Insulin
Key Points
- Insulin is a pancreatic hormone (released by beta cells) that facilitates cellular glucose uptake — essential for Type 1 DM; used when oral agents fail in Type 2 DM
- Four main types: rapid-acting, short-acting (regular), intermediate-acting (NPH), and long-acting — differ in onset, peak, and duration
- Hypoglycemia is the primary adverse effect — risk is highest at the peak time for each insulin type
- NPH is the only cloudy insulin — all others are clear; mixing insulins requires clear before cloudy
- ISMP High-Alert Medication — requires independent double-checks; use only insulin syringes for administration
- Insulin must bypass oral digestion (unstable in gastric acid) → subcutaneous injection only (except IV regular insulin in critical care)
- In diabetes-affected pregnancy, insulin is commonly preferred over noninsulin agents when lifestyle therapy is insufficient.
Types of Insulin
| Type | Examples | Onset | Peak | Duration | Clinical Use |
|---|---|---|---|---|---|
| Rapid-acting | Aspart (Novolog), Lispro (Humalog), Glulisine (Apidra) | 15–30 min | 1–2 hr | 2–4 hr | Give 15 min before or immediately after meals |
| Short-acting (Regular) | Humulin R, Novolin R | 30 min–1 hr | 2–3 hr | 3–6 hr | Give 30–60 min before meals; also used IV in critical care |
| Intermediate-acting | NPH (Humulin N, Novolin N) | 2–4 hr | 4–12 hr | 12–18 hr | Cloudy — covers overnight or 12 hours; often combined with rapid/short-acting |
| Long-acting | Glargine (Lantus), Detemir (Levemir), Degludec (Tresiba) | 1–2 hr | No peak | Up to 24 hr | Once-daily basal coverage; do NOT mix with other insulins |
NPH is the Only Cloudy Insulin
All other insulins are clear. When mixing insulins in one syringe: draw up clear (rapid/short) before cloudy (NPH). Never mix long-acting insulin (glargine, detemir) with any other insulin.
Mechanism of Action
Insulin is secreted by beta cells of the pancreatic islets of Langerhans in response to rising blood glucose levels. Exogenous insulin replaces or supplements endogenous insulin:
- Facilitates glucose uptake into skeletal muscle and adipose cells
- Stimulates glycolysis and hepatic glycogen synthesis
- Inhibits glycogenolysis and gluconeogenesis
- Promotes triglyceride and protein synthesis
Normal fasting blood glucose: 80–130 mg/dL (ADA) | A1C target: <7% (equates to average blood glucose ~154 mg/dL)
Administration
Injection Sites
Subcutaneous insulin is injected into sites with adequate adipose tissue:
- Abdomen (fastest absorption)
- Back of upper arms
- Upper outer thighs
- Lower back / buttocks (slowest absorption)
Absorption trend is generally abdomen → arms → thighs → buttocks.
Rotate injection sites within the same anatomical area each day to prevent lipodystrophy and support more consistent absorption rates.
Delivery Devices
| Device | Description |
|---|---|
| Insulin syringe | U-100 calibrated; use only insulin syringes — never tuberculin or other syringes |
| Insulin pen | Prefilled or cartridge-based; dial-dose; attach disposable needle; convenient for outpatient use |
| Insulin pump | Continuous subcutaneous infusion; delivers programmed basal rate + bolus at meals |
Dosing Methods
Basal-bolus therapy (recommended):
- Basal insulin (long-acting): One daily injection maintains steady glucose throughout the day
- Bolus insulin (rapid/short-acting): Mealtime dose matched to carbohydrate intake
Sliding scale coverage (in hospital settings): Short-acting insulin dose based on pre-meal glucometer reading — historically common but less preferred due to poor glucose control.
ISMP High-Alert Safety Requirements
Insulin is classified as an ISMP High-Alert Medication due to significant risk of harm from medication errors:
Independent Double Checks — REQUIRED before every insulin dose:
- Correct type of insulin (rapid vs. regular vs. NPH vs. long-acting)
- Correct product (brand and generic name)
- Correct dose (units, not mL)
- Correct vial or pen (especially when patient uses multiple types)
- Correct patient identifiers
Insulin Syringe Only
Insulin must be administered using insulin syringes calibrated in units. Using a tuberculin syringe or other non-calibrated syringe risks major dosing errors. Only U-100 insulin syringes for U-100 insulin.
Adverse Effects: Hypoglycemia
Hypoglycemia (blood glucose <70 mg/dL) is the primary and most dangerous adverse effect — risk is highest during the peak action phase.
Signs and symptoms: Shakiness, diaphoresis, tachycardia, confusion, headache, dizziness, visual changes → seizures and loss of consciousness (severe)
15-15 Rule (conscious patient):
- Give 15 g simple carbohydrates (4 oz juice, 4 oz regular soda, glucose tablets)
- Wait 15 minutes
- Recheck blood glucose — if still <70 mg/dL, repeat
- Once glucose normalizes, eat a protein-containing snack
Unconscious patient:
- Administer glucagon injection (IM/SQ) — stimulates hepatic glycogenolysis
- IV dextrose (D50W) in hospital setting
- Do NOT give oral anything — aspiration risk
Other Adverse Effects
- Hypoglycemia (primary risk)
- Lipodystrophy — fat deposits or atrophy at injection sites (prevented by site rotation)
- Weight gain (anabolic effect of insulin)
- Hypokalemia (insulin drives potassium intracellularly; IV insulin in DKA treatment requires potassium monitoring)
- Allergic reaction — rare with modern human insulin
Nursing Priorities
Before Administration:
- Check blood glucose with glucometer (identify if hypoglycemia is already present)
- Perform independent double-check per ISMP protocol
- Verify meal tray is ready (for mealtime rapid-acting insulin) — do NOT administer if patient is not eating
- Verify insulin integrity and storage status: correct product, not expired, no unexpected clumping/discoloration, and stored per policy (unopened refrigerated; opened vial per policy conditions)
- Assess injection site condition and rotate appropriately
- In pregnancy pathways, use pregnancy-specific glucose targets and treat clinically significant hypoglycemia at lower thresholds (commonly below 60 mg/dL) per protocol.
After Administration:
- Monitor for hypoglycemia during peak action period
- Assess blood glucose per protocol
- Document units administered, injection site, and pre-administration glucose level
- Educate patient on peak timing and early hypoglycemia signs
- Around labor and immediate postpartum periods, anticipate rapid insulin-requirement changes and coordinate dose adjustment with frequent glucose reassessment.
Related Concepts
- diabetes-mellitus — Pathophysiology of DM Type 1 and Type 2; DKA and HHS management using insulin
- pregestational-and-gestational-diabetes - Pregnancy-specific glucose targets and intrapartum/postpartum insulin adjustment context.
- high-alert-medications — ISMP classification and double-check requirements for insulin
- analgesics — Sliding scale insulin dosing in analogy to pain PRN protocols
- potassium-balance-disorders — IV insulin in DKA drives K⁺ into cells; monitor for hypokalemia
- nutritional-assessment-framework — Carbohydrate counting and meal planning integrated with insulin dosing
Self-Check
- A patient is scheduled for breakfast at 0730 and has been ordered rapid-acting insulin (Humalog) before meals. The nurse draws up 8 units at 0700 but discovers the patient’s breakfast tray will not arrive until 0800. What should the nurse do?
- A nurse is about to administer NPH insulin and notices the vial is clear. What should the nurse do before proceeding?
- A patient receiving NPH insulin at 0800 becomes shaky, diaphoretic, and confused at 1200 (noon). What is the most likely cause, and what is the priority nursing action?