I have had scotties for years and all have suffered on-again off-again ear infections.  The only way I've found to keep it under control is to keep their ears cleaned out and use the antibiotic ear drops as needed.  It's a "space" problem, the space in the ear, not a systemic problem.  I've found if you keep the ears as clean as you can the infection rates drop and the animal does much better.  I use an over the counter ear cleaner.