Susie, Diabetic Cat - Insulin & Injections

Insulin & Injections

Introduction

In most cases of diabetes, insulin has to be administered manually because the body can't make its own or can't use what it makes. For diabetic animals this normally means the owner buying insulin and syringes from the veterinary surgery and administering the insulin at home, in consultation with the vet.

Insulin bought in this way is usually supplied in vials (very small bottles) with a sealed rubber top through which the needle of the syringe is pushed. This minimises the chance of contamination.

As well as some practical suggestions on issues such as storage, handling, timing and injection tips, there is also information on the different types of insulin that are available. This can seem rather complex at first, but any veterinary surgeon should be able to advise on the ranges available.

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Storage and Handling

In the insulin vial, the insulin is supplied as a suspension in water and it will settle out over time. It needs to be handled sensitively. Here are some tips, a combination of good ideas that I've read elsewhere and from my own experience:

Store vials upright in the fridge, but do not freeze.
The insulin settles out and needs to be gently mixed immediately before use. The bottle should be gently rolled between the hands, never shaken.
Once dispersed, fill the syringe to the correct level and return the vial to the fridge. The filled syringe can then be left for a few minutes to allow the contents to warm up before injecting. It should not be heated, even with hot water.
I always kept at least one spare vial. As soon as I started the next to last vial, I would order some more from the vets. This meant that if I accidentally broke a vial, there was always another one available.
I kept the spare vials in their box in the fridge, although any suitable container in the fridge would do. The main points are to keep the vials secure, upright and cool.
The vial that I was using I would keep in a small plastic tub lined with some tissue paper. This ensured that if I dropped it when taking it out of the fridge (which did happen a few times over the years), the vial was much more likely to survive and I could continue to use it.

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Timing of Injections

Ideally, insulin should be injected immediately before feeding, but in practice it is safer to ensure that the cat will eat first. This is so the dosage can be reduced slightly if the cat chooses not to eat, or appears unwell. Any reduction in dosage for this sort of situation is a matter of judgment. Susie's hypos were all because she had been unwell and had either not eaten, been ill, or both.

The timing of insulin injections (which reduces blood glucose) relative to feeding (which raises blood glucose) is critical. If timed correctly, a fairly consistent BG level can be maintained. If not, there can be dangerous variations in the BG. There is an excellent set of graphs illustrating this on the Pets With Diabetes site.

If a cat is going to become hypoglycaemic after an injection, it is most likely to happen during the peak time of the insulin activity. Typically this might be around 6 hours after injecting. It is worth being aware of when this might be, in relation to the normal daily routine, as it might coincide with being out of the house or asleep.

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Injection Tips

At first, the thought of giving injections is is often very stressful for pet owners and I was no exception, but Susie quickly learned to accept her injections as part of a normal routine. From my experience, injecting is much easier than trying to give her a tablet. I tried to establish a very recognisable routine with a treat and this approach has worked consistently well over the years.

Two excellent sets of injection tips are available on the Feline Diabetes and Pets With Diabetes websites. Other websites also have excellent tips and there is even a video on one of the Caninsulin websites (see links page).

One important point is what to do if you're not sure whether all or even any of the insulin has been injected properly. There can be all sorts of reasons for this, including:

"missing" and injecting into the fur
the cat moves during the injection
the needle might not have been in properly
the fur looks or feels a bit wet afterwards

My approach to this sort of issue was always to play it safe. If in any doubt at all, I would never re-inject. The risks of a hypo were simply too high. By taking this approach, it meant that Susie's BG might be a bit high for up to 12 hours, but this was much safer than risking a hypo from a possible overdose.

Injections are subcutaneous (i.e. under the skin) so the insulin takes a short while before it begins to reach the blood (the 'onset' time). The normal injection site is the scruff of the neck.

My injection method was based on the following:

I would fill the insulin syringe whilst preparing Susie's food. This allowed it to warm up naturally to room temperature.

After feeding, I would prepare a small treat (usually a few small pieces of sliced cooked ham, pork or chicken, available from any supermarket) and offer her a small piece to help signal what is about to happen. She would normally anticipate this eagerly.

I would usually talk to her throughout the process, although she was very familiar with the routine.

I would kneel on the floor and sit her down in front of me, facing away, towards the bowl with the meat a short distance in front of her.

Gently holding her collar with my middle finger, I would pinch an area of skin on the back of her neck with the same hand so that I could see the skin beneath her fur. In this way, I was easily able to scruff her if needed, but in practice this was extremely rare.

