Micro 2 - Antimicrobial agents 2 Flashcards
Sensitive or resistant
o If MIC < breakpoint =
o If MIC > breakpoint =
o If zone diameter < breakpoint =
o If zone diameter > breakpoint =
o If MIC < breakpoint = sensitive or intermediate
o If MIC > breakpoint = resistant
o If zone diameter < breakpoint = sensitive
o If zone diameter > breakpoint = resistant
Define breakpoint
A concentration above which the abx is felt not to be useful (organism is resistant), below which the abx is felt to be clinically useful (organism sensitive)
When can you switch IV abx to PO?
IV to PO switch recommended in hospital for most infections if the patient has stabilised after 48h of IV treatment
In CNS infections + severe infections (osteomyelitis, endocarditis) do not switch to PO
The local concentration of the antimicrobial will be affected by factors such as
- pH at the infection site
- Lipid-solubility of the drug
- Ability to penetrate the blood-brain barrier (CNS infections)
What is the most important factor in Type 1 abx?
• Most important = Cmax (Peak above MIC)
What is the most important factor in Type 2 abx?
• Most important = time above MIC
What is the most important factor in Type 3 abx?
• Most important = AUC above MIC
How do type 1 abx work best?
- Most important = Cmax (Peak above MIC)
- Maximize concentrations
- These antibiotics have a concentration-dependent effect
- Given as one big dose once a day try to get the Cmax as high as possible
- The higher the Cmax the better the clinical outcome for infections treated with Type 1 antibiotics
• Achieving a high Cmax must be balanced with the risk of adverse effects (nephrotoxicity, ototoxicity)
o Measure trough concentration make sure that the drug is being eliminated
o If trough is too high adjust frequency of doses (do not compromise Cmax but reduce accumulation)
o Therefore if accumulation occurs, adjust frequency NOT dose
- Peak influences the dose of the drug given
- Trough determines frequency
- E.g. Aminoglycosides, Daptomycin, Fluoroquinolones, ketolides
Trough concentration = the concentration reached by a drug immediately before the next dose is administered
Concentration dependent killing + prolonged persistent effects
PK/PD parameter –> 24-AUC/MIC + Peak/MIC
https://d3i71xaburhd42.cloudfront.net/5776222800f3da17903a37ac6f6a2b032fcf39cf/19-Figure2-1.png
How do type 2 abx work best?
- Most important = time above MIC
- Maximize duration of exposure
- Time-dependent
- Concentration above MIC is not very important
- Take abx quite frequently – multiple daily dosing
- E.g. penicillins, cephalosporins, carbaenems, erythromycin, linezolid
time dependent killing + minimal persistent effects
PK/PD parameter –> T>MIC
https://d3i71xaburhd42.cloudfront.net/5776222800f3da17903a37ac6f6a2b032fcf39cf/19-Figure2-1.png
How do type 3 abx work best?
- Most important = AUC above MIC
- Maximize amount of drug
- Both concentration and time-dependent effects
- Infusions can maintain an AUC above MIC
• E.g. clindamycin, azithromycin, vancomycin, tetracyclines, oxazolidinones
time dependent killing + moderate to prolonged persistent effects
PK/PD parameter –> 24-AUC/MIC
https://d3i71xaburhd42.cloudfront.net/5776222800f3da17903a37ac6f6a2b032fcf39cf/19-Figure2-1.png
Examples of type 1 abx
Aminoglycosides
Daptomycin
Fluoroquinolones
ketolides
Examples of type 2 abx
penicillins cephalosporins carbapenems erythromycin linezolid
Examples of type 3 abx
clindamycin azithromycin vancomycin tetracyclines oxazolidinones
A patient has grown a fully susceptible E. coli in their urine. Which of the following is the narrowest spectrum agent you should deescalate to?
AMOXICILLIN
Ceftriaxone
co-amoxiclav
meropenem
piperacillin/tanzobactam
(last 4 are very broad spectrum)
things to consider when prescribing antimicrobials
• CHAOS –
o C – Choice of correct antimicrobial depends upon the:
o H – Host characteristics (e.g. renal failure, pregnancy, allergy, age, genetics, hepatic function)
o A – Antimicrobial susceptibilities of the:
o O – Organism
o S – Site of infection (i.e. bone, CSF, urine)
