Drug Review: Insulin

Insulin is life-saving for type 1 diabetics.  Many type 2 diabetics will eventually, if not at the outset, need to take insulin for adequate control of blood sugars, which should help prevent diabetes complications.

My comments here are simply a brief review of insulins used by type 2 diabetics.  Anyone taking insulin must work closely with a physician or diabetes nurse educator on proper dosing, injection technique, and recognition and management of hypoglycemia (low blood sugar).

This is NOT an insulin rig! Modern insulin injections barely hurt, if at all.

Insulin’s Mechanism of Action



Insulin is made by the pancreas to keep blood sugars from rising above a fairly strict range: 70-140 mg/dl or 3.89-7.78 mmol/l.  [It has many other actions that I won’t bother to outline here.]  When we eat a meal containing carbohydrates (and proteins to a lesser extent), blood sugar starts to rise as we digest the carbs.  Insulin drives the sugar into our body’s cells for use as immediate energy or conversion to fat as stored energy.  About half of the insulin produced by a healthy body is “basal,” meaning it’s secreted into the bloodstream in a steady, low-volume amount, to keep the liver from making too much sugar (glucose) and controlling fasting sugar levels.  The other half is secreted in to the bloodstream in response to meals.

In type 2 diabetes, the body’s tissues, at first, are resistant to the effect of insulin.  So the pancreas has to secrete more than usual (hyperinsulinism). As the illness progresses, the pancreas cannot keep up with demand for more insulin and starts to “burn out,” producing less insulin.  This is when many type 2 diabetics need to start insulin injections.  [These are generalities; there are exceptions.]

Types of Insulin

Specific names of insulins vary by manufacturer and by country.  By convention, I capitalize only the brand names below, plus NPH and NPL.

We could break them down into two types: human (identical in structure to human insulin) and analogs (minor molecular modifications to the usual human insulin molecule).  But most people don’t care about that.  It’s more helpful to distinguish them by the timing of their action:

  • Rapid acting:  lispro (e.g., Humalog), aspart (e.g., Novolog), glulisine (e.g., Apidra)
  • Short acting:  regular (e.g., Novolin R, Humulin R)
  • Intermediate to long acting:  NPH, glargine (e.g., Lantus), detemir (e.g., Levemir), degludec (e.g., Tresiba), NPL (neutral protamine lispro)

Rapid-acting insulins have onset of action between 5 and 15 minutes, peak effect in 30 to 90 minutes, and duration of action of 2 to 4 hours.

Short-acting “regular insulin” has  onset in 30 minutes, peaks in 2 to 4 hours, and works for 5 to 8 hours.

Intermediate to long-acting insulins start working in 2 hours, don’t have a well-defined peak of action, and may keep working for 20 or more hours (glargine), for 6 to 24 hours (detemir), or 30 to 42 hours (degludec).

All these times are gross approximations.  Once the insulin is injected into the fat below the skin, it has to be absorbed into the bloodstream and transported to the tissues where it does its magic.  Lots of factors affect this process. For instance, the thicker the fat tissue at the injection site, the slower the absorption.  Absorption tends to be  faster from the abdominal wall, slower from the arms, even slower from the thighs or buttocks.  Absorption can vary from day to day in an individual even when injection site and technique are identical.

As you might have guessed, the short- and rapid-acting insulins are usually injected before a meal in anticipation of blood sugar rising as food is digested.  The intermediate- and long-acting insulins imitate the healthy body’s “basal” insulin.

Manufacturers also supply premixed insulins, combining intermdiate or long-acting insulin with a short- or rapid-acting insulin.  Examples are Humalog 75/25, Humulin 70/30, and Novolog 70/30.

Dose and Selection of Insulin

See your physician or diabetes nurse educator for details.  Many type 2 diabetics get started just with an intermediate or long-acting insulin once or twice daily, with or without diabetes drugs by mouth. Nearly all type 1’s will need a long-acting “basal” insulin (one-third to one-half of their total daily insulin requirement, plus meal-time “bolus” dosing with a rapid-acting insulin. Insulin pumps are a topic for another day.

Side Effects

By far the most common and worrisome is hypoglycemia.

Steve Parker, M.D.

Last update: August 1, 2016

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