Antifungals

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Author:
ehamm
ID:
119074
Filename:
Antifungals
Updated:
2011-11-26 17:45:37
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Antifungals
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Antifungals
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  1. Amphotericin B
    • Polyene, binds to ergosterol and disrupts cell membrane, leading to cytolysis and death
    • Affinity for cholesterol
    • Wide spectrum: yeasts, molds, dimorphic fungi
    • Only available in IV admin
    • Pharmacokinetics: no distribution to CNS or adipose, non-linear kinetics (15 day t1/2), little drug
    • metabolism
    • Toxicities: Infusion - fever and chills, phlebitis (use central venous line) cardiac arrythmias; Renal - K wasting, renal tubular acidosis/dysfunction
    • Admin: IV, daily, D5W preperation, test dose 1 mg/hr to check for cardiac toxicity, K and Mg monitoring, bolus IV saline after admin (newer lipid formulations less toxic, more expensive
    • Nystatin: other polyene, used topically
  2. Azoles
    • Imidazoles vs triazoles
    • MW and solubility
    • Mechanism: blocks demethylation of lanosterol, precurser of ergosterol
    • imidazoles: ketonazole - not used as much
    • triazoles: fluconazole, voriconazole (both have high oral bioavailability, high CSF concentrations)
    • Adverse rxn: induce/inhibit CYP 450 enzymes, drugs that induce 3A4 will speed up metabolism (rifampin, rifabutin), Grapefruit juice blocks 3A4, decreasing absorption of itonazole
    • Inhibits: 3A4, 2C19, 2C9; affects warfarin, statins, rifampin
    • Uses: mostly yeasts, dimorphics, not as good with molds (exp zygomycetes)
    • Resistance: intrinsic (C. Krusei vs fluconazole), acquired - production of efflux pumps
  3. Echinocandins
    • Large size, only IV
    • Once daily admin
    • Not useful for UTIs as inactivated by liver
    • Mechanism: block B glucan synthesis via block UDP glucose and Rho
    • Use: Candida Spp, Aspergillus
  4. Terbinafine
    • Blocks conversion of squalene to ergosterol
    • Only allylamine in US
    • Mostly used against dermatophytes
    • Oral/topical preperations
    • Highly lipophilic - attracted to keratinized tissues
    • Metabolized by liver
  5. 5-FC
    • Mechanism: increases missense mutations, decreases DNA synthesis
    • Only active against yeasts
    • Well absorbed orally, 90% excreted in urine unchanged, t1/2=4 hours
    • Toxicities: antimetabolite in human cells; GI issues, elevated AST, bone marrow toxicities (thrombocytopenia, leukopenia, anemia)
    • Use: Combine with Amphotericin B for Cryptococcal meningitis

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