For Type 1's insulin resistance is far more prevalent in those that use higher doses due to the high carb diet that many follow. Nobleheads beloved DAFNE (have your cake and eat it) course recognises that but rather than reduce carbs they recommend using metformin to counteract insulin resistance. See Mo's post over at the DCUK forum below:
Mo wrote:I'm T1 and take metformin. My consultant told me it improves insulin sensitivity. My recent DAFNE course confirmed this as one student who was taking fairly large doses of insulin was told metformin can help reduce this.
http://www.diabetes.co.uk/forum/threads/mdi-and-metformin.53516/#post-489668