During which phase is the drug's dosing regimen often established?

The correct answer is associated with Phase 2 of clinical trials, where the drug's dosing regimen is commonly established. During this phase, researchers focus on evaluating the drug's efficacy and side effects in a larger group of participants who have the disease or condition the drug aims to treat.

Phase 2 trials typically involve a defined cohort of patients and are crucial for determining the optimal dosing by assessing various dosing strategies and their outcomes. This phase allows researchers to refine the dosing to maximize therapeutic effects while minimizing adverse reactions, establishing a more precise dosage that can be tested in later stages.

In contrast, Phase 1 primarily focuses on the safety profile of the drug, testing on a small group of healthy volunteers to determine the pharmacokinetics and pharmacodynamics, but not on dosing efficacy. Phase 3 takes a larger population to confirm effectiveness and monitor adverse reactions in a more comprehensive manner, while Phase 4 occurs after the drug has been approved, involving post-marketing surveillance to track long-term effects and further monitor safety and efficacy. Therefore, dosing regimens are crucially developed and established in Phase 2.