Antibiotics are ranked by Health Canada based on their importance to human medicine, ranging from Categories I to Category IV. Category I antibiotics are those considered to be of the highest importance to humans: they are essential for serious human infections as there are few or no alternatives available. They are considered to be antibiotics used as a “last resort” in human medicine. Category IV antibiotics, on the other hand, are not used in human medicine.

Because Category I antibiotics are those considered most important to human health, the chicken industry took steps to significantly reduce their use. As of May 15, 2014, their preventive use was no longer permitted in the Canadian chicken sector. Additionally, the chicken industry eliminated the preventive use of Category II antibiotics at the end of 2018.