Nora Apothecary

Insulin Update

For many years, veterinarians have used human-approved insulin products in diabetic animals, since there is no veterinary-approved product. The most frequently used insulin product in animals was PZI, a long-acting mixed beef/pork combination. A few years ago, Eli Lilly & Company stopped production of PZI, leaving veterinarians with fewer effective choices, especially for treating some cats. Many veterinary patients were converted to other mixed beef/pork insulin products at that time. Now, Lilly has announced its intention to discontinue production of all mixed beef/pork insulins in late 1998. Existing stock will remain on the market, and it is anticipated that supplies will last until sometime in 1999. The company will presently continue to manufacture purified pork insulin (the only remaining animal insulin). According to the company, demand for animal insulin has sharply declined during the last decade due to the availability of human recombinant DNA insulin (referred to as human insulin).[1]


Veterinarians will likely want to start newly diagnosed patients on human insulin while monitoring the availability of remaining supplies of the animal insulin for patients currently using the mixed beef/ pork insulins. The biggest challenge in switching from animal to human products has been in some cats. The reason is likely due to the fact that feline insulin more closely resembles beef insulin than human insulin. Another challenge in cats and small dogs is due to the strength of the human-approved products, which is 100 units per milliliter. Some animals require such small doses that the insulin must be diluted prior to use. Dilution of insulin presents still another challenge, since insulin products are incompatible when diluted with normal diluents. Stability of diluted insulin may last from a few hours with normal saline up to 24 to 48 hours with sterile water according to some reports, depending upon the insulin product diluted. While this time frame may be acceptable for immediate use in a clinic, it is unacceptable for use at home. Fortunately, pharmacists have access to specific insulin diluents and can assist veterinarians in meeting these patients’ special needs. When insulin is diluted with specific insulin diluents using aseptic technique, the diluted product can generally be used safely for six to eight weeks when kept under refrigeration. (The product is actually reported to be stable until the expiration date of the original bottle, but good standards of practice limit the length of time a multiuse injectable should be used). Note: Clients should also be instructed to watch all insulin products for cloudiness or discoloration and should discard those products immediately.


The manufacturer of insulin recommends storing insulin products in the refrigerator. However, the main reason for refrigeration applies to previously available “acidic” insulin products, which were relatively unstable at room temperature and required refrigeration at all times to maintain potency. The currently available products have a “neutral” pH, which gives them much greater stability at room temperature. One study has shown that neutral regular insulin is stable at room temperature for 24 to 30 months. [2]

Pharmacists and veterinarians often receive calls from patients and clients who have unintentionally left insulin out of the refrigerator for extended lengths of time. If the vial is returned to the refrigerator, it will likely retain its stability until expiration date. But, the client should be instructed to observe the product continually for signs of flocculation, which can be seen as an “etched or frosted” appearance with the insulin apparently clumping and adhering to the side of the vial. Flocculation causes the insulin to become subpotent and has been attributed to heat/overagitation of the vial & using a small volume from the vial over an extended period of time. Also, freezing may cause “clumping” of insulin suspensions resulting in a separation between insulin and diluent. Insulin which has been frozen or which is flocculated should be discarded to avoid inaccurate dosing and a loss of diabetes control. [2]


[1] Eli Lilly & Company: Toll-free telephone number for information about insulin: 1-888-885-4559.
[2] Micromedex
[3] “CVM Update,” Center for Veterinary
Medicine, FDA:



The Food and Drug Administration’s Center for Veterinary Medicine, on July 24, 1998, approved the use of enrofloxacin, a fluoroquinolone, in cattle. The drug, marketed as Baytril 100 Injectable Solution, is restricted to use by or on the order of a licensed veterinarian and is intended to be used for the treatment of individual animals for bovine respiratory disease associated with Pasteurella haemolytica, Pasteurella multocida, and Haemophilus sommus. The product is not to be used in cattle intended for dairy production or in veal calves. There is a 28 day slaughter time. Veterinarians should be reminded that the drug must be used only in accordance with the label, since extralabel use of fluoroquinolones in food animals is banned by the FDA. [3]


Since enactment of the Animal Medicinal Drug Utilization Clarification Act (AMDUCA) by Congress, which legalized extra-label drug use by veterinarians in animals under certain circumstances, many questions have arisen regarding the legal responsibilities of veterinarians under this legislation. One of the frequently asked questions concerns labeling requirements when a drug is prescribed and dispensed by a veterinarian in an extra-label manner. The following information must be included on the label of the dispensed drug: (1) Name & address of the prescribing veterinarian; (2) Name of the drug; (3) Directions for use; (4) Class/ species or identification of the animal or herd, flock, pen, lot, or other group; (5) Dose, frequency, route of administration; (6) Length of treatment; (7) Any cautionary statements; (8) Specified withdrawal, withholding, or discard time(s) for meat, milk, eggs, or any other food that might be derived from the treated animal(s). It should be noted that individual bottles of medication need to be labeled except “when large numbers of animals need to be treated in an extra-label manner for a short period (e.g. feedlot use).” In that event, “case-labeling” is appropriate. [3]

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