Empiric antimicrobial therapy with appropriate agent (considering antimicrobial spectrum) and dose, taking patient factors into consideration, such as age, history of adverse drug reactions, comorbid conditions and medications, and local or national guidelines

Principles

Empirical antimicrobial therapy selection should match spectrum to the likely causative organism(s) for the specific clinical syndrome and site, while accounting for patient-specific factors (age, comorbidity, allergy history, recent antimicrobial exposure, and local resistance patterns) - a "one-size-fits-all" empirical regimen is inappropriate given how much these factors can shift the likely organism and appropriate spectrum
Central to essentially all infection management before culture/susceptibility results are available, given treatment urgency in many infective presentations not allowing time to wait for definitive microbiological results

Patient-specific risk factors (recent hospitalisation/antimicrobial exposure increasing resistant organism likelihood, specific comorbidities predisposing to particular organisms, allergy history restricting available agent classes) each shift the probability distribution of likely causative organisms away from the "textbook" population-level empirical choice, requiring individualised adjustment rather than a fixed protocol applied uniformly

Local antibiogram data (organism-specific resistance patterns for the local population/institution) should inform empirical choice given substantial geographic and institutional variation in resistance prevalence
Recent culture results (even from a different infective episode) can provide useful individual patient-level information about likely colonising/resistant organisms relevant to a new presentation

Empirical therapy should be reviewed and de-escalated/rationalised once culture and susceptibility results are available, per core antimicrobial stewardship principles - continuing broad empirical cover unnecessarily once a specific organism and susceptibility are known increases resistance selection pressure without added clinical benefit
Documented allergy history should be carefully assessed for genuine vs mislabelled reactions (see ) before restricting first-line agent options unnecessarily

Local antibiogram-guided empirical selection, recent antimicrobial exposure increasing resistant organism risk, comorbidity-specific organism risk (e.g. diabetes and specific skin/soft tissue pathogens), allergy history impact on available agent choice

Empirical antimicrobial selection should be individualised using patient-specific risk factors (recent antimicrobial exposure, hospitalisation, specific comorbidities, allergy history) and local resistance data, rather than applying a fixed, generic regimen for a given clinical syndrome regardless of these modifying factors - each factor can substantially shift the likely causative organism and appropriate empirical spectrum

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