Pharmacology Exam II

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Rx2013
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65370
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Pharmacology Exam II
Updated:
2011-02-09 19:19:18
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Antifungal Agents
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Antifungal Agents
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  1. Drugs for subcutaneous and systemic mycoses
    • amphotericin B
    • fluconazole
    • flucytosine
    • itraconazole
    • ketoconazole
  2. Drugs for superficial mycoses
    • clotrimazole
    • econazole
    • griseofulvin
    • miconazole
    • nystatin
  3. 3 categories of antifungal agents
    • systemic
    • oral drugs
    • topical drugs
  4. Systemic drugs
    • amphotericin B
    • flucytosine
    • azoles
    • echinocandines
  5. Four formulations of Ampho B
    • plain
    • cholesteryl sulfate complex
    • lipid complex
    • liposomal
  6. Pharmacokinetics of Ampho B
    • poorly absorbed from GI tract
    • 90% protein bound
    • widely distributed in all tissues but not CSF
    • t1/2 = 15 days
  7. Mechanism of Action for Ampho B
    • fungicidal or fungistatic depending on the organism
    • binds ergosterol in the cell membrane and forms pores or channels
    • disrupts membrane function and electrolytes (k+) leak from the cell resulting in cell death
  8. Ampho b targets fungal cells rather than mammalian cells because
    it targets ergosterol not cholesterol
  9. spectrum of Ampho b
    broad
  10. Clinical use of Ampho B
    • candidiasis
    • endemic mycosis
    • fungal pneumonia
  11. Side effects of Ampho B
    • shake and bake syndrome (fever and chills, spasms)
    • treated with NSAIDS
    • reversable renal damage
    • liver damage
    • anemia
  12. Irreversible renal damage occurs with doses of Ampho B greater than
    4 grams
  13. Drugs that increase hematologic and renal side effects of Ampho B
    • foscarnet
    • ganciclovir
    • tenofovir
    • adefovir
  14. a synthetic pyrimidine antimetabolite used in combo with Ampho B for systemic mycoses and meningitis
    flucytosine
  15. Disadvantages of flucytosine
    • spectrum of action is narrow compared to Ampho B
    • resistance can develop during therapy (not with ampho B)
  16. Flucytosine kinetics
    • 90% oral absorption
    • present in CSF because of poor protein binding
    • renal excretion
  17. Mechanism of action for Flucytosine
    • enters cell through cytosine-specific permease
    • enzyme is absent in mammalian cells
    • converted to 5-FU which is converted to 5-FdUMP
    • this false nucleotide inhibits thymidylate synthetase inhibiting thymidylic acid synthesis (dna component)
  18. Flucytosine + Ampho B
    • synergistic effects
    • used in combo to lower doses of Ampho B so there is less toxicity
  19. Clinical use of flucytosine
    • cryptococcus neoformans
    • candida
    • chromoblastomycosis
  20. side effects of flucytosine
    • bone marrow toxicity resulting in anemia, leukopenia and thrombocytopenia
    • GI irritation
    • liver toxicity (less common)
  21. 4 systemic azole drugs
    • ketoconazole
    • itraconazole
    • fluconazole
    • vorconazole
  22. frequent drug interactions
    ketoconazole
  23. inhibition of mammalian sterol synthesis
    ketoconazole
  24. drugs that have no inhibition of mammalian sterol synthesis
    • fluconazole
    • itraconazole
  25. Clinical uses of Azoles
    • broad spectrum antifungals
    • effective for ampho B resistance
  26. Mechanism of action for Azoles
    • inhibit ergosterol synthesis by inhibition of CYP450
    • higher affinity for fungal CYP450 than for human CYP450
  27. ADRs assocated with Azoles
    • minor GI irritation
    • some effect on liver enzymes, rarely hepatitis
    • some affinity for human CYP450 = drug interactions
  28. Ketoconazole
    • highest affinity for human CYP450
    • typically used topically
    • pregnancy category C
  29. Mechanism of action for ketoconazole
    • inhibits conversion of lanosterol to ergosterol
    • disrupts membrane function and increases permeability
  30. Drugs that may be effected by ketoconazole
    • cyclosporine
    • phenytoin - important not to mess with this (seizures)
    • sucralfate
    • terfenadine
    • tolbutamide
    • warfarin
  31. Ketoconazole + ampho B
    • contraindicated
    • ketoconazole antagonizes ampho B antifungal activity
  32. Itraconazole
    • good oral absorption
    • 90% protein bound (no CSF use)
  33. Itraconazole is used for
    • histoplasmosis
    • blastomycosis
    • onychomycosis
  34. Fluconazole
    • can replace intrathecal ampho B
    • not effective against aspergilli or filamentous fungi
    • treatment failures in HIV pt.
  35. safest azole because least effect on human CYP450
    fluconazole
  36. Vorconazole
    • newest azole
    • causes rash and elevated liver enzymes
  37. Echinocandins
    • newest class of antifungals
    • cyclic peptides linked to long chain fatty acids
    • not orally absorbed
    • short half life
    • not active against cryptococcus neoformans
  38. Echinocandin drugs
    • caspofungin
    • micafungin
    • anidulafungin
  39. Mechanism of action for echinocandins
    • inhibit synthesis of beta-glucan via beta-glucan synthase which results in disruption of fungal cell wall
    • fungistatic
  40. side effects of echinocandins
    • minor GI irritation
    • elevated liver enzyme with cyclosporin
    • anidulafungin may cause histamine release
  41. Agents for mucocutaneous infection
    • griseofulvin
    • fungistatic
  42. Griseofulvin absorption
    better with a fatty meal
  43. mechanism of action for griseofulvin
    binds keratin in keratin precursor cells and makes them resistant to fungal infections
  44. ADRs of griseofulvin
    • serum sickness
    • hepatitis
    • drug interactions by CYP induction
    • potentiates the effect of alcohol
  45. griseofulvin has been replaced by
    • itraconazole
    • terbinafine
  46. only fungicidal agent
    amphotericin B
  47. Terbinafine
    • synthetic allylamine
    • fungistatic
  48. terbinafine mechanism of action
    blocks squalene epoxidase in fungal cell wall leading to accumulation of sterol squalene which is toxic to the organism
  49. Topical antifungal agents
    • nystatin
    • clotriazoles
    • miconazoles
  50. used for volvovaginal candidasis
    clotriazole and miconazole
  51. Inhibit ergosterol synthesis
    azoles
  52. inhibit DNA synthesis
    flucytosine
  53. disrupt membrane structure and function
    nystatin and ampho B

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