Michelle Carrihill educates us on how to use various insulins with their unique actions to meet the desired requirements.
There is no ‘easy-peasy’
As a student, I remember being taught that the only thing wrong with a Type 1 diabetic is that they are deficient in insulin. So, the treatment is simple – replace the insulin, and all is returned to normal. Easy-peasy.
Except it is not. Each person is an individual. Each person has variable insulin requirements, and these may change minute-to-minute, hour-to-hour, day-to-day, week-to-week, and especially year-to-year as the body grows and changes.
Very few people have predictable, regular lives. Nevermind predictable regular metabolic rates. Add the variability that is introduced with different amounts and types of carbohydrates, plus protein and the altered absorption with fat in a meal; throw in exercise, emotions and stress, and it might feel almost impossible to exactly figure out which insulin and how much of it should be given at any one time.
Another factor is that each individual may respond slightly differently to a brand or type of insulin, and that the individual’s response may not be the same at each injection.
Also, unlike the insulin produced naturally, once insulin is injected in the body, it cannot be switched off. Once it is in the body, it will continue working, whether needed or not!
Individualise insulin treatment
The most important thing is to individualise the insulin treatment regimen to best fit the individual’s needs. Obviously, the available insulins, the budget and the willingness of the diabetic (or their carer) to test sugar levels and adjust doses are important to take into consideration when designing insulin replacement therapy.
To understand this, let’s look at the available insulins, and their action times. This information is provided by each of the manufacturers.
Type of Insulin & Brand Names |
Onset |
Peak |
Duration |
Role in Blood Sugar Management |
Rapid-Acting |
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| Lispro (Humalog) | 15-30 min. | 30-90 min | 3-5 hours | Rapid-acting insulin covers insulin needs for meals eaten at the same time as the injection. |
| Aspart (Novorapid) | 10-20 min. | 40-50 min. | 3-5 hours | |
| Glulisine (Apidra) | 20-30 min. | 30-90 min. | 1-2 1/2 hours | |
Short-Acting |
||||
| Regular (R)
Actrapid Biosulin R Humulin R Insumam R |
30 min. -1 hour | 2-5 hours | 5-8 hours | Short-acting insulin covers insulin needs for meals eaten within 30-60 minutes |
Intermediate-Acting |
||||
| NPH (N)
Biosulin N Humulin N Insumam N Protophane |
1-2 hours |
4-12 hours |
18-24 hours | Intermediate-acting insulin covers insulin needs for about half the day or overnight. |
Long-Acting |
||||
| Insulin glargine (Basaglar, Lantus, Toujeo, Optisulin) | 1-1 1/2 hours | No peak time. Insulin is delivered at a steady level. | 20-24 hours | Long-acting insulin covers insulin needs for up to one full day. |
| Insulin detemir (Levemir) | 1-2 hours | 6-8 hours | Up to 24 hours | |
| Insulin degludec (Tresiba) | 30-90 min. | No peak time | 42 hours | |
Pre-Mixed* |
||||
| Humulin 30/70
Actraphane |
30 min. | 2-4 hours | 14-24 hours | These products are generally taken twice a day before main meals. |
| NovoMix 30 | 10-20 min. | 1-4 hours | Up to 24 hours | |
| Humalog mix 25 | 15 min. | 30 min.-2 1/2 hours | 16-20 hours | |
| *Premixed insulins combine specific amounts of intermediate-acting and short-acting insulin in one bottle or insulin pen. (The numbers following the brand name indicate the percentage of each type of insulin.) | ||||
If you combine these insulin profiles, and superimpose them over what the individual’s insulin requirements are, you then get to understand when the insulin will be working for them, and which combination will suit their needs. These needs may vary from time-to-time and over time, so it is important they monitor their sugars, either with finger-prick tests, or if viable, a continuous glucose monitor.
Let’s look at some regimens:
Twice a day insulin
| Benefits: | Disadvantages: |
| Easiest regimen | Must be given 30 minutes before the meals. |
| Only two injections a day | Midmorning snack required. |
| Lunch carbohydrates may not be adequately covered. | |
| No flexibility in meal component of the insulin (if using a premixed insulin combination). | |
| The intermediate-acting insulin given before an early dinner may mean inadequate basal cover by the early morning – a risk of waking up with a high fasting sugar, and some ketosis. |
Three times a day insulin
| Benefits: | Disadvantages: |
| Covers overnight requirements better by the later injection of the intermediate insulin, decreasing the chance of morning high levels. | Regular insulin must be given 30 minutes before the meals. |
| Midmorning snack required. | |
| Lunch carbohydrates may not be adequately covered. | |
| Requires a bedtime snack. |
Basal bolus regimen
| Benefits: | Disadvantages: |
| Flexible dosing for carbohydrates and correcting. | In-between meal carbohydrates need to be counted and dosed for. Or carbohydrate free snacks considered. |
| More frequent injections (and testing) required. | |
| More expensive. |
Long-acting insulin analogues
| Benefits: | Disadvantages: |
| Flexible dosage for carbohydrates and correcting. | ‘In-between’ meal carbohydrates need to be counted and dosed for. Or carbohydrate free snacks considered. |
| Fasting is possible. | More frequent injections (and testing) required. |
| Flexibility in the timing of the meals/snacks. | Much more expensive. |
| Less risk of nocturnal hypoglycaemia. | |
| No need for night time snack. |
Continuous sc insulin infusion
| Benefits: | Disadvantages: |
| Built in calculator for carbohydrate counting and corrections. | Only rapid insulin is used, so any disruption in delivery can rapidly lead to ketoacidosis. |
| Insulin can be suspended. | Very expensive. |
| Basal rates can be individually set. | Needs high quality training and ongoing interaction. |
| Dawn phenomenon can be covered. | Permanently attached to a device. |
| Fasting easy to achieve. | |
| Temporary increase or decrease in basal requirements easy to achieve. |
Mix and match
Mixing and matching of insulins is also possible. For example, a child attending primary school might do well on regular and intermediate-acting insulins half an hour before breakfast, without requiring any insulin for their school break; a rapid insulin analogue for after-school lunch and dinner; and then a long-acting basal analogue for their basal insulin overnight.
As mentioned already, monitoring the blood glucose then opens the eyes to the effect of the insulin doses – both for the individual dose, as well as for the pattern of dosing. Fasting sugars reflect the long-acting doses and post-meal levels reflect the bolused doses for carbohydrates and corrections.
Carbohydrate counting affords the closest-to-physiology use of mealtime insulin, and is to be encouraged. Even if using a fixed-dose insulin regimen, knowing how much carbohydrate is in a meal allows for consistency of insulin to carbohydrate dosing – which then helps prevent sugar variability after meals.
Monitoring sugar levels before and after activities and sports helps with planning of extra carbohydrates or a change in insulin dose for the meal before or after the exercise.
The message is that getting sugars to target is possible by knowing what the individual needs, and using the available insulins to suit those needs. Monitoring sugars and adjusting doses and types of insulin along the way will keep the person with diabetes healthy, and able to get on with living their lives.
MEET OUR EXPERT
Dr Michelle Carrihill is a paediatric endocrinologist working with children and adolescents with diabetes and chronic endocrine and metabolic conditions. She runs the adolescent sub-speciality ward at Groote Schuur Hospital and has a large ambulatory service for the chronic medical needs of these patients.