From what I've read, no, it's not an antibiotic. It is an antiparasitic. It states in the instructions that it is harmless to your biological
filters and when I've used it I have found that to be true. So it has no effect on bacteria.
http://inkmkr.com/Fish/FlubendazoleTreatment.pdf
Commercial F-MG products like Proform-C and Broad Spectrum Disease Treatment instructions list the parasites/diseases that
they effectively treat and flukes are not one of them (Listed are "Ich, Costia, Trichodina, Chilodonella, Oodinium, and fungal infections").