Insulins

What insulin does in the body

Insulin is produced by beta cells of the pancreas and is the primary hormone that lowers blood glucose. It binds insulin receptors on muscle and fat cells, triggering glucose transporters to move to the cell surface so glucose can leave the bloodstream and enter the cell to be used or stored. In the liver, insulin suppresses gluconeogenesis and glycogen breakdown, reducing the amount of new glucose the liver releases. Insulin is also anabolic in a broader sense: it promotes fat storage, drives protein synthesis, and shifts potassium into cells by stimulating the sodium-potassium pump, which is why insulin is used therapeutically to treat dangerously elevated potassium levels even in people without diabetes. When insulin is deficient or ineffective, as in type 1 or advanced type 2 diabetes, glucose stays in the blood, the liver keeps producing more, and cells are starved of fuel despite a glucose surplus.

Classification by time-action profile

Insulin products are grouped by onset, peak, and duration rather than by chemical novelty alone.

• Rapid-acting analogues (lispro, aspart, glulisine) are engineered so they are absorbed quickly and clear quickly, making them ideal for covering the glucose rise from a meal when given close to eating.
• Short-acting regular insulin has a slower onset and longer tail than the rapid analogues and is the only insulin type approved for intravenous administration, which matters in settings like diabetic ketoacidosis where IV dosing allows rapid, titratable control.
• Intermediate-acting NPH has a cloudy suspension appearance, an onset and duration between rapid and long-acting products, and a distinct peak that must be anticipated when planning meals and monitoring.
• Long-acting basal analogues (glargine, detemir, degludec) are designed to release slowly and evenly, producing a flat, peakless profile that provides steady background coverage over an extended period without a pronounced action spike.
• Premixed products combine a rapid- or short-acting component with an intermediate-acting component in a fixed ratio, simplifying dosing for patients who need both mealtime and background coverage but cannot manage separate injections.

Basal-bolus therapy and technology

Physiologic insulin replacement mimics how a healthy pancreas works: a steady basal level suppresses hepatic glucose output between meals and overnight, while bolus doses cover the glucose load from food and correct unexpected highs. Bolus dosing conceptually has two components: a carbohydrate ratio that estimates how much insulin is needed per amount of carbohydrate eaten, and a correction factor that adds extra insulin when the pre-meal reading is above target. This basal-bolus approach better matches natural physiology than older fixed-dose regimens. Insulin pumps deliver rapid-acting insulin continuously as programmed basal rates plus patient-activated bolus doses, eliminating the need for separate long-acting injections. Continuous glucose monitors track interstitial glucose in real time and, paired with a pump, can adjust or suspend delivery automatically, reducing both highs and dangerous lows.

Administration essentials

Insulin is a high-alert medication, and administration technique is a major focus of nursing practice. Subcutaneous injection sites (abdomen, thigh, upper arm, buttock) should be rotated systematically to prevent lipohypertrophy, a buildup of fatty tissue that causes erratic absorption. Insulin vials and pens should never be shaken, since agitation can damage the protein structure or cause uneven suspension of the intermediate-acting types; they should instead be gently rolled or rotated between the palms if resuspension is needed. When regular insulin and NPH are mixed in the same syringe, the clear regular insulin is always drawn up before the cloudy NPH to prevent contaminating the regular insulin vial with NPH particles. Long-acting analogues such as glargine and detemir must never be mixed with any other insulin or diluted, because altering their formulation destroys the mechanism that gives them a smooth, peakless release. Insulin-specific syringes marked in units, and correct pen technique including priming and adequate skin dwell time after injection, are essential to prevent dosing errors. Unopened vials and pens are stored refrigerated, while an opened, in-use vial or pen is generally kept at room temperature and used within a manufacturer-specified window before discarding. Because errors carry serious consequences, many facilities require an independent double check by a second clinician before administration.

Hypoglycemia and other adverse effects

Hypoglycemia is the dominant and most dangerous adverse effect of insulin therapy. Autonomic (sympathetic) warning signs include shakiness, sweating, palpitations, and anxiety, while neuroglycopenic signs reflect the brain being starved of glucose and include confusion, slurred speech, blurred vision, and, if untreated, seizure or loss of consciousness. The standard response for a conscious patient is to give a fast-acting carbohydrate source and recheck the response shortly after, repeating if the response is inadequate. For a patient who is unresponsive or unable to safely swallow, glucagon is given to stimulate the liver to release stored glucose, or IV dextrose is given if a line is available. Beta blockers are an important safety caveat because they blunt the autonomic symptoms of hypoglycemia, particularly the tremor and rapid heartbeat, which can mask the warning signs and delay recognition. Other notable effects of insulin therapy include weight gain from its anabolic, fat-storing action, and hypokalemia from driving potassium into cells, which is a concern especially with IV insulin infusions. Two patterns of morning hyperglycemia are distinguished in practice: the Somogyi effect, in which overnight hypoglycemia triggers a rebound release of counter-regulatory hormones that raises morning glucose, and the dawn phenomenon, in which natural early-morning hormone surges raise glucose without a preceding low; distinguishing them typically guides whether an evening dose should be reduced or adjusted differently.

Sick days and changing insulin needs

During illness, insulin needs typically rise because stress hormones raise blood glucose even when oral intake drops, so patients are taught never to stop insulin entirely during sick days without guidance, to monitor more frequently, and to stay hydrated. Corticosteroid use similarly raises blood glucose and often requires a temporary increase in insulin. Exercise increases insulin sensitivity and glucose uptake by muscle, which can lower insulin needs or increase hypoglycemia risk around activity. Pregnancy alters insulin requirements substantially as placental hormones increase insulin resistance as gestation progresses, requiring ongoing dose adjustment and close monitoring.