Insulin

The variety of types and brands of insu1in u e available today. It is important to know the exact pharmaceutical component and properties of the insulin being prescribed,Below is a list of commonly used insulins, followed by a brief review of branded insulin pcns.

Source and Purity of hsulins

The most easily available insulin is human insulin derived from genetic engineering techniques. The most common method is insertion of the human insulin gene into the yeast saccharomyces and this produces human insulin. These ins~llins are known as mono-component, which means that there are no contaminating impurities such as proinsulin and pancreatic polypeptides. This avoids the side-effect of antigenicity which is the cause of reduced and erractic efficacy through inteiference by insulin antibodies. Bovine and porcine insulin are also available from animal sources in no no component purity and are cheaper.

Insulin Analogues

It was noticed that insuIin chains, after subcutaneous injection, tended to stick together (polymerization). This hampered absorption and delayed and interfered with optimal action. It was discovered thal if some of the amino-acids were rearranged in the two insulin chains (insulin analogue), this tendency for polymerization was inhibited and resulted in rapid onset of action. This knowledge has been transIated into the clinical sphere and both short-acting and long-acting forms of insulin analogues are available as follows:

Time of Activity of Human Insulin

1) g-largble insulin

2) lispro insulin.

These insulins are extremely expeilsive and are not indicated for routine use.

Insulins in Common Usage

Plain (soluble, regular) insulin: This is unmodified insulin and is shol-t-acting, and useful in emergencies such as keto-acidosis, acute illness, surgery etc. After subcutaneous injection action starts within 30 rnins. peaks at two hours and finishes by six hours. The pH of the isulin is neutral thus allowing it to be mixed in a syringe with modified insulins without conversion to long-acting forms, as was the case when older soluble insulins were thus mixed.