Samuel Grossman, BS Pharm, Pharm.D, CDE Answered 3/19/2015

Priming insulin pens is necessary to prevent accidental injection of air instead of insulin. The company accounts for the loss of insulin and the pen is filled with enough insulin to serve the purpose of priming. Before priming, point the pen up and tap the pen to allow air bubbles to rise to the surface, then dial 2 units on the pen and inject those units into the air.