For decades after the discovery of insulin, the only option for getting the lifesaving medicine into your body was with a vial and syringe. Today, while vials are still used, many types of insulin are also available in pen form, which takes some of the hassle out of injecting.

Insulin pens come in two basic varieties: disposable and reusable. The disposable kind comes prefilled with insulin and should be stored in the refrigerator before use, then stored at room temperature once opened. When the insulin is used up, these pens are discarded. Reusable pens are loaded by the user with insulin cartridges, purchased separately. While the cartridges can be stored in the refrigerator prior to use, the reusable pens should not be put in the refrigerator at any time. To use either type of pen, you screw on a special pen needle, dial in a dose, insert the needle under the skin, and press a button to inject the insulin.

Choosing an insulin pen may be dictated by what type of insulin you use. There are three makers of insulin in the United States: Eli Lilly, Novo Nordisk, and Sanofi-Aventis. Each company manufactures its own pens for use only with its insulin. (In addition, Owen Mumford Inc., a medical device manufacturer, makes a reusable pen compatible with Eli Lilly insulin cartridges.) However, some types of insulin are not available in pen form at all.

One thing to consider when selecting a pen is how much insulin you need to deliver at one time and how precise changes in your dose might be. Insulin pens can administer doses in increments of half a unit, one, or two units, with maximum doses ranging from 21 to 80 units. Children taking mealtime insulin, for example, may need a pen that allows dosing in half-unit increments, while someone who takes a daily injection of basal (long-acting) insulin may require a pen that can give a larger dose.