General principles of insulin therapy in diabetes mellitus

●Commonly used insulin preparations

Human insulin or an insulin analog can be used to treat diabetes. The approximate time of onset, peak activity, and duration of action of the most commonly used insulins are shown in the table. The insulin analogs (lispro, aspart, glulisine, glargine, detemir, degludec) were developed to provide more physiologic insulin profiles. The rapid-acting insulin analogs (insulin lispro, lispro-aabc, aspart, faster aspart, and glulisine) have both faster onset and shorter duration of action than regular insulin for pre-meal coverage, while the long-acting analogs have a longer and flatter profile than NPH for basal coverage.

●Concentrated forms of insulin

Concentrated forms of insulin can be used to control hyperglycemia in severely insulin-resistant patients (eg, requiring more than 200 total units of insulin daily). 

●Premixed insulin

We typically do not prescribe commercially fixed-ratio pre-mixed insulins in the treatment of type 1 diabetes. Intensive regimens in people with type 1 diabetes require frequent adjustments of the pre-meal bolus of short- or rapid-acting insulin. Pre-mixed insulin may be used in some people with type 2 diabetes for convenience, if the insulin ratio is appropriate to the person’s insulin requirement. Specific guidelines should be followed for pre-mixing to avoid changes in speed of absorption and peak action. 

●Determinants of insulin efficacy

Effective use of insulin requires an understanding of the major variables that affect the degree of glycemic control: the insulin preparation, injection site, injection technique, the size of the subcutaneous depot, and subcutaneous blood flow. 

•Insulin injection sites

Absorption is fastest from injections into the abdominal wall, especially with human insulins, and therefore, abdominal wall may be a preferable site for pre-meal insulin. Slower absorption from the leg or buttock may be appropriate for evening doses of intermediate-acting insulin. The absorption of the long-acting basal insulin analogs, glargine and degludec, do not appear to be significantly influenced by injection site.

•Insulin injection technique

All people using insulin should be instructed in proper insulin injection technique

•Size of subcutaneous depot

Insulin absorption is variable between people and in the same person, especially for longer-acting preparations. Variability is greater with larger injection doses.