NPH Insulin
Mixing regular insulin with a fish protein called protamine forms a crystal (neutral protamine
Hagedorn, NPH), which dissolves slowly when injected subcutaneously, so that the effect on average lasts for
about eight hours (shorter duration for very small doses and longer duration for large doses). The crystals of
NPH insulin appear white to the naked eye, and they tend to settle in the insulin vial. This is why you should
mix the NPH insulin (by rolling the bottle between the palms of your hands) before drawing it up in the
syringe.
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