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Glargine (Lantus) and Detemir (Levemir) Insulin
Revised: November 14, 2023
Published: December 19, 2004

Brand Names: Lantus®, BASAGLAR® (bio similar) and SEMGLEE® (bio similar)

  • Insulin glargine and insulin detemir are available in 3 ml (300 unit) pen ejectors and in 10 ml (1,000 unit) bottles.
  • Lantus®, SEMGLEE®, and generic insulin glargine are available in either vial or pen.
  • BASAGLAR® is only available in a pen.

Insulin pens are commonly sold in bundles of five. 

The generic insulin glargine is now available in the U.S. While Insulin glargine and SEMGLEE® are almost equally expensive, the generic is far less expensive. BASAGLAR® is approximately 30% less than Lantus® or SEMGLEE® (in the US).

Regulating a diabetic cat can be tricky. Finding an insulin that lasts long enough is a substantial problem in most cats. Insulin glargine (brand names Lantus® and BASAGLAR®) is approved only as a human product, but its use has become common in diabetic cats, and many consider it to be the first choice of insulin for a newly diagnosed feline diabetic. Detemir (Levemir®) insulin is another long-acting insulin for humans that is gaining popularity in veterinary use. ProZinc® is another insulin that tends to have a long enough duration in cats.

In human diabetes mellitus, the trend has been towards the use of ultra-short-acting synthetic insulin (like Humalog®) at mealtime and a once-a-day, long-acting peakless insulin (slow-release, such as insulin glargine) to provide general blood sugar control throughout the day. Insulin glargine is available at any drug store and is designed to be long-acting and provide a diabetic person with a "tone" of sugar control that lasts all day.

In cats, insulin glargine and detemir are not peakless; they have a high point and low point, but in most cats, they last long enough to control blood sugar levels throughout the day. In newly diagnosed diabetic cats, studies with insulin glargine showed such good control when used in combination with an all-canned low-carbohydrate diet and weight loss (if the cat is obese) that many cats revert to a non-diabetic status in a matter of weeks.

It is important to realize that diabetic remission is about good regulation early in the course of the disease, and there is no magic product. Cats that have been diabetic for some time tend not to experience remission. If your cat is well-regulated on one type of insulin, it is not worth changing and having to re-regulate your cat.

What You Need to Know

  • Even though insulin glargine and detemir are long-acting insulins, either one will probably need to be given twice a day, just like other insulins. Furthermore, every cat is different, and some cats metabolize these insulins so quickly that they are not long-lasting at all, and another insulin is a better choice.
  • Insulin glargine cannot be diluted, nor can detemir. The feline dose of insulin is generally only a few units, and the gradations on an insulin syringe are tiny. With insulins other than insulin glargine or detemir, dilution is possible so that measuring is easier. The long activity of insulin glargine depends on the formation of small crystals at the injection site. Diluting insulin glargine or determir interferes with the crystals.
  • Insulin glargine and detemir are available in 3 ml (300 unit) pen ejectors and in 10 ml (1,000 unit) bottles. To be cost-effective, vials and pens must be refrigerated after they are opened (despite the label instructions to humans that it may be unrefrigerated). Insulin glargine has been formally studied and found to retain activity for six months if refrigerated. The 10 ml bottle of insulin glargine will expire in one month if it is not kept refrigerated. Its manufacturer has studied detemir, and the vial or pen will last 40 days whether it has been refrigerated or not. Open pens or vials are commonly refrigerated for three to four months and appear to maintain strength.
  • It is standard practice in veterinary medicine to keep an open bottle or pen of insulin glargine for four to six months in the refrigerator. Discard if the clear appearance of the insulin turns cloudy.

Since the insulin is kept for so long, buying the bundle of five pens is more cost-effective, as each contains 3mls (300 units). It is unusual to use a 10 ml bottle (1000 units) in a cat, even if the bottle is kept for four to six months before discarding, so more insulin is wasted when the remainder left in the 10 ml bottle is discarded. 

If the bundle of 5 pens is opened one at a time, keeping open and unopened pens in the refrigerator and discarding each open pen after four to six months means that the bundle of five pens will last 20-24 months in total.

  • Pen needles must be purchased when using an insulin pen. The biggest problem is that the disposable needles, which screw onto the pen for single use, are made for humans; they are 5/16", which is only about 1/4" in length, and may not penetrate thick cat skin fully. If the insulin is injected into the skin itself (Intradermal), it is quite painful.
  • If you choose a pen instead of a vial for insulin use, you will likely need to get compatible needles in a longer length. Be sure to order the half-inch needles (12.7 ) for your pen rather than the 5/16" that human diabetics use. Check with your pharmacist about what needle tips go with your brand of pen.
  • Insulin doses that are in whole units (e.g., one, two, or three units) are injected using the pen. If the insulin dose contains a half-unit (0.5 units) (e.g., 1.5 units, 2.5 units, 3.5 units), that dose cannot be dialed into the pen. In this circumstance, use a U100 insulin syringe to withdraw the dose of insulin from the insulin cartridge in the pen and inject your cat with that syringe.
  • Because of the strong chance of a cat going into remission (i.e., becoming non-diabetic), it is important for you to be well-informed on the signs of hypoglycemia and to adhere to your veterinarian’s recommendation on when to have your cat’s glucose checked.
  • The expense of human insulin has come to be extreme in the U.S., and all the insulins discussed here are made for humans. It is helpful to know that BASAGLAR® pens are typically around 60% of the cost of Lantus or SEMGLEE®. Generic insulin glargine is approximately 20% of the cost of Lantus or SEMGLEE®.
  • The high remission rates reported for diabetic cats apply to cats newly diagnosed with diabetes, who are on an all-canned cat food diet containing very low carbohydrate content, and who are monitored aggressively to ensure their blood glucose levels go into the normal range as quickly after diagnosis as possible.
  • Cats switched to insulin glargine or detemir for better glucose control after being diabetic for years do not tend to revert to non-diabetic status.

Learn more on how to give insulin to your cat.

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