Family doctor



INSULIN - a patient's guide


There are several different types of insulin from new fast acting products to ones that can take about four hours to work. This article looks at the various types and how to use them.


Brand Names:

Very fast acting:

Contains Insulin Lispro. Starts acting in 15 minutes. Lasts 2 to 5 hours.

  • Humalog
Fast acting:

Contains Soluble Insulin (Neutral). Starts acting in 30 minutes. Most effect in 1 to 3 hours. Lasts 6 to 8 hours.

  • Actrapid
  • Humulin R
Medium acting:

Contains Isophane Insulin or Insulin Zinc Suspension. Usually starts acting in 2 hours, most effect in 4 to 12 hours and last up to 24 hours.

  • Humulin L
  • Humulin N
  • Monotard
Long acting:

Contains Insulin Zinc Suspension (Crystalline). Usually starts acting in about 4 hours, most effect around 10 to 20 hours and last up to 36 hours.

  • Humulin U
  • Ultratard
Mixed long and short acting insulin (biphasic):

Neutral and Isophane Insulin

  • Humulin 80/20 or 70/30
  • Mixtard 30/70 or 50/50
  • Penmix 10, 20, 30, 40, or 50

The time effect of insulin and length of action can vary from person to person, and can also depend on where the injection was given, temperature, physical activity and blood supply. The above figures are only a very rough guide. Similar forms of insulin may have matching label colours.


Insulin is important to our health because it allows the energy from our food to be used by the body. Food is made into glucose which goes into the bloodstream and travels around the body. Insulin controls the level of glucose in the blood, helping it to act as a fuel for our body. Without insulin glucose does not leave the bloodstream, but instead accumulates in the blood, causing major problems. Before insulin was available, the insulin-dependant diabetes (Type 1) was fatal.

A diabetic does not have enough insulin (or is resistant to it), so needs to use insulin injections to help the food he or she eats to be used by the body as fuel. Usually the aim is to keep blood glucose between 4 and 10 mmol/L (72-180mg/dL) during the day, or as you and your doctor decide. Good control means that you have less risk of the long-term effects of high blood glucose, such as damage to the eyes and kidneys. Good control of diabetes has been convincingly shown to reduce these complications.

Insulin is usually given by injection just under the skin (sub-cutaneous) in the following areas: upper arms, thighs, buttocks or abdomen. If the insulin is given by mouth it will not work because enzymes in the stomach and intestine make it inactive. Where you inject the insulin can affect how fast it works; e.g. injecting under the skin around the abdominal (stomach) area is more evenly available. Increased blood flow in an area being injected may also make the insulin work quicker, e.g. strenuous exercise or a hot bath. For dialysis patients, insulin can be given in the dialysis fluid.

It is common to use two different forms of insulin - a medium-acting one and a fast-acting one, these are often mixed together. Some products such as Penmix and Mixtard contain a mixture of medium-acting and fast-acting. This can save mixing them yourself.

Insulin lispro is a more recent type of insulin that works very quickly. It can be given up to 15 minutes before a meal, or after a meal has begun. For small children with changeable appetites the injection can be given during or straight after a meal; this means you can give the right amount of insulin for how much they have eaten. The faster action means that you have less risk if a meal is delayed as you can inject just before the meal (when it arrives) rather than 30 minutes before.


  • Do not use insulin if the blood glucose is too low (hypoglycaemic).
  • Do not use in people who are not diabetic.
  • Changing from one insulin to another, or to do more intensive treatment may change the usual warning signs of a "hypo". Only do this under a doctor's supervision and take blood glucose tests frequently.
  • The amount of insulin needed will usually increase with illness, stress and during operations. Extra monitoring and extra care with food is needed at these times.
  • The amount of insulin needed will reduce with liver or kidney damage.

Side effects:

  • Skin reaction where the insulin is injected (e.g. red itchy skin) but this doesn't usually last.
  • Fat buildup if the injection site is not rotated (which can then make insulin absorption from that spot changeable).
  • Extremely uncommon: allergy to insulin.


If too much insulin is given, or less food is eaten than usual, or food is delayed, or there is unexpected exercise a "hypo" or hypoglycaemic attack may happen. The usual symptoms can include pins and needles around the mouth, sweating, shakes, feeling the heart beating fast and hunger. Sugar must be taken immediately, e.g. glucose tablets, jellybeans, barley sugars or a glass of lemonade. Then it is important to have food with carbohydrates to stop it happening again. If a hypo is not treated immediately the person can become unconscious. Do not drive while having a hypo.

There may be other side effects, so if you have any unexpected symptoms while taking this medicine, tell your doctor or pharmacist.


In pregnancy very good control of blood glucose is important for having a healthy baby, so you are best to talk to your doctor if you are planning to become pregnant. You will probably need less insulin than usual in the first trimester and more in the second and third trimesters. There can be an increased chance of "hypos" during the night.


  • Some beta-blockers (e.g. propranolol) may make the symptoms of hypoglycaemia less obvious.
  • Alcohol may enhance the effect of insulin, and may make it work longer (increasing the risk of a hypo); it is important not to have alcohol without eating some food.
  • ACE inhibitors may reduce the amount of insulin needed.
  • Aspirin.
  • Oral contraceptives can have a small effect.
  • Thiazide diuretics, e.g. bendrofluazide.
  • Corticosteroids e.g. prednisone or prednisolone.
  • Thyroid hormones.
  • Diltiazem and other calcium channel blockers.
  • Cold remedies containing a decongestant.
  • Liquid medicines often contain sugar and/or alcohol.

Check with your doctor or pharmacist about a possible interaction if other medicines are prescribed for you.

Patient information:

  • Follow the instructions on the label of the medicine or as directed by your doctor.
  • Keep your extra stocks of insulin refrigerated.
  • The insulin vial you are using can be left at room temperature. If you will soon be changing to a new vial, the new vial can be removed from the refrigerator so that it can come up to room temperature before you need to inject it.
  • Most insulin can be kept at room temperature (up to 25¬? C) for up to a month. Discard any remaining insulin in a vial four weeks after first using.
  • Insulin must not be frozen; if it is frozen do not thaw then use, throw it away.
  • Regular blood glucose monitoring is important and will give you control over your diabetes.
  • Do not miss meals or snacks.
  • Always carry something sugary with you (e.g. glucose tablets, jellybeans) in case of a "hypo" or hypoglycaemic incident.
  • If you get sick your insulin needs might change. It is important you check your blood glucose regularly, and you should not stop your insulin. Your doctor or diabetes nurse should be able to advise you on what to do if you become ill.
  • Frequent high blood glucose will cause long-term problems such as eye and kidney problems, so should be avoided.
  • If you are thinking of getting pregnant, talk to your doctor first. It is best to get your diabetes very well controlled before conception.
  • Rotate your injection sites.
  • Check blood glucose levels before driving and every couple of hours during long journeys. It is important to avoid a hypo while driving.
  • Wash your hands well before drawing up the insulin and injecting the dose.

See also:

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