Insulin actions, types and treatments

Insulin is a chemical produced in the pancreas by special ‘beta cells’.

Insulin acts as the ‘key’ that allows glucose to enter the body cells to act as fuel. As soon as we eat food the pancreas increases its production of insulin. The pancreas senses the correct amount of insulin needed, depending on the level of glucose in the blood. Insulin in the bloodstream reaches the different cells in the body, allowing glucose to enter the cell. This glucose is then used in the cells and so the blood glucose is kept steady.

A small amount of insulin is needed, even between meals and at night. This is the ‘basal’ insulin as compared to the ‘bolus’ insulin released in response to food.

In a person with diabetes the pancreas no longer produces insulin, so this is injected to try to keep the glucose levels constant.

Insulin also allows storage of glucose in the liver and makes fat and protein from carbohydrates not used as fuel.

Insulin levels vary from day to day, minute to minute depending on the amount of glucose in the blood. In a person without diabetes the pancreas constantly makes these adjustments naturally. In a person with diabetes, however, these changes will need to be made by them.

Types of Insulin

Ultra-fast acting 

Name	Brand	Starts work in	Best action in	Stops work in
Insulin lispro	Humalog	5 to 15 minutes	45 to 90 minutes	3 to 4 hours
Insulin aspart	NovoRapid	10 to 20 minutes	1 to 3 hours	3 to 5 hours
Insulin glulisine	Apidra	5 to 15 minutes	45 to 90 minutes	3 to 4 hours

Fast-acting 

Name	Brand	Starts work in	Best action in	Stops work in
Soluble insulin	Actrapid / Humulin S	30 minutes	2 to 5 hours	5 to 8 hours

Medium-acting 

Name	Brand	Starts work in	Best action in	Stops work in
Isophane	Insulatard Humulin I	1 to 4 hours	4 to 12 hours	16 to 20 hours

Long and ultra-long acting 

Name	Brand	Starts work in	Stops work in
Protamine zinc suspension	Protamine zinc	1 to 2 hours	18 to 24 hours
Insulin glargine	Lantus	1 to 2 hours	18 to 24 hours
Insulin detemir	Levemir	1 to 2 hours	18 to 24 hours
Insulin degludec	Tresiba	1 to 2 hours	24 hours

Pre-mixed insulins 

These are a mixture of short-acting and intermediate acting insulin in different proportions.

Name	Brand
Soluble insulin (30%) & isophane insulin mix	Humulin M3
Biphasic insulin aspart	Novomix 30 (30% fast acting)
Biphasic insulin lispro	Humalog mix 25 / 50

Different insulin regimens used

• Once a day – usually only in very young children
• Twice daily – usually mixed insulin before breakfast and tea
• Three times a day – usually mixed insulin before breakfast, lunch and tea
  or mixed insulin before breakfast, fast-acting before tea and long-acting at bedtime
• Basal bolus regime – ultra-fast acting insulin before all meals (requires carbohydrate counting) and long-acting at bedtime
• Insulin pup therapy – ultra-fast acting insulin given continuously by the pump (pre-programmed) and bolus given before meals (by the patient, depending on carbohydrate content of the meal)

With any current treatment regime, even in a well-controlled person, there will be occasional unpredictable high and low sugars.

High sugars – feeling unwell

How much insulin?

The effect of a dose of insulin depends on many things:

• Amount of food eaten
• Type of food
• Exercise level before and after food
• How much insulin has been taken earlier?
• Levels of stress, lumpy sites, etc

Roughly one unit of insulin will bring the sugar down by a value of 4 mmol/l but this varies with age, puberty, stress, illness etc.

Occasional high glucose levels are impossible to avoid in real life

If you are feeling well and there are no ketones in the blood:

• Drink plenty of water (fluids)
• If you are close to meal time, add extra ultra-fast acting insulin to the usual meal time dose

Check blood glucose between 2 am and 3 am if extra insulin is given before bedtime.

Summary

• Insulin is produced by the pancreas
• It is the ‘key’ required for glucose to enter cells
• Insulin is required in varying amounts throughout the day and night
• Many types of insulin are available
• Different treatments are used depending on individual needs.
• If sugars are high and patients are well, one unit of ultra-fast
  acting insulin will generally bring level down by 3-5 mmols.

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