Insulin Types: Onset, Peak, Duration, and Safe Administration

Insulin is one of the highest-yield nursing pharmacology topics because exam questions almost always hinge on onset, peak, and duration — and on knowing which insulins can be mixed, given IV, or used to cover meals. This guide organizes the essential rules into a quick, exam-ready reference.

Master Insulin Timing Chart

• Rapid-acting (Lispro, Aspart, Glulisine): onset 10–30 min, peak 1–3 hr, duration 3–5 hr
• Short-acting (Regular): onset 30–60 min, peak 2–4 hr, duration 5–8 hr
• Intermediate (NPH): onset 1–2 hr, peak 4–12 hr, duration 12–18 hr
• Long-acting (Glargine, Detemir): onset 1–2 hr, no peak, duration ~24 hr
• Ultra-long-acting (Degludec): onset ~1 hr, no peak, duration 42+ hr

Peak = highest hypoglycemia risk.

Comparing Rapid, Regular, NPH, and Long-Acting

• Meal timing
  • Rapid: eat immediately
  • Regular: give 30 minutes before meal
  • NPH: covers meals and snacks
  • Long-acting: independent of meals
• Peak/hypoglycemia risk
  • Rapid: high
  • Regular: moderate
  • NPH: very high (especially overnight)
  • Long-acting: none
• Appearance
  • Rapid, Regular, Long-acting: clear
  • NPH: cloudy (the only cloudy insulin)
• IV use
  • Only Regular insulin can be given IV

When Hypoglycemia Is Most Likely

• Rapid-acting: 1–3 hr post-dose
• Regular: 2–4 hr post-dose
• NPH: 4–12 hr post-dose (overnight risk)
• Long-acting: minimal risk

Insulin and Meal Rules

• Rapid-acting should only be given when the food tray is present.
• Regular insulin is given 30 minutes before meals.
• NPH requires a bedtime snack to prevent nocturnal hypoglycemia.
• Long-acting is given at the same time every day and does not require meals.

Mixing Insulins

• Allowed: Regular + NPH
• Never mix: Glargine, Detemir, Degludec
• Mixing order: Clear before Cloudy — draw up Regular first, then NPH
• Remember: only NPH is cloudy

Exam Commandments

• Peak = hypoglycemia risk
• No peak = basal insulin
• Cloudy = NPH only
• Long-acting = never mix
• Regular insulin = the only IV insulin

Helpful Mnemonics

• LARGine is LONG → glargine is long-acting with no peak
• RN = Right Now → rapid insulin; eat immediately
• Clear before Cloudy → mixing order (Regular before NPH)

Common Exam Traps

• Giving rapid insulin without food available
• Mixing glargine with NPH
• Missing NPH overnight hypoglycemia
• Confusing Regular vs. Rapid timing
• Assuming long-acting covers meals (it does not)

Key takeaways

• Rapid-acting insulin is given right before eating; Regular is given 30 minutes before meals.
• NPH is the only cloudy insulin and has a strong peak at 4–12 hours — watch for overnight hypoglycemia.
• Long-acting insulins (glargine, detemir, degludec) have no peak and should never be mixed.
• When mixing, always draw Clear before Cloudy (Regular before NPH).
• Regular insulin is the only insulin that can be given IV.
• Hypoglycemia risk is highest at each insulin’s peak time.