Canine Diabetes Wiki




All insulins have and need preservatives so that the insulin--whether in vials, pens, or cartridges--has some "shelf life" after the container is opened/started. Preservatives keep bacteria from growing in the containers of insulin once they've had their first use. [1] If bacteria begins growing in a vial, it can degrade the insulin, thus making it ineffective. [2][3]

Though most of the food we eat has some kind or preservatives in it to keep it fresher longer, no one expects that a loaf of bread, will keep indefinitely in the refrigerator without becoming moldy.

The same is true for insulin; it also has preservatives in it to allow us to keep it for a given time period. [4] Just as the bread's preservatives won't keep the bread fresh forever, neither will the insulin's preservatives. This is one of the reasons manufacturers provide information regarding how long opened insulins should be kept.



Use of the wrong preservative with the various types of insulin can make it totally worthless; this is why when using manufactured diluents, care must be taken to match the proper diluent with the insulin. [5]

Meta-cresol preservative[]

Meta-cresol and phenol preservatives: non-mixed[]

Meta-cresol and phenol preservatives: mixed[]

NPH/isophane,Levemir, all NPH/isophane Mixed insulins--regardless of origin--have both m-cresol and phenol as preservatives.

Phenol preservative[]

PZIs contain only phenol as a preservative.

Methylparaben preservative[]

Lente, semilente and ultralente use methylparaben as a preservative. Another name for it is methyl hydroxybenzoate. [13]


  1. Diabetes Forecast-page 5. American Diabetes Association (2006).
  2. Cook, Audrey (1 April 2010). Identifying the reasons behind difficult-to-control diabetes in dogs. DVM 360.
  3. Insulins-How To Store Insulin. DiabetesNet.
  4. Resource Guide. American Diabetes Association (2005).
  5. Lilly Discontinues Diluent for all Lente & Ultralente Insulins. Diabetes In Control.
  6. Insulin. InChem.
  7. Insulin. InChem.
  8. Insulin. InChem.
  9. Insulin. InChem.
  10. Insulin. InChem.
  11. Insulin. InChem.
  12. Insulin. InChem.
  13. Insulin. InChem.