Antimicrobial drugs

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Antimicrobial drugs
2015-03-30 12:55:54

Antimicrobial drugs
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  1. Quinine
    • Cinchona tree bark extract
    • –Malaria treatment
  2. •Ehrlich: first “magic bullet” drug Salvarsan
    – An arsenic derivative used to treat syphilis
  3. •Domagk: first sulfa drug (Prontosil)
    –Used to treat Streptococcus
  4. •Alexander Flemming
    –Discovered penicillin via a lucky accident

    –Developed term “antibiosis”
  5. •Chain and Florey
    –Purified Penicillin

    –Performed large clinical trials
  6. Where do most antibiotics come from?
    other microorganisms
  7. Chemotherapeuticagents
    Drug used to kill cancer cells or make them less active
  8. Selective toxicity
    antimicrobial drug selects harmful microorganism without damaging host
  9. Synthetic drugs
    •drugs whose origins are not primarily organic, but produced via chemical synthesis
  10. Antibiotics
    inhibits or abolishes growth of microorganisms
  11. Semi-synthetic antibiotics
    Natural products that have been chemically modified in the lab
  12. Features of Antimicrobial Drugs
    •Selective toxicity

    • •Antimicrobial action
    • –Bacteriostatic vs. Bactericidal
    • –Broad spectrum vs. Narrow spectrum

    • •Tissue distribution and metabolism
    • –Drug half-life
  13. Effects of drug combinations
    –Synergistic - drugs that work together - mixing drugs

    –Antagonistic - taking multiple drugs
  14. Effects of drug combinations: Adverse effects
    • –Allergies
    • –Toxicity
    • –Suppression of normal flora
  15. Intrinsic
    –Drug has no effect on microbe
  16. Acquired resistance
    Due to mutation or new genetic element (plasmid)
  17. How can microbes become resistant?
    • 1.Inactivation of the antibiotic
    • –Ex. b-lactamase

    • 2.Alteration of target site
    • –Ex. mutation in ribosome

    • 3.Decrease uptake of drug
    • –Ex. alteration in cell wall porin

    • 4.Increased elimination of drug
    • –Ex. efflux pumps
  18. Prevention and Control of Antibiotic Resistance
    •Role of physicians and other HCW’s

    –Proper prescribing practices

    –Patient education
  19. Prevention and Control of Antibiotic Resistance 2
    •Role of patients

    –Follow instructions; Take dosages at proper time; Complete entire course of antibiotic
  20. Prevention and Control of Antibiotic Resistance 3
    •Role of public

    –Understand  limitations of antibiotics

    –Ex. Penicillin doesn’t cure the common cold!
  21. Modes of Action by Antibiotics
    1.Inhibit cell wall synthesis

    2.Inhibit protein synthesis

    3.Injure the plasma membrane

    4.Inhibit nucleic acid synthesis (DNA/ RNA)

    5.Inhibit synthesis of essential metabolites (inhibit specific metabolic pathways)
  22. Penicillins
    Beta lactam antibiotic

    inhibits cell wall synthesis by targeting peptodoglycan cross links in the cell wall
  23. 2 forms of penicillin
    • Penicillin G - injectable
    • Penicillin V - oral
  24. Penicillin
    Resistant  to b-lactamases (penicillinases)

    B lactamases - break beta lactam ring so that its not functional
  25. B-lactam drugs
    interfere with the formation of the peptide side chains between adjacent strands of peptidoglycan by inhibiting penicillin-binding proteins
  26. Vancomycin
    binds to the amino acid side chain of NAM molecules, interferring with peptidoglycan synthesis
  27. Bacitracin
    interferes with the transport of peptidoglycan precursors across the cytoplasmic membrane
  28. Penicillin Augmentin
    •Penicillin + b-lactamase inhibitor

    –Clavulanic acid + amoxicillin = Augmentin
  29. Clavulanic acid
    noncompetitive inhibitor of penicillase
  30. Antimycobacterial
    specific for Mycobacterium

    –Mycolic acids

    –Isoniazid (INH)

  31. Chloramphenicol
    –Binds 50S ribosome, inhibits peptide bond formation

    –Broad spectrum

    –Toxicity– aplastic anemia
  32. Aminoglycosides
    –Binds 30S ribosome, causes mRNA to be read incorrectly

