NG-370

💉 Insulin & Patient Education

Onset, peak and duration; the rules that never bend; and what you actually teach before discharge.

⏱️ The four types — onset, peak, duration

The peak is where the hypoglycemia is. On one clock the peaks line up visibly, which a table of numbers never manages. Swipe it sideways if it is cut off, or tap to open it full size.

Peak is when hypoglycemia happens. If you know when an insulin peaks, you know when to have the patient eat and when to watch. That is why the table is worth memorizing rather than looked up.

Type	Examples	Onset	Peak	Duration
Rapid-acting	lispro, aspart, glulisine	`10–30 min`	`30 min – 3 h`	`3–5 h`
Short-acting (regular)	regular insulin	`30 min – 1 h`	`2–4 h`	`5–8 h`
Intermediate	NPH	`1–2 h`	`4–12 h`	`12–18 h`
Long-acting	glargine, detemir, degludec	`1–2 h`	No pronounced peak	`24 h` or more

The two rules that follow straight from the table.

Rapid-acting goes with food. Give it within 15 minutes of the meal — and only when the tray is actually in front of the patient. Giving it and then finding the meal is delayed is a straightforward route to hypoglycemia.
NPH peaks in the middle of the night. An evening NPH dose peaks while the patient sleeps, which is why 3 a.m. hypoglycemia is a recurring exam scenario.

⚠️ The rules that never bend

Only regular insulin goes intravenously. Never give NPH, glargine or any cloudy or long-acting insulin IV. That is a fixed rule and it is asked directly.

Clear before cloudy. When mixing regular with NPH: air into NPH, air into regular, draw up regular first, then NPH. "RN" — Regular before NPH. Drawing cloudy first contaminates the regular vial.
Never mix glargine or detemir with anything. They are given in their own syringe.
Never shake insulin. Roll a cloudy vial gently between the palms; shaking damages the protein and creates bubbles.
Insulin syringe only, marked in units. Never a tuberculin or standard syringe.
Two-nurse check for insulin doses wherever policy requires it — insulin is a high-alert medication.
Write "units" in full. The abbreviation U is misread as a zero and has caused ten-fold overdoses.

🧠 Storage

Unopened vials and pens: in the refrigerator until the expiry date.
In use: room temperature is fine, usually for 28 days — check the specific product.
Injecting cold insulin stings, so a vial in use is often kept out deliberately.
Never freeze insulin, and never leave it in a hot car or in direct sun. Discard it if it has.
Discard if a clear insulin looks cloudy, or a cloudy one has clumps or frosting on the glass.

💉 Injection technique & rotation

Subcutaneous, at 90° with a short needle; 45° for a very thin patient.
Absorption speed by site: abdomen fastest, then arm, then thigh, then buttock slowest.
Stay at least 2 inches from the umbilicus.
Do not massage the site — it speeds absorption unpredictably.
No need to aspirate for subcutaneous insulin.
Exercise speeds absorption from the limb being used — do not inject the thigh before a run.

Rotation — the modern rule. Rotate within one anatomical region, moving about a finger’s width from the last injection, rather than jumping between abdomen, arm and thigh day to day. Keeping to one region keeps absorption predictable; moving around inside it prevents lipohypertrophy.

Lipohypertrophy is a lumpy, thickened patch from injecting the same spot repeatedly — and insulin absorbed from it is erratic. Inspect and palpate the sites; unexplained swings in control are sometimes a lump nobody looked for.

💬 What you teach before discharge

Hypoglycemia first. It is the complication that hurts people fastest and the one they must be able to handle alone.

Signs: shaky, sweaty, hungry, irritable, fast heartbeat, confusion, headache — cold and clammy, needs some candy.
Rule of 15: 15 g of fast carbohydrate, wait 15 minutes, recheck. Repeat if still under 70 mg/dL.
15 g looks like: 4 oz juice or regular soda, 3–4 glucose tablets, 1 tablespoon honey.
Then a snack with protein if the next meal is more than an hour away.
Nothing by mouth if the patient is unconscious or cannot swallow — glucagon, and call for help.
Beta blockers mask the warning signs — the shakiness and fast heartbeat may not appear. Sweating still does.

Sick-day rules — the ones patients get wrong

Never stop insulin because you are not eating. Illness raises blood glucose even without food. Stopping insulin is how people arrive in DKA.
Check glucose every 3–4 hours while unwell.
Check ketones if glucose is over about 240 mg/dL, or if vomiting.
Drink fluid hourly; if you cannot eat normally, take carbohydrate as liquid.
Call the provider for vomiting beyond a few hours, moderate or large ketones, or glucose that will not come down.

Everyday living

Carry fast carbohydrate at all times. No exceptions.
Medical identification — bracelet or card.
Never share a pen, even with a new needle — blood can track back into the cartridge.
Dispose of needles in a sharps container, never household rubbish.
Alcohol lowers glucose, and does so hours later — eat with it, and check before bed.
Have the patient demonstrate drawing up and injecting before discharge. Teach-back, not a nod.

If they can show you the injection and tell you the Rule of 15, the teaching worked.

Sources. CDC, Manage Blood Sugar, Diabetes and Insulin and Managing Sick Days. NCBI Bookshelf StatPearls, Insulin, Hypoglycemia and Insulin Injection Technique. MedlinePlus, Insulin Injection and Diabetes — Type 1. Public-domain and openly licensed; written for this site.