Does taking metformin cause bun to increase? my fathers' is at 24also how can it be decreased to normal?

No: Doctors often hold or stop metformin when someone's kidney function is too low because of the potential for a lactic acidosis. The metformin itself does not cause kidney injury, part of which may be suggested by a higher BUN. In Florida, I've found that people tend not to drink much fluid during the day, so that may be one thing to explore. He'll need to see his PCP or nephrologist for context.