NPH insulin, also known as isophane insulin, is an intermediate–acting insulin given to help control blood sugar levels in people with diabetes. It is used by injection under the skin once to twice a day. Onset of effects is typically in 90 minutes and they last for 24 hours.Versions are available that come premixed with a short–acting insulin, such as regular insulin.

The common side effect is low blood sugar.Other side effects may include pain or skin changes at the sites of injection, low blood potassium, and allergic reactions. Use during pregnancy is relatively safe for the baby. NPH insulin is made by mixing regular insulin and protamine in exact proportions with zinc and phenol such that a neutral-pH is maintained and crystals form.There are human and pig insulin based versions.

Protamine insulin was first created in 1936 and NPH insulin in 1946.It is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system.

MEDICAL USES

NPH insulin is cloudy and has an onset of 1–4 hours. Its peak is 6–10 hours and its duration is about 10–16 hours.

It has an intermediate duration of action, meaning longer than that of regular and rapid-acting insulin, and shorter than long acting insulins (ultralente, glargine or detemir).

VARIOUS NAMES

NPH stands for neutral protamine Hagedorn, and the words refer to neutral pH (pH = 7), protamine (a protein), and Hans Christian Hagedorn (an insulin researcher). Brand names include Humulin N, Novolin N, Novolin NPH, Gensulin N, SciLin N, Insulatard, and NPH Iletin II.