How to manage Dexamethsone for Chemotherapy with Diabetes?

I don't really know, haven't gone through this myself, but let's discuss this. Doing a quick search I found a statement that the way steroids affect blood sugar is by raising insulin resistance "in the liver". I'm not sure that makes sense, actually, but let's key on the word "liver". So first question, do you also take metformin? If you're not already at full-dose metformin, that would be an obvious thing to try.

Some more numbers would help the discussion. What was your BG reading before treatment, and how high is it going now, in spite of increased insulin? How much insulin were you taking before and how much have you increased it?

What kind of diet have you been following, how many carbs? Can you go full keto, at least for the duration of this treatment? Worth considering.

Now there are other drugs and possibly dietary equivalents. Drugs like Jardiance allow you to excrete sugar, you could talk to the doctor about adding that during treatment. Or there is possibly the "home version" of this - cinnamon! Have you been using cinnamon at all as part of your diet or treatment? About 2000 grams twice a day, about half a teaspoon, sprinkle on whatever it works with, or you can get capsules. But wait, it gets better! Have you tried "resistant starch"? Make some pasta (whole wheat pasta is best), and then put it in the fridge overnight - it becomes "resistant"! Have a small serving of it (about half a cup, about 15 carbs) as part of your meals, say twice a day (this is non-keto, obviously). Not only do these carbs not count quite like normal carbs, but in my experience they seem to help regulate BG effects from other foods. Easy to try. Also works with rice! In fact, one of my regular food items is - rice pudding! Can even find pre-made rice-puddings in the market, complete with cinnamon! Again, not only does this seem to count less as carbs but tends to encourage the liver to behave generally - as best I can figure. I've never tried these against steroids.

Finally - what about exercise? Are you getting your regular exercise while on chemo? If possible, keep moving, walk around the block a time or three, whatever you can manage.

Now with all my tricks when I have stress, apparently the same effect you get from steroids, yeah, the BG goes up. But these are things to try. Only the Jardiance requires a prescription (and is expensive - $600 list price for 30-day supply, of course your insurance may help). So, try the cinnamon first! For extra credit search out some "Ceylon Cinnamon" which is necessary if you are going to use it in volume for more than a couple of weeks, you can search online to see why.

Good luck!