Mixed insulins are a type of insulin mostly used to treat type 2 diabetes. They are a combination of both rapid acting and intermediate acting insulins. They can be a helpful tool to help treat diabetes especially for those patients who are prone to hyperglycaemia after meals.
In this guide I will tell you everything you need to know about mixed insulins.
What are mixed insulins work
Mixed insulins are a combination of two different types of insulin. The first part is rapid acting insulin which is to help absorb carbohydrates from your food and drink. The second type is an intermediate acting insulin which helps to stop your liver releasing too much glucose into the blood.
You can usually identify mixed insulins because they have a number in their name. Examples include:
- Humulin M3
- Humalog mix
- Novomix 30
- Novomix 50
- Insuman comb 25
- Insuman comb 50
The number in the name corresponds to the amount of rapid insulin in the mixture. For example, Humulin M3 and Novomix 30 means 30% rapid insulin whereas Insuman comb 50 means 50% rapid insulin.
Mixed insulin appear cloudy in appearance and need to be mixed together prior to injecting. This can be achieved with a gentle shake of the insulin pen prior to injecting.
Mixed insulins used to be the treatment for type 1 diabetes but, in modern times, have transitioned more into to type 2 diabetes care. This is because mixed insulins have been replaced with basal bolus regimens in type 1 diabetes care. A basal bolus regimen is a combination of rapid insulin with meals and one to two injections of long acting insulin per day. Check out our other guides on these topics for further info.
How do they work
As mixed insulins are a combination of two different types of insulin, I’d recommend reading my blogs on rapid acting insulin (found here) and intermediate acting insulin (found here).
As a summary though, rapid acting insulins last about 4.5 hours in your body. They are primarily taken to help absorb carbohydrates in your diet and prevent glucose spikes after meals. If patients are prone to high glucose levels after meals, it can be difficult to prevent this without some rapid acting insulin.
Taking rapid acting insulin as a mixed insulin is slightly different to taking rapid insulin on its own. Normally, patients taking rapid acting insulin use methods like carbohydrate counting to adjust their rapid acting insulin dose. This gives them flexibility to adjust their dose based on what they eat and what their glucose level is. However, with mixed insulins we do not have this luxury as any adjustment also effects the intermediate acting insulin component.
Intermediate acting insulins are more concerned with stopping the liver releasing too much glucose into the blood. Without these types of insulins, the liver can release far too much glucose into the blood stream. Intermediate acting insulins last 12-18 hours in your system before they are cleared. Mixed insulins, like intermediate acting insulins are usually administered 2 times per day.
Therefore, mixed insulins kill 2 birds with one stone. They offer the ability to prevent post meal glucose rises and stop your liver releasing too much glucose.
When are mixed insulins used
As mentioned, mixed insulins are used when patients obviously have a post meal glucose rise. Other types of insulins on their own can’t always manage dietary related glucose spikes. Long acting insulins are inflexible and too flat in their profile to deal with some post meal spikes. Intermediate acting insulins may also not be enough to prevent this on their own.
In these circumstances the temptation is to keep increasing your long or intermediate acting insulin. This creates a problem though. The increase may slightly help with the post meal glucose rise but when you increase these insulins, you increase the dose for its entire duration. Increasing a long acting insulin for example, increases the average dose across 24 hours. Therefore, I find this can lead to low glucose levels later in the day after the food has been digested.
Rapid insulin used with long acting insulin is the preferred choice in type 1 diabetes to manage post meal spikes. However, this can be difficult to manage in type 2 diabetes. This is because patients may require large doses of insulin in type 2 diabetes and thus calculating the correct insulin doses at meals can be tricky. Furthermore, rapid and long acting basal bolus insulin regimens are quite intensive from a daily management perspective and therefore mixed insulins are a good alternative.
Problems with mixed insulins
There is a catch with mixed insulins that need to be addressed. When you use either rapid acting or intermediate acting insulins by themselves you can adjust them accordingly.
However, with mixed insulins one cannot be adjusted without effecting the other. This can be problematic because if, for example, you have a specific problem with glucose levels after meals the temptation is to increase your mixed insulin. This increase helps to prevent the high glucose level after your meal but also increases the amount of intermediate acting insulin administered. This can then leave you prone to low glucose levels later.
Alternatively, if you want to adjust your intermediate acting insulin to prevent high or low glucose levels later in the day, it will also effect your rapid insulin meal time dose.
