Clinical Trial Feasibility & Site Selection: A Sponsor's Guide to Getting It Right

Feasibility is the single most consequential phase of study start-up. Get it right and your trial enrols on time, your sites are engaged, and your programme stays on budget. Get it wrong and you inherit months of delays, underperforming investigators, and costly protocol amendments that could have been avoided.

Yet feasibility is also the phase most sponsors rush. The pressure to activate sites quickly — driven by milestone commitments, investor expectations, or competitive enrolment — often leads to shortcuts that compound downstream. This article lays out how to do feasibility properly, what data actually matters for site selection in the UK, and where the common pitfalls catch even experienced sponsors.

Why Feasibility Matters More Than You Think

Clinical trial failure rates are staggering. Roughly 80% of trials fail to meet their original enrolment timelines. The root cause is rarely the protocol itself — it is almost always a mismatch between the study's requirements and the sites selected to execute it.

Feasibility is the process that prevents this mismatch. It is the structured assessment of whether a proposed study can realistically recruit its target population within the planned timeline and budget, at the specific sites under consideration. Done well, it identifies the optimal number and mix of sites, flags protocol elements that will slow enrolment, and gives sponsors evidence-based confidence in their activation plan.

Poor feasibility does not just delay enrolment. It forces protocol amendments, burns investigator goodwill, and can undermine the entire development programme's credibility with regulators and investors.

The Two Phases of Feasibility

Effective feasibility splits into two distinct phases, each with different objectives and methods.

Phase 1: Strategic Feasibility

Before you identify a single site, strategic feasibility asks the fundamental questions:

• Is the target patient population available in the geographies we are considering? Epidemiological data, NHS digital records, and disease registry data can answer this with far more precision than a site principal investigator's optimistic enrolment estimate.
• Can the protocol requirements be met in routine clinical practice? Complex visit schedules, invasive procedures, and restrictive inclusion/exclusion criteria all reduce the eligible patient pool. A protocol that looks clean on paper may be unworkable in a real NHS trust with competing clinical demands.
• What is the competitive landscape? How many other trials are competing for the same patients at the same sites? In therapeutic areas like oncology and immunology, patient pools are finite and oversubscribed.
• What is the realistic timeline? Not the timeline the business plan assumes — the timeline that actual site activation and enrolment data supports.

Strategic feasibility is a sponsor responsibility. It cannot be delegated entirely to a CRO because it requires alignment between clinical development strategy, commercial objectives, and operational reality. The best CROs — and the ones worth partnering with — will challenge your assumptions here rather than simply confirming what you want to hear.

Phase 2: Operational Feasibility and Site Selection

Once strategic feasibility confirms the study is viable, operational feasibility identifies which specific sites can deliver. This is where most of the practical work happens.

What Actually Predicts Site Performance

The single most reliable predictor of future site performance is past site performance. Not the PI's reputation, not the site's facilities, not the size of the institution — actual historical enrolment data for studies with similar patient populations and complexity.

Key data points that matter for UK site selection:

• Historical enrolment rates for the therapeutic area, adjusted for protocol complexity. A site that enrolled 20 patients on a simple Phase III may struggle to recruit 5 on a complex Phase I/II.
• Site activation timeline — how long from site selection visit to first patient in, including NHS Research Ethics Committee, HRA approval, and local R&D processes.
• Principal investigator availability — not just their CV, but their actual capacity. How many concurrent studies? What is their sub-investigator delegation plan? What happens when they are on annual leave?
• Research nursing and coordination capacity — the research nurse is often the single most important person at a site for enrolment success. Sites with dedicated, experienced research nurses outperform those without by a significant margin.
• Pharmacy and lab capabilities — can the site handle the investigational product storage, preparation, and accountability requirements? Are local labs equipped for the protocol's central laboratory kit requirements?
• Feasibility questionnaire honesty — sites that return realistic enrolment estimates (lower than you hoped) are generally more reliable than sites that promise aggressive numbers. Optimism bias in feasibility questionnaires is endemic.

The UK Site Landscape

UK clinical trials benefit from the NIHR Clinical Research Network (CRN), which provides infrastructure and support across England's 15 local CRNs. This network means sponsors have access to a structured site ecosystem that is unusual in global clinical research.

