Methods: Trainer devices of 3 commercially available epinephrine auto-injectors with 3 different forms (cylindrical, elliptical, and prismatic) were tested in a laboratory-based repeated measures experiment with 20 adults (aged 18-30 years). Participants performed 2 tasks using a power grip with each of the 3 auto-injectors: a maximum force capability task in which they applied their maximum possible force onto a force plate positioned over their thigh and an application task in which, after watching the device’s training video, they practiced an injection using the trainer. For the application task, device performance included time to hold force, force, and device orientation and its variability during the hold segment. Participants rated their force confidence and preference for the 3 devices.
Results: The device with the elliptical form had the greatest force capability (64) followed by the prismatic and cylindrical forms (62 and 61, respectively), with the difference between the elliptical and cylindrical forms being statistically significant (P=0.0387). For the application task, the elliptical form had the fastest time to force (72 s compared with 230 and 243 s for the cylindrical and prismatic forms, respectively; P<0.001). The prismatic form had the largest angle (13°) compared with the cylindrical and elliptical forms (9° each; P<0.001).The prismatic form also had the highest variability in angle of resultant applied force (1.7°) compared with the cylindrical and prismatic forms (1.1° and 1.3°, respectively; P<0.001). Participants reported the highest force confidence when using the elliptical and cylindrical devices, ranking the elliptical as their preferred device.
Conclusions: The results suggest that the elliptical form may have better success in drug delivery in a larger set of the population.