▪️ Antimicrobials Flashcards
What is an antibacterial drug?
An antibacterial drug is a chemical substance that kills or inhibits the growth of bacteria at a discrete target site
What is an antibiotic?
An antibiotic is an antibacterial drug of microbial origin e.g. penicillin from Penicillium mold
What is the unique property of antimicrobials?
Antimicrobials target microbial biochemistry
Identify some antibiotics which target DNA synthesis
〰️ Quinolones e.g. ciprofloxacin
〰️ Folic acid antagonists e.g. trimethoprim sulphonamides
Identify some antibiotics which target protein synthesis
〰️ Aminoglycosides e.g. gentamicin
〰️ Macrolides e.g. erythromicin
〰️ Tetracyclines
Identify some antibiotics which target cell wall synthesis
〰️ Beta-lactams e.g. penicillins, cephalosporins, carbapenems
〰️ Glycopeptides e.g. vancomycin
What are the two reasons for antibiotics?
〰️ Prevention of infections
〰️ Therapy of significant bacterial infections
Identify some groups of people at increased risk of infection
〰️ Peri-operative – prevention of surgical site infections
〰️ Short term – meningitis contacts
〰️ Long term – asplenia, immunodeficiency
What are clinically significant infections?
Clinically significant infections are infections that if left untreated will cause death, permanent harm or medium to long term disability
What are the two ways in which one can treat a clinically significant infection?
〰️ Treatment of culture-proven infection
〰️ Empirical treatment of suspected infection
What are the two different ways that one might use antibiotics empirically?
The easy way
Follow the local
antibiotic formulary
The thoughtful way
What is the likely cause of infection?
Which antibiotics are likely to be
effective?
Which one is the best choice?
Which factors helps one determine the likely cause of an infection?
age
anatomical site,
duration of illness
past medical history,
occupational history,
personal background,
time of year,
travel history
Which factors helps one determine which antibiotics are likely to be effective?
•Likely susceptibility
•Consequences of wrong choice
Is determined by:
Community or Healthcare onset?
Severity of infection
Baseline rate of resistance
Immune status of patient
Which factors helps one determine which antibiotic is the best choice?
Safety is determined by :
Age, organ function, toxicity, drug interactions, allergies, pregnancy, breast-feeding, efficacy, cost, administration route
What are the adverse events of antibiotics?
Toxicities
Allergic reactions
Idiosyncratic reactions
Ecological effects – C.difficile, selection of resistance
Drug interactions
What would ideal antibiotic therapy look like?
Clean kill of infecting bacteria – minimal impact on commensal organisms, no resistance in any surviving pathogens
No unwanted effects in patient e.g. drug interactions, toxicities
Illustrate how one measures the susceptibility of bacteria to antibacterials
This is can be measured directly by bringing the pathogen and the antibiotic together in a growing environment, such as nutrient media in a test tube or agar plate, to observe the effect of the antibiotic on the growth of the bacteria.
Antibiotic susceptibility is determined by measuring the diameter of the zones of bacterial inhibition around the antibiotic disks and comparing the diameter with disk diffusion interpretive criteria updated annually by CLSI
What is the minimum inhibitory concentration?
MIC is the minimum concentration of antibiotic required to inhibit growth of a bacterium in vitro (mg/l)
Therapeutic drug monitoring is used to ensure a non-toxic adequate dose for some antibiotics.
Identify these
Aminoglycosides
Glycopeptides
Describe the mechanism of antibiotic resistance through the following pathways:
- Antibiotic inactivation
- Alteration of target site
- Alteration of metabolic pathways
- Reduced intracellular antibiotic accumulation
- Beta lactamase
- Penicillin binding protein
- Para-aminobenzoic acid is normally required by bacteria but some can use preformed folic acid instead
- Active efflux mechanisms + Decreased permeability
What does it mean when a pathogen is multi-drug resistant?
Multi-drug resistant – non-susceptibility to at least one agent in three or more antimicrobial categories
What does it mean when a pathogen is extensively drug resistant?
Extensively drug resistant – on-susceptibility to at least one agent in all but two or fewer antimicrobial categories
What does it mean when a pathogen is pan drug resistant?
Pan drug resistant – non-susceptibility to all agents in al antimicrobial categories
Identify the two ways in which bacteria can become resistant to carbapenem
Reduced bacterial intracellular concentration
Carbapenemase production
