Antifungals Flashcards
Half life of Amphotericin B
15 days
Amphotericin B elimination route
urine, slowly
Amphotericin is selective for fungi because it targets this molecule
Ergosterol, a fungi cell membrane sterol not found in humans
Amphotericin B MOA
Creates larger and larger pores that disrupt membrane potential and ion balance
Describe induction therapy for Amphotericin B
Pt is started with a does of Amphotericin to aggressively attack fungal infection, and is then switched to a newer azole drug for chronic treatment or prevention
Flucytosine MOA
Taken up by fungal enzyme cytosine permease, converted into metabolites that inhibit DNA and RNA synthesis (it’s a pyrimidine analog)
Describe the toxic effects of flucytosine
Conversion to anticancer compound 5-FU can cause bone marrow toxicity with anemia
The two kinds of azoles
imidazoles and triazoles
The imidazoles
Ketoconazole, miconazole
The triazoles
Itraconazole, fluconazole, voriconazole, and posaconazole
Imidazoles or triazoles - which have higher specificity for fungal targets?
Triazoles (thus fewer adverse effects)
Imidazole and triazole MOA
Targets fungal P450s that synthesize ergosterol
Why are azoles at high risk for interacting with other drug types?
SInce they target (fungal) P450s, there is some overlap with human P450 interaction as well
This azole has the highest propensity to inhibit mammalian P450 and isn’t used much anymore
ketoconazole
Taking these drugs with itraconazole will result in reduced bioavailability
Rifamycins (e.g., rifampin)
Itraconazole is the drug of choice to treat these fungi
Dimorphic
Azole of choice to treat Aspergillus
vorizonacole
Compare the oral bioavailability of fluconazole, ketoconazole, and itraconazole
Fluonazole high others low
This azole has the least effect on human P450 enzymes
Fluconazole
Drug of choice to treat fungal meningitis
Fluconazole (best CSF penetration)
Several azoles inhibit this specific liver enzyme
CYP3A4 (does statins, cyclosporine, and tacrolimus)
Broadest spectrum of the azoles
Posaconazole
Echinocandins members
Caspofungin, micafungin, anidulafungin
Echinocandins available ROA
IV only
Compare the tolerance of echinocandins and azoles
Echinocandins are much better tolerated
Griseofulvin has significant interaction with these two drugs
Warfarin and phenobarbital
Griseofulvin is now only used for this one problem
Systemic treatment of dermatophytosis
Griseofulvin - fungistatic or fungicidal?
Fungistatic
Terbinafine - fungistatic or fungicidal?
Fungicidal
Describe terbinafine MOA
Inhibits ergosterol synthesis by inhibiting fungal enzyme squalene monooxygenase, leading to accumulation of the toxic compound squalene
Azoles target this enzyme
14-alpha-demethylase
Amphotericin B is in this drug class
Polyenes
Allylamines drugs
Terbinafine
Terbinafine target
squalene monooxygenase
Echinocandins enzyme target
B-1,3-D-glucan synthesis inhibition
Flucytosine target
thymidylase synthase
Griseofulvin MOA
mitosis inhibition
Are echinocandins effective against dimorphic fungi?
No
Vorizonacole is a substrate for this P450
CYP2C19
All azoles have these significant side effects
Hepatic - CYP450 interactions; cardiac QT prolongation
Amphotericin B side effects
Hepatic; renal toxicity; infusion reacitons, anemia from reduced epoetin from BM
5-FC side effects
hepatic; GI, bone marrow suppression
Echinocandins side effects
Hepatic, infusion reactions
Voriconazole side effects
Renal toxicity; CNS toxicity; photopsia; photosensitivity/malignancy
Itraconazole side effects
GI; cardiac (CHF contraindication); ED; breast pain, gynecomastia; hot flashes, etc.
Posaconazole side effects
GI
Almost all antifungals have this side effect
rash
Most azoles are hepatically eliminated, except for this one
Fluconazole (renal)
These azoles should never be used in a pregnant patient
Fluconazole and Voriconazole (Very Foolish to give!)