1 Insulin Therapy

Insulin’s role and safe use

Insulin replaces or supplements the body’s insulin and lowers blood glucose. Insulin plans and product instructions vary, so this guide is educational and is not a basis for starting, stopping, or changing an individual’s dose.

Safe use depends on the prescribed treatment plan and the specific insulin product. Verify the insulin and dose, use the correct injection technique, rotate sites, monitor glucose as directed, and avoid unplanned dose changes or overlapping correction doses.

Insulin action profiles

Insulins differ in onset, peak, and duration. Rapid-acting insulin generally starts working sooner and lasts a few hours; it commonly covers the rise in glucose associated with meals. Long-acting insulin provides more sustained background, or basal, coverage between meals and overnight. A regimen may prescribe rapid-acting insulin with meals and long-acting insulin once daily, but exact timing varies by product and person.

NPH insulin is an intermediate-acting suspension that is typically cloudy and has a noticeable peak. It should be gently mixed according to its product instructions. Regular insulin is usually clear and short-acting. A peak can increase the chance of hypoglycemia if food intake or activity changes.

Calculations and correction doses

A prescribed insulin-to-carbohydrate ratio links insulin to the amount of carbohydrate in a meal. For a hypothetical ratio of $1$ unit per $10$ grams of carbohydrate, a meal containing $45$ grams gives this calculation:

The result is $4.5$ units by calculation, before considering other prescribed dose components. This arithmetic example does not establish a real dose. Rounding, device increments, correction doses, and whether a dose is appropriate must follow the person’s prescribed plan.

A correction dose may still be active when another is taken. Earlier rapid-acting insulin can overlap with a later correction and lower glucose more than expected; this is insulin stacking. Account for active insulin and follow prescribed instructions rather than making extra corrections without guidance. Correction factors and the time between corrections are individualized.

Injection technique and mixing

Insulin is generally injected into the fatty tissue under the skin, not into muscle. Repeated injections in the same small area can cause lipohypertrophy, a firm change in the tissue that may make insulin absorption less predictable. Avoid injecting into a lump and rotate among appropriate sites according to the care team’s instructions. Do not share insulin pens or needles.

Mix insulin only when the care team and product instructions say to do so. For a specifically prescribed regular-plus-NPH mixture, draw up the clear regular insulin before the cloudy NPH. Do not assume this sequence applies to every combination: mixing rules are product-specific, and some insulins, including insulin glargine, should not be mixed with other insulins. Confirm the exact products and sequence.

Monitoring and adverse effects

Monitor glucose at the times specified in the person’s plan. Examples include around meals and bedtime, during or after physical activity, when symptoms or a CGM alert suggest a low or high, and after treating hypoglycemia until glucose has recovered. Monitoring can help identify patterns and guide safe treatment.

Timing depends on the regimen and the person’s needs. A CGM may help detect low glucose, but users should follow device and care-team instructions.

Insulin can cause hypoglycemia. Sweating, shakiness, hunger, and confusion are symptoms that should prompt consideration of low glucose. Check glucose if possible and follow the person’s treatment plan. Other possible adverse effects include injection-site reactions, lipodystrophy, allergic reactions, and weight gain. A glucose level below $70$ mg/dL is clinically important.

Responding to low glucose

For an alert adult who can safely swallow and has a low glucose reading, a typical initial response is to take $15$ grams of fast-acting carbohydrate and recheck glucose after $15$ minutes. If glucose remains low, repeat the treatment and recheck. Glucose is preferred when available; examples include glucose tablets taken according to the label or about $4$ ounces ($\frac{1}{2}$ cup) of juice. Foods high in fat or protein are not ideal for initial treatment because they act more slowly. Follow individualized instructions, including those for automated insulin-delivery systems.

If someone with suspected severe hypoglycemia is unconscious or cannot swallow safely, do not give food or drink by mouth because it can cause choking. A trained bystander should give prescribed glucagon if available and call emergency services. People using insulin should have an appropriate glucagon plan, and close contacts should know where it is and how to use it.