Insulin is the body's main anabolic, glucose-lowering hormone, made by pancreatic beta cells. It binds the insulin receptor on liver, muscle, and fat cells and:

• Moves glucose into muscle and fat cells (GLUT4 transporters)
• Stores glucose as glycogen and stops the liver from making new glucose
• Builds fat and protein and blocks lipolysis and ketone formation
• Shifts potassium into cells (the basis of its use in hyperkalemia and the cause of hypokalemia)

Therapeutic insulin replaces or supplements the body's own supply. Normal secretion has two parts, and insulin regimens copy them:

• Basal — a steady low level between meals and overnight (intermediate- or long-acting insulin)
• Bolus (prandial) — bursts with meals (rapid- or short-acting insulin), plus correction doses for high readings

Insulin is a protein destroyed in the gut, so it is given subcutaneously, intravenously (regular insulin), or by inhalation (one rapid-acting product).

Indications: type 1 diabetes (required for survival); type 2 diabetes not controlled by other drugs, or with marked hyperglycemia, catabolism, or ketosis; gestational diabetes and pregnancy (insulin does not cross the placenta); DKA and HHS; hospital hyperglycemia; parenteral nutrition; and hyperkalemia (IV regular insulin with dextrose).

Insulin types (times are approximate and product-specific)

Concentrations — standard is U-100 (100 units/mL). Concentrated products — examples include icodec U-700, regular U-500, glargine U-300, and degludec or lispro U-200 (not a complete list; always read the label) — are given with their dedicated pens, which dial the dose in units. Never draw insulin from a concentrated pen into a syringe. Regular U-500 in vials must be drawn up only with a U-500 syringe; a standard U-100 syringe causes fivefold overdoses. Detemir has been discontinued in some markets, including the US.

Mixing regular + NPH in one syringe: inject air into NPH (cloudy), then into regular (clear); draw up clear (regular) first, then cloudy (NPH) so NPH cannot contaminate the regular vial.

Hypoglycemia — the most common and most dangerous effect.

• Level 1: below 70 mg/dL (3.9 mmol/L); Level 2: below 54 mg/dL (3.0 mmol/L); Level 3: severe event with altered mental or physical status requiring help
• Adrenergic signs: shakiness, sweating, tachycardia, palpitations, anxiety, hunger
• Neuroglycopenic signs: confusion, headache, slurred speech, behavior change, seizures, coma
• Causes: dose error, delayed or missed meals, extra exercise, alcohol, weight loss, kidney failure (slower insulin clearance), insulin given at the wrong time relative to meals

Hypokalemia — especially with IV insulin (DKA treatment, hyperkalemia treatment).

Weight gain; lipohypertrophy (fatty lumps from repeated use of the same site — slows and makes absorption erratic) and lipoatrophy; local reactions; rare systemic allergy.

Rebound patterns

• Somogyi effect — nighttime hypoglycemia followed by rebound morning hyperglycemia; treat by reducing the evening dose or adding a bedtime snack
• Dawn phenomenon — early-morning rise from overnight growth hormone and cortisol; may need an adjusted basal dose
• Tell them apart by checking glucose around 2–3 AM

Inhaled insulin — cough, bronchospasm, decline in lung function.

• Contraindicated during hypoglycemia; hypersensitivity to the product
• Inhaled insulin: asthma, COPD, other chronic lung disease; not recommended in current smokers or within 6 months of quitting
• Hypokalemia: in DKA, replace potassium and delay insulin if K⁺ is below 3.5 mmol/L
• Kidney or liver failure, older age: lower requirements and prolonged hypoglycemia
• Never share insulin pens between clients, even with a new needle (bloodborne infection risk)
• Pioglitazone plus insulin: fluid retention and heart failure risk

Drugs that raise glucose (increase insulin needs): corticosteroids, thiazide diuretics, atypical antipsychotics, epinephrine, levothyroxine, some protease inhibitors, oral contraceptives.

Drugs that increase hypoglycemia: sulfonylureas and meglitinides, alcohol, salicylates (high dose), MAOIs. Fluoroquinolones can cause both hypoglycemia and hyperglycemia (dysglycemia).

Beta blockers mask adrenergic warning signs (tremor, tachycardia) and delay recovery; sweating and confusion still occur.

Pregnancy and lactation — insulin is the preferred drug for glucose control in pregnancy; requirements rise in the second and third trimesters and fall sharply after delivery (watch for postpartum hypoglycemia). Safe in breastfeeding.

Listed in priority order.

