Evaluation of injection force of three insulin delivery pens

Objective: Reduced injection force is among the modifications to the Next Generation FlexPen (R) (NGFP). This force was compared with two other prefilled pens: SoloStar (R) (SS) and KwikPen (R) (KP). Research design/methods: The injection force of the pens was measured, with either a BD Micro-Fine (TM) 31G thin-wall needle, or a NovoFine (R) 32G Tip extra thin wall needle attached. Pens of each type were tested with both needles, during injection of 20 U insulin, at speeds 3.3, 5 and 8.3 mm/s. Results: NGFP had a significantly (p < 0.05) lower mean injection force than SS or KP, at all injection speeds, with both needles. Injection forces (mean +/- s.d.) with NGFP and the BD Micro-Fine (TM) 31G thin-wall needle were: 8.1 +/- 0.7, 10.7 +/- 1.4 and 15.6 +/- 0.9 N at the three speeds, respectively. For SS, the corresponding values were: 9.2 +/- 0.5, 13.3 +/- 0.8 and 20.7 +/- 2.4 N. For KP they were: 12.5 +/- 1.6, 16.9 +/- 1.2 and 24.5 +/- 2.6 N. Attached to the NovoFine (R) 32G Tip extra thin wall needle, the NGFP injection forces were: 5.7 +/- 0.4, 8.2 +/- 0.7 and 12.7 +/- 0.5 N; with SS were: 6.7 +/- 0.3, 10.4 +/- 2.1 and 16.3 +/- 1.1 N; and with KP were: 9.1 +/- 1.3, 13.1 +/- 0.8 and 21.6 +/- 2.0 N. The injection force with NGFP was 12 - 25% lower compared with SS and 35 - 41% lower compared with KP. Conclusions: This study shows that NGFP has a significantly lower injection force than SS or KP.