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From Valley Forge, Pennsylvania, USA:

I'm totally confused about the activity duration of Iletin II (pork NPH). I searched your website under Insulin and found the following profile for NPH:

Begin: 2-4 hours; Peak: 6-8 hours; Gone: 12-15 hours.

I called Eli Lilly and they gave me the following numbers for NPH:

Begin: 4-6 hours; Peak: 8-14 hours; Gone: 16-20 hours.

Which one is correct? I also asked about the peak activity and Lilly stated that the NPH remains at peak level during the 8-14 hour period, a 6 hour peak level. Is this also accurate and if not what exactly is?


You will find slightly differing opinions as to when each insulin starts to work, peaks, and ends. In my experience, there is tremendous individual variability in when each insulin starts to work, peaks, and ends. (There may also be day to day variability with the same insulin in the same individual.)

A few points which are almost always true:

  • lispro insulin [Humalog® brand] works faster than Regular which works faster than NPH, which works faster than Ultralente. Lente and NPH have similar times of action though lente may last an hour or two longer in some individuals.
  • Smaller doses don't last as long as larger doses of the same insulin in the same individual.
  • Human insulins may work slightly faster than the corresponding pork or beef insulin.
  • The same insulin may start to work faster if injected into an exercising limb.
  • The same insulin may start to work faster when the temperature is warmer.

I usually recommend to patients if they want to figure out when a particular insulin is working in themselves, to make small changes of one insulin at a time and see when the blood sugars really changed (as opposed to when you predict they will change based on published times of action).


Original posting 10 Dec 97


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Last Updated: Tuesday April 06, 2010 15:08:56
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