However, the UK landscape also has specific characteristics that feasibility must account for:

• NHS trust capacity constraints: Many NHS trusts are under severe operational pressure. Research activity competes with clinical service delivery for space, staff, and patient access. Feasibility must assess whether a trust has genuine research capacity, not just a willing PI.
• Study setup timelines: HRA and ethics approval processes have improved, but local R&D and capacity and capability checks still vary widely between trusts. Some trusts activate in 30 days; others take 90+.
• Private research sites: The UK has a growing network of private research sites and clinical pharmacology units, particularly for early-phase and healthy volunteer studies. These sites often offer faster activation but may have different regulatory requirements.
• Devolved nation differences: Scotland, Wales, and Northern Ireland have separate research governance processes. Multi-nation UK studies need to account for these regulatory variations in feasibility planning.

Common Feasibility Mistakes

After years of clinical programme delivery, these are the mistakes we see repeatedly:

1. Selecting Too Many Sites

The instinct when worried about enrolment is to add more sites. This usually makes things worse. More sites mean more startup costs, more monitoring visits, more TMF complexity, and more variation in data quality. The marginal return of each additional site diminishes rapidly after the first tranche of high-performers.

Better approach: Start with fewer, carefully selected sites based on data. Add sites only if the first tranche is demonstrably underperforming against realistic targets.

2. Ignoring Site-Level Operational Burden

Feasibility questionnaires focus on patient availability but rarely assess whether the site's operational team can handle the protocol's visit schedule, source data requirements, and safety reporting obligations. A site that can recruit patients but cannot manage the operational workload will generate deviations, missing data, and queries.

3. Over-Relying on PI Relationships

Key opinion leader PIs bring credibility and expertise, but they are also the busiest people in the hospital. A PI who is enthusiastic at the investigator meeting but unavailable for screening visits three months later is a well-known pattern. Feasibility must assess the entire site team, not just the PI.

4. Not Accounting for Competing Studies

In热门 therapeutic areas, a site may be running five or more competing protocols for the same patient population. Unless feasibility accounts for the site's complete trial portfolio, enrolment estimates will be unreliable.

5. Rushing the Process

Feasibility takes time. Proper site assessment, historical data review, and PI interviews cannot be compressed into a two-week window without sacrificing quality. The irony is that rushing feasibility to start faster almost always results in starting later.

A Data-Driven Approach to Site Selection

The best feasibility processes combine multiple data sources rather than relying on any single input:

• ClinicalTrials.gov and ISRCTN registry data — to understand competitive trial density and historical site performance.
• NIHR CRN performance data — recruitment metrics by therapeutic area and site.
• Internal feasibility databases — if you or your CRO have run studies in the same therapeutic area, historical enrolment data from those studies is invaluable.
• Site feasibility questionnaires — useful when triangulated against other data, unreliable in isolation.
• Investigator interviews — a 20-minute conversation with a PI reveals more about realistic enrolment potential than any questionnaire.
• AI-assisted feasibility analytics — emerging tools can analyse protocol complexity against site characteristics to predict enrolment rates with increasing accuracy.

Feasibility as a Continuous Process

Feasibility does not end when sites are selected. The most effective sponsors treat feasibility as an ongoing discipline throughout the trial:

• Pre-activation feasibility review: After site selection but before activation, a final review of each site's readiness — staff in place, equipment available, IP supply chain confirmed.
• Enrolment monitoring: Tracking screen-to-enrolment ratios, screen failure rates, and enrolment velocity against feasibility predictions. Early deviation from predicted rates is the signal to intervene.
• Underperforming site management: A clear, pre-agreed process for sites that fall below enrolment targets. This should include root cause analysis, corrective action plans, and defined thresholds for site closure.
• Lessons learned: Every study's feasibility predictions should be compared against actual enrolment outcomes. This data becomes the foundation for better feasibility on the next study.

Key Takeaways

• Feasibility is the highest-leverage phase of study start-up. Time invested here pays back throughout the entire trial.
• Past performance data is the most reliable predictor of future site performance. Use it.
• UK site selection must account for NHS capacity constraints, regional timeline variations, and the specific requirements of UK research governance.
• Fewer, better-selected sites outperform larger portfolios of marginally assessed sites.
• Feasibility should be continuous — not a one-time exercise before site activation.
• Demand evidence-based feasibility from your CRO, not enrolment estimates that tell you what you want to hear.

Getting feasibility right is not complicated, but it does require discipline, honest data, and the willingness to challenge assumptions. For sponsors running UK clinical programmes, the difference between a well-feasibilitied study and a poorly-feasibilitied one can be measured in months of timeline, hundreds of thousands in budget, and the credibility of the entire development programme.