You probably know this better than I, but the doctor advised us that Humulin N and Novolin N are not interchangeable; while they are the “same” insulin (NPH), the manufacturing process is different, affecting dosage.

In our pet’s case, the Dr. had conducted a series of exams to determine Humulin N dosages — which he advised us we would have needed to redo if we switched her to Novolin.

I think in humans it is easier to get blood readings, but in the dog’s case the Dr. needed to keep her in hospital to do a series of “curves;” this was expensive, so we did not want to redo.