This may be old news for folks outside the US, but within the US our most common treatment of coccidiosis is corid (amprolium). I recently introduced several new chickens to my flock all on Medicated feed, one came down with coccidiosis. Put her on corid as well as a prescription sulfa antibiotic from a vet for severe coccidiosis, but after 10 days of this there was no improvement. I very much thought she would not make it. I ordered Endocox from Jedds bird supply and gave her 5mg per day dissolved in 1ml water (she was not eating or drinking at this point, we were hand feeding). This was adjusted to body weight. In 3 days she was 100% recovered. Wanted to share this for others who are struggling with severe and possibly drug resistant coccidiosis. It has been a few weeks now with no relapse. She is good as new!