Types
Two types of insulin pens are available on the market: 1. Insulin ready-to-use pens (disposable pens, flexpens): with the insulin ampoules already inserted, they are ready for immediate use. When the ampoule is empty, the entire pen is disposed of. 2. Reusable insulin pens: the empty insulin ampoule is replaced with a new, filled insulin ampoule.
Structure
Structure of an insulin pen needle
Advantages
The advantage of an insulin pen over an insulin syringe is mainly the much easier handling. The cumbersome drawing up of the insulin from the ampoule is no longer necessary. The whole equipment, such as insulin ampoule and syringe, does not have to be carried individually.
Disadvantages
The cartridges of the pre-filled pens are not suitable for mixing different insulins, and unlike traditional insulin syringes, the pens can only be used to administer whole or half doses.
Application
The desired insulin dose can be set by turning the pen’s dosing knob. After inserting the pen needle into the adipose tissue, the set insulin dose is injected by pressing the dosage knob. This principle applies to all insulin pens, despite the differences in handling details (see package insert).
Injection sites
Insulin is injected into the subcutaneous fatty tissue (subcutaneous), i.e., the fatty tissue between the skin surface and the muscle. This allows for good distribution and absorption of the insulin. Injection of insulin into the fatty tissue of the abdomen, buttocks, and outer and outer thighs is recommended. The speed of insulin action varies. Insulin uptake and insulin action occur most rapidly on the abdomen, followed by the thighs and buttocks. In order to better assess insulin action, injections should always be given at the same time of day into the same body regions, but at alternating injection sites. Short-acting insulins are usually injected in the abdominal region, long-acting insulins usually in the thigh or buttocks. Injection sites must be changed regularly to prevent hardening of the tissues.
