The first step is to figure out why Biscuits needs a larger dose of insulin. That means a blood draw, and asking the vet to send the blood to Michigan State University to test for both acromegaly and IAA or insulin auto antibodies. Once you know what you are dealing with, then you think about treatment options. In the mean time, we search for that dose that will move him. My Neko had both conditions and lived five years with them. One in four diabetic cats has acromegaly. The autobodies are less common. Not all cats with one or both of these conditions needs large doses.
Acromegaly is a benign pituitary tumour that causes the output of excess growth hormone. I did get Neko’s tumour treated with radiation, or sterotatactic radiation therapy. I had it done at Colorado State University. Sarah had Pig treated at Washington State University. Costs at CSU have gone up considerably since I was there. Other kitties here who have had SRT and whose peeps still post sometimes are Bronx and Leo. A second newer option is hypophysectomy, there are a few stories of it on the acro/IAA forum, namely Sophie, Titan and Schmee. The surgeries were done either in New York or London, England. WSU has done a few in the past. There are a couple of medical options, cabergoline being the most common here due to the cost. Amethyst and Olive are two whose peeps post often. We have had three acros go into remission on cabergoline, most have some reduced doses and side effects, though studies have been inconslusive. Between you and me, those studies tested less cats than we have here. Pasireotide is a drug with better research results but it costs an arm and a leg. Finally, some people just treat with the insulin you need. The goal is to get the cat under renal threshold as much as possible, a goal whether or not treatment is done.
IAA is simpler, the antibodies tend to be self limiting around after a year. But can make dosing challenging. Loudogg is an example of an small dose IAA positive kitty here.
Keep asking questions. I am stopping my novel now.