In short

  1. Late-phase asthma trials are increasingly constrained, requiring tailored, site-specific operational strategies to sustain enrollment
  2. A sponsor partnered with PSI to deliver a global asthma study on time in a highly competitive and evolving treatment landscape
  3. Site selection prioritized geographies based on real-world treatment access and reimbursement dynamics, improving both enrollment and protocol adherence
  4. Differentiated strategies were deployed in regions with high versus limited access to advanced therapies
  5. Early pre-screening reduced screen failure rates in a patient population where eligibility can fluctuate
  6. Site teams were trained using technical and patient-experience perspectives, improving procedure quality and retention
  7. Transparent, performance-based engagement across sites accelerated enrollment, and strengthened study ownership
  8. The trial met its milestones as planned

The challenge

Enrolling patients in clinical trials for asthma is becoming progressively more difficult. In a global late-phase study, the sponsor required a delivery model that could reliably meet timelines, despite increasing competition for eligible patients and stringent protocol requirements. What was behind PSI’s efficient operational execution of the trial?

What makes asthma trial enrollment difficult today?

Enrollment barriers in asthma are no longer driven by prevalence alone; they are shaped by patient behavior, evolving SoC, and protocol complexity.

A recent shift in treatment paradigms, guided by frameworks such as the Global Initiative for Asthma [1, 2], has evolved current clinical practice in asthma. Considering a majority of adult and adolescents with asthma receive inhaled corticosteroid (ICS) therapy with LABA, these combination regimens (SMART, or Single Maintenance And Reliever Therapy) mean fewer patients remain on minimal or outdated treatment approaches, reducing the pool of easily eligible participants.

These factors together create a constrained enrollment environment:

  • Patients are hesitant to participate for a number of reasons, including perception that their asthma isn’t serious enough to warrant enrolling in a clinical trial, and fear of disrupting their current medication with washout periods or being assigned to a placebo group
  • Fewer patients meet eligibility criteria at any given time. Restrictions around exacerbations, eosinophil levels, concomitant medications, comorbidities, and spirometry exclude a large portion of patients with asthma and drive high screen failure rates. High forced expiratory volume (FEV1) requirements are a common reason for patients to drop out of trials
  • Investigators are more cautious about enrolling well-controlled patients, meaning competition between trials is concentrated within a smaller, more defined patient population, often with a predominant disease severity

Despite an expansion in global site networks and competition for patients among asthma trials, enrollment has declined over time. These changes necessitate a modern approach to clinical trial design and patient engagement: shifting from volume-driven to precision-driven execution.

Insights from 30 years of enrollment data: Enrollment rates in asthma clinical trials (1995–2025)

Average enrollment rate in phase 2 and 3 trials (patients/site/month) from 1996 to 2024. Dashed line depicts linear average. Data weighed based on number of sites involved in the trial; outliers (recruiting >1 patient/site/month) adjusted to 1. Trialtrove 2026.

The solutions

Delivering this study meant identifying not just where patients are, but where they are most likely to qualify, and where they would be likely to remain engaged.

Rather than focusing only on prevalence, we mapped enrollment strategy to real-world treatment landscapes. In regions with broad access to advanced therapies, and well-optimized standards of care, fewer patients were both eligible and willing to participate. These settings required a differentiated approach, focusing on:

  • Careful site selection based on patient segmentation
  • Clear communication of trial value beyond standard treatment
  • Targeting specific patient subgroups aligned with protocol requirements

In contrast, in regions where access to certain therapies or reimbursement was more limited, participation offered a clearer clinical incentive. These geographies had:

  • Higher patient motivation to enroll
  • Stronger adherence to study procedures
  • More stable engagement throughout the trial

This dual strategy ensured enrollment efficiency, and appropriate patient representation without reliance on any single region.

It is important to understand the asthma landscape – not only the countries where asthma is prevalent, but also where patients trust their physicians and where healthcare reimbursement gaps create trial participation incentives.

A key operational risk in asthma trials in particular is that patient eligibility is not static – it can change between initial identification and formal screening.

To address this, PSI implemented structured pre-screening at the site level, allowing investigators to assess likely eligibility before committing patients to full screening procedures.

By reducing unnecessary screen failures, we could preserve site resources, maintain site motivation, and improve the predictability of enrollment timelines. It also enabled better patient guidance ahead of screening, thus aligning real-world clinical management with protocol requirements.

Patients provide informed consent, but the extent to which they understand their role and the related procedures in the trial is often extremely low [3]. Active patient cooperation can influence data quality and retention.

Spirometry is an exception – while patients with asthma understand the need [4], many find it unpleasant or difficult. Poor spirometry technique introduces measurement variability, which compromises data quality and can lead to patient dropout if investigators cannot communicate the importance of the procedure or help patients perform it comfortably.

PSI embedded therapeutic understanding into site support by ensuring that the site-facing team had asthma and spirometry experience – often including personal experience.

By enabling the site-facing teams to train investigators not only on protocol execution and the operational needs of the trial, but also on how procedures are experienced by patients, helped sites communicate these procedures more effectively, reducing patient discomfort, and improving consistency in data collection.

Parallel proactive management of study equipment and logistics ensured that operational constraints did not limit enrollment momentum, particularly during periods of high recruitment activity.

This kind of therapeutic expertise integration is formalized through PSI’s 4S (Specialized Study Support Services) team, which expanded 5x in 24 months to embed therapeutic area specialists into site-level trial execution. The asthma trial site-facing strategy was an early proof point for 4S’s operational value: when site support team understands the patient experience at a personal level, they train sites more effectively, and sites retain patients more reliably.

Recruitment was also made competitive through regular email “enrollment newsflashes” among participating sites – highlighting the top enrollers increased engagement, ensuring enrollment targets were met on time. But going beyond the motivation aspect, this also ensured full visibility and transparency of the trial:

  • Implementing a shared sense of purpose and community
  • Encouraging best practices through knowledge distribution
  • Offering sites around the world an insight into where they stand in the broader context of the trial

These approaches turned enrollment from an isolated site activity into a coordinated global effort.

The outcome

The study met its milestones on schedule. Consistent performance across regions, combined with proactive management of eligibility and site engagement ensured delivery aligned with the sponsor’s timeline.

Key takeaways

Successful asthma trials now depend on aligning operational strategy with the realities of modern clinical practice.

Enrollment strategies must reflect current treatment paradigms: Patient eligibility is dynamic, and only proactive management will result in an on-time trial. Geographic strategy must be driven by access, behavior, and motivation, and site engagement improves when operational execution is paired with patient insight.

PSI’s 95% first patient in (FPI) on-time rate and 97% last patient in (LPI) on-time rate reflect exactly this kind of site relationship discipline.

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Abbreviations

FEV1, forced expiratory volume in 1 second;
LABA, long-acting beta agonists;
SoC, standard of care.

References

1. Reddel, H.K., et al., GINA 2019: a fundamental change in asthma management: Treatment of asthma with short-acting bronchodilators alone is no longer recommended for adults and adolescents. Eur Respir J, 2019. 53(6).
2. Dubin, S., Patak, P., and Jung, D., Update on Asthma Management Guidelines. Mo Med, 2024. 121(5): p. 364–367.
3. Pietrzykowski, T. and Smilowska, K., The reality of informed consent: empirical studies on patient comprehension-systematic review. Trials, 2021. 22(1): p. 57.
4. Johnson, B., et al., Improving spirometry testing by understanding patient preferences. ERJ Open Res, 2021. 7(1).