L20, 21 Introduction to Antibiotics Flashcards
(57 cards)
Appropriate antibiotic therapy depends on what factors?
- Knowledge/suspicion of the site of infection and subsequent infecting pathogen (where/what)
- Spectrum of activity of the antibiotic
- Host characteristics
True or false - it does not matter when you obtain a culture from a patient.
False - obtain cultures from the suspected site before antibiotics are initiated.
True or false - isolation of an organism from a clinical specimen does not always indicate the presence of infection.
True
What are the four possibilities when an organism is detected in culture?
- Normal flora
- Contamination
- Colonization
- Infection
What happens to a patient’s flora within 48 hours of admission?
They are colonized with “new flora” (usually gram-negative aerobes)
Why do normal flora suppress the growth of pathogenic bacteria?
They colonize sites that might be otherwise colonized by pathogenic bacteria.
What are the 7 sterile body sites and the fluids found in each?
- Bloodstream (blood)
- Subarachnoid space (CSF)
- Pleural space (pleural fluid)
- Peritoneum (peritoneal fluid)
- Pericardiam (pericardial fluid)
- Synovium (synovial fluid)
- Urinary tract (urine - directly from bladder)
What is contamination and a common example?
Organism inadvertently introduced into the specimen during collection or processing; coagulase negative staph in the blood of the patient
What is colonization and a common example?
Organism is present at a body site but is not invading host tissue or invading signs and symptoms of infection; pseudomonas aeruginosa in the sputum of a patient without signs of pneumonia
What is infection and a common example?
Pathogenic organism is damaging host tissue and eliciting signs and symptoms of infection; S. pneumoniae in the sputum of a patient with fever, productive cough, and shortness of breath
Certain bacteria have a propensity to commonly cause infection in particular ___. Give 2 examples.
Body sites or fluid; E. coli in the urine and S. aureus in skin abscesses
What information can help choose an antibiotic before the results of a culture are available?
- Site of infection
- Likely causative organism
- Gram-stain result
Why are antibiotics initiated when an infection is suspected but not confirmed?
Undue delay may lead to significant morbidity or mortality
What is the difference between empiric and direct/targeted therapy?
Empiric is chosen based on activity against likely pathogens; direct/targeted is modified once culture and susceptibility results are available
What is the antimicrobial spectrum of activity?
General list of bacteria that are killed or inhibited by an antibiotic; established during early clinical trials
What type of antibiotic has activity against a limited group of bacteria?
Narrow spectrum
What type of antibiotic has activity against a wide variety of bacteria?
Broad spectrum
___ testing is performed on individual bacterial isolates once grown and identified in culture.
Antibiotic susceptibility
What is the MIC (minimum inhibitory concentration)?
Lowest concentration of an antibiotic that inhibits visible bacterial growth
What is the MBC (minimum bactericidal concentration)?
Lowest concentration of an antibiotic that kills bacteria (decreases inoculum by 99.9%)
What are interpretive guidelines established by the CLSI that categorize specific antibiotic MIC values for a given bacteria?
Susceptibility breakpoints
What are the 3 susceptibility breakpoints and what do they mean?
- Susceptible: organism will most likely be eradicated with normal doses of the antibiotic
- Intermediate: treatment may be successful using maximal doses of the antibiotic
- Resistant: MIC exceeds usual serum concentrations of the antibiotic, so less than optimal results are expected
Why do S, I, and R vary for each antibiotic and each bacteria?
They are based on the PK of the drug, general activity of the antibiotic, site of infection, and data from clinical efficacy trials.
In general, can MIC values be compared between different antibiotics?
No
