Diabetes Forecast

Can I Switch to Once-a-Day Insulin?

I have injected 15 units of Humulin N [human NPH] insulin when I first get up and again at 4 p.m. each day for years, as directed by my doctor. I carefully regulate my eating, and my A1C is good. Could I change to a once-a-day insulin pen and get the same results? Frank Eberdt, Little Rock, Arkansas

Belinda Childs, APRN, MN, BC-ADM, CDE, responds:

First, congratulations on maintaining a good A1C on twice-daily NPH. This tells me you have worked hard to keep a consistent meal plan, exercise schedule, and timing of your insulin doses.

What to Know:

NPH is an intermediate-acting insulin. It begins working after two hours, has its most potent action or peaks between five and nine hours, and lasts up to 12 to 14 hours after being injected. It can last longer in some people, and the action increases with dose size. Insulin glargine (Lantus) and insulin detemir (Levemir) are the only insulins that generally last 24 hours. They are usually peakless and do come in a pen. These insulins will cost more than your Humulin N.

Find Out More:

You did not note if you were experiencing hypoglycemia. Your current dosing schedule could lead to an overlap of doses that could increase your risk of hypoglycemia in the late evening or early night. In addition, because NPH has a peak action, you may actually be covering your meals with the peaks of this insulin if you are eating a late-morning meal and a late-evening meal. If you change to Lantus or Levemir, which have no peaks, you may find that you need mealtime insulin.

The best way to find out how well your current regimen is working is to test your blood glucose levels at different times of day for a few days, until patterns become clear. I'd suggest testing your blood glucose at fasting, before and two hours after you eat your meals, at bedtime, and occasionally at 1 to 2 a.m. The goal for fasting, before-meal, and nighttime blood glucose levels is 70 to 130 mg/dl; after meals, the goal is under 180 mg/dl. Testing at night will help confirm that you are not going low then. Share the results with your health care provider.


It is important to verify that hypoglycemia is not occurring with your current insulin and two daily injections. If you and your physician decide to convert to Lantus or Levemir, which provide steady background insulin, it will be important to test after meals to confirm that you do not need mealtime insulin to prevent high blood glucose (hyperglycemia) after you eat.



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