Table I.

Classification of medically important antimicrobials.

Medically important antimicrobials (35 classes). Apply criteria:
Criterion 1: Sole, or one of limited available therapies, to treat serious bacterial infections in people.		Criterion 2: Used to treat infections caused by bacteria (1) possibly transmitted from nonhumansources, or (2) with resistance genes from nonhuman sources.
Neither criteria met: important antimicrobials
One criterion met: highly important antimicrobials
Both criteria met: critically important antimicrobials. Apply prioritization factors:
P1: Used to treat a large number of people with infections for which limited antimicrobials are available	P2: Used with high frequency in human medicine or in certain high-risk groups	P3: Used to treat human infections in which extensive evidence exists on the transmission of resistant bacteria or genes from nonhuman sources
Not all prioritization factors met: high priority
All prioritization factors met: highest priority

Reproduced from the World Health Organization.³⁶