This is not the one I as looking for but it does contain an antibiotic. The one I was looking for listed four different chicken feeds in the US market available in feed stores that contain an antibiotic but I could not find it. The vast majority of medicated feed sold in feed stores in the US are medicated only with Amprolium, but the majority does not mean all.Where would you even get chick starter with antibiotics? I've never seen it in any feed store targeted at the general public - big chain or local. This is something mass producers do to cut corners on having crappy living conditions for their overcrowded birds. It's not something that backyard chicken owners like us need to be concerned about.
https://www.backyardchickens.com/th...d-50-for-coturnix-quail.945529/#post_14581243
And as LaFleche clearly points out not all forum members are in the US. I have no idea what is available in other countries.
That's why I think you should always check the label to see what medicine is in medicated feed instead of assuming. Until you know you are guessing.
Where you typically find a chicken feed with an actual antibiotic in the US is a feed intended for a backyard flock of meat birds, Cornish Cross especially. They poop so much that disease is a threat if you are doing many of them. Poop management can be an issue. Don't depend on feed store people to help much either. Some know what they are talking about but some don't, just like in any other business that deals with the public.