A Prefilled Insulin Pen with a Novel Injection Mechanism and a Lower Injection Force than Other Prefilled Insulin Pens

Background: FlexTouch (R) (Novo Nordisk A/S, Bagsvaerd, Denmark) is a new prefilled insulin pen for people with diabetes, with a novel injection mechanism and no push-button extension at any dose setting. This study compared the injection force of Flex Touch with that of SoloStar (R) (sanofi-aventis, Paris, France) and KwikPen (R) (Eli Lilly & Co., Indianapolis, IN). Methods: Injection force was measured with the manufacturers' recommended needle attached to each pen (NovoFine (R) [Novo Nordisk] 32-gauge tip extra thin wall 6 mm needle for Flex Touch and BD [Franklin Lakes, NJ] MicroFine (TM) 31-gauge 5 mm needle for Solo Star and KwikPen) during injection of the maximum dose (60 IU for KwikPen and 80 IU for Flex Touch and Solo Star). Injection was performed at three different constant push-button speeds. Results: Flex Touch had a significantly (P<0.0001) lower injection force than SoloStar and KwikPen at all injection speeds. The mean +/- SD injection force of FlexTouch was 5.1 +/- 0.5 N. At 4, 6, and 8 mm/s push-button speeds, the injection force of SoloStar was 13.5 +/- 2.1, 19.1 +/- 1.9, and 26.9 +/- 2.4 N, respectively, and the injection force of KwikPen was 14.5 +/- 1.9, 20.9 +/- 1.4, and 28.2 +/- 1.4 N, respectively. Conclusions: The injection mechanism of FlexTouch means that insulin injection is driven by a torque spring and not the thumb pressure of the user. This results in a 62-82% lower injection force with FlexTouch than other prefilled insulin pens.