Older participants are frequently excluded from Parkinson's disease research

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Abstract

Background

The exclusion of older participants from clinical research is common and limits the generalisation of research findings. We aimed to assess the current potential for older patients to participate in Parkinson's disease (PD) research.

Method

We performed a systematic analysis of data extracted from the World Health Organization Clinical Trials Registry Platform regarding 206 actively recruiting PD research studies. Data regarding study variables and exclusion on the grounds of an upper age limit was extracted from each registry entry and subsequently used for statistical analysis.

Results

Exclusion by arbitrary upper age limit is common, with 101 (49%) of studies excluding participants by age and with a mean upper age limit for exclusion of 79.3 years (range 64–95 years). Exclusion by age was significantly more common in studies with an estimated enrolment of fewer than 100 participants; OR 1.92 (95%CI 1.13–3.42) P = 0.018. Rates of exclusion by age were not significantly influenced by study subject, study location, source of funding, study duration or number of centres.

Conclusion

Exclusion of participants from PD research on the basis of an upper age limit is common and particularly problematic in smaller studies. The exclusion of older participants seriously compromises the generalisation of findings from PD research to the large numbers of elderly PD patients seen in clinical practice.

Introduction

Parkinson's disease (PD) is predominantly a disease of older age, with the prevalence of PD rising from 0.6% for those aged 65–69 years to 3.5% for those aged 85–89 years [1]. With an ageing population the number of patients with PD in the world's most populous countries is predicted to double from an estimated 4.6 million in 2005 to between 8.7 and 9.3 million by 2030, the majority of these patients will be elderly [2].

Despite an ageing population, older patients are frequently excluded from medical research on the basis of arbitrary upper age limits [3], with clinical trial populations being noted as varying significantly from the older, frailer patients seen in clinical practice [4], [5].

Given the well-recognised differences in physiology, pharmacodynamics, polypharmacy and co-morbidities seen in older patients, it is probable that the results of studies excluding the elderly may not be relevant to the patients seen in actual clinical practice; hence research findings in studies of younger individuals should not be extrapolated to the elderly. This is of particular importance in PD where the majority of patients are in the seventh decade or older.

One previous study has investigated the exclusion of older participants from PD research; this retrospective review of PD randomised control trials published between January 1966 and September 1996 found only 37% of trials included PD patients over the age of 75. While the reporting of actual numeric levels of recruitment amongst specific age groups was poor in the published studies included in this work, where this demographic data was reported, only 5.5% of trial participants were aged over 75 years [6].

To investigate to the current potential for older patients to take part in actively recruiting PD research we performed a systematic analysis of the online World Health Organisation Clinical Trials Registry. We aimed to assess the degree to which older participants are excluded from PD research on the basis of upper age limits and to investigate associations between study characteristics and exclusion by age.

Section snippets

Data source and sampling method

Our method was based on an adaptation of that recently published by the Increasing the PaRticipation of the ElDerly in Clinical Trials (PREDICT) project (http://www.predicteu.org) [7].

Information regarding ongoing PD research studies was extracted from the WHO International Clinical Trials Registry Platform (WHO-ICTRP) (http://www.who.int/ictrp/en/) on the 1st of April 2011. This database collates data from national and regional registers of clinical studies and is updated on a weekly basis

Trial characteristics

The initial search described above returned 210 results. 206 research studies were included for analysis. 2 studies were excluded as they concerned Wolff–Parkinson–White syndrome rather than PD and 2 entries were excluded as duplicate entries.

The total estimated recruitment to the studies included for analysis was 47,224 participants. Study characteristics are outlined in Table 1.

Randomised control trials made up 116 (51.5%) of the studies included, of the remaining studies the largest groups

Discussion

The exclusion of older people from clinical research is well recognised as a significant barrier to the translation of research findings to real-world clinical applications. Given that the PD patient population is predominantly elderly the recruitment of older people to PD research is critical to ensure the relevance of study findings. We aimed to assess the current potential for participation of older individuals in PD research and to identify features of studies associated with exclusion of

Declarations of interest

PR Fitzsimmons – has received educational sponsorship and/or speaker honoraria from GlaxoSmithKline, Orion Pharma and Teva–Lundbeck Pharmaceuticals

S Blayney – None

S Mina-Corkhill – None

GO Scott – None

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