I would just like to add to Björn's excellent answer but to focus on the pharmacokinetic (PK) and pharmacodynamic (PD) work that is usually carried out in Phase II as part of what Björn talks about. These trials, especially the 2b phase, are important in refining our understanding of a drug's behaviour in the target population.
In Phase II, particularly in non-oncology settings as Björn mentioned, the main goal is often to identify the optimal dosage and understand the drug's kinetics and dynamics. This intensifies the focus on PK/PD aspects and involves fairly complex mathematical and statistical modelling, extending the initial models developed in Phase I (which are usually based on data from healthy humans). In Phase II, these models are adapted and expanded to the target patient population, aiming to determine key factors such as:
Efficacy and Safety Windows: This involves identifying the range of doses at which the drug is both effective and safe for the target population.
Minimum/Maximum Effective Dose: Determining the smallest dose that produces the desired therapeutic effect and the maximum dose before adverse effects outweigh benefits.
Maximum Tolerated Dose: Establishing the highest dose that the target population can tolerate without significant side effects.
Timing of Efficacy and Tolerability Effects: Understanding how long it takes for the drug to exhibit therapeutic effects and at what point side effects might become intolerable.
Titration Steps and Dosing Intervals: Developing guidelines for safely increasing the drug dose and determining the frequency at which the drug should be administered.
Identification of Potential Subgroups for Dose Adjustment in Phase III: This involves recognising specific patient subgroups that might need different dosing strategies in the subsequent phase of the trial.