In its most recent Model List of Essential Medicines, WHO adopted a new classification for antibiotics. This new model comprises three categories: Key Access antibiotics (eg, β-lactam, aminoglycoside, and first-generation or second-generation cephalosporin antibiotics) that “should be widely available, affordable and quality-assured”; Watch Group antibiotics (including most of the highest priority critically important antimicrobials for human medicine—eg, macrolides, quinolones, glycopeptides, penems, and third-generation cephalosporins) recommended only for specific, limited indications; and Reserve Group antibiotics (eg, fourth-generation and fifth-generation cephalosporins, aztreonam, polymixins) for situations when all alternative antibiotics have failed.

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