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Chemotherapeutic agents
chemicals used to treat diseases
Antimicrobial agents/antimicrobials
chemotherapeutic drugs that treat infections
Antibiotics
antimicrobial agents that are produced naturally by an organism
Semisynthetic antimicrobials
chemically altered antibiotics; more effective, longer lasting and easier to administer than antibiotics
Synthetic drugs
antimicrobials completely synthesized in a laboratory
Selective toxicity
an effective antimicrobial agent must be more toxic to a pathogen than to the pathogen’s host
Beta-lactams
antimicrobials whose functional portions are called beta-lactam rings; prevents the cross-linkage of NAM subunits
Bacitracin
antimicrobial that also prevents cell wall formation; blocks transport of NAG and NAM across the cytoplasmic membrane to the wall
Isoniazid (INH) and ethambutol
disrupt the formation of mycolic acid in the cell walls of mycobacteria
Echinocandins
a class of antifungal drugs that inhibit the enzyme that synthesizes glucan–which assists in the formation of fungal cell walls
Aminoglycosides
change the shape of the 30S subunit of a prokaryotic ribosome, making it impossible for the ribosome to read the codons of mRNA correctly
Tetracyclines
block the tRNA docking site (A site), preventing the incorporation of additional amino acids into a growing polypeptide
Chloramphenicols
block the enzymatic site of the 50S subunit, preventing translation
Lincosamides, streptogramins and macrolides
bind to a different portion of the 50S subunit, preventing movement of the ribosome from one codon to the next, freezing translation
Antisense nucleic acids
RNA or single-stranded DNA molecules designed to be complementary to a pathogen’s mRNA molecules; block ribosomal subunits from attaching to pathogenic mRNA with no effect on human mRNA
Oxazolidinones
stop protein synthesis by blocking the initiation of translation
Mupirocin
a topical drug that selectively binds to isoleucyl-tRNA synthetase, making translation stop once an isoleucine codon is reached
Polyenes
an antifungal and antiprotozoal group of drugs that disrupt the cytoplasmic membrane by forming a channel through the membrane, damaging its integrity
Azoles and allylamines
antifungal and antiprotozoal drugs that act by inhibiting the synthesis of ergosterol, an important lipid in a fungal cell’s cytoplasmic membrane
Sulfonamides/sulfa drugs
antimetabolic drugs that are analogs of PABA, a molecule important in the synthesis of nucleotides in DNA and RNA synthesis; works as a competitor of PABA in the binding of an enzyme converting PABA to dihydrofolic acid
Quinolones
inhibit DNA gyrase, the enzyme in bacteria necessary for coiling and uncoiling of replicating bacterial DNA; have little effect on viruses and eukaryotes but may act on mitochondrial DNA in some eukaryotes
Nucleotide analogs/nucleoside analogs
molecules with structural similarities to nucleotide building blocks of nucleic acids; distort shapes of nucleic acid molecules and prevent further replication, transcription, or translation; used most often against viruses
Spectrum of action
the number of different kinds of pathogens a drug acts against
Narrow-spectrum
drugs that work only against a few kinds of pathogens
Broad-spectrum
drugs that are effective against many kinds of pathogens
Diffusion susceptibility test (Kirby-Bauer test)
involve uniformly inoculating a petri plate with a standardized amount of pathogen in question. Then small disks of paper containing standard concentrations of the drugs to be tested are firmly arranged on the surface of the plate. After incubation, the plate is observed for whether the drug(s) effectively inhibited the bacterial growth
Zone of inhibition
a clear area where bacteria do not grow (a large zone of inhibition = more effective drug (in general))
Minimum inhibitory concentration (MIC) test
determines the lowest concentration of an antimicrobial agent that prevents visible growth of a microorganism
Broth dilution test
where a standardized amount of bacteria is added to serial dilutions of antimicrobials in tubes or wells containing broth. After incubation, turbidity is measured
Minimum bactericidal concentration (MBC) test
determines the amount of drug required to kill a microbe (different from MIC–which tests for inhibition, not killing)
Therapeutic index (TI)
the margin of safety of a drug–a ratio of the dose of a drug that is toxic to 50% of a patient population to the dose of the drug that is therapeutic in 50% of patients
R plasmids/R factors
resistance genes in bacteria that can be obtained through acquiring these genes via horizontal gene transfer
Multiple-drug-resistant pathogens (superbugs)
pathogens resistant to three or more types of antimicrobial agents
Cross resistance
a phenomenon where resistance to one antimicrobial may confer resistance to similar drugs; occurs when drugs are similar in structure
Synergism
where one drug may enhance the effect of a second drug