Types of Insulin–Rapid, Short, Intermediate and long acting insulin.

Insulin is the final choice of therapy for a type 2 diabetic patients. Usually, a type two diabetic patient is shifted to insulin therapy when oral hypoglycemic drugs fail to control the Diabetes.
There are various types of insulin that can be used. Each type has its own time on the onset of action, the Peak time of action and duration of action. These types are named after, onset and duration of action. According to this, insulin has the following 4 types.

1. Rapid-acting Insulin
2. Short-acting insulin
3. Intermediate-acting insulin
4. Long-acting insulin

There is a 5th type of insulin which is called “Premixed insulin”. In this type a short acting and intermediate acting insulin is mixed in different proportion (eg. 70:30, 50:50, 75:25). Usually Regular insulin and NPH are mixed.

1. Rapid-acting insulin.

This is called rapid acting because it’s action starts within 10-30 minutes of injection. Insulin lispro, aspart and glulisine are included in this category. Their peak action starts within 30-90 minutes of injection. The duration of action for lispro and aspart is 3-5 hours, and that of glulisine is 2- 2 ^1/2 hour.  Insulin aspart action reaches its peak in the shortest duration (30-50 minutes).
When should rapid-acting insulin be administered?
A rapid-acting insulin is injected at the same time when the meal is taken. Rapid-acting insulin usually used in combination with long-acting insulin.

2. Short-acting insulin.

Regular insulin (Humulin) is a short-acting insulin. It’s onset, peak and duration of action are longer than rapid-acting insulin. It’s action starts within 30 minutes to one hour of injection. It action reaches its peak in 2-5 hours and its duration of action is 5-8 hours. Velosulin which is used in insulin pumps is also short-acting insulin. Its duration of action 2-3 hours which lesser than regular insulin.
When should short-acting insulin be injected?
Short-acting insulin should be injected 30-60 minutes before a meal. It is usually combined with intermediate-acting insulin, unlike that of rapid-acting insulin, which is usually combined with long-acting insulin. It is also used to control hyperglycemia in an emergency situation.

3. Intermediate-acting insulin.

NPH is intermediate-acting insulin. Its action starts within 1-2 hours, reaches its peak in 4-12 hours and its duration of action lasts for 18-24 hours. Intermediate-acting insulin can control the sugar for half a day (12 hours). So it is given in two doses (morning and evening). It is usually given in combination with short-acting insulin, which covers the transient hyperglycemia, that is induced by meal.

4. Long-acting insulin.

Long-acting insulin is enough for the whole day. Insulin glargine and Levemir are included in this category. These are also used in combination with rapid or short-acting insulin to control the hyperglycemia that occurs after taking a meal.

5. Mixed insulin.

Mixed insulin is usually a combination of intermediate-acting (NPH) and short-acting (Regular insulin). It is given in 2 or 3 divided doses to control the sugar level for the whole day. For example 15 units in the morning and 10 units in the evening or 10 units in the morning, 10 in the noon and 10 in the evening.