You should talk with your doctor about this. If you paid for an office call and he prescribed this med for you and you don't take it, that's a bit of a waste.
You should call the dr and ask him what to do. If you stop an antibiotic in the middle of treatment, or after two days, you will make the whole treatment plan questionable.
BAK is not a good thing, but I think taken for a couple of weeks or so will not do damage. It's likely to cause trouble if taken consistently over a long period of time. I don't know what that length of time is since I'm not a dr.
Mastiff, good luck with your eye situation. Lucy
Don't trust any refractive surgeon with YOUR eyes.
The Dry Eye Queen