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A comparison of injection force and dosage scale size between NovoPen 3 and NovoPen 4.

BACKGROUND
Easy-to-use insulin devices are an important tool in the treatment of diabetes. In this study, injection force requirements and dosage scale displays were evaluated for NovoPen 3 and NovoPen 4 (both from Novo Nordisk A/S, Copenhagen, Denmark).


METHODS
To simulate 5 years of expected lifetime usage, 5,475 injections were performed automatically. Before and after lifetime testing, the force required to expel 60 U of insulin from NovoPen 3 and NovoPen 4 with 30-gauge or 31-gauge needles was measured. To compare dosage scale displays, digital images of multiple settings were made, and the total inked areas of digits were converted to mm(2).


RESULTS
At baseline, the mean +/- SD injection force of NovoPen 4 was 9.14 +/- 0.87 N and 16.55 +/- 1.17 N, which was significantly lower (P < 0.001) than for NovoPen 3, at 18.36 +/- 1.06 N and 29.81 +/- 1.26 N, with the 30-gauge and 31-gauge needle, respectively. After simulated lifetime testing, mean +/- SD injection force was 10.93 +/- 0.77 N and 17.77 +/- 1.14 N for NovoPen 4, which was significantly lower than the injection force of 18.54 +/- 0.94 N and 31.69 +/- 1.98 N for NovoPen 3 (P < 0.001). The mean dosage scale digit size was 1.63 mm(2) for NovoPen 3 and 7.82 mm(2) for NovoPen 4, with a mean difference of 6.19 mm(2). The display for NovoPen 4 was 4.74 times larger (P < 0.001).


CONCLUSIONS
The mean injection force required to operate NovoPen 4 was reduced up to 50% compared with NovoPen 3 (P < 0.001), and the mean dosage display for NovoPen 4 was over four times larger than for NovoPen 3 (P < 0.001). Based on these findings, patients with diabetes who have manual or visual impairment should find it easier to dose insulin with NovoPen 4.