Reader Questions: What you want to know about diabetic regulation

Editors' note: In our April issue as an accompaniment to the article "Identifying the reasons behind difficult-to-control diabetes in dogs" by Dr. Audrey Cook, we asked you if you had questions for Dr. Cook about diabetes. Here are her responses.

Dr. Audrey Cook

TRANSITIONING TO A NEW INSULIN

Q. Now that Vetsulin (Intervet/Schering-Plough Animal Health) is difficult to obtain, what is the best way to transition dogs from Vetsulin to NPH? How will transition differ between regulated and not yet regulated dogs? How easy is it to transition them?

A. The safest way to switch an established diabetic dog from Vetsulin to NPH is to start NPH at 0.25 U/kg given subcutaneously twice daily and then adjust the dose based on the response. I would plan to do a blood glucose curve (with a measurement every two hours) the day I first give the new insulin, as I am always worried about causing hypoglycemia when I make a switch. If the glucose concentration goes below 100 mg/dl, I would decrease the insulin dose by 25%. If the nadir was > 150 mg/dl, I would increase the dose by 10% to 20%. (I'd start at 10% but may have to increase the dose a bit depending on the number of units.)

For a new diabetic, I'd start the NPH at the same dose, but the rules about the target nadir are different. In a new diabetic, I want my lowest measured glucose concentration on that first day's curve to stay above 150 mg/dl because most dogs become more responsive to insulin after the first week or so as the metabolic effects of untreated diabetes are reversed. If I was starting NPH in a very poorly regulated dog, I would treat it like a new diabetic, as those dogs also suffer substantial metabolic derangements from inadequately managed diabetes. After the first week, I'd recheck the dog or have the owner do a glucose curve at home and then adjust the insulin doses as necessary based on the nadir, average blood glucose concentration, and duration of effect.

Q. If you have a personal preference between PZI and glargine, I would like to hear it. We are leaning more toward glargine because it is a human product and easy to obtain. Any hints on transitioning cats?

A. Now that there is a newly FDA-approved PZI U40 product for cats (ProZinc—Boehringer Ingelheim Vetmedica), availability of PZI should not be a concern. I think that choosing glargine or PZI is a matter of personal preference and experience. I still reach for glargine in a newly diagnosed diabetic cat because I am comfortable with this insulin and have had good success with it. For both insulins, I start at 0.25 U/kg of lean body weight twice daily, which is usually 1 U/cat. If the cat is truly large (and not just fat), I would start at 2 U twice daily.

Again, I would try to do a glucose curve to identify hypoglycemia after the first dose and also encourage the owner to start checking blood glucose concentrations at home. On that first day, I do not want to see the glucose concentration go below 150 mg/dl. Because many cats undergo diabetic remission, I want to be vigilant for hypoglycemia so that I can promptly decrease the insulin dose as necessary. I am very cautious about increasing the insulin dose in a cat during the first month of therapy, as weight loss, dietary changes, and the management of insulin resistance will often improve insulin sensitivity dramatically.

If I had a feline patient that was receiving Vetsulin, I would start with the same dose of 0.25 U/kg of lean body weight when I switched to glargine or PZI.

HOW HIGH IS TOO HIGH?

Q. I have a patient named Sandy who is a 10-year-old spayed female terrier mix. She was diagnosed with diabetes mellitus in November 2009. At the time, she was a slightly obese dog (BCS 6.5/9), but she is now 25 lb (BCS 5/9) and receiving 8 U NPH twice a day.

I have been monitoring her glucose concentrations (every seven to 10 days the first two times and then every three to four weeks), usually five to six hours after the morning insulin dose. According to the owner, Sandy does not have polyuria, polydipsia, or polyphagia; does not have an urgency to urinate during the night; and is doing well in general. The last glucose concentration was 333 mg/dl, which, again, was measured five to six hours after the last insulin dose. Unfortunately, she is a very aggressive patient.

A glucose concentration of 333 mg/dl is still high, but I am hesitant to change the dose because of the owner's good subjective opinion about signs of glucose control and the dog's stable physical examination findings. Should I increase the insulin dose until the glucose concentration decreases, regardless of the clinical signs? Measuring a fructosamine concentration is not an option because of financial limitations. And I think performing a glucose curve in the clinic is not an option either. If I do not increase the insulin dose, will the dog have significant complications from having a glucose concentration higher than ideal?

A. I would not feel comfortable increasing an insulin dose based on a single glucose measurement. The reason for this is that you do not know what the true nadir (true lowest value) was, and there is a real risk of an overdose. In addition, it is always important to look at the whole patient for signs of good regulation or poor regulation. If the owner reports minimal clinical signs, and body weight is holding on target, then I would certainly not increase the insulin dose based on this one reading. This dog may be a good candidate for at-home monitoring, and it would be an inexpensive way to get a lot more information. Your client can review several great Web resources.

Q. I have a feline patient with a glucose concentration of 409 mg/dl (measurement obtained four to six hours after the morning insulin dose) that is doing well according to the owner. Since this is a high concentration, should I increase the insulin dose?

A. With feline patients, glucose concentrations measured in the hospital are often a poor representation of glucose concentrations in the home. Stress can trigger massive sustained hyperglycemia in cats, so it is always important to look at the whole picture. Again, checking glucose concentrations at home is often a great option. Otherwise, I would look at clinical signs (including weight) and consider measuring a fructosamine concentration. If this is on target, you have good evidence of acceptable glycemic control.

Audrey Cook, BVM&S, MRCVS, DACVIM, DECVIM-CA

Department of Small Animal Clinical Sciences

College of Veterinary Medicine

Texas A&M University

College Station, TX 77843