Bacteriostatic vs Bacteriocidal
- Bacteriostatic: stops bacteria from dividing but will not decrease number of bacteria
- Bacteriocidal: decreases number of viable bacteria
Drugs can be both.
Minimal inhibitory concentration (MIC) definition.
MIC: the lowest concentration of a drug (mcg/ml) that will inhibit growth of bacteria.
Breakpoint (related to medication dose).
The concentration of antimicrobial achieved in the blood after one dose.
When are bacteria susceptible to a drug?
If teh MIC is below the breakpoint of the drug. (ie. If the concentration in the blood after a dose is enough to inhibit the growth of bacteria, the bacteria are susceptible.)
Medications whose effect is concentration dependent.
Fluoroquinolones and aminoglycosides among others.
- With concentration dependent meds, a larger dose is given less frequently.
- These drugs may exhibit a post-antibiotic effect.
Define post-antibiotic effect.
Antibiotic activity even after the serum drug level drops below MIC level.
Examples of time-dependent medications.
PCNs and cephalosporins.
These drugs muse be given more frequently in order to maintian the serum concentration above the MIC.
What factors affect the baterial response to antimicrobial therapy?
- Drug determinants (distribution - does it get to the bacteria, dose, and route)
- Host determinants (immune status of pt, adherance, clearance of drug, source of infection)
- Bacterial determinants (colonization vs infection, nosocomial infections)
Define selective toxicity related to antimicrobials.
Antibiotics should be more toxic to the infecting organism than to the host. Selective toxicity is made possible by exploiting biological differences between the bacteria and the host.
Give examples of how an antimicrobial might be selectively toxic.
- - Inhibiting cell wall synthesis (because humans don't have cell walls); ex. PCNs, cephalosporins, vancomycin
- - Inhibiting protein synthesis (becuase bacteria make protein differently than humans); ex. aminoglycosides, clindamycin, macrolides
- - Antimetabolites (blocks metabolism of chemicals necessary for bacterial function); ex. sulfonamides, trimethoprim, bacrim
What is the goal of antimicrobial therapy?
To kill the infecting organism without hurtingthe host.
How is the effect of an antimicrobial measured?
- - subjective data (appearance)
- - objective data (VS, CBC, cultures, physical signs)
What are some expected changes in VS with bacterial infection?
- - increased temp (may be masked by NSAIDs/acetamenophen
- - decreased BP (r/t shock)
- - increased HR (r/t fever)
- - increased RR (r/t fever)
What changes would be expected in CBC with infection?
increased WBC, shift to left, increased percentage of bands
What would be signs of a physical infection?
Redness, heat, swelling at site.
What would be signs of CNS infection?
signs of meningeal irritation: HA, fever, neck stiffness, altered mental status
What factors should be considered when choosing an antimicrobial?
- - spectrum of activity (narrowest is best, consider common bugs for emperic therapy)
- - susceptibility (bug should be susceptible to drug)
- - drug distribution (drug must get to site of infection at high enough concentrations)
- - toxicity and cost (want both low)
- - patient allergies (avoid if possible)
If a pt is allergic to a medication, what info should be collected?
- - name of drug
- - description of reaction
- - severity of rxn
- - temporal relationship between exposure and symptoms
- - date of occurence
- - any exposures to drug since first rxn
How should dosage be determined for antimicrobials?
Enough drug should be used to maintain a concentration at site of infection in excess of MIC (follow labels).
When should combination therapy be considered?
- - emperic therapy in seriously ill pt
- - mixed infections
- - to prevent resistance (TB)
- - attainment of synergy (immunocompromised)