Rational Antimicrobial Therapy

Flashcards covering core concepts from the notes on rational antimicrobial therapy, including goals, empiric vs. specific therapy, culture and susceptibility testing, MIC/MBC, disk diffusion, and E-test concepts.

What are the three factors that must be considered for rational antibacterial therapy?

Host, drug, and organism (disease) factors.

What are the goals of successful antibacterial therapy mentioned in the notes?

Achieve effective drug concentrations at the infection site; eradicate the organism; avoid host toxicity; minimize resistance; avoid violative drug residues in food-producing animals.

What does empiric therapy mean in this context?

Therapy chosen based on the most likely organisms and their drug susceptibility, often before culture results are available; sample the infection site if possible.

What does specific therapy mean in this context?

Therapy guided by culture and susceptibility testing to target the identified organism.

When are cultures and susceptibility testing strongly recommended?

For complicated infections; lack of response to empirical therapy; relapsing infections after stopping antibacterials; long-standing infections; possible nosocomial infections; life-threatening infections; unknown susceptibility.

What does MIC stand for and what does it measure?

MIC stands for Minimum Inhibitory Concentration; it is the lowest concentration of an antimicrobial that inhibits visible growth in vitro (tube dilution method).

How is MBC determined?

Minimum Bactericidal Concentration—determined by plating out the MIC and higher concentrations to see which kill the organism.

What is the Kirby-Bauer disk diffusion method used for?

Disk Diffusion method used to assess antimicrobial susceptibility by measuring the zone of inhibition around antibiotic-impregnated disks.

What is an E-test and what does it measure?

E-test uses gradient drug strips; MIC is read at the intersection of the strip with the zone of inhibition; often covers a broader MIC range than the tube dilution method.

What is the recommended approach for empiric therapy in uncomplicated infections?

Use the narrowest spectrum agent possible; base decisions on history, physical findings, and additional diagnostics; sample if accessible; if not, choose based on site and most likely pathogens and their susceptibility.

Are cultures mandatory for first-time empiric therapy of many uncomplicated infections?

Cultures are not mandatory for first-time empiric therapy of many uncomplicated infections.

In culture and susceptibility testing, what factors influence the choice of therapy for specific infections?

Therapy is guided by organism identification and susceptibility testing; complicated infections may require combination or broader-spectrum therapy based on results.

What does the presence of a larger zone of inhibition indicate in disk diffusion testing?

A larger zone of inhibition generally indicates greater bacterial susceptibility to the antibiotic being tested.

What practical diagnostic tool reads MIC directly from a gradient strip and is often able to cover a wider MIC range?

The E-test (E-test strip); reads MIC at the intersection of the strip with the zone of inhibition.