I used antibiotics for almost 2 years and never experienced any signs that they were causing catabolism. I'm natural too, so it would affect me more than it would a juicer. I was even looking for signs of catabolism and reduced protein synthesis, but noticed nothing. I used both tetracycline and doxycycline. I think the dose given by doctors is way too low to affect human protein synthesis noticably.
Never heard it lowers testosterone, at least the doses given to humans, I never noticed any signs of lower testosterone either.