Why Do You Administer Insulin Before Meals & Not After?

Your doctor prescribes medicinal insulin to replace or supplement your body's naturally occurring insulin. The goal with medicinal insulin is to mimic the normal patterns of insulin secretion as closely as possible. Depending on what type of insulin you take, administration may occur before or after meals, or at other times during the day. Always follow your doctor's instructions about when to administer your insulin to prevent extreme highs and lows in your blood sugar level.

Syringe and insulin shot. (Image: Creatas Images/Creatas/Getty Images)

Insulin Type and Timing

Your pancreas normally secretes a background amount of insulin throughout the day and greater amounts after meals in response to increasing blood sugar. Different types of medicinal insulin mimic either background or post-meal insulin secretion. Background, or basal, insulins are intermediate- or long-acting and include glargine, detemir and NPH. Mealtime insulins are rapid- or short-acting and include regular, lispro, glulisine and aspart. The timing of administration of the different types of insulin depends on how quickly the drug enters your bloodstream, when the peak levels occurs and how long the medication remains active in your body.

Rapid-Acting Insulin

Insulin glulisine, lispro and aspart are rapid-acting, mealtime insulins. These drugs begin working within 15 minutes of administration and mimic the insulin increase that occurs when you eat. You typically take insulin glulisine within 15 minutes before a meal or within 20 minutes after you begin eating. With insulin lispro, you administer your injection within 15 minutes before a meal or immediately afterward. If you take insulin aspart, your doctor will likely advise you to take the drug 5 to 10 minutes before meals. Administering rapid-acting insulin close to mealtime ideally means the drug enters your bloodstream at roughly the same time as sugars from your meal.

Regular Insulin

Regular insulin is a short-acting, mealtime insulin that enters your bloodstream more slowly than rapid-acting insulin. You typically administer regular insulin approximately 30 minutes before beginning a meal. Although regular insulin is absorbed into your circulation more slowly than rapid-acting insulin, it remains active in your body for a longer period.

NPH Insulin

NPH insulin can be used as a replacement for background or mealtime insulin. NPH typically begins working within 1 to 3 hours and peak activity occurs 4 to 10 hours after administration. The timing of NPH insulin administration varies, depending on how it is used and if you take it in combination with another type of insulin. Your doctor will advise you about the timing of your NPH insulin injections.

Long-Acting Insulin

Insulin glargine and detemir enter your bloodstream at a slow, steady rate. Because these drugs are basal insulin replacements, the timing of administration in relationship to your meals is not as critical as it is with the other types of insulin. Your doctor will advise you when to inject your long-acting insulin. It is important to take your injection at the same time each day to maintain a steady level of background insulin in your body.