I was recently diagnosed with type 2 and I take metformin and glipizide. My doctor directed me to skip the glipizide on days of long rides (more than a couple hours). Before doing so, my blood sugar would crash towards the end of the ride and I could not raise it throughout the day. No problems since dropping the glipizide on ride days.
This is just my experience. You should certainly talk to your doctor about what is best for you.
For what it is worth, my doctor did not want me to alter my intake during rides. I still use plenty of gels, bars and sports drink. I now substitute some Hammer gel and HEED for Gu and Cytomax. A little less sugar to easy my mind, but plenty of energy to get me home.