9. antimicrobial drugs II Flashcards
the successful chemotherapeutic agent has _____ toxicity. therefore, it kills or inhibits the pathogen while damaging the host as little as possible
selective toxicity
the degree of selective toxicity may be expressed in terms of what two types of doses?
- therapeutic dose
- toxic dose
this is the drug level at which the agent becomes too toxic for the host
the toxic dose
this is the drug level required for treatment of a particular infection
the therapeutic dose
this is the ratio of the toxic dose to the therapeutic dose
the therapeutic index
the ______ (smaller/larger) the therapeutic index, the better the chemotherapeutic agent in general
larger
a drug that disrupts a microbial structure or function not found in host cells often has greater selective toxicity, fewer side effects, and a _____ (low/high) therapeutic index
high
what are the three categories that antimicrobial drugs can be classified as?
- natural
- semisynthetic
- chemical synthetic
this type of antimicrobial drugs can be natural antibiotics that have been structurally modified by the additional of chemical groups to make them less susceptible to stomach acids and inactivation by pathogens (e.g. ampicillin and amoxicillin)
semisynthetic
this type of antimicrobial drugs are produced by bacteria and fungi (e.g. penicillin)
natural
this type of antimicrobial drugs includes sulphonamides, trimethoprim, ciprofloxacin, etc.
chemical synthetic
this type of antimicrobial agents are effective only against a limited variety of pathogens. e.g. may affect only gram positive and not gram negative bacteria, or may only affect a specific group of gram negative bateria
narrow-spectrum drugs
this type of antimicrobial agents attack many different types of bacteria. eg. affect some gram negative and gram positive bacteria
broad-spectrum drugs
T/F: chemotherapeutic agents are only bactericidal
false - chemotherapeutic agents can be either cidal or static
these agents reversibly inhibit growth. therefore if the agent is removed, the microorganisms will recover and grow again
static agent
T/F: the effect of chemotherapeutic agents may vary with the target species. they may be cidal for one species and static for another
true
these type of drugs help the immune system get rid of bacteria/infection; if the immune system his weak, elimination of the infection may not occur
static agent
the estimate of the effectiveness of an antimicrobial drug against a pathogen can be obtained from the ____________
minimal inhibitory concentration (MIC)
the _____ is the lowest concentration of a drug that prevents the growth of a particular pathogen; static drugs
MIC
the ______ is the lowest drug concentration that kills the pathogen; cidal drugs
minimal lethal concentration (MLC)
what are the three antimicrobial activity tests?
- dilution susceptibility tests
- disk diffusion tests
- the E-test
this antimicrobial activity test uses small paper disk, each impregnated with a different antibiotic, and placed on the inoculated agar to test the bacterial susceptibility to drugs
disk diffusion tests
this is the most commonly used type of disk diffusion test. the results are interpreted using a table that related zone diameter to the degree of microbial resistance
kirby-bauer method
this antimicrobial activity test is often used in sensitivity testing. the MIC can also be determined by this test. the bacterial isolate to be tested for antimicrobial sensitivities is inoculated on the surface of an agar medium and then strips are placed on the surface. each strip contains a gradient of an antibiotic and is labeled with a scale of MIC values. after the incubation time, an elliptical zone of inhibition appears.
E-test
where is the MIC determined on the strip of an E-test?
the MIC is determined from the point of intersection between the inhibition zone and the strips scale of MIC values
this antimicrobial activity test is used to determine MIC and MLC values. a series of tubes containing broth media with antibiotic in serial concentrations (twofold dilution) are inoculated with the test pathogen.
dilution susceptibility tests/broth dilution test
how is the MIC determined from the dilution susceptibility tests/broth dilution test
the lowest concentration of the antibiotic resulting in no growth after incubation is the MIC`
how is the MLC determined from the dilution susceptibility tests/broth dilution test
the MLC can be ascertained if the tubes showing no growth are then cultured into fresh medium lacking antibiotic. the lowest antibiotic contraption from which the pathogen do no subsequently grow is the MLC
