Development of an advanced injection time model for an autoinjector

Abstract

Background

This work describes an advanced physics-based mathematical model that accurately predicts autoinjector injection time. Autoinjectors are a well-established technology for parenteral drug delivery and quantifying the probability to achieve a given injection time is critical to the successful development and commercial launch of the autoinjector.

Method

Each parameter that can influence injection time was treated as a statistical variable with an appropriate distribution function. Monte Carlo simulation was used to obtain the probability of achieving the required injection time. Sensitivity analyses were performed to identify those parameters most critical in contributing to the overall injection time. To validate the model, a number of experiments were conducted on autoinjectors, with key contributors to injection time measured and characterized.

Results

The results showed excellent agreement between modeled and measured injection time. The modeling error for all investigated device configurations was smaller than 12% and the error range was less than 6%. The consistent over-estimation of injection time suggests a small bias in the model which could be accounted for by reducing internal friction.

Conclusion

This work provides evidence that the selected modeling approach, which aims for a simple yet computationally inexpensive model, is accurate and enables running comprehensive statistical simulations to determine the full range of expected injection times due to component variability.

Keywords:

• plunger force
• viscosity
• stopper friction
• sensitivity analysis
• model validation

Acknowledgments

The authors would like to thank Chris Muenzer and Stefan Fischer for work on the viscosity model; Fred Bathke, Jean-Michel Courtois and Lothar Vorgrimler for execution of experimental work; Neil Cammish and Ajay Deshmukh for expert advice on modeling.

Disclosure

The authors are all employees of F. Hoffmann-La Roche. The authors report no other conflicts of interest in this work.