Eating with mixed insulins
You cannot take rapid insulin without eating or drinking some form of carbohydrates. Without eating carbohydrates with your insulin and throughout the day, you are at a high risk of having low glucose levels.
Increasing your mixed insulin to deal with high post meal glucose levels, leaves you prone to low glucose levels later. Therefore, you may need to eat extra carbohydrates throughout the day.
Increasing your mixed insulin for high glucose levels related to your liver e.g. overnight, then means, you might need to eat more carbohydrate at your meal.
As you can see then, with mixed insulins, often the diet needs to work for the insulin as opposed to the insulin working for your diet. This can create a scenario where you become locked into your eating habits and may need to eat more than you want to.
If this is the case, a change to different type of insulin should be discussed with your medical team.
How are intermediate acting insulins administered
All insulins are given by an injection. An insulin injection is different from the types of injections you might be thinking of though. Insulin needles are very thin. In fact, they are smaller than a hair follicle. Over the years these needles have become smaller and smaller and now are only 4mm long. If you’re using a longer needle than this, it might be worth speaking with your medical team.
One difference with mixed insulins is the need to gently mix the insulin together prior to injecting it. This can be done with an easy rotation of your wrist whilst holding the insulin. I have written a blog all about injection technique which you can find here.
If you need more information on injecting here’s a guide to how to do it or watch it here.
How many times a day do I take it
A benefit of mixed insulins is they can be given either once or twice per day. This will be dictated by what your glucose levels are doing.
A high glucose level throughout the day and particularly after breakfast might mean taking a dose at breakfast. A high glucose level after your evening meal or in the morning, might mean taking a dose with your evening meal.
How much insulin do I need
Unlike the other insulins, mixed insulins are unique in regards to how much you might need. The rapid insulin element will depend on your diet and what you are eating. If you have a large fish and chips meal you will need more rapid insulin than if you just had a sandwich.
Conversely, your intermediate acting dose will be dependent on how much glucose your liver releases and how sensitive you are to insulin overall.
Unfortunately, you can’t just adjust one type of these insulins at a time because they are mixed. Therefore, getting a fairly steady diet with a similar carbohydrate intake at each meal is a good idea.
How often do I need to test my blood glucose levels
Usually you will only need to test your glucose levels twice per day if you are taking a mixed insulin. The first test is usually first thing in the morning. If you are taking 2 injections per day, this morning test tells you how well your dose the previous night has controlled your glucose levels.
The second glucose test is usually before your evening meal. This helps us understand how well your morning insulin dose has controlled your glucose levels.
How do I know if my dose is correct
We work backwards when assessing whether an insulin dose is correct. Therefore, your morning glucose reading is effected by your evening insulin dose.
If your glucose levels are low or high before your evening meal, it means you should adjust your morning insulins dose.
It is usually recommended to adjust your insulin by 10% if increasing the dose or 20% if reducing the dose. Alternatively, speak with your diabetes team who can advice you about how to adjust your dose.
If making dose adjustments, it tends to be good practice to gather a few readings first to establish a pattern. However, if you have hypos, it might be safer to adjust the next insulin dose and then gradually increase the dose again if the insulin reduction turns out to be too much.
Sometimes it can be good practice to add in additional tests to asses how well the rapid acting element of the insulin is working. Taking a lunch time and before bed glucose test will help show you whether the rapid acting element of the mixed insulin is appropriate. This is because the rapid insulin lasts about 4.5 hours which is about the same time between breakfast and lunch and dinner and bed. If your glucose levels are frequently low or high you might need to adjust your insulin. Remember though, adjusting for one insulin will also adjust the other type of insulin.
How often should I adjust my dose
Mixed insulins can be adjusted day to day as they only last a maximum of 18 hours in your body. It’s good practice to find a routine with them and try to stick with this going forwards.
What if my blood glucose levels drop too low
I have written a complete guide on this, which you can find here.
As mixed insulins have a rapid acting component to them, they make hypoglycaemia more likely. If you experience any of the symptoms discussed in my hypoglycaemia post, make sure you text your glucose levels and take appropriate action.
As you can see mixed insulins have many pros but also some cons. On the positive side, they help patients manage both dietary and liver related glucose spikes. On the flip side, you cannot adjust one without effecting the other.
Often patients need to eat regularly with these types of insulins. This can make it quite difficult to change your lifestyle or vary your diet.
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