WITH THE release of NPH insulin for sale on the open market, details concerning its action become of importance to physicians and patients. This new modified protamine insulin is an "intermediate insulin," with a duration of action longer than that of unmodified (crystalline or regular) but shorter than that of protamine zinc insulin.1 NPH insulin, however, resembles protamine zinc insulin in its action much more closely than it does unmodified insulin.
The effect of NPH insulin lasts 26 to 30 hr. in the average nonfasting diabetic patient, and the intensity of action is greater than that of protamine zinc insulin at any given time. Thus, patients who previously required an injection of crystalline2 insulin along with that of protamine zinc insulin may now, in certain instances, achieve comparable control of diabetes with a single injection of the NPH variety. In certain less easily controlled patients taking NPH insulin,
STEPHENS JW, DONALDSON RM, MARBLE A. USE OF MIXTURES OF NPH AND UNMODIFIED INSULINS. AMA Arch Intern Med. 1951;88(3):356-361. doi:10.1001/archinte.1951.03810090087008