Antimicrobial medications history mechanisms risks and benefits How do you test effectiveness? How is resistance spread?. First steps: chemotherapeutics drugs that killed the microbe but not the patient! Salvarsan (Ehrlich; arsenic; syphilis)
risks and benefits
How do you test effectiveness?
How is resistance spread?
drugs that killed the microbe but not the
Salvarsan (Ehrlich; arsenic; syphilis)
Pronotsil (Domagk; sulfa drugs; streptococcus)
Antibiotics: produced by microorganisms
More recently, compounds have been altered
(why do most come from soil microbes?)
Type of action
Depends of stage of growth of microbe; sensi-
tivity to immune mechanisms
Spectrum- broad or narrow
broad can be prescribed quickly but kill
normal flora, too
Must drug be injected?
How long does drug persist in system?
Can drug cross blood-brain barrier?
Does patient have normal liver and kidney
Suppression of normal flora
(what types of organisms make them?)
Enzyme inhibitors (-lactam rings)
Prevent formation of peptidoglycan (vancomycin)
Interfere with precursor transport (bacitracin)
See table 21.2, pp. 513-514
Aminoglycosides- kidney damage, deafness
Neomycin can’t be taken internally
Tetracyclines can discolor teeth in children
Chloramphenicol- aplastic anemia
Newer drugs are less toxic
Tend to be broad spectrum (not always)
nucleic acid synthesis (fluoroquinolones,
metabolic pathways, etc. folic acid
(humans lack this pathway, therefore
cell membranes (polymixin B)
specialty drugs- antituberculars
slow growth; waxy coat; intracellular
Minimum inhibitory concentration (MIC)
Minimum bactericidal concentration (MBC)
(giving combinations is risky for toxicity,
hypersensitivity, drug resistance)
p. 519; tests have been modified
microbes to become
Mutation or gene transfer?
MRSA (methicillin-resistant S. aureus)
Penicillin-resistant S. pneumoniae
Multiple-drug-resistant M. tuberculosis
Health workers: prescribe appropriately!
Patients: take drugs as prescribed!
Don’t take antibacterials for viral infections!
Should antibacterials be easily available?
Should we use them in animal feed?
What are appropriate treatments for
unique target structure
If immune system doesn’t control infection:
Prevent viral replication
Prevent viral polymerase activity
Prevent assembly and release of new virions
cells: drugs toxic to fungi are generally
Exception: ergosterol (found in plasma
membrane). Drugs are usually safe topically
but not systemically
Inhibit cell division or metabolism
Neurotoxins for helminths (see p. 529)
New targets for antimicrobials?
Interfere with resistance mechanisms?
Enhance host defenses?
New vaccine concepts?