Principles of Antimicrobial Therapy Flashcards
Why is selective toxicity relative?
Concentration of drug must be carefully controlled to avoid damage to the host.
Antimicrobial agents must be chosen based on
Identity of the organism Organisms susceptibility to agent Site of infection Patient factors (kidney and liver function) Safety of the agent Cost of therapy
Empiric Therapy
It is often not clinically possible to determine the organism prior to treatment.
Take sample
Initiate therapy
Get results
Make changes if needed
Drug choice is determined by
Site of infection
Patient medical history
Broad spectrum antibiotic is usually choice. Attacks many organisms.
Bacteriostatic vs bactericidal
Bacteriostatic drugs arrest the growth and replication of bacteria. Then body’s immune system clears. Requires good immune system of pt. (may become bacteriocidal at high concentrations)
Bactericidal drugs kill bacteria. More aggressive, used for seriously ill patients.
How does a Bacteriostatic vs bactericidal drug look on a graph
Number of viable bacteria will decline quickly with a bactericidal drug.
Number of viable bacteria will remain the same with bacteriostatic drug.
Minimum Inhibitory Concentration (MIC)
Lowest concentration of antibiotic that inhibits bacterial growth.
Clinically obtainable antibiotic concentration must be greater than the MIC.
Minimum Bactericidal Concentration
Lowest concentration of antibiotic that kills the bacteria.
Entry to CNS is influenced by
- Lipid solubility. Molecules that are ionized cannot enter. CNS inflammation (meningitis) can decrease function of BBB.
- Molecular weight. Smaller is better. Larger compounds still have a hard time getting thru BBB, even if there is inflammation.
- Protein binding. Will restrict entry.
Why antibiotic selection should be influenced by the condition of the patient. and what are examples of things that can affect the immune system?
Immune system of the patient should be considered. Host defense system must ultimately eliminate the invading organisms.
Things that affect the immune system: Alcoholism Diabetes HIV Malnutrition Autoimmune disease Pregnancy Age Immunosuppressive drugs.
Why it’s important to ask pt about kidney and liver function when prescribing meds
Poor kidney function can cause accumulation of antibiotics (if pt can’t eliminate)
Poor liver function will reduce metabolism. Some antibiotics should not be used.
Rational dosing is based on
Pharmacodynamics. Relationship of concentration to effect. and Pharmacokinetics. ADME.
Three properties have significant influence:
- Concentration dependent killing
- Time dependent killing
- Post antibiotic effect.
Concentration dependent killing
The more you increase the concentration of the drug, the better it will be at killing bacteria. Rate of killing increases.
These type of agents favor once-a-day bolus infusion.
If you ever notice a dose increase and rate of taking drug decrease, what is it due to?
Concentration dependent killing.
Certain agents show significant increase in the rate of bacterial killing as the concentration of the antibiotic increases. Favor 1x per day bolus infusion.
Ex: aminoglycosides.
Time dependent killing
Increasing concentration does not significantly increase the rate of kill.
Concentration Independent
Time dependent killing is best predicted by
Effect is best predicted by the percentage of time that blood concentrations remain about MIC.
Time dependent killing favor what kind of administration?
Extended or continuous infusion instead of intermittent dosing.