Rational Antimicrobial Therapy

Question 1

What is the goal of antimicrobial therapy?

Answer 1

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

Question 2

What natural defences of the host help prevent infection?

Answer 2

Mucocilliary escalator Flushing effect of urination Gut normal Flora

Question 3

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

Answer 3

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

Question 4

What are the atypical bacterial species?

Answer 4

-Rickettsia -Mycoplasma -Chlamydia -Bartonella -Mycobacterium

Question 5

How does bacterial resistance develop?

Answer 5

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

Question 6

When is antimicrobial use appropriate?

Answer 6

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

Question 7

What should antimicrobial prescription be based on?

Answer 7

The likely organism to be involved.

n.b. culture and sensitivity if recurring problem!

Question 8

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

Answer 8

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.

Question 9

What are the considerations of antimicrobial selection/prescription?

Answer 9

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

Question 10

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

Answer 10

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

Question 11

Where could bacteria come from?

Answer 11

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

Question 12

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

Answer 12

• 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.

Question 13

What is the MIC?

Answer 13

Minimum inhibitory conentration

i.e.

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

Question 14

Which antimicrobials inhibit cell wall synthesis?

Answer 14

• Penicillins
• Cephalosporins
• Bacitracin

Question 15

Which antimicrobials inhibit cell wall function?

Answer 15

• Polymixin
• Imidazoles
• Amphoteracin B
• Nystatin

Question 16

What do the following antimicrobials have in common?

• Chloramphenicol
• Lincosamides
• Macrolides
• Tetracyclines
• Aminoglycosides

Answer 16

They inhibit bacterial protein synthesis.

Question 17

Which antimicrobials inhibit bacterial protein synthesis?

Answer 17

• Sulphonamides
• Trimethaprim
• Quinolones
• Metronidazole
• Rifampin

Question 18

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

Answer 18

• 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

Question 19

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

Answer 19

• Penicillins
• Cephalosporins
• TMPS

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

Question 20

Which bacteriocidal drugs are concentration dependant?

Answer 20

• Aminoglycosides
• Fluoroquinolones
• Metronidazole

Question 21

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

Answer 21

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

Question 22

Which bodily tissues are hard to access for antimicrobials?

Answer 22

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

Question 23

What external factors may interefere with antimicrobial effectiveness?

Answer 23

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

Question 24

How does foreign material interfere with microbe killing?

Answer 24

• 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

Question 25

What other environmental conditions can affect drugs and how?

Answer 25

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

Question 26

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

Answer 26

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

Question 27

To be effective, what must a surgical prophylactic be?

Answer 27

Present at site of infection at time of surgery

Effective against most bacteria