Pinch Force Endurance and Usability Considerations for Pre-Filled Syringe Designs Used by Chronic Obstructive...

Prefilled syringes (PFSs) are commonly used for self-administered injectable drugs, particularly for chronic conditions. A critical design factor is the injection force needed to depress the plunger, which varies by drug viscosity and syringe mechanics. This is especially important for patients with potential strength limitations. Human factors studies help evaluate these physical demands to ensure PFSs can be used safely and effectively across diverse users. Assessing both maximum force capabilities and endurance provides key insights for optimizing syringe design and minimizing patient discomfort. This study evaluated chronic obstructive pulmonary disease (COPD) patients' experience with PFS samples of varying injectability (injection force and duration) and measured pinch force endurance-an indicator for PFS physical demand. Those insights aimed to guide PFS design for users with strength limitations. Forty-two COPD patients performed simulated injections using three PFS samples (28 N, 37 N, 47 N force) and rated perceived demand. They also measured pinch force endurance by gripping a surrogate PFS device at 28 N and at their maximum voluntary force. Data predicted the 5th percentile pinch force endurance for COPD patients. The estimated COPD patients' 5th percentile pinch force endurance at 28 N was 16 seconds. Notably, when asked to push at their maximum pinch force, COPD patients' endurance was around 4.4 seconds. Males pinched and held 28 N longer than females, but no gender difference was observed at the maximum force. Endurance decreased as required force approached maximum capacity (consistent with Rohmert's Curve). PFS usage can be challenging for users with strength limitations. A 28 N force was sustainable for 16 seconds for 95% of COPD patients. Developers should minimize injection force where possible and accommodate varied injection styles-lower forces improve endurance, aiding users with reduced strength. These findings support designing accessible PFSs for diverse populations.