A phase 2 trial is designed to provide data on safety in target populations as well as ‘proof of concept’ that a drug has a therapeutic effect.
Positive results in a phase 2 trial are needed to justify investment in a larger and more costly phase 3 trial to provide a definitive assessment of efficacy.
Phase 2 trials also provide scope for additional pharmacokinetic/pharmacodynamic (PK/PD) studies so that the metabolism of a drug and its action on pathogens can be better understood.