I've never heard that they cancel out one another.
The flagyl is supposed to work on the cyst "form" of lyme, but I am not sure I really believe it
The flagyl also keeps any C diff at bay from the effects from the abx.
This is the combo I was given when I started on abx for lyme. I did it for 5 months.
The world breaks every one and afterward many are strong in the broken places