The Symposium on Antimicrobial Therapy – the 1st of a 15-part series

Last month, the Mayo Clinic Proceedings published the first of a 15-part series, “Symposium on Antimicrobial Therapy.” The purpose of this series is to educate practicing physicians on the key concepts and best practices in antimicrobial therapy and stewardship. An introduction to the series written by Dr. Zelalem Tamasgen can be found here

The February article titled “General Principles of Antimicrobial Therapy” is a useful overview of important principles in determining appropriate antimicrobial therapy in relation to clinical diagnoses, microbiology lab results, and patient history while taking into consideration drug characteristics and special circumstances. I am highlighting some key points in this post. You can purchase the complete original article here.

Use narrow spectrum antibiotics as soon as possible

The use of broad spectrum antibiotics is often necessary in situations where the patient is critically ill and that therapy is required before microbiology lab testing results are known. The optimal therapy should take into consideration the site of infection, the most probable organism, organism colonization history in the patient, and resistance patterns from the hospital’s institutional antibiogram. Once microbiology results are known, narrow spectrum antibiotics should replace broad spectrum antibiotics as soon as possible to prevent the emergence of antimicrobial resistance in the community.

Infection site is important for AST interpretation

Antimicrobial susceptibility testing (AST) is the lab test used to predict the effectiveness of an antibiotic against an organism. Labeling the site of the specimen is important because different antibiotics have different penetration capabilities in various body sites. By knowing the specimen site the lab can test antibiotics that are likely to have good bioactivity at the site.

Combination therapy is most appropriate for infections that may be caused by organisms that have shown multidrug resistance in the past.

These include hospital acquired infections, HIV, and TB. Providing multiple drugs helps assure that one will be effective in suppressing the infection until actual susceptibilities are known

Avoid “one size fits all” approach

The condition of the patient must be considered when prescribing antibiotics.

Some critical factors are kidney and liver function, age, genetics, allergies, pregnancy, and history of recent antibiotic use.

Common misuses of antibiotics:

• Prolonged antimicrobial treatment without clear evidence of infection
• Treatment of a positive clinical culture in the absence of disease
• Failure to narrow antimicrobial therapy when a causative organism is identified
• Prolonged prophylactic therapy
• Excessive use of certain antimicrobial agents