Anti-fungal mechanisms Flashcards
Most important drugs to remember regarding Drug-Drug interactions via hepatic mechanisms
Azoles and Griseofulvin
Mitotic spindle inhibitor
Griseofulvin
Anti-metabolite
Flucytosine
Examples of endemic fungi that cause disease in immunocompromised pt.’s
histoplasma
coccidoides
paracoccidoides
Why are fungal infeaction increasing
- increases in medical technique (intravascular catheters)
- greater percentage of immunocompromised pt.’s are surviving with better treatments (eg. HIV, cancer, transplants)
* number of immunodefficient patient has grown–>therefore the rates have gone up
three classes of currently available anti-fungal drugs
- systemic drugs (oral or parenteral) for systemic infections
- oral systemic drugs for mucocutaneous infections
- topical drugs for mucocutaneous infections
types (areas) of fungal infections
*increase in severity as you go deeper
- superficial (from bad hygeine)
- cutaneous (ring worm and athletes foot)
- subcutaenous (from a wound)
- systemic
- opportunistic
Tx for aspergillosis
Voriconazole IV
Tx for Blastomycosis
itraconazole PO
Tx for blastomycosis
amphotericin B IV then Itraconazole PO
Tx for candidiasis
Fluconazole PO
Tx for coccidiomycosis
Fluconazole IV/PO or itraconazole PO
Tx for cryptococcus
3
*amphotericin B IV + Flucystosine PO, then Fluconazole PO
Tx for histoplasmosis
amphotericin B IV + itraconazole PO
Tx for mucomycosis
amphotericin B
Tx for sporotrichosis
amphotericine B IV and/or itraconazole PO
Flucytosine has only one indication….
cryptococcal infections
Drug class which inhibits membrane function
amphotericin B
Drugs class that disrupts ergosterol synthesis
Azoles, terbinafine, naftiline
Drugs that inhibit Cell Wall Synthesis
caspofungin (echocandins)
Drugs that inhibit nucleic acid synthesis
5-flourocytosine
MOA for terbinafine
blocks the conversion of squalene to squalene epoxide
toxic byproduct that accumulates due to terbinafine
squalene
Azole group MOA
prevents the conversion of lanosterol to ergosterol
Toxicity associated with amphotericin B
RENAL TOXICITY
amphotericin B MOA
amphipathic–> binds to ergosterol with its double bond side and H2O on its -OH side–> multiple drug molecules aggregate to form pores–> pores allow leakage, leading to cell death
most anti-fungal agents are
fungicidal
what accounts for prominent renal toxicity associated with amphotericin B
binding of human membrane sterols
Is Amphotericin B orally absorbed?
no
Amphotericin B–> means of administration
IV—> ALWAYS
Common adverse effects with amphotericin B: IMMEDIATE
“INFUSION-RELATED REACTIONS”
- fever chills, muscle spasms, vomiting, headache and HYPOtension
- premedications often given :antipyretic, antihistamines, meperidine, corticosteroids
Common adverse effects with amphotericin B:
DELAYED
“RENAL TOXICITY”
–sometimes necessitates dialysis
sodium loading to reduce pre-renal toxicity
anemia: due to loss of erythropoeitin
abnormal liver function tests
seizures: followoing intracthecal drug administration
will abnormalities resolve upon discontinuation of amphotericin B
Yes
Only drug comparable to amphotericin B
Nystatin
Uses for nystatin
topical application in tx of candidiasis
*identical mechanism of action to that of apmho B
nystatin can only be administered
topically
three types of candidiasis
mucocutaneous candidiasis
oropharyngeal candidiasis (thrush)
vulvovaginal candidiasis
“The fungins”
echinocandins
echinocandins MOA
inhibit beta 1,3 glucan synthesis
–>leads to loss of membrane integrity and cell death
examples of an echinocandin
caspofungin (major)
micofungin (minor)
Caspofungin is used against
aspergillus
candida
two classes of AZOLEs and strucutral differences
imidazoles: 2 N’s in azole ring
triazole: 3 N’s in azole ring
Imidazole drug
ketaconazole
triazoles
all the rest
MOA for Azole drugs
avidly combine with CYP450 enzyme and prevent the 14-aplha demethylation of lanosterol–> prevention of ergosterol–>disturbs membrane integrity–>inhibits growth
*therefore if it inhibits human CYP’s–> possible ADE’s
all azoles inhibit which CYP
CYP3A4
All azoles are substrates for CYP3A4 except
posaconazole
drug class with the biggest impact on hepatic metabolism
AZOLES
also grisofulvin
Azoles that have low solubiulity and thus have no utility in penetration of CSF
Ketoconazole
Itraconazole
substrates for P-gp in BBB
ketaconazole
itraconazole
fluconazole elimination is through
urine
other azoles are eliminated via
hepatic mechanisms
azoles with the highest incidence of GI side effects
pasaconazole
itraconazole
azoles contraindicated in pregnancy
fluconazole
voriconazole
FDA has limited use of which AZOLE?
