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Flashcards in Antifungal drugs Deck (50)
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1

Amphotericin B, a polyenes used to treat systemic antifungal infections, what makes it so good and what makes it so bad?

good: broadest spectrum
bad: significant adverse side effects
(there are newer liposomal formulations associated with increased efficacy and decreased toxicity)

2

How is amphotericin given, what is its mechanism of action?

IV
1. binds to ergosterol in fungal membrane
2. forms pore in the membrane thereby increasing membrane permeability
3. efflux of essential molecules
4. fungal death
-binds only weakly to cholesterol

3

What is amphotericin B not active against?

1. Candida Lusitaniae
2. Pseudallescheria boydii (scedosporium apiospermum)

4

When is amphotericin used?

initial induction therapy (usually 4 weeks) to reduce fungal burden, then replaced by newer less toxic AZOLE drugs for consolidation therapy and prevention of relapse

5

What is the ONLY antifungal agent that is approved in pregnant/ breast feeding women?

Amphotericin

6

What is amphotericin the treatment of choice for?

Zygomycosis/mucormycosis

7

What are the adverse infusion related effects for amphotericin a drug with a low therapeutic index ?

1. infusion related
-fever, chills, muscle spasms, vomiting, headache and hypotension
a. slow rate/decrease dose
b.preemptive meds like antipyretic,antihistamine, corticosteroids

8

What are the cumulative toxicities of amphotericin B?

1. nephrotoxicity
a. reversible-decreased renal perfusion via vasoconstriction
-reduce by using saline drip (Na loading)
b. non reversible
-renal tubular injury(prolonged administration)
-tubular acidosis and severe K+ and Mg2+ wasting
-more common in presence of diuretics or other nephrotoxic meds eg. aminoglycosides/cyclosporine

2. hepatotoxicity (occasional)

3. anemia
-reversible suppression of erythrocyte production due to decreased EPO

9

What are the bad parts of flucytosine and the good part?

bad:
1. narrow spectrum of activity
2. use is restricted by high incidence of resistance
-mutations in cytosine permease, cytosine deaminase, uracil phosphoribosyl transferase or increase in cytosine synthesis

good:
good penetration into the CSF
-used for cryptococcal meningitis

10

Is flucytosine used alone?

no typically in combination with other antifungal drugs
-especially ampho B and an azole
-ampho enhances flucytosine permeability

11

How is flucytosine eliminated?

renally-dosage adjustment required in presence of renal insufficiency

12

What is the mechanism of action of flucytosine?

1. taken up via cytosine permease
2. fungal specific cytosine deaminase -->5 fluorouracil
2. inhibits both DNA(thymidylate synthase) and RNA synthesis

13

What does flucytosine+amphotericin B treat?

cryptococcosis and candidiasis
-cryptococcal meningitis (good CSF penetration of flucytosine and ampho b enhances fungal uptake of flucytosine)

14

What does flucytosine + itraconazole treat?

chromoblastomycosis

15

What are the adverse effects of flucytosine?

1. endogenous gut microflora express cytosine deaminase -->5 fluorouracil (antimetabolite)-->toxicity

-GI: nausea, vomiting diarrhea
-Bone marrow toxicity: anemia, leukopenia, thrombocytopenia

Tetratogenic

16

What is the prototype imidazole?

ketoconazole

17

What is the order of spectrum of activity for the triazoles?

Fluconazole

18

What is the mechanism of action of azoles?

Azoles are fungistatic/fungicidal

1. Inhibit 14 alpha demethylase (CYP45) involved in biosynthesis of ergosterol from lanosterol
-impairs membrane function
-increases membrane permeability
-decreases activity of membrane associated proteins

19

What are the common adverse side effects of all azoles?

1. GI distress
2. Hepatotoxicity-requires hepatic enzyme monitoring
3. fetal abnormalities

20

When should itraconazole and voriconazole never be given to a patient?

when the patient is taking statins due to increased risk of developing rhabdomyolysis

21

What azoles have good CNS penetration?

fluconazole and voriconazole

22

What azole needs real adjustment?

Fluconazole

23

What limits ketoconazole use?

-oral ketoconazole requires acidic environment for absorption
-poor penetration into CSF and urine
-many adverse effects due to inhibition of CYP450 enzymes involved in adrenal and gonadal steroid synthesis
-->decreased cortisol and decreased testosterone
--->gynecomastia, libido, impotence, menstrual irregularities, hypotension and fatigue

-many drug interactions of CYP450 3A4

-rarely used now, largely replaced by itraconazole
-still used topically to treat dermatophyte infections

24

What is the spectrum of activity fluconazole?

Narrowest spectrum of activity of all azole drugs but

-good oral bioavailability and EXCELLENT penetration into the CSF

-fewest drug interactions of all azoles

25

Does fluconazole have many adverse effects?

no only minor effects: nausea, headache, skin rash and GI, and alopecia (reversible, long/high dose)

26

How is fluconazole eliminated?

80% of drug eliminated unchanged in the urine
-useful in treatment of fungal BLADDER infections

27

What does fluconazole used to treat?

1. Candida
-mucocutaneous candids
-poor activity toward C. glabrata and no activity against C. krusei

2. TREATMENT OF CHOICE
for cryptococcal meningitis
-used as consolidation/maintenance therapy with ampho b/flucytosine

3. good activity against coccidioides

4. variable activity against endemic dimorphic fungi
-less active than itraconazole against histoplasmosis, balstoplsmisis, sporotrichosis
-only used if itraconazole not well tolerated

5. dermatophytes

28

What is fluconazole the therapy of choice for?

1. Cryptococcal meningitis
2. coccidioidal meningitis

29

What should itraconazole not be used for?

-meningitis
-bladder infections

30

HOw is the spectrum of activity of itraconazole vs. fluconazole?

broader spectrum but more adverse effects and many potential drug interactions