Feasibility, acceptability, and user perspective of a next-generation wrist-worn receiver and digital pills for HIV pre-exposure prophylaxis: a pilot study.

Objective: The objective of this study was to assess the feasibility and acceptability of the next-generation wrist-worn receiver ("Reader") coupled with the ID-Cap digital pill system (DPS) to measure adherence to oral HIV PrEP (pre-exposure prophylaxis) via an ingestible radiofrequency sensor. Methods: This prospective cohort study enrolled 15 participants who were prescribed oral tenofovir diphosphate/emtricitabine (TDF/FTC) as PrEP. Participants were asked to ingest one digital pill daily for 30 days. Adherence was also measured using pill counts at the 30-day follow-up visit, which was compared to DPS-recorded ingestions (including both system-detected and manually annotated ingestions). The primary outcomes were system feasibility, defined as the ability of participants to engage with and operate the DPS throughout the 30-day study period and acceptability, as reported via the System Usability Scale (SUS). Qualitative interviews were conducted to receive feedback from the participants. The secondary outcome was the accuracy of the DPS, measured via a Pearson correlation comparing system-detected ingestions with pill count at 30-day follow-up. Results: 14 participants consistently recorded ingestions using the DPS over the 30-day study period, demonstrating feasibility of the system. A technical error occurred on one participant's wrist-worn Reader that rendered it unable to detect ingestions. Weekly engagement remained consistent across the study period. N = 12 participants returned pills at the final study visit. Based on pill count, 343 doses were ingested overall; 278 doses (81%) were detected by the DPS. DPS-based detection was strongly correlated with pill counts (r=0.75, p=0.0047). Participants had a mean SUS score of 78.0 (± 9.4), indicating good acceptability of the system. Qualitative feedback demonstrated good usability and convenience of operating the DPS. For N = 6 participants who had previously used a lanyard-based DPS Reader, all preferred the new wrist-worn system. Conclusion: A wrist-worn ingestible sensor system is acceptable and feasible among individuals to record PrEP adherence. The system is accurate in detecting ingestion events, in comparison to more traditional measures of adherence, and individuals can maintain engagement with the system over time. These findings warrant further evaluation in larger studies but strongly suggest that wrist-based form factors are suitable for integration into DPS technology.