Ch. 9 - Chemotherapy

• selective toxicity


  ability of drug to kill or inhibit pathogen while damaging host as little as possible
• therapeutic dose


  drug level required for clinical treatment
• toxic dose


  drug level at which drug becomes too toxic for patient, produces side effects
• therapeutic index


  ration of toxic does to therapeutic dose
• narrow-spectrum drugs


  attack only a few different pathogens
• broad-spectrum drugs


  attack many different pathogens
• minimal inhibitory concentration


  lowest concentration of drug that inhibits growth of pathogen
• minimal lethal concentration


  lowest concentration of drug that kills pathogen
• dilution susceptibility tests


  inoculating media containing different concentrations of drug to test for MIC and MLC
• e test


  similar to disc diffusion but with strips that contain a gradient of an antibiotic, for use with anaerobic pathogens
• penicillins


  inhibit cell wall synthesis by blocking the enzyme that catalyzes the links in peptidoglycan leading to lysis of cell; acts only on growing bacteria, can also bind to PBPs, activate autolysins, or stimulate holins to form holes in the membrane
• cephalosporins


  broad-spectrum drugs that can be used when a patient is allergic to penicillin
• vancomycin and teicoplanin


  glycopeptide drugs that inhibit cell wall synthesis, important for treatment in MRSA/E infections
• aminoglycosides


  inhibit protein synthesis by binding to 30S ribosomal subunit and cause the misreading of the mRNA
• tetracyclines


  broad-spectrum and bacteriostatic drugs that inhibit protein synthesis by binding to the 30S ribosomal subunit and stops bind of aminoacul-tRNA molecules to the A site of the ribosome
• macrolides (erythromycin, clindamycin, zithromax)


  broad-spectrum bacteriostatic drugs that inhibit protein synthesis by binding to the 23S and 50S ribosomal subunits to stop peptide chain elongation; used for patients allergic to penicillin
• chloramphenicol


  inhibits protein synthesis by binding to the 23S and 50S ribosomal subunits and stopping peptidyl transferase reactions; toxic, not used often
• sulfonamides


  antimetabolites that are structurally similar to PABA, which is used for the synthesis of folic acid which is a precursor to nucleic acids
• trimethoprim


  broad-spectrum antimetabolite that blocks DHFR in folic acid pathway; has lots of side effects
• quinolones


  broad-spectrum drugs that inhibit NA synthesis by stopping bacterial DNA-gyrase and topoisomerase II
• mycoses


  topical and oral treatments like candida that disrupt membrane permeability and inhibit sterol synthesis; may inhibit protein and DNA synthesis by disrupting mitotic spindle
• systemic mycoses


  difficult to treat and often fatal, amp B binds to sterols in membranes, 5-flucytosine disrupts RNA function, and fluconazol (preventative)
• antiprotozoans


  antiviral drugs that block steps in NA synthesis, ETC, protein synthesis and folic acid production
• mechanisms of drug resistance

  prevent entrance of drug, drug efflux, chemical inactivation of drug, modification of target enzyme or organelle, and use of alternative metabolic pathways
• immunity genes


  resistance genes that exist in nature to protect antibiotic producing microbes from their own antibiotics
• horizontal gene transfer


  transferred immunity genes from antibiotic producers to non-producers