Cool, thanks! I did some looking into it, and it appears that as of 1 Jan 2017, in the US such uses of medically important antibiotics will be banned in the US (http://www.fda.gov/AnimalVeterinary/NewsEvents/CVMUpdates/uc...). The EU has had a ban since 2006. China and some other countries may still be a problem. Not sure how much meet the US/EU imports from those countries.

With these bans in place, it doesn't seem necessary to implement a tax on their use. Perhaps a ban on importing meat that was produced using antibiotics for growth.