Controlling Diabetes Mellitus without Insulin (Spoiler: It Only Works in Special Situations)
In people, diabetes is readily classified into Type I and Type II forms. The Type I human diabetic has no capacity for insulin secretion and is totally insulin dependent. The Type II diabetic develops diabetes later in life and simply has an inadequate (i.e. only partial) capacity for insulin secretion. Since insulin injections are unpopular among people, there is a demand for oral products to control blood sugar. Unfortunately, there is just no substitute for insulin when you need it. That said, there are ways to improve insulin secretion where there is potential to do so, plus we may be able to make what little insulin there is work better.
Insulin injections are not only unpopular with people receiving them; they are also unpopular with people administering them to their pets. Dogs, like Type I human diabetics, are universally insulin dependent and oral products have been a crashing failure in this species, with the exception of acarbose (see below). In cats, there is a more positive outlook, though insulin is necessary for most patients. We will summarize what is available.
Oral Agents for Cats
It seems that in general, cats experience a diabetes that is analogous to human Type II diabetes mellitus; that is, these cats are still able to produce at least some insulin. Many feline patients (up to 30%) are able to experience diabetic regulation using oral medications alone; however, there is no way to identify these patients without trying medication and seeing if it works. For most of the oral products we are about to review, the goal is simply to improve the response to insulin injections.
Glipizide acts by increasing the pancreas’ secretion of insulin, and it is possible that a level of adequate control can be achieved by maximizing the pancreas’ secretion in this way. There is some capacity for side effects (15% of cats taking this medication will get an upset stomach) plus the majority of cats will not be controlled with this medication alone. Glipizide is often used as a last resort (i.e. when it is not possible to give insulin injections) as it increases the pancreas’ insulin secretion, it also increases the pancreas’ amyloid build up, which is what probably caused the diabetes in the first place.
At this time, glipizide is the only oral medication that can be expected to replace insulin injections and it only works for 25 to 30% of cats.
Other oral products reviewed below are meant as supplements to insulin injections.
Metformin (Diabex®, Glucophage®, Diaformin®)
This medication acts by increasing tissue sensitivity to insulin (i.e., it makes insulin stronger). Unlike glipizide, metformin does not cause low blood sugar but lethargy, vomiting, and appetite loss have been reported side effects in cats. It cannot safely be used in cats with kidney insufficiency, with ketoacidosis or any other form of acidosis, or in cats where an iodine-containing radiographic contrast agent is going to be used in the next few days. Since ketoacidosis can come up unexpectedly in a diabetic pet, this product may not be a good choice. Feline studies are in progress but look promising for cats as a supplement to insulin treatment though drug interactions may be problematic. (Interactions have been noted with trimethoprim, ranitidine, cimetidine, furosemide, and digoxin.)
This is a trace mineral present virtually everywhere. It seems to have insulin-like properties and minimal side effects potential but is not likely to be helpful by itself. The form that has been studied was vanadium dipicolinate, which is not commercially available. The vitamin stores sell vanadium sulfate (Vanadyl Fuel®) but we do not know if it works as well as the dipicolinate form did in the research setting.
This product is a mineral supplement that can be found in many vitamin stores. It seems to potentiate the effects of insulin (i.e. the insulin becomes stronger). In cats, chromium picolinate would be used similarly to vanadium, i.e., as a supplement to insulin therapy.
Photo by Dr. Teri Ann Oursler.
Acarbose (Glucobay®, Precose®)
This medication inhibits the digestive enzymes responsible for breaking down starches. Its use leads to a more gradual absorption of sugars after a meal, which in turn leads to a more stable blood sugar level. The medication itself is not absorbed from the intestine and thus can be combined with other medications, but it can produce some intestinal side effects: flatulence, weight loss, and diarrhea. Acarbose was originally developed as a treatment for obesity since it interferes with sugar absorption and should not be used in underweight cats. Acarbose must be given with food if it is to work. Acarbose can be used in both dogs and cats.
In cats, one of the most important aspects of managing diabetes mellitus is using a low-carbohydrate diet, and it would be incomplete not to mention it here. Most experts feel that this change alone is more significant in regulating diabetic cats than any of the above supplements and medications combined. Diet in a diabetic cat should not be taken lightly; if you have not done so already, see current recommendations in this regard.
Dietary therapy is also important for dogs but in a different way. Rather than a focus on low-carbohydrate diets, high-fiber diets have been found to be more helpful.