Managing
Feline Diabetes Mellitus
Fiona McClure, BVSc MVSc DACVIM
I doubt that anyone will ever tell you that managing diabetes mellitus (DM) is
a "piece of cake". For a disease with a fairly straight forward
pathophysiology, it really does provide a challenge to all of us. Some new
ideas pertaining to managing this disease in our feline friends are interesting
and in my experience have made treatment a lot easier and more successful. I
now recommend a low carbohydrate diet (Purina DM canned and dry, canned kitten
food) for diabetic cats unless they are moderately to severely azotemic (I use
a cut-off of BUN ~ 80 mg/dl). I have found that the canned kitten food is the
tastiest and have had less success with the dry DM compared with the canned DM
(the cats seem to need more insulin). The diet should be meal-fed (BID
feedings), not given free choice. When I meet a diabetic cat that is already
receiving insulin and I change his diet to a low carbohydrate diet I definitely
decrease the insulin dose (best to halve it) to be sure that hypoglycemia does
not occur
For a newly diagnosed feline DM patient I choose between insulin and an oral
hypoglycemic agent. An oral hypoglycemic agent is more likely to work in an
obese cat. The majority of the time I use insulin - certainly I do this if
there is already neuropathy or if there is a history of ketosis or marked
weight loss. I usually start with human recombinant insulin, usually NPH,
although other veterinarians use Lente or Ultralente with success, proving that
there is not really a "wrong" type to start with (although absorption
of ultralente can be problematic in some cats). I generally reserve beef PZI
for cases that are not doing well on the other types of insulin. Almost all
cats need BID insulin, so I generally start with 1 unit BID and work upwards
from there. The site of insulin administration is varied to prevent fibrosis at
one site (leading to subsequent poor absorption) and thick skinned/fatty areas
of the body are avoided. A new bottle should be purchased every 2-3 months.
If I decide to use an oral hypoglycemic agent, I usually use glipizide (dose
2.5 to 5 mg PO BID), but other choices are glimiperide (1-2 mg PO SID) and
acarbose (12.5 mg PO BID). Glipizide and glimiperide work by promoting insulin
release and increasing insulin receptor sensitivity. The side effects are not
that common but include anorexia, vomiting and liver disease. Giving the drug
with food helps to reduce side effects. Acarbose is another oral hypoglycemic
drug and although I haven't used it much, I have seen a few patients do quite
well with this medication. Acarbose works by impairing carbohydrate digestion
and subsequently glucose absorption from the intestine. Side effects are
flatulence and diarrhea. Don't use metformin in cats - it doesn't work well and
it has severe side effects. I usually don't give insulin and oral hypoglycemics
together.
I send the owner home with ketodiastix to monitor the urine several times a
week. Here I am looking for ketonuria (if present, the client should call
immediately) and the absence of glucose in the urine. If the latter occurs for
more than several days in a row, then a dose reduction of insulin needs to be
considered. I NEVER increase the insulin dose based on a urine glucose concentration
alone.
When starting insulin therapy in a newly diagnosed diabetic cat, I usually
monitor the blood glucose (BG) several times per day after the first dose of
insulin. I do this to make sure that hypoglycemia does not occur. I may do a
glucose curve near the beginning of treat
ment mainly to assess the duration of effect of the insulin. This has to be
interpreted cautiously. We all know about the possible effect of stress on BG
measurements in our patients. Another word of warning about glucose curves
comes from a research abstract at the ACVIM conference last year which showed
that a glucose curve can vary a huge amount on 2 consecutive days. In fact,
treatment recommendations in the patients studied were different 65% of the
time depending on which curve was assessed. In the majority of patients, the
recommendations were completely opposite (i.e. one curve suggested a decrease
in dose was needed but the curve the following day suggested an increase in the
dose was needed!).
In cats I try to rely on fructosamine concentrations and "spot" BGs
taken 6-8 hours after the insulin dose. I do these 2 tests together every 3-4
weeks or until control is adequate, then 2 to 4 times per year. Fructosamine
reflects the overall BG in the last 2-3 weeks. I aim for fructosamine < 400
mg/dl and a BG < 180 mg/dl. If fructosamine is ideal, but BG is high, this
probably just reflects a stressed cat at venipuncture. If both are high, the
insulin dose is increased and if the BG and fructosamine are low, the insulin
dose is reduced. If the BG is low, but the fructosamine is high, I might
suspect that owner compliance is not optimal at home (i.e. missing doses of
insulin on some days but doing a great job on the day that the cat needs to
visit the vet).
Finally, one of the things that I have learned about feline diabetics is to not
"over-control" them. Definitely I want to avoid ketoacidosis, marked
weight fluctuations, excessive PU/PD and polyneuropathy, but I also want to
avoid hypoglycemia. I think that it is very important to take a step back from
the patient and base a lot of decisions on attitude, appetite, severity of
PU/PD and body weight rather than getting bogged down with laboratory data.
This article was originally printed in Spring
2002 SouthPaws Newsletter
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