Development and Usability Validation of a Custom Medication Adherence Mobile Application for Chronic Disease Patients in Resource-Constrained Settings: A User-Centred Mixed-Methods Study

Abstract Background: Mobile health applications offer a scalable platform for medication adherence support in chronic disease management; however, most available tools are designed without systematic attention to the usability constraints of rural, low-literacy populations in low- and middle-income countries. This study describes the user-centred development and formal usability validation of a custom medication adherence application designed specifically for chronic disease patients in resource-constrained ambulatory care settings in southern India. Methods: The study was conducted in two phases. Phase 1 involved user-centred development of the Android application, incorporating voice-prompted bilingual (Kannada and English) medication reminders, customisable dosing schedules, drug information, disease-specific educational content, and low-bandwidth offline functionality. Phase 2 involved formal usability evaluation using the System Usability Scale (SUS) in a consecutive subgroup of 20 participants from the parent interventional study after a minimum of 30 days of application use. Results: The application was successfully developed and deployed, incorporating five core modules tailored to the barrier profile of the target population. Among 20 usability evaluators, the mean SUS score was 91.75 (SD = 3.76; median = 92.50; range 80.0–95.0). Eighty-five percent of evaluators (n = 17) achieved excellent usability ratings (SUS ≥90); the remaining 15% (n = 3) achieved good ratings (SUS 80–89.9). No participant scored below 80. Conclusions: The application achieved exceptional usability across a predominantly rural, low-literacy, elderly user population, establishing the efficacy of user-centred design and bilingual voice-guided features in bridging the digital literacy gap for mHealth tool adoption in low-income settings. These findings support the application's readiness for integration into structured pharmacist-led telehealth programmes and its potential for scale-up within national digital health frameworks. Keywords: mobile application; usability; System Usability Scale; medication adherence; mHealth; user-centred design; chronic disease; rural India; low-bandwidth; voice prompts