I would inject the needle of the syringe into the area where I could see her skin, then depress the syringe to inject the insulin over about 1/4 second. I found that being able to see the skin where the needle penetrated helped to ensure that the needle went in properly.

After withdrawing the needle, I encouraged her to eat the meat (no encouragement usually needed!).

It took Susie about 1-2 weeks to begin to accept the injections, and about 4-6 weeks to accept them relatively easily on most occasions. After that, it was very rare for Susie to react to the needle and she seemed to enjoy the attention and the treats.

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Strengths

Insulin is measured in "units" (24 units=1 mg of pure insulin).

It is normally supplied as a suspension. The most common concentrations are 40 units per mL, 50 units per mL or 100 units per mL. These might be written in slightly different ways, for example: 40iu/mL; 40iu; U40; U-40.

Insulin syringes are marked in units rather than in mL which makes it easier to avoid errors, but it is important to use the right type of syringes (U-40 syringes for U-40 insulin, U-100 syringes for U-100 insulin, etc). Otherwise, the differences in strength between the insulin and the syringe markings have to be taken into account. This should always be avoided because it would mean giving a dosage that looks incorrect on the syringe and it increases the chance of a potentially dangerous error.

The picture on the left illustrates syringes for U-40 insulin. They are 0.5ml syringes marked in insulin units so that the scale on the syringe is from 1 to 20. This is the type of syringe that I used to inject Susie's insulin.

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Speeds

Different types of insulin are designed to work at different speeds. This can be quite difficult to fully understand at first, but most vets should have experience of different types, so they should be are able to advise which type to try first. It is common for a bottle of insulin to contain a mixture of two different types. The 3 speeds used in the treatment of animal diabetes are:

Regular or short acting (e.g. Semi-Lente)
Intermediate (e.g. NPH and Lente)
Long Acting (e.g. PZI and Ultra-Lente)

Not all insulins are compatible with each other, because they may contain different types of stabilisers, so it is important to use mixtures that have been prepared by the manufacturer or compounded professionally.

There are 3 stages in the activity of all types of insulin:

Onset - the length of time before it reaches the blood and begins to lower the blood glucose (BG)
Peak Time - the period when it has maximum effectiveness in lowering the BG
Duration - how long it continues to lower the BG before it is all used up

As a rough guide, the following is typical of figures that I have seen on other websites for the time for different stages of each type of insulin, although there was some variation between the figures on the different sites (Sugarcats, Pets With Diabetes, Canine Diabetes).

Onset Peak Duration

Regular <1/2 hour 1-4 hrs 5-7 hrs

Intermediate 1/2-2 hrs 3-8 hrs 6-18 hrs

Long Acting 2-8 hrs 4-16 hrs * 8-24 hrs

* The peak for long acting insulin is often quoted as "minimal", because it continues to work for so long.

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Sources

Veterinary insulin is manufactured from a range of sources. Each source produces an insulin that has slightly different characteristics from the others. Sometimes, individual cats can be more suited to insulin one particular source rather than another. To a large extent, it is a process of trying different types to find one that seems to work well, so the experience of the vet might be a key factor.

Insulin is a natural hormone and veterinary insulin can be manufactured from different animal sources, for example beef (bovine) or pork (porcine) or it can be made genetically. Chemically, beef insulin is closest to that of cats, but it doesn't necessarily follow that cats will always do best with bovine insulin.

For Susie, I used a brand called Caninsulin supplied by Intervet, which is a U-40 intermediate (Lente) insulin. It is a mixture of 2 pork based sources, 30% Regular (Semi-Lente) and 70% Long Acting (Ultra-Lente). As far as I am aware, Caninsulin is not currently available in the USA, although it is available throughout Europe and in Canada.

Purely for background, here's a bit on the chemistry of insulin. As a hormone, insulin is made up of a series of amino acids arranged together in a chain. In all sources of insulin, most of the structure of the chain is identical, but there are a few small differences at specific points along the chain. As mentioned above, beef insulin is the closest to that of cats. This is because it differs by only 1 amino acid (i.e. only one point on the chain is different). Pork insulin differs by 3 amino acids and human insulin by 4 amino acids. If you'd still like to know more, there is a page on the Pets with Diabetes site that illustrates the amino acid sequence of insulin. Beef insulin is illustrated with a table summarising the differences for pork, cat, dog and human insulin.

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Important note: All information and opinion in the Susie, Diabetic Cat pages is from personal experience. Nothing in these pages is intended to be a substitute for proper professional advice, which should always be sought from a qualified veterinary surgeon.

This page was last updated
May 2006