The 3 routes of administration for insulin

Insulin is only available as a liquid preparation.

Depending on different circumstances it can:

• be injected subcutaneously (in the skin) via an insulin syringe, pre-filled pen device or insulin pen
• for certain patients with type 1 diabetes, be delivered as an insulin infusion via a wearable personal insulin pump
• be administered through an intravenous insulin infusion

1. Injecting insulin subcutaneously

How insulin is supplied

There are several means by which it can be supplied for use subcutaneously (in the skin):

• It can be drawn out of an insulin vial ONLY using an insulin syringe. When injecting insulin, it is important to allow at least 10 seconds before the needle is removed. This helps to ensure that the full insulin dose administered is absorbed. Wet skin at the injection site after the needle is removed could be insulin that has not been absorbed.

_{Figure: using an insulin syringe to draw insulin out of an insulin vial}

• It can be provided as a prefilled pen device, which is disposed of once empty.
• It can be provided as a cartridge that can be loaded into an insulin pen.

Insulin should never be drawn out of a cartridge using a syringe.

_{Figure: insulin should never be drawn out of a cartridge using a syringe}

How insulin should be administered subcutaneously

1. When insulin is to be administered subcutaneously by injection, the injection site should be clean and the person giving the insulin should wash their hands.
2. In the UK, 4-6mm sized needles tend to be used most commonly.
3. Prior to each administration, blood glucose levels MUST be checked to help inform the dose of insulin required. Administering insulin without checking the glucose level first could be dangerous. Whilst physical symptoms might help to inform if someone has high or low glucose levels, these symptoms cannot always be directly linked to a precise glucose level. Hence, by checking the glucose level first, one can be assured that the proposed insulin dose to be administered is appropriate.
4. Prior to each administration, the usual advice is to draw up insulin or dial up the dose using an insulin pen. The user is then asked to perform an ‘air shot’. This is where 2-3 units are discharged into the air to ensure that the syringe or insulin pen are working correctly.
5. Provided that this demonstrates insulin release, the required treatment dose can then be drawn or dialled up.
6. The appropriate injection site is then chosen.
7. The recommended sites for insulin injection are the abdomen, buttocks and thighs. Once the site is chosen, the skin should not be pinched up prior to injection unless the person has been advised to do so.
8. The insulin is administered at a 90^o angle and the user is typically asked to keep the syringe or pen plunger fully depressed for 6 to 10 seconds before withdrawing, which seeks to ensure that all insulin administered is delivered subcutaneously.
9. Injection sites should always be rotated to prevent lipohypertrophy. This is the growth of local fat in the skin as a consequence of the anabolic property of insulin which can impede the absorption of insulin and hence its action on lowering blood glucose levels.
10. The needle must then be disposed of in a safe manner using an appropriate container.

2. Administered by personal insulin pump

For patients with type 1 diabetes, a pre-filled insulin cartridge can also be inserted into a personal insulin pump.

This device is permanently worn by the patient and constantly delivers an infusion of insulin, at a rate defined by the user.

_{Figure: fitting a wearable insulin pump}

The cartridge is changed every few days.

In the United Kingdom, only people with type 1 diabetes who meet essential criteria are entitled to a trial of insulin pump therapy.

Did you know? Research with new technology (i.e. not in routine clinical practice) called the ‘artificial pancreas’ has been shown to be effective in controlling blood glucose concentrations in people with type 1 diabetes, including pregnant women.

This system continuously checks blood glucose levels and the calculates how much insulin is required before automatically delivering the correct amount of insulin through the pump. This leads to improved glucose control. For more information, see the guidelines for continuous glucose monitoring in Diabetes UK.

3. Administered intravenously