Until the development of recombinant DNA technology in the 1980s, insulin was purified from porcine or beef pancreatic tissue. Human recombinan insulins are now the most widely used forms and are the recommended first line preparations in the paediatric age group. Bovine insulins remain a useful second line group of insulins, especially in the very young and in those in whom there seems to be an exaggerated tendency to hypoglycaemia at the time of peak action of the insulin preparation.

Formulations of Insulin
The onset, peak effect and duration of insulin action may vary both between individuals and for the same individual depending on :

• age
• fat mass
• puberty
• the dose used
• the site of injection
• exercise

Ultra Short - acting Insulin
Insulin has a tendency to aggregate into dimers and hexamers which retard the absorption and biological availability. Analogues which prevent the insulin molecule from forming dimers or hexamers are in clinical trials. These monomeric insulins have a very rapid onset of action, peak within 1 hour and have a duration of less than 4 hours. Their use in paediatric diabetes is being investigated. Early indications suggest that they may be of great use as pre-meal bolus doses and in the management of sick days.

Short-acting Insulin
Short-acting insulin is also known as soluble or regular insulin and is a clear solution. It is used in the management of acute diabetic problems as well as being an essential component of daily replacement therapy. It is often used by itself as a pre-meal bolus injection in a basal-bolus regimen or combined with an intermediate-acting insulin in a twice-daily injection regimen. It is the only suitable form for intravenous insulin therapy.

Intermediate-acting Insulins
These insulins are present in suspension and are therefore referred to as cloudy insulins. Their time-course of action make them ideal insulins for twice-daily insulin regimens and for pre bed dosage in basal bolus regimens. The vials need to be gently mixed prior to each use to ensure a uniform concentration. Vigorous mixing may cause protein degradation. Two principal preparations currently used are:

• Isophane or NPH (Neutral Protamine Hagedorn) insulins
• Crystalline zinc-acetate insulins (lente insulins)

Long-acting Insulins
These preparations may be used to meet basal insulin requiqements, especially in multiple injection regimens. Beef ultralente insulin has a duration more than 24 hours. Human ultralente may have a shorter action in some individuals and may be preferred as the evening insulin.