I asked my doctor one day about his. So I wasn't too crazy because he's had the question before.

So he says, yeah, in general they can be used as it obviously is the antibiotic humans use. Only two things he mentioned: 1 was the pharmaceutical quality, where they are manufactured. The standards are not the same (think meningitis), and 2: the biggest difference are the binding agents. Fish meds are meant to be dissolved in water and the binding agent is very different than human meds as we have acid to break down the meds. So he said dosing is very difficult. Usually the problem is that by the time you would take your last dosage, because of the different binding agent, the first dosage would just be taking effect.
He didn't seem concerned about the actual danger, just the effectiveness. But, if things really really really got bad, it's worth a stab I suppose. I just wouldn't be taking them to save money. Lol.