pharmacology: anti fungal drugs flashcards
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Pharmacology for medical students, nursing students, pharmacology students, and university students! Great to use as and adjunct for your courses or board exams!TRANSCRIPT
Anti-Fungal Drugs
Drug ClassesPolyenes: Amphotericin B & NystatinFlucytosineAzolesEchinocandinsGriseofulvinTerbinafineTolnaftate
PolyenesAmphotericin B & NystatinMoA: binds ergosterol on fungal cell
membrane creates pores fungicidal/fungistatic
Amphotericin B is insoluble in water so complexed with bile salt or lipids; it is for general use (affects many spp) in SYSTEMIC infections
Nystatin has poor absorption from mucous membranes; use for Candida spp good for obese and diabetic pts
Polyene ToxicityAmphotericin B
TI is narrowAcute: HA, arthralgia, nausea/vomiting, fever,
hypotension, Thrombophlebitis, delirium, seizures
Chronic: Malaise, weight loss, NEPHROTOXICITY, anemia
Flucytosine (5 – FC)Distributes in all body tissuesAlmost entirely excreted by kidneysConverted to 5 – FU (fluorouracil –
chemotherapeutic agent)Fungal resistance develops fast during
flucytosine monotherapy use in combination with other antifungals
Flucytosine MoA5-FC is taken up into fungal cells converted
to 5-FU 5-FU is phosphorylated to produce 5-fluorouridine monophosphate (5 – FUMP) – this metabolite can be used in 2 pathways
First pathway: 5-FUMP is converted to 5-FdUMP acts as an irreversible inhibitor of Thymidylate Synthetase (aids in making molecules for new DNA) – thus, inhibits fungal DNA synthesis
Second pathway: 5-FUMP converted to 5-FUDP inhibits RNA synthesis
Ultimate effect: Fungicidal/Fungistatic
Flucytosine ToxicityAdverse effects due to 5 – FU
Reversible MYELOSUPPRESSION (13%)LIVER DYSFUNCTION (10%)
AzolesKetoconazole, ItraconazoleStructure contains 5 membered azole ringMoA: Inhibition of fungal ergosterol synthesis inhibits Lanosterol 14 – α – Demethylase fungicidal/fungistatic
Cross resistance is commonKetoconazole can inhibit human sterol
synthesis & Cyp P450 enzymesSeborrheic Dermatitis – ketoconazole
shampoo
Azole ToxicityGynecomastia (ketoconazole)Liver toxicityHypokalemia, hypertension
Itraconazole
EchinocandinsNewest class of antifungals; large cyclicCaspofungin, Micafungin, AnidulafunginMoA: noncomp inhibitors of Beta-D-Glucan
Synthase (makes components of fungal cell wall) disrupts integrity of fungal cell wall (not cell membrane!) Fungicidal
Targets: Aspergillus & CandidaResistance develops via FSK1 mutationsNo major toxicities
GriseofulvinAbsorption ~ 50% improved by fatty foodsIneffective topicallyInduces liver enzymesDistributes only in keratinized tissuesMoA: inhibits fungal mitosis FungistaticUse: Dermatophytes – tx is continued until tissue
is replaced with normal healthy tissueHair: 1 month; Skin/Finger nails: 6 – 9 months;
Toe nails: 12 monthsToxicity: induces CYP enzymes,
PhotosensitivityItraconazole is more effective for toe nail
infections (Onychomycosis)
TerbinafineDistribution almost only in keratinized tissue
and fatMoA: inhibits fungal enzyme Squalene
Epoxidase (inhibits ergosterol biosynthesis) accumulation of squalene is toxic to fungi fungicidal
Effective for onychomycosisContraindicated in use with CYP
inducers/inhibitors
Summary
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