What phase of a clinical trial provides a new drug given to a large group of 100-300 to observe the effectiveness and to further evaluate safety?

The phase of a clinical trial that involves administering a new drug to a larger group of participants, typically ranging from 100 to 300 individuals, is Phase II. This phase is crucial for gathering initial data on the drug's effectiveness and continuing to evaluate its safety after initial results from Phase I, which focuses on a smaller group primarily to test safety and dosage.

In Phase II, researchers monitor the drug’s therapeutic effects and determine whether it has the desired effect on the conditions it is intended to treat. Safety is still a primary concern, but the focus shifts more towards effectiveness, as the sample size allows for a more comprehensive assessment of how the drug behaves in a larger population.

Phases III and IV are concerned with larger scale studies and post-marketing surveillance, respectively, while Phase I deals with safety and dosage in a small number of healthy volunteers or patients. Therefore, understanding the structure of clinical trials and the purpose of each phase is essential for recognizing the specific objectives and challenges involved at each stage of drug development.