Protamines are proteins derived from the sperm or testes of salmon or related fish. They are added[1] are added to insulins NPH Neutral Protamine Hagedorn and PZI protamine zinc to delay their absorption.

The difference between isophane/NPH insulins and PZI insulins is the amount of protamine used; there is more in PZI than in NPH/isophane insulins. It's the extra protamine which makes the PZI a slow-acting insulin.

The basis of absorption of any insulins containing protamine[2] is the breakdown of this protein by proteolytic enzymes[3] or proteases in the body. Only after this is accomplished can the insulin itself be absorbed. More protamine in the suspension means insulin absorption will be delayed longer; less protamine means the insulin will be act faster.

Protamine, like insulin itself, is a protein. In the case of antibody formation, it is possible that the insulin itself is not the cause of them; the proteins present in the suspension, such as protamine, may be[4]. In this case, changing the type of suspension would solve the problem.

Protamine has other medical uses as well.

See also suspension.


  1. Journal Allergy & Clinical Immunology 1998-Protamine
  2. Copy of text from Endocrinology
  3. Wikipedia: Proteolytic Enzymes
  4. Vetsulin-Problems With Regulation of Diabetes Mellitus-Antibodies
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