Exogenous insulin is the synthetic form of the hormone administered externally to regulate blood sugar levels. This medical intervention treats hyperglycemia (high blood glucose) in individuals whose bodies cannot produce or effectively use their natural insulin. The therapy stabilizes glucose levels, preventing dangerously high concentrations that can lead to acute complications and long-term organ damage.
Defining Exogenous Insulin and Its Role
Insulin’s primary function is to act as a metabolic “key,” facilitating the absorption of glucose from the bloodstream into cells (such as muscle and fat tissue) where it is used for energy or stored. This natural hormone, produced by the beta cells in the pancreas, is known as endogenous insulin. The body constantly adjusts its release of endogenous insulin in response to changing blood sugar levels to maintain a healthy balance.
Exogenous insulin is a manufactured version, often created using recombinant DNA technology, that mimics the structure and function of the human hormone. This external insulin becomes necessary when the pancreas fails to produce sufficient endogenous insulin (Type 1 diabetes), or when the body’s cells become resistant to the insulin being produced (Type 2 diabetes). By supplying this synthetic hormone, exogenous insulin ensures that circulating glucose can enter the cells, lowering blood sugar concentrations to a safer range.
Classification by Action Time
Exogenous insulin is categorized based on its pharmacodynamics, specifically how quickly it begins to work, when it reaches its maximum effect (peak), and how long its action lasts (duration). This classification allows for precise tailoring of a treatment regimen to match the body’s varying insulin needs. Insulins are designed either to cover meals or to provide continuous background coverage.
Rapid-acting insulin analogs (e.g., insulin lispro or insulin aspart) have a fast onset (5 to 15 minutes), peak in one to two hours, and last four to six hours. These are taken just before or immediately after a meal to manage the sudden rise in blood glucose following carbohydrate consumption. Short-acting insulins, sometimes called Regular insulin, start working within 30 minutes, peak around two to three hours, and last for three to six hours.
Intermediate-acting insulin, like NPH (Neutral Protamine Hagedorn) insulin, has a slower onset (two to four hours), peaks between four and twelve hours, and lasts up to 18 hours. This type covers insulin needs for about half a day or overnight. Long-acting and ultra-long-acting insulins (including glargine or degludec) provide a steady, peakless background level of insulin for up to 24 to 42 hours. These basal insulins maintain stable blood glucose levels between meals and during sleep.
Methods of Delivery
The most common way to administer exogenous insulin is through subcutaneous injection, meaning into the fatty layer just beneath the skin. Historically, this involved using a vial and a traditional syringe, requiring the user to draw the correct dose before injecting. While simple and relatively inexpensive, this method requires careful measurement and is less discreet than other options.
Insulin pens have largely replaced syringes for many users, offering a more convenient and portable delivery method. These devices look similar to a writing pen and contain a pre-filled cartridge or a reusable reservoir. The user can dial the precise dose and inject with a smaller, more comfortable needle, improving ease of use and accuracy.
A more advanced method involves the continuous subcutaneous insulin infusion (CSII) pump. This small, computerized device delivers rapid- or short-acting insulin through a thin tube (cannula) inserted under the skin. The pump provides a continuous trickle of basal insulin and allows the user to program a larger “bolus” dose for meals or to correct high blood sugar. This method offers high precision and flexibility, closely mimicking the body’s natural insulin release patterns.
Managing Common Side Effects
The most frequent side effect of exogenous insulin administration is hypoglycemia (low blood sugar), which occurs when the insulin dose is too high for the amount of circulating glucose. Hypoglycemia is defined as a blood glucose level below 70 mg/dL. Symptoms can include shakiness, sweating, dizziness, confusion, and a fast heart rate. If not addressed promptly, severe hypoglycemia can lead to seizures or loss of consciousness.
Immediate management of mild to moderate low blood sugar involves consuming fast-acting carbohydrate. The rule of thumb is to consume 15 to 20 grams of glucose, wait 15 minutes, and then recheck the blood sugar level, repeating the process if necessary.
Fast-Acting Carbohydrate Sources
- Glucose tablets.
- Four ounces of juice or regular soda.
- A tablespoon of sugar.
- A tablespoon of honey.
Other potential side effects include weight gain, as insulin promotes the storage of energy, and injection site reactions, such as lipohypertrophy. Lipohypertrophy is a build-up of fatty tissue caused by repeated injections in the same spot. Rotating injection sites prevents these skin changes and ensures consistent insulin absorption.