What is insulin?

Updated: Oct 04, 2017
  • Author: Mini A Mathew, DO, PharmD; Chief Editor: George T Griffing, MD  more...
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Insulin is the cornerstone of therapy in the management of type 1 diabetes. Insulin therapy also has a clear role in type 2 diabetes mellitus in patients with long-standing or poorly controlled disease.

Since the discovery of insulin approximately 80 years ago, insulin therapy has undergone various changes in formulations with different pharmacokinetics. In the 1930s, protamine zinc insulin, the first long-acting preparation, was introduced. In the 1950s, the neutral protamine hagedorn (NPH) and insulin zinc (lente) were introduced. [1] Newer formulations have since been developed, allowing insulin to be provided in more physiologically appropriate ways. These provide more flexibility in dosing, mimic endogenous production of insulin, and lower the incidence of nocturnal hypoglycemia. [2, 3, 4]

When used as monotherapy, oral hypoglycemic drugs generally lower glycated hemoglobin (HgbA1C) by only 0.5%-1.5%. Most patients with type 2 diabetes eventually require multidrug therapy or insulin. Some guidelines encourage early use of insulin if HgbA1C remains poorly controlled on maximal-dose, single-drug therapy. Insulins have varying pharmacokinetics that allow for specific products from which to choose. Table 1 provides a comparison between insulins for onset of action and duration of action. Table 2 provides a list of combination insulin products.

Table 1. Insulin Pharmacokinetics (Open Table in a new window)



Onset of Action

Duration of Action

Insulin aspart (NovoLog)


5-15 minutes

3-5 hours

Insulin aspart (Fiasp) Rapid-acting 16-20 minutes 5-7 hours

Insulin lispro (Humalog)


5-15 minutes

4-5 hours

Insulin glulisine (Apidra)


5-15 minutes

3-4 hours

insulin regular (Humulin R, Novolin R)


30-60 minutes

8-10 hours

Insulin NPH (Humulin N, Novolin N)


2-4 hours

12-18 hours

Insulin detemir (Levemir)

Intermediate-to-long acting

3-4 hours

6-23 hours (dose dependent)

Insulin glargine (Lantus)


3-4 hours

>24 hours (range, 11-32 hours)

Table 2. Insulin Combination Products (Open Table in a new window)

Insulin Combination

Brand Name

Insulin aspart protamine/insulin aspart

NovoLog Mix 50/50

NovoLog Mix 70/30

Insulin lispro protamine/insulin lispro

Humalog Mix 50/50

Humalog Mix 75/25

Insulin NPH/insulin regular

Humulin 70/30

Novolin 70/30

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