Rapid vs. Fast‑Acting Insulin — Clinician Quick Reference

Clear PK timelines, perioperative guidance, and use‑case table
Rapid‑Acting Analogs (Lispro, Aspart, Glulisine) Fast‑Acting Regular (Human) Insulin
Insulin Onset–Peak–Duration Curves Comparison of rapid-acting analogs versus regular insulin over a 0–8 hour window. Y-axis is relative insulin action; X-axis is time in hours. 0 1 2 3 4 5 6 7 8 Peak ~1–2h Onset ~10–20 min Duration ~3–5 h Peak ~2–4h Onset ~30–60 min Duration ~5–8 h Relative Insulin Action Time (hours)
Rapid‑acting analogs
Onset 10–20 min · Peak 1–2 h · Dur 3–5 h
Fast‑acting regular
Onset 30–60 min · Peak 2–4 h · Dur 5–8 h
Peri‑op within ~1 h
Use IV Regular Insulin

Use‑Case Guide

Match onset/peak to carbohydrate exposure, consider safety and practicality.
Clinical Scenario Preferred Insulin Rationale Notes
Outpatient mealtime bolus Rapid‑acting analog Closest physiologic match; flexible dosing up to meal start Lower late hypoglycemia risk vs. regular
Correction (hyperglycemia) outpatient Rapid‑acting analog Shorter duration reduces stacking and late hypoglycemia Educate on correction factor and timing
Insulin pump (CSII) Rapid‑acting analog Stable basal infusion and precise boluses Adjust for meal patterns and activity
Enteral/parenteral nutrition coverage Regular (fast‑acting) Longer action overlaps continuous carb exposure Consider basal insulin co‑administration
Resource‑limited / cost barrier Regular (fast‑acting) Lower cost, broad availability Dose 30 min pre‑meal; counsel on timing
Inpatient urgent reduction (peri‑op within ~1 h) IV Regular insulin Immediate onset; titratable and predictable Standard of care for rapid control
DKA, HHS, hyperkalemia IV Regular insulin Protocol‑driven continuous infusion or bolus Frequent glucose/electrolyte monitoring

Teaching Pearls