Hi and welcome. Please read all the topics on Lantus on the Lantus Board. We start low and go slow. Lantus is given twice a day. The weeks you were only giving it once a day , and at 3 units, could have lowered your cat too much and maybe caused rebound. Start at 1 unit and stay there for 2 weeks, but test your cat with the blood tests and urine for ketones. But read, read and read, so you know how Lantus works. Donna