Antimicrobial pharmacology (Proceedings)

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Antimicrobial pharmacology (Proceedings)

General principles
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Apr 01, 2008

Therapeutic decision making



  • Often a difficult and complex process
  • Often confusing and contradictory information (researchers, horse owners, websites & list serve's)
  • Frequently our decisions are based on:
  • Our last successful case
  • Our last failure
  • Our last case

Pharmacological Considerations



  • Target
  • Mechanism of action
  • Route of delivery
  • Disposition
  • Metabolism/ elimination
  • Potential for toxicity

Operant Conditioning

A Historical Perspective

  • An ancient peasants house burned down. In it was his pig. When the peasant became hungry enough he tasted the cooked pig and reported its flavor to be miraculous.
  • Thereafter, when the villagers wanted to eat roast pig they put one in a house and burned it down.
  • Pharmacokinetics

What the body does to the drug

Describes the movement of drugs in the body

  • Absorption
  • Distribution
  • Metabolism
  • Elimination

Clinical pharmacokinetics is important for formulating dosage regimens in animals with disease

Pharmacodynamics

What the drug does to the body

Describes the action of the drug on the body- typically related to:

  • Plasma/serum concentrations (window into the body)
  • Exceptions: Macrolides for respiratory disease & other compounds that are 'tissue-loving'

Values poorly defined in horses- we extrapolate desired 'dose' from human or small animal lit.



Drug concentration in the blood stream usually proportional to drug concentration at site of action

Identify the agent

1. Gram stain (+) (-)

2. disk diffusion test; susceptible, intermediate, resistant. (based on human serum concentrations)

3. MIC - more expensive but more info. resistance often a concentration phenom. (minimum concentration of an AB that inhibits growth of a pathogen in vitro)

Kirby-Bauer susceptibility test

Inexpensive & considerable experience in vet.med.



Disadvantage- difficult to standardize, information on relative susceptibility hard to interpret (accurate??) and temptation to choose drug with largest zone (appropriate?)