Carac is a.005 solution while Efudex is a .05 (or 5%) solution of the active ingredient flouracil.
They have different bases.
Carac does state that the medicine is absorbed in 2 hours while you have to call Valeant's hotline where they would say 3 hours.
Like in most things there are more gray areas than black and white with this treatment.
Many different protocols for many different people with many different conditions and goals.