Healthy volunteers in US phase I clinical trials: Sociodemographic characteristics and participation over time

Abstract

Background: Increasing the diversity of research participants is an important focus of clinical trials. However, little is known regarding who enrolls as healthy volunteers in Phase I clinical trials, which test the safety and tolerability of investigational new drugs. Despite the risk, healthy volunteers can derive no medical benefit from their participation, and they are financially compensated for enrolling.

Objective: This study's purpose is to describe sociodemographic characteristics and clinical trial participation histories of healthy people who enroll in US Phase I trials.

Methods: The HealthyVOICES Project (HVP) is a longitudinal study of healthy individuals who have enrolled in Phase I trials. We describe self-reported sociodemographic information and Phase I trial history from HVP recruitment (May-December 2013) through the project's end three years later (December 2016). Trial experiences are presented as medians and quartiles.

Results: The HVP included 178 participants. Nearly three-fourths of participants were male, and two-thirds were classified as racial and ethnic minorities. We found that some groups of participants were more likely to have completed a greater number of clinical trials over a longer timeframe than others. Those groups included participants who were male, Black, Hispanic, 30-39-years-old, unemployed, had received vocational training in a trade, or had annual household incomes of less than $25,000. Additionally, the greater the number of clinical trials participants had completed, the more likely they were to continue screening for new trials over the course of three years. Participants who pursued clinical trials as a full-time job participated in the greatest number of trials and were the most likely to continuing screening over time.

Implications: Participation as a healthy volunteer in US Phase I trials is driven by social inequalities. Disadvantaged groups tend to participate in a greater number of clinical trials and participate longer than more privileged groups.

Fig 1. Narrative summary of demographic findings.

Overall demographics of Phase I participants: Sex: Male participants are overrepresented. Race/Ethnicity: Racial/ethnic minorities are overrepresented. Age: Participants are typically in their 30s and 40s. Education: Participants typically have low educational attainment. Employment: Participants are generally un- or underemployed. Income: Participants’ household income is generally less than US$25,000 annually. “Occupational” Participation: About one-third of participants pursued clinical trials as a full-time job. There are no demographic differences distinguishing occupational participants from the others. First-Time Participation: Only one-fifth of participants were in their first clinical trial when they enrolled in the HVP. There are no demographic differences distinguishing them from other participants.

Fig 2. Summary of phase I trial history and experience by demographic group.

Overall: The average participant had been enrolling in trials for 3 years and had completed 5 trials. Over the course of the HVP, the average participant completed 3 additional trials. Sex: Male participants had a longer history of enrolling and had completed more trials. They completed double the number of new trials in 3 years compared to females. Race/Ethnicity: Black participants had a longer history of enrolling and had completed more trials compared to Hispanics and Non-Hispanic Whites. Hispanic participants had completed more trials than Non-Hispanic Whites, but the length of their involvement in trials was the same. Black participants completed double the number of new trials in 3 years compared to both Hispanics and Non-Hispanic Whites. Age: Participants over 30 had a longer history of enrolling and had completed more trials. Participants between the ages of 30 to 39 enrolled in slightly more new trials in 3 years compared to all other age groups. Education: Participants with a trade or vocational training had the longest history of enrolling and had completed the most trials. Participants with less than a high school diploma were newest to enrolling and had completed the fewest trials. Participants with a trade or vocational training enrolled in slightly more new trials in 3 years compared to the other groups. Employment¹: Unemployed participants had the shortest history of enrolling compared to full-time or part-time workers, but they had completed the same number of trials as full-time workers, which was fewer than part-time workers. Over the course of the HVP, unemployed participants completed the most trials, followed by part-time workers, then full-time workers. Income¹: Participants who earned between $25,000 and $50,000 annually had participated in the most clinical trials over the longest period of time. However, over the course of the HVP, those who earned less than $25,000 annually participated in a greater number of trials than those who earned between $25,000 and $50,000 annually, who in turn enrolled in a greater number of trials than those who earned more than $50,000 annually. “Occupational” Participation: Participants who pursued trials as their full-time job had a longer history of enrolling and had completed more trials. They enrolled in four times as many new clinical trials in 3 years compared to non-occupational participants. ¹ Employment and income are highly dynamic variables that may not provide accurate depictions of clinical trial participation over time. See Results and limitations sections for more details.

Fig 3. Narrative summary of attrition from phase I participation.

Attrition from phase I participation over 3 years: Overall: About half of participants stopped screening for and enrolling in new trials. Sex: There was no difference in attrition from screening for new trials between female and male participants. However, females were less likely to have enrolled in a trial in the final year of the HVP. Race/Ethnicity: The most attrition from screening occurred in Non-Hispanic White participants. Black participants were more likely than Hispanic and Non-Hispanic White participants to have enrolled in at least one trial in the final year of the HVP. Age: There was more attrition from clinical trial screening and enrollment among younger participants. Education: Participants with a bachelor’s degree or higher had the most attrition from clinical trial participation. Participants with a trade or vocational training were the most likely to still be screening and enrolling in trials. Employment: The most attrition occurred among full-time workers followed by part-time workers. Unemployed participants were the most likely to still be screening and enrolling in trials 3 years later. Income: The least attrition from clinical trial screening and enrollment was among participants who reported an annual household income of less than $25,000. “Occupational” Participation: Participants who were occupation participants at baseline were more likely to be screening and enrolling in trials at the end of the HVP compared to non-occupational participants. However, there was a smaller total number of individuals who continued to be occupational participants 3 years later, even if they continued to screen and enroll in trials. Clinical Trial Experience: The less trial experience a participant had at baseline, the more likely they discontinued screening and participating in trials by the end of the HVP. About half of first-time participants did not enroll in any subsequent trials. First-time participants who were 40 and older were less likely to enroll in new clinical trials compared to those under 40.