Background: Injection force requirements for four insulin pen-type injection devices were evaluated using the AGS-IkNG Autograph force measurement device (Shimadzu Corp., Kyoto, Japan). Results: Compared with the Humulin® Pen (the Japanese brand name is Humacart® kit; the same device as the Humalog® Pen; Eli Lilly, Indianapolis, IN), HumaPen® Ergo (Eli Lilly), and NovoPen® 3 (Novo Nordisk A/S, Bagsvaerd, Denmark), the InnoLet® (Novo Nordisk) required the lowest injection force to both initiate piston movement and commence insulin delivery and required the lowest overall force throughout delivery. InnoLet and NovoPen 3 showed the most even load-displacement curves, suggesting a smoother delivery of insulin during injection. In contrast, the Humulin Pen and HumaPen Ergo demonstrated marked fluctuations in the force required to complete injection. Conclusions: These performance characteristics appeared consistent with mechanical features of these insulin delivery devices, and the results highlight the potential importance of careful pen selection for patients with neuromuscular weakness or impaired manual coordination.
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