Prefilled epinephrine autoinjectors are sometimes improperly used by patients, caregivers, and physicians. A user-centered design process led to the development of 2 prototype epinephrine autoinjectors (INT01 and INT02) that have a unidirectional perceived injection end, a self-retracting needle, and, with INT02, voice instructions to assist in guiding users through administration. To compare the usability and patient preference among 4 epinephrine autoinjectors: EpiPen, TwinJect, INT01, and INT02. A total of 48 participants were divided equally among 3 age groups: 7 to 10, 11 to 15, and 16 to 55 years. In each group, half had prior TwinJect or EpiPen training. In 1-hour sessions, without training, participants performed simulated-use testing under observation for all 4 epinephrine delivery systems. Usability (i.e., the ability to perform the manufacturer's labeled instructions), task completion time, and preferences were assessed and analyzed based on device, age, previous experience, sex, device malfunction, and testing order. More participants correctly followed all device instructions with INT02 (22 [46%]) than with INT01 (13 [27%]), EpiPen (6 [12%]), or TwinJect (0 [0%]). The difference among devices was significant (P < .01) after adjusting for device malfunctions and age group (the youngest age group [those aged 7-10 years] performed significantly worse than the other 2 groups). Prior experience, sex, and testing order did not significantly affect this measure. The first choice of overall preference was greater (P < .001) for INT02 (35 participants [73%]) vs. INT01 (7 participants [15%]), EpiPen (5 participants [10%]), and TwinJect (1 participant [2%]). The user-centered device design may have a significant impact on correct epinephrine autoinjector use and patient preference.
