L1 Pharm: Intro to Abx & Gen. Principles of Antimicrobial Therapy Flashcards
Antibiotic Therapy depends on 3 things:
- Knowledge/suspicion of the ______ of infection and infecting pathogen
- Spectrum of ________ of the antibiotic
- ______________________
- Knowledge/suspicion of the site of the infection (different flora found in different parts of the body and you can suspect different pathogenic organisms based on the site of infection)
- Spectrum of activity of the antibiotic
- Host characteristics
APPROPRIATE DIAGNOSIS IS CRUCIAL.
T/F: Antibiotic therapy should be started before cultures are obtained from a suspected site of infection.
False. Obtain cultures from the suspected site of infection before antibiotics are initiated. This helps with proper diagnosis.
This is important because isolation of an organism from a clinical specimen does not always indicate the presence of infection (normal flora vs. contamination vs. infection)
Normal flora can be found on the skin, respiratory tract, GU tract and GI tract.
How does normal flora affect pathogenic bacteria?
Suppress growth, compete with pathogenic organisms for nutrients, and stimulate cross-protective antibodies.
What happens to the flora of patient’s who are hospitalized within 48 hours of admission?
Patients become colonized with “new flora,” usually gram-negative aerobes.
What specimens are found in the following sterile body sites?
- Bloodstream
- Subarachnoid Space
- Pleural Space
- Peritoneum
- Pericardium
- Synovium
- Urinary Tract
- Bloodstream- Blood
- Subarachnoid Space-CSF
- Pleural Space- Pleural Fluid
- Peritoneum - Peritoneal Fluid
- Pericardium- Pericardial Fluid
- Synovium- Synovial Fluid
- Urinary Tract - Urine (directly from the bladder)
T/F: You take a specimen from a patient and isolate bacteria from it. This is indicative of infection.
False:Isolation of a bacteria from a clinical specimen is not always an indication of infection
Differentiate between contamination, colonization, and infection.
Contamination
Organisms inadvertently introduced during ________ _____________ or processing.
Organism inadvertently introduced during specimen collection or processing
An example is isolation of coagulase negative staphylococci (normally found on skin) in the blood of a patient where the blood is drawn via a peripheral stick and the patient does not have signs of infection. Normal skin flora bacteria contaminated blood culture.
Colonization
Organism is present at body site but is not _______ host tissue or _______ signs and symptoms of infection.
Organism is present at body site but is not invading host tissue or inducing signs and symptoms of infection.
Ex: isolation of pseudomonas aeruginosa from a sputum culture in a patient without fever, cough, or infiltrate on chest X-ray. Pathogenic bacteria is in the patient without clinical/radiological signs of pneumonia.
Infection
_______ organism is damaging host tissue and eliciting signs and symptoms of infection.
Pathogenic organism.
An example of infection is streptococcus pneumonia in the CSF of a patient with headache, fever, and neck stiffness.
Antibiotics may be chosen before the results of the cultures are available based on some preliminary information. Name two:
1.
2.
- Site of infection and likely causative organism- certain bacteria have a propensity to commonly cause infection in particular sites of the body (E.Coli in urine for example)
- Gram stain results (does result correlate with most likely suspected organism?)
Interpretation of lab culture requires knowledge of:
- Sites with normal flora vs. ___________ _________
- Contamination (lab), colonization (no infection) and infection
Sterile Sites
Antibiotics are usually initiated when an infection is __________ because delaying treatment may lead to significant morbidity or mortality.
Infection is suspected.
Antibiotic are chosen that have activity against likely pathogens (empiric therapy)
The regimen is modified once culture and susceptibility results are available (targeted therapy)
An antibiotic’s spectrum of activity tells you what?
Spectrum of activity is a general list of bacteria that are killed or inhibited by an antibiotic.
It is established during clinical trials, and because of resistance, susceptibility patterns of each bacteria should be continuously evaluated.
Narrow Spectrum = antibiotic has activity against a ______ _____ of bacteria
Broad Spectrum = antibiotic has activity against a _____ variety of bacteria
Narrow spectrum: works against a limited group
Broad spectrum: kills a wide variety of bacteria
What do the MIC and MBC tell you? Which one is a greater concentration?
MIC: Minimum Inhibitory Concentration- lowest concentration of an antibiotic that inhibits visible bacterial growth
MBC: Minimum Bactericidal Concentration- lowest concentration of an antibiotic that kills bacteria; decreases innoculum by 99.9%.
MIC is less than or equal to the MBC
Susceptibility Breakpoints categorize specific antibiotic _____ values for a given bacteria as:
S- susceptible
I- intermediate
R- resistant
Should these values be compared amongst antibiotics?
MIC values
Susceptible: organism will most likely be eradicated with normal doses of the abx
Intermediate: treatment may be successful using maximum dose of the abx
Resistant: MIC exceeds usual serum concentrations of the antibiotic, so less than optimal results are expected.
MIC values should not be compared between different antibiotics! They depend on pharmacokinetics, activity of abx, site of infection, and data from clinical efficacy trials.
MIC Determination- Are broth dilutions (micro/macrodilutions/serial dilutions) quantitative or qualitative?
Quantitative tests of the in vitro activity of an antibiotic- yields an MIC or MIC RANGE**.
MIC is the lowest concentration of antibiotic that prevents visible growth of the bacteria.
Macrodilution- results yield the _________ MIC of the antibiotic against the infecting organism. How can you tell what the MIC is? Can you tell the MBC from this test?
Gives EXACT MIC.
The MIC is the first tube without visible growth.
You can determine MBC from macrodilution. MBC is an extension of the test- test tubes without visible growth are cultured on agar plates. After incubation colonies are counted- MBC is the concentration that reduced the original inoculum by 99.9% after 24 hrs of incubation.
Macro dilution is a 2 fold serial dilution of an antibiotic thats incubated with a standard inoculum of the infecting bacteria in test tubes.
Microdilution
Microtiter plates or cassettes with serial dilutions of ________ antibiotics at the same time.
What test is more common, macrodilution or microdilution? Why?
Is it Qualitative or Quantitative?
Tests several antibiotics at the same time. Due to size restraints of cassettes, not all concentrations of an antibiotic can be tested for susceptibility.
Microdilution is automated and is the MOST COMMON METHOD for quantitatively determining MIC! Macrodilution is labor and resource intensive.
- QUANTITAVE (but often only gives a RANGE of the MIC)
Kirby Bauer Disk Diffusion Test
Qualitative or Quantitative?
What does a clear zone represent? What do their diameters correlate to?
Qualitative test of the in vitro activity of an antibiotic- MIC is NOT determined!
Clear zones represent antibiotic inhibition. No growth occurred here. Bacteria only grow where concentrations of the antibiotic are below those required to inhibit bacterial growth.
Zone diameters mm size correlate with S, I, R.