Insulin Types: Onset, Peak and Duration

What it is

Insulin moves glucose into cells and lowers blood glucose; insulin products differ mainly in onset, peak and duration of action. Basal insulin (long-acting, or intermediate-acting NPH) controls glucose between meals and overnight, while bolus insulin (rapid- or short-acting) covers meals and corrects high readings. Hypoglycemia is most likely at the peak of action, so the nurse times meals, glucose checks and teaching to each product's profile.

What the NCLEX focuses on

• Rapid-acting insulin (lispro, aspart, glulisine) is given within 15 minutes before a meal; confirm the meal tray is available first.
• Regular insulin is given about 30 minutes before a meal and is the insulin used for IV infusions, such as in DKA.
• NPH is cloudy: roll the vial or pen gently and never shake it; a morning dose peaks in the afternoon, the time of highest hypoglycemia risk.
• Mixing regular and NPH: inject air into NPH, then into regular, withdraw regular (clear) first, then NPH (cloudy).
• Long-acting insulin (glargine, detemir) is given at the same time daily, has no pronounced peak and is never mixed with another insulin.
• Absorption is fastest in the abdomen; rotate sites within one area, and exercising the injected limb speeds absorption.
• Storage: unopened insulin in the refrigerator; the vial or pen in use at room temperature for the labeled number of days, often 28; never use insulin that was frozen or overheated.

Priority nursing actions

1. Check the blood glucose and confirm the client will eat (tray available, not NPO, no vomiting).
2. Verify the insulin type, dose, route and timing; insulin is a high-alert medication, so follow the facility's independent double-check policy.
3. Give rapid-acting insulin within 15 minutes before the meal and basal insulin at the same time each day.
4. Monitor for hypoglycemia during the expected peak of each insulin.
5. Clarify mealtime insulin with the provider when the client is NPO or vomiting, and do not omit basal insulin without a prescription.

Numbers to know

Common exam traps

• Choosing to draw glargine and lispro into one syringe: wrong because glargine is never mixed; give separate injections.
• Choosing to give rapid-acting insulin before the meal tray arrives: wrong because the client becomes hypoglycemic if the meal is delayed.
• Choosing to shake NPH to mix it: wrong because shaking creates bubbles and inaccurate doses; roll it gently.
• Choosing an extra dose of glargine to correct a high pre-lunch glucose: wrong because basal insulin is not a correction insulin; give the prescribed rapid-acting correction dose.
• Choosing NPH or glargine for an IV infusion: wrong because regular insulin is the insulin used IV.

What to teach

• Know when your insulin peaks, keep food on hand then, and eat within 15 minutes of rapid-acting insulin.
• Rotate injection sites within one area and check for lumpy, thickened skin, which slows absorption.
• Keep unopened insulin refrigerated; discard in-use insulin after the labeled number of days, or if it was frozen, overheated, or a clear insulin looks cloudy.
• Never share insulin pens, even with a new needle.

Client handout: Using Insulin at Home (nurse guide and printable patient handout).

Sources

• Harding MM, Kwong J, Hagler D, Reinisch C. Lewis's Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 12th ed. Elsevier; 2023; Chapter: Diabetes.
• American Diabetes Association Professional Practice Committee. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes-2025. Diabetes Care. 2025;48(Suppl 1):S181-S206.