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(10) Diabetes

Types of Insulin

Since the discovery of insulin, countless people with diabetes have injected themselves with insulin extracted from the pancreas of cows and pigs. In the last 20 years or so human insulin has become widely available.

 However, human insulin is not extracted from human pancreas in the same way beef or pork insulin is. A great deal of research went into producing ‘human’ insulin by means of genetic engineering. This means that the genetic material of a bacterium or yeast is reprogrammed to make insulin instead of the proteins it would normally produce.

The insulin manufactured in this way is rigorously purified and contains no trace of the original bacterium.

The first insulin to be made was clear soluble insulin also called short-acting insulin. Injected under the skin, this insulin has a relatively rapid onset of action and lasts for 4–8 hours. Various modifications were made to this original insulin so that it would last longer after injection. When protamine or zinc is incorporated into the soluble insulin, a single injection could last from 12 to 36 hours. For many years a single daily injection was advised by doctors but people realized that this was not a good way of controlling the variations in blood glucose that occur during the day.

Nowadays many people who need insulin have a mixture of short- and intermediate- or long-acting insulin twice a day, but an increasing number have insulin four or more times a day that they can inject with an insulin pen. A new generation of insulin’s, also called insulin analogues, where the chemical makeup of the insulin is changed, are also available today. By changing the molecular structure of the insulin, manufacturers can alter the way it works, allowing it to be absorbed differently.

I have been on ordinary pork insulin for 12 years and my doctor has just changed me over to human insulin. I feel upset because I was given no real explanation. Can you please help?

There has been a gradual switch to human insulin since it was introduced in 1982. Many doctors felt that human insulin was generally better because it led to less antibody formation than pork insulin. However, these antibodies probably do no harm and they may even be of some benefit by making the insulin injection last longer. There are also commercial pressures as insulin manufacturers would prefer to make only the human variety, which would in turn reduce production costs.

Most people are able to swap from animal to human insulin without any difficulty but it is usual to reduce the dose by about 10% to be on the safe side and to compensate for the reduction in antibodies. This may be a gradual process lasting up to 6 weeks.

Obviously during this transition period you will need to be especially careful to do frequent blood checks and if necessary to adjust the dose of insulin. If the new type of insulin causes any problems, you can always ask to go back on pork insulin. Since changing to human insulin my hypos have changed.

There is less warning and on several occasions I needed help from my wife to get me back to normal. Have other people had the same experience?

This is a fairly common complaint and is very worrying because people rely on their warning signs to help them cope with the problem of hypos. Before human insulin was introduced, exhaustive tests were performed to try and find ways in which it differed from animal insulin. In conclusion, these tests failed to show any significant differences apart from the lower levels of antibodies to insulin. It came as a surprise when a few people reported that their hypos were different on the new insulin and no real explanation has been found for this observation, but you may find it worthwhile to try the pork insulin again.

A self-help group exists for people who are treated with insulin, and their careers. The Insulin Dependent Diabetes Trust has highlighted a number of problems connected with insulin and the delivery of care. It has been an effective pressure group over the question of human insulin.

I have had problems with human insulin and would like to go back to pork insulin. However, my chemist tells me that Velosulin is only available in the human form. Any suggestions?

It is true that pork Velosulin is no longer manufactured. However, the same company still makes Actrapid in both pork and human form. This is highly purified soluble insulin comparable to Velosulin. You should be able to substitute porcine Actrapid for your original dose of porcine Velosulin. Alternatively, there are other companies like CP Pharmaceuticals who manufacture animal insulins exclusively.

There is no pork zinc insulin the same as Monotard, but Insulatard is often a good substitute, and this is available in both human or pork forms. For the record, Mixtard 30, a premixed solution of short and intermediate acting insulin, is also available in both forms. Cartridges for the insulin pen are available as human, bovine, or porcine insulin.

My diabetes has been well controlled on beef insulin (soluble and isophane) for the past 22 years. Should I use human insulin instead?

Provided that you are doing well on your present insulin, there is no need to change. although the major insulin companies have not made beef insulin for many years, a firm called CP Pharmaceuticals supplies beef and pork insulin under the brand names Hypurin Bovine and Hypurin Porcine. They produce short-acting insulin: Hypurin Bovine Neutral and Hypurin Porcine Neutral; intermediate-acting insulin: Hypurin Bovine Isophane and Hypurin Porcine Isophane; long-acting insulin: Hypurin BovineLente and Hypurin Bovine PZI; and also premixed insulin: Hypurin Porcine 30/70. All of these except Lente and PZI are available in cartridges as well as vials.

I have been taking beef insulin for many years and am worried about the possibility of this insulin being contaminated with BSE. Is this possible?

The manufacturers of beef insulin consider that the risk of any BSE (bovine spongiform encephalopathy) agent remaining after the intensive purification processes used to extract insulin is either negligible or non-existent. In addition, beef insulin used in most developed countries of European Union and  is derived from cattle originating in countries considered to have a negligible incidence of BSE, so that the risk of coming into contact with BSE through beef insulin is very small indeed.

I have seen a programme on television, which says that human insulin may be dangerous. My 14-year-old son has just developed diabetes and I see that the doctor has put him on human insulin. You can imagine how worried I am about it.

Yes, it is unfortunate that this programme appeared at such a bad time for you. The people who make these programmes do not realize the fear and anxiety that they can cause.

First you must believe that your son needs insulin – without it he would soon become very ill. It does not really matter at this stage what sort of insulin he has, although most doctors in this country start people who need insulin on the human variety. The only problems with human insulin seem to be caused by the change over from animal to human insulin. As your son has been on human insulin from the start he should not run into any difficulties. Perhaps you should talk to a family in which one of the children has had diabetes for a few years. They would probably be able to give the reassurance you need.

I was changed from pork to human insulin 4 years ago and I have not really noticed any difference. I have recently heard that human insulin can be dangerous. Should I be worried?

There has been adverse publicity about human insulin, which has been mentioned in the preceding questions. A number of people changing from animal to human insulin have noticed that they get less warning of hypos. This change of awareness may result from other factors but some people are convinced that the problem was caused by human insulin.

There have also been reports of unexpected deaths in people who have changed to human insulin. These deaths may have been due to hypoglycaemia but this has not been proved. Nor has it been shown that the numbers involved have increased since human insulin was introduced. Diabetes UK for example has been carrying out research into these vital questions but so far no cause for alarm has been found.

There seem to be a lot of different types of insulin on the market. Can you give me some details?

The range of insulins available can be confusing, although they do fall into four separate groups. Please note that the times of insulin action vary greatly from one person to another and those given here must only be regarded as a rough guide. The vials mentioned in the table are bottles of insulin for use with a syringe, and cartridges are for use with an insulin pen.

I am taking a mixture of short- and intermediate-acting insulin twice a day and do not understand which insulin is working at which time of day.

Many people are confused by the length of action of their insulin particularly when taken more than twice a day regimens. However, as a general rule the short-acting insulin works rapidly (morning and evening) and the intermediate-acting insulin takes longer and covers the afternoon and the night. If you are still unclear about it have another word with your doctor or diabetes specialist nurse.

Can I get AIDS from human insulin?

Definitely not. Human insulin is either made from bacteria or yeast ‘instructed’ to produce insulin that has the same structure as human insulin, or from pork insulin modified to resemble human insulin. It is rigorously purified and cannot be a source of infection.

Is it possible to be allergic to insulin?

Very occasionally people may develop an allergy to one of the additives to insulin such as protamine or zinc, but the insulin itself is unlikely to cause an allergy.

 

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