Principles of Antimicrobial Therapy

What is an empiric antibiotic?

Covers ALL suspected pathogens based on infection type & specific patient factors

What is a definitive antibiotic?

One that targets SPECIFIC microorganisms

What is an antibiotic used for prophylaxis?

One that prevents infection (normally preoperative)

What is narrow spectrum?

• Acts on single or limited group of microorganisms
• Example: Beta lactams target staph

What is extended spectrum?

• Structurally modified so it is more effective against a greater # of microorganisms
• Example: Gram + and Gram - (amox → strep, staph, e.coli)

What is broad spectrum?

• Very wide spectrum and used empirically in severe infections

What do broad spectrum abx have a risk of?

High risk of C.Diff infection

Define bacteriostatic

Stops growth but does NOT kill bacteria; dependent on immune system

Define Bacteriocidal

Kills the organism (must have 3 log kill w/in 24 hrs); independent of immune system

What are examples of Bacteriostatic abx?

• Clindamycin
• Macrolides (clarithro, erythro, azithro)
• Tetracyclines (cyclines)
  "Country Music Television"

What are examples of Bacteriocidal abx?

• Aminoglycosides (tobra, genta)
• Beta Lactams (cillins, cephalosporins, carbapenems)
• Quinolones (floxacins)

What are the possible results of abx combo therapy?

• Indifference: adding the second drug doesn't create a significantly different effect
• Synergy: adding the second drug creates a significantly improved effect
• Antagonism: adding the second drug reduces the overall efficacy of the drug therapy

What antimicrobials inhibit cell wall synthesis?

• Beta Lactams (penicillins, cephalosporins, carbapenems, monobactams)
• Vancomycin
• Bacitracin
• Polymyxins

What antimicrobials inhibit nucleic acid synthesis?

• Sulfonamides
• Trimethoprim
• Quinolones
• Rifampin

What antimicrobials inhibit protein synthesis?

• Macrolides
• Clindamycin
• Linezolid
• Chloramphenicol
• Streptogramins
• Tetracyclines
• Aminoglycosides

What are the 7 factors to consider when initiating antimicrobial therapy?

1. Site of infection
2. Usual causative pathogens
3. Antimicrobial resistance (Use antibiogram → want susceptibility >90)
4. Identity & drug sensitivity of organism
   (Minimum Inhibitory Concentration (MIC))
5. Bacterial vs bacteriostatic effect of drug
6. Safety, cost, drug formulary
7. Patient specific factors

What is an example of considering site of infection when choosing abx?

For meningitis, give drug that crosses BBB

What is an example of considering usual causative pathogens when choosing abx?

For CAP, give drug that covers Strep pneumo, etc

What are patient specific factors to consider when choosing abx?

• Status of host defenses/immune fxn
• Pharmacogenetics
• Renal/hepatic fxn
• Perfusion status
• Drug allergies/drug interactions
• Pregnancy/lactation

What is time dependent drug dosing?

Bacterial kill rate improves the longer the concentration is above MIC

What is an example of time dependent drug dosing?

Beta lactams which need multiple doses over shorter periods

What is concentration dependent drug dosing?

Bacterial kill rate improves w/ higher concentrations above MIC

What is an example of concentration dependent drug dosing?

Aminoglycosides which need higher concentration peak for greater post abx effect

For what drug is AUC/MIC important?

Vancomycin

Do gram - organisms have a thick or thin cell wall?

Thin

Do gram + organisms have a thick or thin cell wall?

Thick

Do gram + or gram - bacterial have an outer membrane?

Gram -

What do acid-fast bacteria have?

Mycolic acids

What is post antibiotic effect (PAE)?

Continued suppression of the drug when the concentration drops below the MIC