What is the antibiotic rule of 90 to 60?
The “90-60 rule” is a clinical finding in infectious disease and microbiology that outlines the forecast accuracy of laboratory antibiotic testing. It states that:
Treatment is successful in 90% of infections caused by bacteria that are classified as “susceptible” in a laboratory.
“Resistant” bacteria are still successfully treated in 60% of infections.
Laboratory Antimicrobial Susceptibility Testing (AST) analyzes a pathogen in a simulated setting (typically an artificial culture medium) after isolating it. However, this does not reflect the complex reality of the human body.
Several clinical realities are reflected in the rule:
What makes it fail 10% of the time (the vulnerable group): Several things affect an antibiotic’s efficacy in the human body, including the patient’s immune response, the drug’s capacity to enter particular tissues (such as the lungs or brain), and individual variations in drug metabolism.
The resistant group’s success rate is 60%: Even if the pathogen is deemed resistant in a lab dish, the human body’s natural immune defenses, combined treatments, and drug concentrations reached at the site of infection (e.g., concentrated levels in urine for urinary tract infections) can frequently defeat it.
Consequences in the clinic
The guideline emphasizes the need to customize patient care by considering the whole clinical picture and avoiding over-reliance on laboratory reports.
Consult the CDC Antimicrobial Resistance guidelines or the Infectious Diseases Society of America (IDSA) for trustworthy, evidence-based antimicrobial stewardship advice.
