As far as I am aware, salt will not affect ketosis. What it does do, though, is increase your tendency to retain water, and can therefore reduce (slightly) your weight-losses, until such time as the water is lost again.
As to anti-biotics, it depends. Some anti-biotics have to be taken with food because they can have nasty side effects if you don't. Others, such as flucloxacillin which I was taking a week ago, are the exact opposite and have to be taken on an empty stomach. It really does depend which ones you have. If you have ones that have to be taken with food, then I think that the Cambridge recommendation is that you move to the 1200 plan whilst taking them.