    –Broad spectrum

    –Ex. Streptomycin, gentamicin, neomycin
  33. tetracyclines
    –Bind to 30S ribosome, block incoming tRNA

    –Broad spectrum, suppress normal flora, discolors children’s teeth

    –Ex. Tetracycline, doxycycline
  34. streptomycin
    changes shape of 30S portion, causes code on mRna to be read incorrectly
  35. •Macrolides
    • –Bind
    • 50S ribosome, block continuation of protein synthesis

    –Used to treat G+ infections (Staph & Strep) for patients allergic to penicillin

    –Ex. Erythromycin, azithromycin, clarithoromycin, telithromycin
  36. •Polymyxin B
    Injures the PM

    –Used topically only

    –Effective against Gram negative bacteria
  37. •Triple-antibiotic ointment contains

    –Polymyxin B


    Injures the PM
  38. •Rifamycin
    –Inhibits RNA polymerase to block synthesis of mRNA
  39. •Quinolones & Fluoroquinolones
    –Inhibits DNA gyrase needed for DNA replication

    –Ex. Ciprofloxacin (Cipro)

    –Ex. Moasifloxacin, gatifloxacin
  40. •Sulfonamides (sulfa drugs)
    –Interfere with different enzymes needed in the metabolic pathway for making tetrahydrofolic acid (a precursor for proteins, DNA,& RNA)

    –Drug synergism
  41. Antifungal Drugs
    •Fungi are eukaryotes!

    •Selective toxicity is more difficult
  42. Mechanisms of action of antifungal drugs
    1.Plasma membrane

    2.Fungal cell wall

    3.Inhibit synthesis of nucleic acids by fungi

    4.Other – block fungal cell division
  43. Plasma membranes of fungi/ animals contain

  44. Antifungals that inhibit synthesis of ergosterol
    • 1.Polyenes
    • •Ex. amphotericin B

    • 2.Azoles
    • •Ex. clotrimazole, miconazole, fluconazole

    • 3.Allylamines
    • •Ex. terbinafine, naftifine
  45. Fungal cell walls are composed of
    •carbohydrate, the main target is b-glucan
  46. Echinocandins
    Antifungal that Target Fungal Cell Walls

    • –Block biosynthesis of b-glucan
    • –Ex. Caspofungin

    • –Used to treat fungal infections in immunocompromised patients
    • •Aspergillus
    • •Pneumocystis
    • pneumoniae
  47. Flucytosine
    –Blocks synthesis of RNA (and therefore synthesis of proteins too)

    –Fungi & not mammalian cells convert flucytosine to 5-fluorouracil

    •5-fluorouracil is a base analog that when incorporated into RNA disrupts protein synthesis
  48. •Griseofulvin
    Blocks Fungal Cell Division

    • •Binds to keratin and blocks microtubule
    • assembly which interferes with mitosis and fungal reproduction

    • •Used to treat superficial (skin) fungal
    • infections
  49. Antiviral Drugs Mechanism of action
    1.Nucleoside and nucleotide analogs

    2.Inhibit viral enzymes or proteins

  50. Antivirals that are Nucleoside/ Nucleotide Analogs
    •Ex. Acyclovir, famciclovir, & ganciclovir are used to treat Herpes

    •Ex. Lamivudine is used to treat hepatitis B

    • •Ex. Zidovudine (AZT), tenofovir are used
    • to treat HIV

    –used by viral reverse transcriptase (RT) and block further DNA synthesis
  51. Antiprotozoan Drugs
    1.Metronidazole – widely used!

    •Interferes with anaerobic metabolism
  52. Antiprotozoan Drugs 2
    • 1.Quinine & synthetics versions: chloroquine &
    • mepacrine used to treat malaria

    •Block replication and transcription
  53. Antihelminth Drugs
    1. Mebendazole, broad spectrum antihelminth

    •Inhibits formation of microtubules in the cytoplasm which blocks absorption of nutrients by the parasites
  54. Antihelminth Drugs
    • Praziquantel is used to treat tapeworm
    • & some flukes

    •Kills by altering the permeability of the plasma membrane

    •May make helminths more susceptible to the immune system