Feline Diabetes Mellitus

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In Part 1 of this article (IVC, Winter 2012), I covered the diagnosis of feline diabetes mellitus, and how early DM can be managed with diet, medication and herbs. Now I’ll discuss insulin stabilization and home monitoring, the complications that can occur with the disease, and the reasons why some cats don’t recover.

Insulin requirements

Feline DM is treated with Rx insulin injections twice a day (BID) combined with home BG monitoring. Cats metabolize insulin twice as fast as dogs or humans, and ideally, a cat with DM should be eating a very low carbohydrate diet twice a day. Hence the ultra-long-acting human insulins, Glargine “Lantus” or Detemir “Levemir”, work best for these cats.

• Rx Glargine = “Lantus”: This acid pH insulin precipitates in the neutral pH of the body and is absorbed slowly. The initial dose is 1 to 2 IU/cat twice a day. It lasts 12 to 18 hours. The bottles are 10 ml and fairly expensive.

• Rx Detemir = “Levemir”: The Detemir insulin is strongly protein bound (that is, albumin bound) and slowly released. The initial dose is 1 to 2 IU/cat twice a day. It lasts 18 to 21 hours. One box contains 5 x 3 ml vials. Detemir appears to be better tolerated than Levemir in some cats, and may have less variability. As Detemir is strongly protein bound, there is the potential for drug interactions. Other drugs commonly used in cats that are also strongly protein bound include the injectable long-acting penicillins, long-acting cephalexin, and Rx Propofol, an injectable anesthetic.

I now prefer “Levemir” insulin in my diabetic cats. I find the BG nadir occurs, on average, about three to six hours after injection, and there is a fairly flat BG curve. On “Lantus” and “Levemir”, over 80% of my newly diagnosed diabetic cats recover within three months. I purchase the box of “Levemir” and dispense the 3 ml vials to owners.

BG testing

Should BG be tested just before or after injecting the insulin? The BG that indicates the dose of insulin is the nadir or lowest level. I recommend that owners initially test three to six hours after injecting insulin approximately once a week, at midday or evening. They also need to test if the cat is acting strangely, is weak or not eating.

• I recommend that all owners of diabetic patients home monitor if possible. In cats, this is usually done by ear vein prick, although the footpad can also be used. Home BG monitoring is best for the patient. I do a Diabetic Consultation (this can be done by a trained Animal Health Technologist). I request that the owners phone in their BG result and plan. I charge for Home Monitoring Phone Consultations either ahead or later.

• The occasional cat requires veterinary BG monitoring, usually due to attitude. In these cats, I recommend the owner give the cat an anti-anxiety medication (Rx Clonazepam 0.5 mg, ½ to 1 tablet) about an hour before the clinic visit. Rx Clonazepam does not affect BG, but it enhances cooperation and reduces the stress of the visit so the BG is more representative of the cat’s glycemic control.

In most diabetic cats, a low carbohydrate diet and glycemic control with insulin injections will result in gradual recovery within three weeks to three months. Often, my diabetic cats have recovered before we have done a BG curve. However, in those cats whose BG becomes stable, and is not decreasing, I do recommend that owners perform a BG curve, testing at three, six and nine hours after the morning insulin injection. If the nine-hour BG is not higher than the six-hour BG, I request a 12-hour BG, just prior to the next insulin injection. This BG curve tells us approximately when the nadir or lowest BG occurs, and hence, when the owner should be spot testing. At the nadir, we aim for a normal BG of 3.5 to 6.0 mMol/L = 65 to 110 mg/dL.

Why do some cats not recover?

Owner problems:
• Cat is eating some dry food or high carbohydrate canned food
• Obesity and little exercise
• Long-standing unstabilized diabetes

Veterinary problems:
• Short-acting insulins with high BG for hours twice a day
• BG done in vet clinic, which causes repeated stress hyperglycemia
• Infection, especially gingivitis or urinary tract infection

Medical problems:
• Hyperthyroidism with T4 > 35 nMol/L = 2.7 ug/dL — I initially use Rx Methimazole, 5 mg, 1/4 tab BID for three days. Depending upon the initial T4, I may test the level or increase the Rx Methimazole to 1/2 tablet BID. After four weeks, I measure T4, collecting the blood about four hours after the morning pill. I prefer to run a CBC, Chemistry and T4, or at least serum creatinine with the T4. Based on the result, I adjust the Rx Methimazole dose, aiming for a T4 of 20 to 30 nMol/L = 1.5 – 2.2 ug/dL. If I am unable to control the T4 medically, then I perform Sx bilateral thyroidectomy, taking care to preserve the parathyroid glands. These cats do extremely well. Of course, the gold standard is radioactive iodine, but this procedure is not available in every city, it’s expensive, and cats cannot be receiving insulin injections nor have significant chronic kidney disease.
• Rx Prednisone, Prednisolone or Dexamethasone — If the diabetic cat requires glucocorticoids for another medical problem, they should be given twice a day along with the insulin injections. As long as the cat is on steroids, he will not recover from the diabetes. Neither Rx Depo-Medrol nor Rx Prednisone should be used in cats. Rx Depo-Medrol predisposes cats to diabetes even more than daily steroids, due to the excessively high level reached initially. Rx Prednisone is poorly hydroxylated to the active form prednisolone in the cat. Rx Dexamethasone has the advantage of being active (not a precursor) and is tasteless, so can be crushed and mixed into the cat’s food. Cats on steroids will require a higher dose of insulin. The aim is the same – normoglycemia.
• Hypersomatotropism (gigantism) — These cats have excessive growth hormone secretion from their pituitary glands. They are big cats with large heads, and are insulin resistant, often requiring 5 to 10 units BID. However, their diabetes is quite stable and they do very well.
• Hyperadrenocorticism (Cushing’s Syndrome) — This problem is rare (two to three cases per vet in a lifetime). These cats are characterized by insulin resistance, recurrent infections, and thin skin that tears easily but heals amazingly well. They remain polyphagic, polydipsic and polyuric. They develop muscle wasting and weakness. They are quite characteristic clinically, and they have elevated alkaline phosphatase levels. Diagnosis is confirmed by ACTH stimulation test. Treatment is done with Rx Trilostane and Melatonin.


Diabetes mellitus in cats is a disorder that can largely be prevented by avoiding or limiting dry cat kibble, as discussed in Part 1. Appropriate protein feeding is the most important thing we can do for feline health. To enable recovery, low carbohydrate food is essential once a cat has become diabetic. Detemir insulin enhances this recovery. Of course, once a cat has been diagnosed as diabetic, he must always remain on low carbohydrate cat food.

Dr. Lea Stogdale, DVM, Diplomate ACVIM, graduated from the Faculty of Veterinary Science, University of Melbourne, Australia in 1970. She worked in general practice in Australia and England before teaching veterinary medicine in South Africa and Saskatoon for eight years. Dr. Stogdale passed the veterinary small animal internal medicine specialty board exams in 1981 to become a Diplomate in the American College of Veterinary Internal Medicine. She has worked in emergency and pet practice for 25 years, taking a special interest in diabetes of dogs and cats, complementary medicine and nutrition (

Diabetic complications

• Cataracts — don’t occur; no glucose oxidase in lens
• Microangiopathy — doesn’t occur • Increased infections — gingivitis, urinary tract infection
• Hind leg plantigrade stance — recovers with a delay
• Diabetic cats do very well, but diabetes makes any other medical problem difficult to manage, especially chronic kidney disease, since insulin is excreted by the kidneys.