Therapeutic antimicrobial agents should be used when

Therapeutic antimicrobial agentsshould ideally bepathogen-directedto minimizeresistance, side effects, and treatment failure. Once thecausative pathogen and its antimicrobial susceptibilities are known, the mostnarrow-spectrum, effectiveagent should be used.

Why the Other Options Are Incorrect?

A. The infecting agent is unknown– Empiric therapy may be necessary initially, but definitive therapy should be based on pathogen identification.

B. The patient's illness warrants treatment prior to culture results– This applies toempiric therapy, but not todefinitive antimicrobial selection.

C. The patient’s symptoms suggest likely pathogens– Clinical presentation guidesempiric treatment, butdefinitive therapy should follow culture and susceptibility testing.

CBIC Infection Control Reference

APIC emphasizes theimportance of selecting antimicrobials based on pathogen identification and susceptibility testingto preventantimicrobial resistance​.