclinical) studies begin prior to human studies and continue throughout the clinical development period. Prior to each phase of human testing, animal testing is done to ensure that the level of planned human exposure is safe. The usual temporal sequence proceeds from an initial classification of the drug to testing for efficacy and finally the exploration of potential side effects in the intended population of use.
Phase I studies represent the initial introduction of the new drug in humans. The studies are closely monitored, conducted usually in healthy volunteers, and identify the properties of the drug and overt toxicities. These studies also establish tolerable doses for further testing. Phase I studies are conducted to obtain sufficient information about the drug to help design scientifically robust phase II studies. The total number of subjects generally ranges from 20 to 80.
Phase II studies include carefully chosen patients with the disease or condition being studied. Phase II studies are closely monitored and optimized for the collection of data on efficacy. The optimal doses of the drug and safety data regarding common short-term side effects are also obtained during this phase.
After preliminary evidence suggesting that the effectiveness of the drug has been established in phase II trials, additional information about effectiveness and safety is needed to evaluate the overall risk-to-benefit relationship of the drug and to provide an adequate basis for product labeling. Phase III studies help expand the information on the effectiveness and safety of the drug to assess the overall risk-to-benefit ratio. The study subjects are selected from a broader pool, in comparison with phase II studies, to help select a population that is more representative of the patients who will be exposed to the drug during marketing. Phase III studies may include several hundred to several thousand subjects, including individuals with a broad range of typical comorbid conditions and concomitant medications seen in the target population.
Phase IV studies refer to the postmarketing activities that are conducted subsequent to the FDA approval of a drug. Active surveillance for rare adverse events and studies designed to look into approval for additional indications are two examples of phase IV studies.

Describe the Different Phases of Drug Development

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