1. Recognize and treat hypoglycemia immediately
   • Conscious and able to swallow → Rule of 15: 15 g fast-acting carbohydrate (4 oz/120 mL juice or regular soda, glucose tablets or gel), recheck in 15 minutes, repeat if still below 70 mg/dL (3.9 mmol/L), then give a snack or meal
   • Unable to swallow or unconscious → glucagon (1 mg IM or SC for adults and children 25 kg or more, 0.5 mg under 25 kg; 3 mg intranasal; or a ready-to-use SC product) or IV dextrose (adults: 50% dextrose, commonly 25 g) per protocol; nothing by mouth; turn on the side after glucagon (vomiting)
2. Check glucose before giving insulin and at protocol times (before meals and at bedtime). Hospital target for many adults: 100–180 mg/dL (5.6–10.0 mmol/L). Hold prandial insulin if the client is not eating and notify the prescriber; basal insulin is usually continued (often at a reduced dose) in type 1 diabetes even when NPO.
3. High-alert medication safety — independent double-check per policy, especially IV insulin and concentrated insulin; use "units" in full (never "U" or "IU"); use insulin syringes or pens only; confirm type, concentration, and dose.
4. Coordinate rapid-acting insulin with meal delivery — the tray should be present or the client ready to eat.
5. IV insulin infusion — regular insulin only; hourly glucose; monitor potassium closely; prime tubing per protocol; add dextrose as glucose falls in DKA; start SC basal insulin 1–2 hours before stopping the drip.
6. Hyperkalemia treatment — IV regular insulin with dextrose (commonly 5–10 units with 25 g dextrose, per protocol) after calcium gluconate when ECG changes are present; monitor glucose for several hours.
7. Injection technique — clean skin, let alcohol dry, 90° angle for most pens and short needles (45° if very thin), do not massage; rotate sites within one region (abdomen absorbs fastest, then arms, thighs, buttocks); avoid lipohypertrophy areas.
8. Assess A1C trend, weight, injection sites, and understanding of the regimen.

• Storage: keep unopened insulin in the refrigerator at 2–8°C (36–46°F); never freeze; in-use vials and pens at room temperature for the period on the label; protect from heat and sunlight; discard insulin that is frozen, clumped, or discolored (clear insulins must stay clear).
• Technique: gently roll NPH and premixed insulin (do not shake); prime pens with 2 units before each dose; hold the pen in place for about 10 seconds; new needle every injection; dispose of sharps in a puncture-resistant container.
• Rotate sites and inspect for lumps; never inject into a lump.
• Hypoglycemia: know the signs; always carry fast-acting glucose; keep glucagon at home and teach family to use it; wear medical identification; check glucose before driving.
• Timing: rapid-acting insulin with meals; do not skip meals after taking prandial insulin.
• Exercise: check glucose before activity; eat carbohydrate first if below 100 mg/dL (5.6 mmol/L); avoid vigorous exercise if above 250 mg/dL (13.9 mmol/L) with ketones.
• Alcohol: take with food — delayed hypoglycemia can occur hours later, including overnight.
• Sick days: never stop basal insulin, even if not eating; check glucose every 2–4 hours and ketones if glucose is above 240 mg/dL (13.3 mmol/L); drink fluids; call for vomiting, moderate or large ketones, or persistent high glucose.
• Insulin pump: know basal and bolus settings; change and rotate the infusion site; a blocked set causes rapid DKA because there is no long-acting insulin on board — check ketones with unexplained high glucose and keep backup pens.

Insulin overdose (accidental or intentional) — prolonged, recurrent hypoglycemia, especially with long-acting products; hypokalemia.

• Antidote: glucose. Give IV dextrose (bolus, then continuous infusion — often 10% dextrose), frequent glucose checks (every 15–60 minutes), potassium monitoring and replacement, and feeding as soon as the client can eat.
• Glucagon works only if liver glycogen is present — it may fail in malnutrition, alcohol use, or prolonged fasting; it is a bridge until IV access.
• Observe for many hours to days after large overdoses of long-acting insulin; consider psychiatric evaluation after intentional overdose.

Common dosing errors — confusing "U" with "0," U-500 given with a U-100 syringe, wrong product (look-alike pens), prandial insulin given when the meal is delayed or cancelled, and duplicate doses at handoff.

Insulin omission — DKA in type 1 diabetes (Kussmaul respirations, fruity breath, abdominal pain, dehydration); screen adolescents for intentional omission linked to weight control.

• Rapid-acting (lispro, aspart): with meals; regular: the only standard IV insulin; NPH: cloudy, peaks (hypoglycemia risk); glargine/degludec: basal, no peak, do not mix
• Mix clear (regular) before cloudy (NPH)
• Hypoglycemia below 70 mg/dL (3.9 mmol/L) → conscious: 15 g carbohydrate, recheck in 15 min; unconscious: glucagon or IV dextrose
• Beta blockers mask tremor and tachycardia, not sweating
• Insulin shifts potassium into cells — watch for hypokalemia; treats hyperkalemia with dextrose
• Rotate sites within a region; do not massage; abdomen absorbs fastest
• Store unopened insulin in the refrigerator, never freeze; in-use at room temperature per label
• Never share pens; write "units" in full; concentrated insulins (icodec U-700, U-500, U-300, U-200) only with their own pens — never drawn into a syringe from a pen
• Somogyi = night low → morning high; dawn = morning high without a night low → check at 2–3 AM
• Sick day: never skip basal insulin; ketones if above 240 mg/dL (13.3 mmol/L)
• Pregnancy: insulin preferred; needs rise, then drop after delivery
• Inhaled insulin: contraindicated in asthma and COPD