Insulin treatment for diabetes
People with type 1 diabetes mellitus, as well as many with type 2 diabetes mellitus, are unable to produce sufficient insulin to regulate the glucose (sugar) levels within their blood. These people must inject insulin one or more times daily in order to manage their condition.
Types of insulin
In the past, most insulin for human use was extracted from the pancreatic tissue of animals, mainly pigs or cattle. Today, most insulins are produced using genetic engineering technology, whereby yeast or bacteria in the laboratory are modified to produce human insulin. Recent advances extend this technology to produce insulin analogues (or ‘copies’) that incorporate a slightly different structure to that of human insulin. This slight change can alter the insulin's duration of action and the time to onset of its effect. As a result, the range of insulins now available is increasing. Some bovine (derived from cattle) insulins are still available.
Apart from how they are derived, the different types of therapeutic insulin for use in diabetes are further categorised according to how quickly they take effect, how long their effect lasts, and when they reach their peak in terms of their ability to lower blood-glucose levels.
Very-short-acting (aspart, glulisine and lispro) insulin
Insulin aspart, insulin lispro and insulin glulisine are synthetic copies (analogues) of human insulin. They are very fast-acting and should be injected immediately before meal times. They start to work about 15 minutes after being injected, peak after about an hour, and last for about 3-5 hours. Because of their short duration of action, these insulins reduce the risk of hypoglycaemia (low blood sugar) occurring several hours after meals.
- Human very-short-acting insulins (human insulin analogues): examples are Apidra (insulin glulisine), Humalog (insulin lispro) and NovoRapid (insulin aspart).
Short-acting (neutral) insulin
Short-acting (neutral) insulin starts to work about half an hour to an hour after being injected, peaks from between 2 and 5 hours, and lasts for about 4-8 hours.
- Human short-acting insulins: such as Actrapid and Humulin R.
- Bovine short-acting insulin: Hypurin Neutral obtained from the pancreas of cattle (bovine insulin).
Intermediate-acting (isophane) insulin
Non-mixed intermediate-acting insulin contains isophane insulin on its own. Isophane insulin starts to work 1-2 hours after being injected, peaks at 4-12 hours and lasts for 16-24 hours.
- Human isophane insulins: examples include Humulin NPH and Protaphane.
- Bovine isophane insulin: Hypurin Isophane is a bovine intermediate-acting insulin.
Intermediate-acting insulin is often used in conjunction with short-acting insulin (see ‘Mixed Insulins’ below).
At the far end of the spectrum is long-acting insulin. There are 2 types: glargine and detemir.
Insulin glargine (brand name Lantus) is a human insulin analogue. It starts to work one to 2 hours after being injected and lasts for over 24 hours. It has no peak effect, and can therefore be helpful in reducing the unwanted peaks and troughs in blood glucose levels that can occur with intermediate-acting insulins.
Insulin detemir (brand name Levemir) is a long-acting human insulin analogue that has a slow onset and long duration of action (up to 24 hours).
Mixed or biphasic insulins
Most pre-mixed insulins come as combinations of a short-acting insulin with an intermediate-acting insulin. They are sometimes referred to as biphasic insulins. The numbers written after the brand name show the mix of the 2 types of insulin. For example, Humulin 30/70 contains 30 per cent short-acting insulin and 70 per cent intermediate-acting insulin. Mixtard 50/50 contains 50 per cent short-acting insulin and 50 per cent intermediate-acting insulin.
All the mixed intermediate-acting insulins available in Australia at present are human insulins produced by genetic engineering.
- Human mixed (short- and intermediate-acting) insulins: these include Humulin 30/70, Mixtard 30/70, and Mixtard 50/50.
The very-short acting insulins lispro and aspart are also available in a biphasic form. In this form some of the insulin is combined with protein to slow down its action.
- Human mixed insulin analogues (with very-short and intermediate-acting properties): these include Humalog Mix25 and Humalog Mix50 (both insulin lispro) and NovoMix 30 (insulin aspart).
