Designing Auto-Injectors for Children: Effect of Form Factor on the Human Factors of Efficient Drug Delivery

Abstract

Because commercially available epinephrine auto-injectors differ in form factor, and are important for children the goal of this study was to evaluate their effect on human factors of efficient drug delivery in children. Auto-injectors with 3 different form factors (cylindrical, elliptical, and prismatic) were tested in a laboratory-based repeated measures experiment with 20 participants (aged 8-12 years). Participants applied their maximum possible force onto a force plate positioned over their thigh (maximum force capability task) and practiced an injection using the trainer auto-injector after watching the device’s training video (application task). Participants rated force confidence and preference for all devices. For the maximum force capability task, the elliptical device exhibited significantly higher axial-applied force compared with the prismatic device (43N vs 38N, respectively). The elliptical device also exhibited the lowest difference between force and device angle compared with the other two devices (1º vs 6º and 12º). For the application task, the elliptical device had the fastest time to force. The elliptical and prismatic devices had significantly lower grip effort compared to the cylindrical. The cylindrical form factor was the least preferred. Overall, these general patterns across form factors were similar to patterns observed in a previous study of adults. However,children exhibited lower force, higher grip effort, higher force angle, and more variability in application force, force angle, and grip effort. General trends were similar between adults and children. The results suggest that the elliptical form factor may have better success in drug delivery in children.