ketaconzaole PO,
- -> severe liver injury and
- ->CYP drug interactions
- -> pro-arrhythmogenic
- ->andrenal gland problems (stops production of corticosteroids like aldosterone, cortisol and testosterone
Azole with good oral bioavailability, high CSF penetration, best tolerance and WIDEST THERAPEUTIC INDEX
FLUCONAZOLE
Voriconazole ADVERSE EFFECTS
photosentsitive dermatitis, elevated liver enzymes, temporary visual disturbances upon IV administration, NEUROLOGICAL SYMPTOMS (HALLUCINATIONS)
only azole with acitivyt against mucomycosis
posaconazole
posaconazole side effects
CYP mediated drug-drug interactions
TOPICAL AZOLES
clotrimazole
miconazole
*absorption is negligible and ADE’s are rare
topical azoles used to treat…
candidiasis
Pyrimidine analog with NARROW THERAPEUIC WINDOW
FLUCYTOSINE (5-FC)
Flucytosine MOA
- enters cell via cytosine permease
- converted to 5-flourouracil (this conversion is not possible in mammals but is carried out by intestinal microflora)
- becomes incorporated into intermediary metabolism
- inhibits DNA and RNA sythesis
antifungal that is an anti-metabolite (cell-cycle inhibitior)
flucytosine
side effects of flucytosine
“typical side effects of cell-cycle inhibition”
- anemia
- leukopenia
- thrombocytopenia (low platelet count)
- elevated liver enzymes
AF drugs linked to hepatic ADE’s
all azoles
amphotericin B
5-FC
echinocandins
AF drugs linked to renal toxicity
amphotericin B
AF drugs linked to CNS ADE’s
voriconazole
AF drugs causing photopsia
variconazole
AF drugs causing GI symptoms
itraconazole
posaconazole
5-FC
AF drugs with cardiac ADE’s
all azoles especially with drug nteractions
AF drugs causing infusion reactions
amphotericin B
echinocandins
AF drugs causing bone marrow suppression
5-FC Amphotericin B (anemia associated with decreased epoetin productions)
AF drugs with cutaneous dermatological side effects
Rash–> all antifungals
photosensitivity/malignancy–> variconazole
Drugs that cause cytoplasmic membrane pores
Nystatin
ampho B
Drugs that interrupt ergosterol synthesis (demethylase)
AZOLES
drugs that interrupt ergosterol synthesis (qualene oxidase)
terbinafine, naftifine
drugs interruptind DNA/RNA synthesis
flucytosine
Gucan synthesis inhibition
Caspofungin, micafungin
Microtubule disruption
griseofulvin
Mitotic spindle inhibitor
Griseofulvin
Griseofulvin reduces the clinical activity of
Warfarin
oral contraceptives
cyclosporin
aprepitant
drug with no effect on CYP
terbinafine
drug requireing routine CBC’s
terbinafine
*transient lymphopenia and neutropenia with oral administration
MOA for terbinafine
inhibits ergosterol synthesis at the level of squaline oxidase
AF’s that cannot be given during pregnancy
fluconazole
voriconazole
Pro-arrythmogenic azoles
fluconazole
posaonazole
voriconazole
only azole that is not a substrate for cyp3a4
pasoconzole
azole drugs useless in csf
keto
itra
low solubility azoles
keto
itra
posa (but posa has high absorption)
End result of ketoconazole
inhibition of steroid synthesis and adrenal insufficiency
only drug wtih activity against mucormycosis
pasoconazole
mucocutaneous candida can be treated with
nystatin
clotrimazole
miconazole
systemic candidiasis can be treated with
*aspergillus with the IV here too
caspofungin IV
fluconazole PO
pyrimidine analog that enters cell via cytidine permease
5-FC
5FC is converted to 5 FU by
intestinal microflora
side effects of 5FC
GI upset anemia leukopenia thrombocytopenia renal toxicity elevated hepatic enzymes