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Flashcards in Rational Antimicrobial Therapy Deck (28):

What is the goal of antimicrobial therapy?

To eliminate infectious organisms from the body without toxicity to the host


What natural defences of the host help prevent infection?

Mucocilliary escalator Flushing effect of urination Gut normal Flora


What are the different groups of bacteria with regards to antimicrobial targetting.

Gram positive aerobes Gram negative aerobes Penicillinase producing staph Obligate anaerobes Atypical species


What are the atypical bacterial species?

-Rickettsia -Mycoplasma -Chlamydia -Bartonella -Mycobacterium


How does bacterial resistance develop?

Genes that code for resistance are already present in the bacterial population. Antimicrobials select for these resistance genes.


When is antimicrobial use appropriate?

When bacterial infection:

  1. Has been definitively diagnosed
  2. Is a likely dx considering other evidence
  3. Is likely to progress without therapy
  4. Will cause critical illness


What should antimicrobial prescription be based on?

The likely organism to be involved.


n.b. culture and sensitivity if recurring problem!


What common things are antibiotics prescribed for and why should they not be prescribed for these conditions?

  1. Vomiting without diarrhoea
    1. This is a dietary indiscretion normally
  2. Feline haematuria
    1. Feline urine highly concetrated so v. bactericidal. More likely idopathic cystitis in this sp.
  3. Haematochezia/Malaena
    1. ABs not needed.


What are the considerations of antimicrobial selection/prescription?

  1. What bacteria are likely involved?
  2. Is culture and sensitivity advisable/possible?
  3. Is antibacterial treatment needed
  4. Does the selected AB have appropriate spectrum of activity?
  5. Pharmakokinetic factors?
  6. Toxicity issues?
  7. Ancillary treatments that may be beneficial?
  8. Residue issues (food producing animals)
  9. Client compliance and cost


What are the factors that may affect success of antimicrobial therapy?

  1. What bugs live where?
  2. Bacterial sensitivity
  3. Distribution to correct site (Pharmacokinetics)
  4. Local conditions (pharmacodynamic)
  5. Client compliance


Where could bacteria come from?

  • Environment
  • Other animals
  • Within animal
    • Skin
    • GI tract


How can bacterial sensitivty vary between in vitro and in vivo?

  • Sensitivity can be overcome in vivo by achieving high concentration e.g. in the urine
  • Factors in the host may decrease effectiveness of an antimicrobial in vivo.


What is the MIC?

Minimum inhibitory conentration


The minimum concentration of a drug that will inhibit bacterial growth.


Which antimicrobials inhibit cell wall synthesis?

  • Penicillins
  • Cephalosporins
  • Bacitracin


Which antimicrobials inhibit cell wall function? 

  • Polymixin
  • Imidazoles
  • Amphoteracin B
  • Nystatin


What do the following antimicrobials have in common?

  • Chloramphenicol
  • Lincosamides
  • Macrolides
  • Tetracyclines
  • Aminoglycosides

They inhibit bacterial protein synthesis. 


Which antimicrobials inhibit bacterial protein synthesis?

  • Sulphonamides
  • Trimethaprim
  • Quinolones
  • Metronidazole
  • Rifampin



Which antibacterials are bacteriostatic and what is important to achieve and maintain with this type of therapy?

  • Chloramphenicol
  • Lincosamides
  • Macrolides
  • Tetracyclines
  • Non-potentiated sulphonamides

MIC needs to be maintained at the site of infection throughout the course of therapy otherwise there is no point


Which bacteriocidal drugs are time-dependent? What is nessessary for them to be effective?

  • Penicillins
  • Cephalosporins
  • TMPS

Bacteria need to be multiplying so don't give them alongside bacteriostatic drucs.


Which bacteriocidal drugs are concentration dependant?

  • Aminoglycosides
  • Fluoroquinolones
  • Metronidazole



What are the 'brown' drugs for the following categories?

  1. Negative aerobes & obligate anaerobes
  2. Anaerobes
  3. All bacteria
  4. All except gram positive aerobes

  1. 1st gen Cephalosporins, cefovicin and amoxycillin (without clav)
  2. Lincosamides except clindamycin
  3. TMPS
  4. Tetracyclines


Which bodily tissues are hard to access for antimicrobials?

  • Brain
  • Eye
  • Prostate
  • Bronchus
  • Intracellular space
  • Poorly vascularised tissue
    • Bone fragments
    • Heart valves


What external factors may interefere with antimicrobial effectiveness?

  • Abscess formation
  • Pus
  • Necrotic debris
  • Oedema fluid
  • Foreign material


How does foreign material interfere with microbe killing?

  • Macrophages deplete their bactericidal substances trying to degranulate the material
  • Can protect bacteria from drugs and phagocytosis
  • Bacteria can form a biofil (glycocalx) at the site



What other environmental conditions can affect drugs and how?

  • Penicillin activity reduced in prescence of haemoglobin
  • Pus inactivates TMPS
  • Low pH reduces activity of
    • erythromycin
    • clindamycin
    • flouroquinolones



What factors increase the risk of bacterial infection during/after surgery?

  • Patients clinical status
  • Nature of the surgery
  • Use of implants
  • Surgeon experience
  • Surgery duration
  • Anaesthsia duration
  • Propofol administration
  • Clipping
  • Age
  • BCS
  • Concurrent endocrinopathies



To be effective, what must a surgical prophylactic be?

Present at site of infection at time of surgery

Effective against most bacteria