Intermediate acting insulins – Insulatard & Humulin I

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Intermediate acting insulins are a type of insulin used to manage high glucose levels, usually as a result of diabetes.

Historically, patients with type 1 diabetes would use intermediate acting insulins as their long acting insulin until newer insulins came to market in the late 90s. Patients began shifting to longer duration insulins that provided longer insulin coverage. As a result, intermediate acting insulins found more of a home in managing type 2 diabetes.

There are lots of different types of intermediate acting insulins but most are pretty comparable.

This article is to explain everything you need to know about rapid acting insulins so you can become the expert.

What are intermediate acting insulins

Intermediate acting insulins last in your body for approximately 12-18 hours but this half life will vary from person to person. Hence the name intermediate acting insulin. You may have also heard them called isophane insulins or NPH (Neutral Protamine Hagedorn) insulins.

In the service I work in we tend to assume they last about 12 hours even though we may get a slightly longer effect.

In type 2 diabetes, they still remain a popular option because they can help to contend with the insulin resistance these patients exhibit.

Examples include:

  • Insulatard
  • Humulin I
  • Hypurine Isophane

The clue to know you have an intermediate acting insulin is to check if one of the words in the name starts with an ‘I’.

How do they work

Your liver releases glucose into your blood stream to provide you with an internal source of glucose. In diabetes, this process is negatively effected. As a result, too much glucose exits the liver causing high glucose levels. Intermediate acting insulins help stop your liver releasing too much glucose into your blood but they can also help with the absorption of food.

As mentioned, intermediate acting insulins hang around in the body for about 12-18 hours. These tend to hit the blood stream after 2 hours and have a peak of insulin release around 4-12 hours after injecting.

This peak on the insulin profile is one reason intermediate acting insulins are no longer the preferred choice in managing type 1 diabetes. Insulins with high peaks mean the release of the insulin is inconsistent throughout the day. Therefore, you may have more insulin entering your system at one time compared to another. This then effects your other rapid insulin injections and can cause more erratic glucose levels and increase the risk of hypo’s. Newer background insulins have flatter profiles and are therefore more consistent in their release into the body. The image below demonstrates this.

Insulin profiles
Comparison of how insulins act in the body. The higher the peak, the more insulin your have in your system at any one time.

Furthermore, newer background insulins generally provide 24 hours or more of insulin coverage. This makes sure you are safe and not missing any insulin coverage throughout the day.

Intermediate acting insulins on the other hand only provide 12-18 hours of coverage. Therefore, it is much easier to have gaps in your insulin coverage throughout the day.

When are intermediate acting insulins used

They are still common in type 2 diabetes. This is because people with type 2 diabetes suffer with insulins resistance and are therefore prone to needing more insulin. People with type 2 diabetes are also prone to having high glucose levels after eating as their body struggles to deal with the carbohydrates entering their blood stream.

They are also frequently used in gestational diabetes. This is because they are proven safe to use and provide flexibility to control glucose spikes. This is particularly true in the morning due to hormone rises causing increased insulin resistance.

Therefore, intermediate acting insulins provide a nice peak of release during the times glucose levels are prone to going high e.g. the post absorptive phase of eating.

People with type 2 diabetes also still produce their own insulin. It just doesn’t work as well as it once did. This makes people with type 2 diabetes a low risk of going into diabetic keto acidosis. As a result, people with type 2 diabetes might only take intermediate acting insulins once a day but it is common to take them twice a day.

Patients with glucose spikes in the morning might need to take insulin before their evening meal or bed. These glucose spikes can happen for multiple reasons. Hormones designed to get you up in the morning can cause higher glucose levels in people with diabetes. Cortisol and growth hormone can make your glucose levels rise during the morning and therefore a dose of an intermediate acting insulin dose before bed can help prevent this. This is quite common in gestational diabetes. Also your liver may simply release too much glucose overnight and therefore some insulin is needed to deal with this.

Enteral nutrition

Intermediate acting insulins can be used to help with glucose spikes caused by articifical nutrition. These are used to feed sick patients who cannot eat. These are called enteral or parenteral nutrition but are often called ‘feeds’ for short.

Enteral nutrition is a liquid form of artificial nutrition often administered via a tube inserted via the nose into the stomach or gastrointestinal tract. Parenteral nutrition is a pharmacological form of nutrition administered via the veins when a patient has an injured or non functioning bowel.

These feeds can vary in the amount of calories, carbohydrate, protein and fat content and importantly vary in their duration. For feeds lasting 12-16 hours and 20 hours+ intermediate acting insulins can be very useful to help manage high glucose levels caused by the feed. The insulin profile matches the duration of the feed and therefore helps with the absorption of the nutrition.


Steroids increase peoples insulin resistance which can leave them prone to high glucose levels. Depending on the person and amount of steroids, the glucose response can vary.

It can take some time for glucose levels to rise after administering steroids. For example, if you take steroids at breakfast, the effect isn’t usually seen until around the evening meal.

Rather than waiting for the glucose level to go high and then trying to correct this later, the diabetes team might recommend an intermediate acting insulin. Usually, the insulin is administered at the same time as the steroids so both work together. This can be useful because it helps to prevent high glucose level occurring in the first place. Therefore, prevention is the best cure for high glucose levels in this situation.

Intermediate acting insulins are good for this effect because the steroid effect tends to wear off around 12 hours after the last dose. Therefore, intermediate acting insulins help match the steroid glucose raising effect without then effecting the period after the steroids have worn off.

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.

Intermediate acting insulins also need a gentle shakes to help the insulin mix. This can be achieved by gently rotating your wrist whilst holding the pen.

If you need more information on injecting here’s a guide to how to do it or watch this YouTube video.

How many times a day do I take it

Another benefit of intermediate acting insulins is their flexibility. Background insulins last for 24 hours and therefore cannot be adjusted once administered. This makes it impossible to adjust this insulin for only certain periods of the day. Whereas, intermediate acting insulins are more flexible due to their shorter duration.

This means you could take more insulin when it is needed. For example, taking more insulin to help with food or with a feed but then give a smaller dose when you are at a higher risk of a low blood glucose level (e.g. overnight or when you are off feed).

Therefore, intermediate acting insulins are usually administered once or twice per day. In type 1 diabetes they should always be used twice per day.

How much insulin do I need

The dose varies depending on how sensitive you are to your insulin and what other clinical circumstances are at hand. Your dose may also change from time to time depending on what is happening with your health and diet. Ultimately, you need what you need.

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 an intermediate acting 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.

How often should I adjust my dose

Intermediate acting insulins can be adjusted every day. Some insulins take a couple of days to reach a steady state but intermediate acting insulins are out of your system after 12-18hours.

What if my blood glucose levels drop too low

I have written a complete guide on this, which you can find here.


I think that’s about all the information we have to offer regarding intermediate acting insulins. Hopefully you found this useful. Remember to join the Facebook group and/or subscribe to the blog. If you want more help lowering your HbA1c, getting fit, preventing erratic glucose levels or losing weight, check out our consultancy services and programme pages.

Need more help

If you need more support we offer a range of 1:1 consultancy services and online programmes focused on helping you improve your glucose control and health for the long term. These include our type 2 diabetes recovery programme, type 1 glucose stability programme and winning weight loss programme. Go to the pages using the links above or in the headers or get in touch if you have questions.