The pancreas of a person without diabetes will always be secreting a small amount of insulin into the bloodstream, constantly throughout the day and night (called basal secretion). After a meal, a larger amount of insulin is secreted to deal with the glucose coming from the food (called bolus secretion).
The goal of all insulin treatment is to mimic this function and provide insulin to the bloodstream. In the past, bovine (beef) and porcine (pork) insulin were used for all people with diabetes. Nowadays, mostly human insulin is used, i.e. insulin with a chemical structure identical to the insulin produced by the human pancreas. Human insulin is produced using gene technology or by semi-synthetic methods. Genetic engineering involves the insertion of human insulin producing genes into a yeast cell or bacteria. In this way yeast cells or bacteria are tricked into producing insulin instead of their own proteins. Short- and rapid-acting insulins are pure insulin without any additives. They are in the form of a clear liquid and don't require stirring or mixing before use. Different additives are used to make the insulin longer-acting, and these are what make it cloudy. The cloudy part of the contents will collect as sediment at the bottom of the bottle or cartridge. This sediment must be mingled again with the rest of the contents by turning over or rolling (but not shaking) the cartridge 20 times before use. The newer basal insulins are clear because they are both solutions rather than suspensions. These types of insulin have an extended effect because of changes to the molecular structure, which slow down their absorption, rather than added molecules such as zinc or protamine.
In intravenous insulin therapy, insulin (usually short-acting) is given directly into the bloodstream. This is the most effective way to treat diabetic ketoacidosis. It is given only in hospitals as an intravenous drip or in a motorized syringe. There is no advantage in giving rapid acting insulin intravenously, since the blood glucose-lowering effect is no quicker than that of regular short-acting insulin. Since the half-life of insulin is very short, only about 4 minutes, the blood glucose will increase sharply if intravenous insulin is stopped. If intravenous insulin is being used, the blood glucose must be checked every hour (even during the night) to monitor the correct dosage.
Intravenous insulin is often used during surgery or if a patient is suffering for any length of time from diarrhoea and vomiting. It also gives us a practical way of working out how much insulin the patient needs over a 24 hour period, for example when starting treatment with an insulin pump.
This content is based on Dr Ragnar Hanas' helpful book, Type 1 Diabetes in children, adolescents and young adults. Click here to order copies of Dr Hanas' book online.