Rational Antimicrobials 1

Question 1

The goal of successful antibacterial therapy:

Answer 1

• achieve effective concentrations of an appropriate drug at the site of
  infection
• eradicating the organism
• avoid unwanted toxicities to the host
• minimizing resistance
• avoid violative drug residues in food producing animals

Question 2

To be rational, therapy must include consideration of:

Answer 2

host, drug and organism (disease) factors

Question 3

treatment decision tree based around uncomplicated infection and empiric therapy - what should we do?

Answer 3

uncomplicated infectiion
> empiric therapy
->based on history, physical findings, additional diagnostics
>if site of infection is accessible, sample
-> cytology, gram stain
>if not, then initial drug choice based on knowledge of *site and pathogens most likely and theirdrug susceptibility
>identify suspected organism
>treat with narrowest spectrum agent possible

Question 4

-EMPIRIC THERAPY-
(Marking Decisions Without Susceptibility Testing)
> do we always need to culture uncomplicated infections? what are examples of these?

Answer 4

Cultures not mandatory for 1st time empirical therapy of many uncomplicated infections
- acute contaminated wounds
- infectious tracheobronchitis
- cat bite abcess
- bacterial cystitis in an adult dog
- superficial pyoderma
- tooth root abcess

Question 5

specific therapy decision tree; animal comes in with uncomplicated or complicated infection, what do we do?

Answer 5

uncomplicated infection
> [life or organ threatening infection?]
> empiric therapy based on suspected organism (combination or broad spectrum therapy?)
-> take into account history, physical findings, additional diagnostics, cytology, gram stain
> treat with narrowest possible spectrum

=> at the same time (or if complicated infection):
> organism culture
> organism ID: G+/-, aerobic vs anaerobic
> specific therapy based on susceptibility testing

Question 6

what is strongly reccomended for complicated infection treatment decisions? what are examples of complicated infections?

Answer 6

Cultures are strongly recommended for complicated infections
-lack of response to a previous empirical antibacterial
- relapsing infection after stopping antibacterials
- long-standing (chronic) infections
- serious life-threatening infections
- possible nosocomial (hospital-acquired)
- infections susceptibility profile of pathogen unknown or unpredictable

Question 7

tube dilution method for culture and susceptibility testing; how it works, what info we gain

Answer 7

culture
> innoculate tubes with increasing concentrations of drug (micro-grams/mL)
> look in tubes to see at which drug concentrations bacteria will still grow
=> the concentration at which bacteria will not grow is the MIC = minimum inhibitory concentration
> use material from tubes to try to start new culture; for MBC plate out MIC and higher
=> the first tube at which no culture will grow is the MBC = minimum bacteriocidal concentration

Question 8

Disk diffusion (kirby-bauer) method of susceptibility testing; how does it work?

Answer 8

• start culture
  > make plate with even distribution of bacteria
  > place disks of paper impregnated with drugs
  > measure zone of inhibition around disks
  > to tell which drug is the best, must check zone of inhibition diameters against calibration score card

Question 9

What is the epsilon E-test and how does it work?

Answer 9

§ strips impregnated with gradient of drug
§ Read MIC directly from intersection of epsilon strip and zone of inhibition
§ Often cover a greater range of MIC’s than the tube dilution method