Designing Early-Phase Clinical Trials: Where to Begin and What to Consider 

4 minute read

Published: December 16th, 2025

Designing an early-phase clinical trial is one of the most important, and most complex, steps in drug development. The choices made here determine how efficiently a program progresses, how robust the data will be, and ultimately, whether a promising treatment reaches patients. 

In this blog, we explore where to begin when planning an early-phase study, from defining scientific objectives and engaging statisticians early, to aligning design choices with mechanism of action and long-term development goals. 

Start with the Question, Not the Design 

A common challenge in early-phase planning is jumping straight to a design without first defining the question. Whether the goal is to identify a safe dose range, understand pharmacokinetics, or explore early efficacy signals, the design must serve the objectives, not the other way around. Clear, well-defined questions guide key parameters such as sample size, escalation strategy, and decision rules. 

Engage Statisticians from the Outset 

Early collaboration between clinical and statistical teams is essential. Expert statisticians help shape how data is collected, modelled, and interpreted. Engaging them early ensures that multiple design options are explored, operating characteristics are well understood, and risks are proactively managed. Effective early-phase design depends on open, iterative discussions between clinical scientists and quantitative experts, ensuring that scientific ambition is matched with statistical rigor. 

Match the Design to the Compound 

The right design depends on the compound’s mechanism of action and the data available. For cytotoxic oncology agents, designs considering only dose limiting toxicities (DLTs) and assuming more drug = better efficacy and more toxicity may suffice; for biologics or targeted therapies, model-based or model-assisted designs that incorporate more information, such as the BOIN12 design, offer more flexibility and precision. 

Endpoints therefore also need careful consideration. While toxicity remains key, pharmacodynamic biomarkers and other exploratory endpoints can help define the Optimal Biological Dose (OBD) rather than just the Maximum Tolerated Dose (MTD). This approach aligns with initiatives like Project Optimus, which encourage a more nuanced understanding of dose–response relationships before progressing to later phases.  

Plan for What Comes Next 

An effective early-phase trial should do more than establish safety, it should build a foundation for future development. The data generated here informs Phase II and III designs, supports regulatory discussions, and guides commercial strategy. Sponsors who take a holistic view, integrating statistical design, data flow, and regulatory planning early, are better equipped to streamline timelines, reduce amendments, and generate evidence that withstands scrutiny. 

Operational Readiness Matters 

However, even the best design can falter without strong operational support. Early-phase studies often involve complex logistics, including rapid data turnaround, dose-escalation meetings, and frequent interim reviews. Ensuring data management systems, site training, and communication processes are in place is essential to maintaining both speed and quality. 

Conclusion 

Designing a successful early-phase clinical trial is crucial and depends on careful collaboration and a commitment to data-driven decision-making. There is no single blueprint, but by starting with the right questions and involving experts early, sponsors can confidently navigate the complexity of this critical stage. 

Phastar’s statisticians and data scientists have extensive experience supporting early-phase studies across therapeutic areas, helping sponsors explore innovative designs, simulate operating characteristics, and make informed, evidence-based decisions. 

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