CH9 Flashcards
chemotherapeutic index
[max. tolerable] / [min for cure]
- many effective agents to use
- topical applications (cream)
antimicrobial agents selective toxicity
- larger is better
- generally smaller for drugs against eukaryotic MO’s/ viruses
chemotherapeutic index
side effects of antimicrobial agents
toxicity
- liver and kidney damage
- nausea and diarrhea
allergy
- immune system responds to foreign substance
- rashes and anaphylactic shock
normal microbial destroyed
-superinfection- Canidia and Clostridium difficile
two ways to determine antimicrobial sensitivity
- kirby- bauer method- measures zone inhibition
- dilution method- MIC (min. inhibition [ ])
5 ways antimicrobial drugs effect MOs with examples
inhibition of cell wall (peptidoglycan) synthesis
-penecillin
disruption of cell pm function
-polymyxin
inhibition of protein synthesis
-tetracycline
inhibition of nucleic acid synthesis
-quinolones
action as antimetabolites
-sulfonilamide
PABA get broken down to
folic acid
- single gene
- frequency low
mutations
- R-plasmids provide multiple resistance
- chromosomal genes
conjugation and transduction
it kills or inhibits the microbial pathogen while damaging the host as little as possible
selective toxicity
the drug level required for clinical treatment of a particular infection
therapeutic dose
the drug level at which the agent becomes too toxic for the host
toxic dose
degree of selective toxicity may be expressed in terms of
- therapeutic does
2. toxic dose
ratio of the toxic dose to the therapeutic dose
therapeutic index
The ______ the therapeutic index, the ______ the chemotherapeutic agent in general
larger
better
they are effective only against a limited variety of pathogens
narrow -spectrum drugs
attack many different kinds of bacteria
broad- spectrum drugs
the lowest concentration of a drug that prevents growth of a particular pathogen
minimal inhibitory concentration (MIC)
lowest drug concentration that kills the pathogen
minimal lethal concentration (MLC)
causing death
cidal
inhibiting or retarding
static
A ______ drug generally kills pathogens at levels only two to four times more than the MIC, whereas a ______ agent kills at much higher concentrations
cidal
static
The wider the clear zone surrounding a disk, the
more susceptible the pathogen i
Zone width also is a function of the antibiotic’s _________, ___________, and its __________ through agar
initial concentration, its solubility, and its diffusion rate
bacterial resistance mechanisms with examples
- alteration of target (often by mutation)
ex: ribosomes - acquire gene(s) for enzymes that modify/destroy antibiotic
ex: beta-lactamase (penicillinase) - alteration of membrane permeability
ex: polymyxin
- inactivates penecillin
- cleaves beta-lactam ring
beta-lactamase
why is treatment of fungal infections generally less successful than that of bacterial infections?
because as eukaryotes, fungal cells are much more similar to human cells than are bacterial cells
strategies to inhibit/slow down development of drug resistance
- avoid indiscriminate use, use when necessary
- over the counter, viral infections
- use high doses of the proper antibiotic
- test when possible, complete the treatment
-switch if signs of resistance
- finish entire antibiotic course
- by not finishing it then you can become get sick again but worse or harm others around you that are not as susceptible as you are to the mo
organisms that produce useful antibiotics
- Streptomycetes (most are produced by)
- Penicillin and Cephalospyrium (fungi)
- Actinomycetes (micro monospora)
are inactive until metabolized
prodrugs
