Pen devices for self-injection: contrasting measured injection force with users' perceived ease of injection

OBJECTIVES

Past research has emphasized injection force as a clinically highly relevant technical attribute of pen devices. However, little work has been conducted to relate these results to in-use studies. This article explores whether and how differences in pen injection force profiles influence users' self-reported perceived ease of injection and preferences.

METHODS

Three different pen systems were subjected to measurements of injection force using an automated mechanical set-up followed by a simulated use study where users assessed perceived ease of injection.

MAIN OUTCOMES MEASURE

Outcomes were measured by fitting data of measured injection force and perceived ease of injection using a linear model.

RESULTS

Although mechanical testing revealed significant differences between the three pen's measured injection forces these differences were not directly perceived by users in simulated injection studies.

CONCLUSION

The article bridges literature on injection force measurement and simulated use. It reveals how users' perceived ease of injection is less sensitive to measured injection forces than prior research has assumed. Thus, future research should holistically integrate patient feedback in new device development. Key limitations of this work are the low number of participants in the simulated use study and the fact that the ease of injection was assessed indirectly.

An analysis of product wastage arising from dosing increment granularity in four modern growth hormone administration devices

OBJECTIVE

Human growth hormone (hGH) delivery systems differ in the size of the dose increments that can be set by the patient, affecting proximity to the target (i.e., prescribed) dose which can be attained. We investigated differences in dosing increment granularity in NordiFlex®, FlexPro®, NordiPen® (all multiple dose devices) and MiniQuick® (single dose) delivery systems.

METHODS

A simulation model was developed to project hGH dosing in pediatric patients with growth hormone deficiency, small for gestational age or Turner syndrome, calculating the nearest dose above the target dose administrable by each device in typical EU and US cohorts and projecting the excess dose (hGH wastage) over 1 year of typical use.

RESULTS

The device with the smallest dosing increment (FlexPro 5 mg; 0.025 mg dosing increment) was projected to administer doses < 1% above the target across all indications. MiniQuick (0.2 mg dosing increment) was projected to deliver between 5 and 6% above the target dose. None of the sensitivity analyses changed the conclusion that larger dosing increments result in more hGH wastage.

CONCLUSIONS

In addition to increasing dosing accuracy, finer dosing increments may result in reductions in unnecessary hGH usage, which may in turn result in reductions in the cost of hGH treatment borne by the health-care payer.