What is intermediate-acting insulin?

Updated: Oct 04, 2017
  • Author: Mini A Mathew, DO, PharmD; Chief Editor: George T Griffing, MD  more...
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Insulin NPH (Humulin N, Novolin N) is an intermediate-acting insulin that is a suspension of crystalline zinc insulin combined with the positively charged polypeptide protamine. Unlike the shorter-acting insulins, NPH has a longer duration of action, yet not as long as the newer long-acting insulins. Insulin NPH's onset of action is 2-4 hours, peak action is 4-10 hours, and duration of action is approximately 12-18 hours.

NPH insulin is also available in combination with regular insulin (insulin isophane human/insulin regular human). They are in a fixed combination of either 70% or 75% of NPH and 25% or 30% of regular insulin. These are marketed as Humulin 70/30 or Novolin 70/30. It is also available with NPH and a rapid-acting insulin combination. NPH/lispro mixtures are Humalog Mix 50/50, Humalog Mix 50/50 KwikPen, Humalog Mix 75/25, and Humalog Mix 75/25 KwikPen. NPH/aspart mixtures are marketed as NovoLog Mix 70/30 and NovoLog Mix 70/30 FlexPen. These combinations are a good option for patients who may be noncompliant, those who want to reduce theirnumber of self-injections, and those who are unable to use more sophisticated regimens. On the other hand, it is hard to manipulate the dosing because they are in a fixed combination.

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