Pre-mixed insulins are often available in a pre-filled insulin pen, rather than a vial and syringe, and are particularly convenient for people who have poor eyesight or co-ordination, or who are unable to draw up insulin accurately from 2 different bottles of insulin.
Which insulin is best for you?
The type of insulin and timetable of doses that is best for you will depend upon a range of different personal factors such as your eating and exercise patterns and your individual reaction to the different types of insulin available.
Insulin therapy for people with type 1 diabetes
Basal-bolus insulin regimen
Some people with type 1 diabetes use what is known as a ‘basal-bolus’ regimen. This means that they take a ‘bolus’ of short-acting or very-short-acting insulin before meals to deal with the associated rise in blood-sugar levels at these times. In addition, they take an evening injection of intermediate- or long-acting insulin that helps normalise their basal (fasting) glucose levels. Sometimes, an additional small dose of intermediate- or long-acting insulin is required in the morning.
Mixed insulin regimen
Other people may opt for a mixed timetable. This means that they take a mixture of short-acting with intermediate- or long-acting insulin once or twice a day. Often people take 30 per cent short-acting and 70 per cent intermediate- or long-acting insulin. This is not as intensive as the basal-bolus timetable. The insulin mixture is taken either once a day, usually before dinner, or twice a day with about two-thirds of the daily requirement taken before breakfast and the remaining one-third before dinner in the evening.
It may take some time to establish the correct type or combination of insulin to stabilise your blood-glucose levels, but your doctor will be able to work with you to help determine the best combination for your lifestyle.
Another method of insulin administration is via an insulin pump. This can be a complicated and expensive method but is useful for people whose blood glucose levels are difficult to control.
Insulin therapy for people with type 2 diabetes
People with type 2 diabetes who are taking oral medicines (known as oral hypoglycaemics) may need to start taking insulin if the oral medicines are not effectively controlling blood glucose levels. Most people with type 2 diabetes eventually require insulin, even after many years of successful treatment with oral hypoglycaemics.
Combination of insulin and oral hypoglycaemic therapy
In this regimen, the person with type 2 diabetes continues their oral hypoglycaemic medicine, and a single dose of intermediate- or long-acting insulin is added at bedtime or breakfast. This allows the oral medicine to maintain normal blood sugar levels more effectively.
Mixed insulin regimen
This schedule involves giving a combination of insulins, either once or twice daily. One-third of the daily requirement is given as short-acting insulin and two-thirds is given as intermediate- or long-acting insulin.
Glossary of insulin terms
|Insulin: glossary of terms|
|Aspart||A copy of human insulin made by recombinant DNA technology (genetic engineering). This is a very-short acting insulin. That means it starts to work very quickly.|
|Bovine||From cattle. Bovine insulin is usually made from the pancreas of cattle.|
|Detemir||Detemir insulin is a long-acting human insulin analogue that has a slow onset and long duration of action.|
|Glargine||Insulin glargine is a long-acting human insulin analogue. Its effect lasts for over 24 hours.|
|Glulisine||Insulin glulisine is a very short-acting human insulin analogue. It starts to work very quickly and lasts only a relatively short time.|
|Human insulin||An insulin produced in the laboratory, using genetic engineering technology, that has the same structure as the insulin found in the human pancreas.|
|Human insulin analogue||Insulin produced in the laboratory, using genetic engineering technology, that has a slightly altered structure compared to the insulin found in the human pancreas; this alteration changes the onset and duration of action of the insulin.|
|Isophane||Scientific name for a type of intermediate-acting insulin. Also known as NPH.|
|Lispro||Insulin lispro is a very-short acting human insulin analogue. This means it starts to work very quickly.|
|Neutral insulin||Scientific name for a type of short-acting insulin. It is a clear fluid with zinc and insulin crystals dissolved in it. Sometimes referred to as regular, soluble insulin, it may have the word neutral or the letter ‘R’ (for regular) after its brand name.|
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