In clinical practice, empiric antimicrobial therapy and definitive antimicrobial therapy represent two essential stages in the management of infectious diseases.

- Empiric therapy is initiated before microbiological culture results are available.
- It is based on the clinician's judgment, considering the patient's clinical presentation, likely pathogens, local resistance patterns, and severity of illness.
- The goal is to promptly address the infection to prevent progression while awaiting specific laboratory data.
- Because the causative organism is not yet confirmed, empiric therapy often involves broad-spectrum antibiotics or a combination of agents to cover the most probable pathogens.

- Once culture and sensitivity results return, definitive therapy can be tailored to target the identified pathogen specifically.
- This approach allows clinicians to select the most effective, narrow-spectrum antimicrobial agent, reducing unnecessary broad antibiotic use and limiting adverse effects and resistance development.

Therefore, the main difference lies in the timing and basis for antimicrobial selection:
- Empiric therapy: Started based on clinical judgment before culture data.
- Definitive therapy: Guided by specific culture and sensitivity results.

This distinction is crucial for optimizing antimicrobial stewardship, improving patient outcomes, and combating antibiotic resistance.

Reference: Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 9th Edition, Volume 1, Chapter 10: Antimicrobial Therapy