Antibiotics are not anti-catabolic, but they do slightly inhibit protein synthesis. I asked my doctor if this was enough to prevent gains for a weightlifter and he said that it works on a different level than that for gaining muscle (can't remember exactly what, it was a while ago).
I was on doxycycline my 1st cycle and still gained 30 lbs, it had no effect on my gains. Since then I have switched antibiotics to Sulfox and have run 2 more cycles with that. Again, it had no adverse effect on my gains. So to answer your ?, no antibiotics will not effect your gains.