Plasmids. Chromosome. Antimicrobials 4: Testing and Selection. Dr Fiona Walsh. Role of Antibiotic Therapy. Prevention or Cure Cure or control Benefits outweigh disadvantages Efficient treatment Test bacteria sensitivity Understand antibiotic in human body . Objectives of lecture.
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Dr Fiona Walsh
Diffusion of antibiotic from a paper disc
periphery of zone
equals the MIC
Minimum Inhibitory Concentration (mg/L)
e.g. S < 8mg/L R ≥ 8mg/L
Breakpoint = 8mg/L
The half-life of the early antibiotics were quite short, perhaps only one hour or so. Therefore the antibiotic had to be administered many times per day.
With oral versions, this causes problems with patient compliance and with parenteral versions, this becomes expensive in resources.
Increasingly, the newer antibiotics have much longer half-lives, some up to 33 hours.
This means that the patient needs to be dosed just once a day in order to maintain sufficient drug concentrations.
The standard equation for PAE is:
PAE (hours) = T - C
T = is the time required for the count of cfu to increase 1 log10 (10-fold) above the count immediately seen after drug treatment
C = is the time required for the count to increase 1 log10 in an untreated control culture
PAE measures the time to reach normal logarithmic growth
Precise mechanism is still not understood
Examples of PAE