Insulin is an anabolic peptide hormone that is produced and secreted from β cells located in the islets of Langerhans of the pancreas. By modulating glucose absorption from the blood, insulin lowers blood glucose levels. Further important metabolic functions of insulin include the promotion of carbohydrate, amino acid, and fat storage in the liver, skeletal muscle, and adipose tissues. There are several insulin analogs (e.g., insulin glargine) with a different molecular structure but similar properties to human insulin, with differences mainly in the onset, peak, and duration of action. Insulin therapy is an important part of treatment for individuals with no or insufficient insulin production (e.g., diabetes mellitus, gestational diabetes). It is crucial that patients receiving insulin therapy undergo in-depth training to prevent potentially life-threatening conditions such as hypoglycemia as a result of an insulin overdose or drug interactions.
See also “and “ .”
|Overview of the different types of insulin|
|Types of insulin||Pharmacokinetics ||Application ||Additional considerations |
|Insulin lispro|| || || |
|Regular insulin|| || |
|NPH insulin|| || |
|Insulin glargine|| || || |
|Mixed insulin|| |
Rapid-acting insulins are your favorite GAL pals (Glulisine, Aspart, Lispro).
Synthesis and regulation
- Stages of insulin synthesis
- Clinical relevance 
The secretion of insulin is chiefly regulated by the levels of serum blood glucose.
- lInsulin secretory pathway: GLUT2-mediated transfer of glucose into the pancreatic β cells → ↑ glucose metabolism → ↑ ATP production → closure of ATP-sensitive potassium channels → cell membrane depolarization → opening of voltage-gated calcium channels → ↑ intracellular calcium levels → ↑ insulin secretion
- Insulin release stimulants 
Insulin release inhibitors 
- α2 agonists
Oral glucose results in a greater increase in insulin levels than IV administration.
Insulin function and metabolic effects
- Insulin binds to insulin receptors (a type of ) located in various tissues in the body (e.g., liver, skeletal muscle, adipose tissue, cell membranes). 
- In target tissues, insulin acts as an anabolic hormone.
|Metabolic actions of insulin|
|Protein metabolism|| |
- Other physiologic actions of insulin
Cellular and insulin-mediated uptake of glucose
- Glucose may enter cells throughout the body via a variety of transporters.
- Different tissue types have unique glucose transporters (e.g., GLUT1, GLUT2, GLUT3, GLUT4, and GLUT5), some of which are insulin-dependent and some of which are insulin-independent.
- See “Important glucose transporters” in " .”
The absorption time determines the onset, peak, and duration of effect. 
- diabetes with secondary
- Acute : A drip containing regular insulin and a solution of glucose reduces blood potassium levels.
- See “Insulin therapy” in “ ” and “ .”
- Hypoglycemia 
- Weight gain 
- Lipodystrophy at the injection site 
- Allergic or hypersensitivity reactions
- Edema 
- Pain and erythema at the injection site
We list the most important adverse effects. The selection is not exhaustive.
Pharmacologic and drug interactions
Certain drugs can either increase or decrease insulin demand. 
- Increased insulin demand
- Decreased insulin demand
Either increased or decreased insulin demand
Basal-bolus insulin regimen 
- Calculate the total daily dose of insulin (TDD) needed.
- If the patient is already on a correction scale: Increase or decrease TDD by 10–20% as needed.
- If the patient is lean, has T1DM, is aged ≥ 70 years, and/or has GFR < 60 mL/min: 0.2–0.3 units/kg
- If none of the above criteria apply, use the blood glucose level:
- BG 140–200 mg/dL: 0.4 units/kg
- BG > 200 mg/dL: 0.5 units/kg
- Divide the TDD of insulin into basal insulin (50%) and nutritional insulin (50%).
- Basal insulin: administer as long-acting insulin (e.g., glargine) at bedtime
- Nutritional insulin: administer as rapid-acting insulin (e.g., lispro) in equally divided doses before meals
- Add sliding scale insulin as supplemental insulin.
- Take 5% of the TDD (e.g., if the TDD is 50 units, 5% is 2.5).
- Round down to the nearest whole number (e.g., round down 2.5 units to 2 units).
- For every 40 mg/dL above the goal serum glucose of 140 mg/dL, increase the nutritional insulin scale by the appropriate increments (see “Sliding scale insulin regimen” below).
- Adjust as needed.
Decrease or hold nutritional insulin if the patient is NPO.
Sliding-scale insulin regimen 
- If the patient is eating all or most of each meal: Administer as short-acting insulin (or rapid-acting insulin) before each meal and at bedtime.
- If the patient is not eating: Administer as short-acting insulin every 6 hours.
|Administration of sliding scale insulin|
|Blood glucose (mg/dL)||Insulin units|
|Insulin sensitive||Usual insulin||Insulin resistant|
If blood glucose is < 70 mg/dL, hold all insulin and administer measures to control hypoglycemia.
Weight-based NPH insulin regimen for glucocorticoid-induced hyperglycemia 
- Convert glucocorticoid to equivalent prednisone dose (see “ ”).
- Calculate daily NPH dose based on prednisone dose equivalent and patient weight.
- Administer glucocorticoid with NPH as a single dose in the morning.
NPH doses should be administered in addition to usual basal insulin in patients who are already receiving insulin.
Insulin regimens for enteral and parenteral nutrition
Enteral nutrition 
- Determine basal insulin needs.
- Add nutritional insulin.
- For patients receiving continuous tube feedings
- For patients receiving bolus feeding
- Add sliding scale insulin as supplemental insulin.
- Adjust as needed to glycemic targets, changes in medication, and changes in nutrition.
Patients with type 1 diabetes mellitus require basal insulin even if (enteral) feeding is discontinued.
Total parenteral nutrition (TPN) 
- Add short-acting insulin to IV parenteral nutrition solution.
- Diabetic patient: 1 unit per 10–15 g dextrose
- Nondiabetic patient: 0.5 units per 10 g dextrose
- Add sliding scale insulin as supplemental insulin: Administer as short-acting insulin (e.g., regular insulin) every 6 hours or rapid-acting insulin (e.g., lispro) every 4 hours.
- Adapt protocol to glycemic targets, changes in medication, and changes in nutrition.
- One-Minute Telegram 11-2020-1/3: Quality over quantity: once-weekly insulin
Interested in the newest medical research, distilled down to just one minute? Sign up for the One-Minute Telegram in “Tips and links” below.