Diabetes is difficult to control in many dogs. It is important to interpret the glucose curves and try to figure out what the administered insulin is doing. In a case in which the insulin does not appear to be working effectively, several things have to be considered. The first thing is handling and administration of the insulin itself. Insulin should not be roughly shaken, very gently mixing the insulin or rolling the bottle between your palms is sufficient to mix it up.
Cloudiness can be a sign of deterioration in some insulin.
Some dogs are hard to inject with insulin. In other cases, scar tissue or irritation may develop if one specific spot is used over and over again. Dog's immune systems can recognize the insulin used as a foreign invader and learn to destroy it. Changing types of insulin can help if this sort of reaction occurs. The next group of things to think of are other health problems that may be complicating the use of insulin.