Insulin types used in type 1 diabetes

Rapid-acting insulin analog (e.g. aspart, lispro, glulisine) starts working within 5-15 minutes after injection, reaches maximum effect in 1-2 hours and lasts 4-5 hours [1]. You use it to cover meals and to correct high blood glucose. Long-acting or basal insulin analog (e.g. degludec, glargine) starts working in 1-2 hours and maintains a constant insulin level in the blood throughout the day [2].

Rapid insulin tries to mimic the pancreas's response to a meal, while long-acting insulin replaces the continuous insulin production that your pancreas releases as an antidote to the sugar coming from the liver [1]. You need both types of insulin for good control. Long-acting insulin helps you between meals and at night, while rapid insulin manages the blood glucose rises when you eat.

For meals you use rapid-acting or ultra-rapid insulin analog. These start working in 5-15 minutes (ultra-rapid 2-4 minutes earlier), so you take them before the meal, and if your blood glucose is good you can start eating fairly soon [3]. The mealtime dose depends on how many carbohydrates you are going to eat and on your insulin-to-carb ratio.

Never use long-acting insulin for meals because it does not act fast enough and cannot manage the rapid rise in blood glucose after a meal [1]. If you use regular human insulin (unlikely these days), you need to know that it starts working in 30 minutes, so it must be taken at least 30 minutes before the meal.

Basal insulin is the long-acting insulin that keeps your blood glucose stable in the absence of meals. You can think of it as an antidote to the sugar made by the liver. It is taken once a day, usually at approximately the same time [4]. It accounts for about 50% of your total daily insulin requirement. This percentage can vary greatly, however, depending on your individual particularities.

The time of day at which it is taken is generally not very important. Most often, basal insulin is taken in the evening, for convenience. Sometimes it is taken in the morning; the idea is that if the duration of action is at the limit of 24 hours, a lower risk of hypoglycemia can be achieved in the early-morning hours, on the tail end of the insulin's action [2]. It is very important to keep taking your basal insulin even when you are not eating anything. The sugar from the liver keeps coming regardless, and an antidote for it is absolutely necessary.

Yes, although all rapid insulins or all long-acting ones have similar actions, there are subtle differences between the various types of insulin within the same category [3]. The ultra-rapid analogs (lispro-aabc and fiasp) come into action faster and have a peak of action approximately 25 minutes earlier compared with the classic rapid analogs (lispro, aspart, glulisine). Among long-acting insulins, degludec and glargine U300 have a flatter action profile and consequently a lower risk of nocturnal hypoglycemia compared with glargine U100 [2].

Individual differences matter too. Some people absorb a particular brand better or have fewer adverse reactions at the injection site. If you change brands, monitor your blood glucose carefully in the first few days because you may need small dose adjustments, even if you keep the same insulin category. Prices and availability in pharmacies may also vary between different insulin brands.

Insulin analogs are genetically modified versions of human insulin, created to have new properties [5]. The human insulin molecule is modified by changing some amino acids, which makes the insulin act either faster (rapid analogs) or slower (long-acting analogs). These modifications do not affect the overall ability to lower blood glucose, only the onset, peak and duration of action.

All modern insulins are analogs. The advantages over human insulin include more predictable action, a lower risk of hypoglycemia and greater flexibility in meal timing [6]. Analogs are more expensive than human insulin, but they are generally reimbursed at least partially, if not fully, for people with type 1 diabetes.

Human insulin has exactly the same structure as the insulin naturally produced by the pancreas, being manufactured through genetic engineering using bacteria or yeasts [6]. Regular human insulin acts more slowly than the rapid analogs. Its effect starts in 30 minutes, has a peak at three hours and lasts six hours. NPH (intermediate) human insulin has a peak of action at 4-8 hours and lasts 12-16 hours. NPH insulin is gradually being withdrawn from everyday practice, being replaced by the long-acting analogs. It should already no longer exist in most countries.

Insulin analogs have slightly modified molecules, a more predictable absorption and a lower risk of hypoglycemia [7]. If you use human insulin you have to be more careful (rigid) with your meal schedule and snacks are mandatory. Analogs offer much more flexibility with meals. Still, human insulin is not all that bad. It works reasonably well when given subcutaneously, is very useful for intravenous administration (e.g. ketoacidosis) and is cheaper.

The choice depends on your lifestyle, your meal schedule, your physical activity and your individual response [4]. Children and adolescents benefit most from analogs because of the unpredictability of their meals and activities. The current standard is to combine the slowest possible analog in the evening with the fastest possible one at meals.

Talk with your diabetologist about the options you have and be prepared for a trial period. The absorption speed at your injection sites, a tendency toward nocturnal hypoglycemia or the dawn phenomenon sometimes influence the choice [8]. There is no universally "best" insulin. The right one for you is the one that gives you the best control with the fewest hypoglycemias.

Ultra-rapid insulin (fiasp, lispro-aabc) is an improved version of the rapid analogs that appears in the circulation in just 4-5 minutes and starts working approximately 5 minutes earlier compared with the classic analogs [3]. In fact it contains roughly the same insulin, but with "additives" that accelerate absorption. Sometimes you can give this type of insulin when you start eating or up to 20 minutes after the start of the meal (best avoided), thus offering greater flexibility.

It is particularly useful for meals with simple carbohydrates that raise blood glucose quickly, for correcting hyperglycemia or when you do not know exactly how much you will eat [8]. Ultra-rapid analogs are ideal for use in insulin pumps, where the rapid response improves postprandial control.

Yes, you can change the insulin type, but the change must be made under medical supervision, with careful monitoring [9]. When you switch, for example, from glargine U100 to glargine U300, the insulin dose will generally increase in order to achieve the same effect. When moving from rapid analogs to ultra-rapid ones, the initial doses may be similar. Monitor your blood glucose more frequently (7-10 tests/day or a glucose sensor) during the first two weeks after such a change.

Note any differences in glycemic control or possible adverse reactions. Changing the basal insulin generally requires more attention because it particularly affects overnight blood glucose [4]. Keep a detailed diary and communicate frequently with your doctor.

There is no single "best" insulin for everyone [4]. The optimal choice depends on your individual needs, your lifestyle and your body's response. For most people with type 1 diabetes, the combination of modern analogs (ultra-rapid + long-acting basal) offers the best glycemic control and quality of life [8].

What matters most is how you use the insulin you have chosen. You need correct timing at meals, precise dose selection and frequent adjustments. A well-educated person can achieve excellent control even with regular human insulin. That same person, however, would do even better with modern treatment. The best insulin for you is the one that lets you reach your glycemic targets with the minimum of hypoglycemias and the maximum of flexibility in daily life.

No, insulin cannot be given orally, in pill form, because it is a protein that is destroyed by the digestive juices in the stomach and intestine [10]. There have been many attempts to create oral insulin, but protecting the molecule and achieving predictable absorption remain major challenges. Research continues with special formulations and various encapsulation technologies.

Any diabetes pills you see other patients taking are for type 2 diabetes and cannot contain insulin. Pills are medications that either stimulate the pancreas to produce more insulin (impossible in type 1) or improve insulin sensitivity. For type 1 diabetes, the only current options, generally available everywhere, are subcutaneous injections or insulin pumps. Inhaled insulin exists in the USA, but not yet in Europe [11].