The Needle Shield Size and Applied Force of Subcutaneous Autoinjectors Significantly Influence the Injection Depth.

BACKGROUND: This study examines how shield-triggered autoinjectors (AIs), for subcutaneous drug delivery, affect injection depth. It focuses on shield size and applied force, parameters that could potentially lead to inadvertent intramuscular (IM) injections due to tissue compression. METHOD: A blinded ex-vivo study was performed to assess the impact of shield size and applied force on injection depth. Shields of 15, 20, and 30 mm diameters and forces from 2 to 10 N were investigated. The study involved 55 injections in three Landrace, Yorkshire, and Duroc (LYD) pigs, with injection depths measured with computed tomography (CT). An in-vivo study, involving 20 injections in three LYD pigs, controlled the findings, using fluoroscopy (FS) videos for depth measurement. RESULTS: The CT study revealed that smaller shield sizes significantly increased injection depth. With a 15 mm diameter shield, 10 N applied force, and 5 mm needle protrusion, the injection depth exceeded the needle length by over 3 mm. Injection depth increased with higher applied forces until a plateau was reached around 8 N. Both applied force and size were significant factors for injection depth (analysis of variance [ANOVA], P < .05) in the CT study. The FS study confirmed the ex-vivo findings in an in-vivo setting. CONCLUSIONS: The study demonstrates that shield size has a greater impact on injection depth than the applied force. While conducted in porcine tissue, the study provides useful insights into the relative effects of shield size and applied force. Further investigations in humans are needed to confirm the predicted injection depths for AIs.

Novel Robust Needle Tip Design Enables Needle Reuse and Reduced Skin Trauma in Combination With Autoinjector Needle Shields.

BACKGROUND: Pen needles and autoinjectors are necessary for millions of patients needing injectable drug treatment but pose economic and environmental burdens. A durable device with a multiuse needle could reduce cost and improve user experience. This study explores a novel robust needle tip (EXP) designed for multiple uses and durability against hooking. METHOD: Needle robustness was investigated through a structural analysis. Furthermore, EXP and control needles (NF30, NF28) were evaluated in an in-vivo porcine model as pen needles or embedded in autoinjectors to study the resulting increase in skin blood perfusion (SBP). The SBP was assessed by laser speckle contrast analysis (LASCA) of 192 randomized and blinded needle insertions. RESULTS: Forming a 33 µm hook against a hard surface requires 0.92 N for the NF30 control needle and 5.38 N for EXP. The EXP did not induce more tissue trauma than the NF30. There was a positive relation between needle diameter and SBP (P < .05). Furthermore, the presence of an autoinjector shield and applied force of 10 N was found to significantly reduce SBP for worn EXP needles (P < .05) compared to insertions without autoinjector shield. CONCLUSIONS: The investigated robust needle EXP is on par with the single-use needle NF30 in terms of tissue trauma, which is further reduced by combining the needle with a needle shield. These results should encourage the innovation and development of durable, reusable injection systems with pharmacoeconomic and environmental value and a simplified and enhanced user experience for patients.