Insulin is indicated for type 1 diabetes as well as for type 2 diabetic patients with insulinopenia whose hyperglycemia does not respond to diet therapy either alone or combined with other hypoglycemic drugs.

With the development of highly purified human insulin preparations, immunogenicity has been markedly reduced, thereby decreasing the incidence of therapeutic complications such as insulin allergy, immune insulin resistance, and localized lipoatrophy at the injection site. However, the problem of achieving optimal insulin delivery remains unsolved with the present state of technology.

It has not been possible to reproduce the physiologic patterns of intraportal insulin secretion with subcutaneous injections of short-acting or longer-acting insulin preparations. Even so, with the help of appropriate modifications of diet and exercise and careful monitoring of capillary blood glucose levels at home, it has often been possible to achieve acceptable control of blood glucose by using various mixtures of short- and longer-acting insulins injected at least twice daily or portable insulin infusion pumps.

1. Characteristics of available insulin preparations

-  Commercial insulin preparations differ with respect to the time of onset and duration of their biologic action.

  a. Species of insulin -  Human insulin is produced by recombinant DNA techniques (biosynthetic human insulin) as Humulin (Eli Lilly) and as Novolin (Novo Nordisk). It is dispensed as either regular (R) or NPH (N) formulations. Five analogs of human insulin - three rapidly acting (insulin lispro, insulin aspart, insulin glulisine) and two long-acting (insulin glargine and insulin detemir) - have been approved by the FDA for clinical use. Animal insulins are no longer available in the United States.

  b. Purity of insulin -  “Purified” insulin is defined by FDA regulations as the degree of purity wherein proinsulin contamination is less than 10 ppm. All insulins presently available contain less than 10 ppm of proinsulin and are labeled as “purified.” These purified insulins seem to preserve their potency quite well, so that refrigeration is recommended but not crucial. During travel, reserve supplies of insulin can thus be readily transported for weeks without losing potency if protected from extremes of heat or cold.

  c. Concentration of insulin -  At present, insulins in the United States are available in a concentration of 100 units/mL (U100), and all are dispensed in 10-mL vials. With the popularity of “low-dose” (0.5- or 0.3-mL) disposable insulin syringes, U100 can be measured with acceptable accuracy in doses as low as 1-2 units. For use in rare cases of severe insulin resistance in which large quantities of insulin are required, U500 regular human insulin (Humulin R) is available from Eli Lilly.