Klin Farmakol Farm. 2026;40(2):92-96 | DOI: 10.36290/far.2026.017

Clinical trials: The evolution of the traditional phase-based approach in contemporary clinical research

Lenka Součková^{1, 2}, Veronika Kunešová¹, Adriána Papiež¹, Hana Blahynková¹

¹ CZECRIN, Lékařská fakulta Masarykovy univerzity, Brno

² Centrum klinických studií, Fakultní nemocnice u sv. Anny v Brně

Clinical trials represent a key component of the development of medicinal products and a fundamental source of evidence for evidence-based medicine. Traditionally, the clinical development of medicines has been described through four sequential phases of clinical trials (I-IV), reflecting the stepwise evaluation of safety, dosing, efficacy, and post-marketing surveillance after a medicinal product is introduced to the market. This model has long served as both a regulatory and educational framework for clinical research. However, in recent decades the clinical development of medicines has undergone significant changes. In practice, sub-phases of clinical trials (e.g., Ia, Ib, IIa, IIb) and combined study designs that integrate multiple phases of develop­ment (e.g., phase I/II or II/III trials) are increasingly used. At the same time, innovative approaches to clinical trial design are emerging, including adaptive, seamless, and platform trials, while the use of real-world evidence is gaining importance. A specific area of development involves advanced therapy medicinal products (ATMPs), such as gene and cell therapies, where clinical development is often conducted in smaller patient populations and, in some cases, regulatory approval may be based on early-phase clinical studies. The aim of this article is to present the traditional concept of clinical trial phases, discuss its limitations, and highlight current trends in clinical research that illustrate the transition from a rigid linear model to a more flexible and continuous approach to clinical drug development.

Keywords: clinical trials, clinical trial phases, drug development, ATMP, adaptive design.

Received: March 23, 2026; Revised: May 4, 2026; Accepted: May 6, 2026; Published: July 1, 2026  Show citation