I don't really know, but I tend to agree with @heavyphil that it seems like it shouldn't be a problem. But you might save yourself some grief and contact the doctors office who's doing the biopsy and inform them. I suspect they have a protocol for someone showing up under care they didn't previously know about that might trigger some action on their part. It'd be a drag to get there and then have them say they can't do the biopsy until he's off the antibiotic. All that said, since they're responding to lesions on an mri and not just a psa rise, it seem to me the biopsy is still needed. Best wishes.