Antibacterial Drugs Flashcards
What are the six major groups of antibacterial drugs?
- Beta-Lactams
- Aminoglycosides
- Tetracyclines
- Sulfonamides
- Macrolides
- Fluoroquinolones
What is a bactericidal?
A drug that kills bacteria independent of host immune function.
What is a bacteriostatic?
A drug that inhibits bacterial growth and division. Immune system can then more rapidly eradicate the non-multiplying bacteria.
Why should you always follow label directions whenever possible?
Some drugs that are approved for one species can be lethal in another. Additionally, some drugs are safe to be given by one route of administration but not another.
What is minimum inhibitory concentration (MIC)?
It is a measure of how much antibiotic is needed to stop a bacteria from growing. This is the lowest concentration needed to stop the bacterial growth.
Explain what time-dependent AMDs means.
Efficacy is associated with length of time the drug concentration remains above MIC. Levels should remain above MIC throughout the course of therapy.
Explain what concentration-dependent AMDs means.
Efficacy depends on peak concentration of the drug. The peak concentration may be well in excess of MIC. It is not necessary to maintain levels above MIC for the entire interval between doses. This means the higher the drug concentration in relation to MIC, the greater the rate/extent of antimicrobial activity.
What rout of administration do we typically not use in ruminants and why?
- Oral
- they may be destroyed in the rumen
- they may destroy rumen microflora causing rumen stasis
- the one exception is giving oral meds to a ruminant who is <6 months of age because they haven’t fully developed the rumen
What could happen if you gave a hind gut fermenter a parenteral drug orally?
- they could release toxins from gut bacteria
- these toxins may be lethal
What is the typical trend between drug usage and antimicrobial resistance?
Increase drug usage = increase antimicrobial resistance
Why does increase in drug usage result in increase in resistance?
The more often you use a drug, the more likely you are to kill off highly sensitive bacteria and the highly resistant ones will stay and fleurish.
What are the five main mechanisms of action for AMDs?
- Damage to the plasma membrane
- Inhibition of cell wall synthesis
- Inhibition of protein synthesis
- Damage to the DNA
- Inhibition of folic acid synthesis
What is serial drug dilution?
Tubes are made using different dilutions of AMDs, bacterial growth medium and a quantity of bacteria to assess for visible bacterial growth. This can give us an idea of MIC.
What is Minimum Bactericidal Concentration (MBC) and how can it be determined with serial dilution?
You can take the tubes from serial drug dilution that did not exhibit bacterial growth but may still have live bacteria in them. You can then culture them in drug-free medium and the drug concentration that sterilized the tube resulting in no growth is your MBC.
What is the Kirby-Bauer disk diffusion test?
Paper disks impregnated with different drugs are placed on a plate that has been uniformly swabbed with bacteria. The drugs will diffuse into the agar creating a zone of inhibition around each disk. The bigger the disk, the more sensitive a bacteria is to the drug. Likewise, the smaller the disk, the more resistant a bacteria is to a drug. Each bacteria is classified as sensitive, intermediate, resistant.
What are five considerations to take when selecting a drug?
- Bacterial sensitivity (try to use narrow-spectrum drugs when possible)
- Bacteriostatic versus bactericidal (is your patient immune compromised?)
- Adverse effects
- Distribution (does it enter all parts of the body?)
- Cost
What are some disease processes that require special consideration when using AMD?
- Osteomyelitis: avascular bone fragments can provide a space for bacteria to avoid exposure to AMDs, therefore when therapy stops we typically see reinfection and tend to need longer term treatment
- Foreign Body: no matter the drug, we need the FB to be removed before infection resolves
- Implants: can sequester bacteria so prophylactic AMDs are typically administered
- Abscess: AMDs sometimes can’t access an abscess or they’re inactivated by it so more effective to drain the abscess
- Intracellular Pathogens: require a drug that enters the cells readily
- Dysfunctional Host Defenses: if a host is immunocompromised it may require a drug concentration much higher than normal or for a longer duration
When would we prophylactically use AMDs?
- high risk of serious infection following trauma
- patient’s condition will allow serious infection like immune system deficiency
What is the goal when prophylactically using AMDs for surgery?
To have adequate AMD levels in tissues at time of incision.
