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PR3151 Antibiotics + Antifungals > Anti-Fungal > Flashcards

Anti-Fungal Flashcards

1
Q

Prokaryotic bacterial cell wall contain peptidoglycan while eukaryotic fungal cell wall contain ________

A

Chitin and B-1,3-glucan

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2
Q

Which two anti fungal agents are polyenes?

Polyene: bind to ergosterol in cell membrane and form pores, disrupt membrane function, allow K+ and small molecules to leak from the cell

A

Amphotericin B (IV)
Nystatin (oral, topical)

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3
Q

Amphotericin B is active against:

A

Candida
Histoplasmosis
Cryptococcus meningitis (in combi w 5-Flucytosine)
Aspergillus

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4
Q

Amphotericin is insoluble in water and hence must be formulated with _____ or ______

A

Conventional: sodium deoxycholate

Liposomal: form liposomes

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5
Q

Which of the 2 formulations of Amphotericin B has better CSF penetration

A

Liposomal
*Though both generally have poor CSF penetration

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6
Q

What are Amphotericin B adverse effects?

A
  1. Fever and chills (infusion-related toxicity)
  2. Nephrotoxicity - bc conventional formulation causes renal vasoconstriction, hence can cause renal dysfunction
    **Hydration
  3. Electrolyte imbalance, hypotension
    - Hypokalemia
    - Digoxin interactions
    **Potassium supplement
  4. Thromboplebitis
    **Add heparin to infusion
  5. Bone marrow suppression
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7
Q

5-flucytosine enters fungal cells through cytosine specific permeases, and is converted by _______ to ________

A

Converted by cytosine deaminase to 5-fluorouracil (5-FU)

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8
Q

What is the action of 5-FU?

A
  1. Converted to FUTP, incorporates into fungal RNA in place of uridylic acid, inhibit protein synthesis
  2. Metabolised to FdUMP, potent inhibitor of thymidylate synthase which is involved in DNA synthesis
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9
Q

5-FC has activity against _____ and _____

A

Candida
Cryptococcus meningitis (in combi w Amphotericin B)

*Also effective against yeast infection

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10
Q

5-FC is cleared via ______
Dose adjustment is required in _______

A

80% excreted unchanged in urine
Dose adjustment required in renal impairment

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11
Q

What adverse effects are associated with 5-FC?

A
  1. GI effects
  2. Hepatotoxicity
  3. Bone marrow suppression
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12
Q

Why must 5-FC be used in combi with Amp B for Cryptococcal meningitis?

A

Some fungal cells express decreased level of the enzymes involved in conversion of 5-FC to 5-FU (cytosine specific permease, cytosine deaminase)

Hence, Amp B can form pores in cell membrane, allow more 5-FC to penetrate the cell (synergistic effect)

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13
Q

Echinocandins bind to _________

A

B-1,3-glucan synthase, hence interfere with the structural intergrity of the cell wall => cell rupture

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14
Q

Echinocandins are active against ______ and _______

It is first line again which?

A

Candida (first-line)

Aspergillus

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15
Q

How is Echinocandin cleared?

A

Metabolised slowly by hydrolysis and N-acetylation, eliminated in urine and feces

NOT cleared renally, no dose adjustment required

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16
Q

Which systemic anti-fungal agent is generally well-tolerated?

A

Echinocandins

17
Q

Azoles are _____ inhibitors

A

C-14a demethylase inhibitors

Block the demethylation of lanosterol to ergosterol, disrupt membrane function, increase membrane permeability

18
Q

What might cause resistance to azoles?

A
  1. Mutation of C-14a demethylase gene
  2. Efflux pump
19
Q

Triazoles are administered via ____ route

A

Oral/IV (except Itraconazole - oral only)

*Posaconazole
- Capsule, Syrup

*Itraconazole
- Capsule (after meal), Solution (empty stomach)

*Voriconazole
- Tablet, Syrup

20
Q

What are Triazole spectrum of activity?

A

Fluconazole: Candida, Histoplasmosis, Cryptococcal meningitis
Posaconazole: Candida, Aspergillus
Itraconazole: Candida, Aspergillus, Histoplasmosis, Onychomycosis
Voriconazole: Candida, Aspergillus (1st line)

21
Q

Which triazoles have good CSF penetration?

A

Fluconazole and Voriconazole

22
Q

Which triazole is cleared renally?

When is dose adj required?

A

Fluconazole
*Require dose adj in renal impairment

For the rest, dose adj in renal impairment is required if given IV (due to cyclodextrin - nephrotoxic)

23
Q

How are Posaconazole, Itraconazole, and Voriconazole cleared respectively?

A

Posaconazole:
- Feces

Itraconazole:
- Metabolized by liver, excreted in feces and urine

Voriconazole:
- Metabolized by CYP450, excreted via urine

24
Q

Itraconazole and Posaconazole absorption are affected by _____

A

Antacids/PPI
incr in pH cause dcr absorption

25
Q

Azoles are CYP450 ______

A

inhibitors

26
Q

What are triazole adverse effects?

A
  • GI effects
  • Skin rash
  • Headache
  • Hepatotoxicity
  • Prolong QT interval

Fluconazole: hair loss after 2months
Itraconazole: cardiotoxicity
Voriconazole: neurotoxicity (visual disturbances, hallucinations), periostitis with long term use due to fluoride excess

27
Q

Name 2 imidazoles

A
  1. Clotrimazole
  2. Miconazole
28
Q

Imidazoles have wide range of action, including activity against ___ and ____

A

Candida
Trichophyton (causes Tinea)

29
Q

What is used to treat oropharyngeal candidiasis?

A

Itraconazole solution
Clotrimazole oral troche
Nystatin gargle (swish and swallow/spit)

30
Q

What is used to treat vulvovaginal candidiasis?

A

Single oral dose fluconazole
Clotrimazole cream
Miconazole pessary
Nystatin pessary

31
Q

What are some adverse effects with imidazole?

A

Topical use:
- contact dermatitis
- vulvar irritation
- edema

Oral use:
- GI disturbances
- Clotrimazole: elevated liver enzymes

32
Q

Why can’t nystatin be used parenterally?

A

IV use is associated with systemic toxicity - acute-infusion related adverse effects + nephrotoxicity

33
Q

Terbinafine is a _______ inhibitor

A

Squalene epoxidase

  • Block conversion of squalene to lanosterol, thus inhibit biosynthesis of ergosterol
  • Accumulation of toxic amount of squalene also causes increase membrane permeability
34
Q

Terbinafine is active against:

A

Trichophyton, dermatophytes
*dermatophytes are fungi that require keratin for growth

35
Q

What are the 2 drugs that can be used for dermatophyte onychomycosis and tinea capitis?

A

Oral Terbinafine (40% oral bioavailability)
Oral Itraconazole

=> require systemic absorption to accumulate in keratin in nails or scalp

36
Q

How is terbinafine eliminated?

A

metabolized by CYP450 enzyme, excreted mainly via urine

*Avoid in renal and hepatic impairment

37
Q

What drugs are metabolized by CYP450?

A

Metronidazole
Voriconazole
Terbinafine

38
Q

Terbinafine adverse effects

A

GI
Headache
Rash
Elevated liver enzymes

39
Q

Terbinafine should not be given to ______

A

Breastfeeding mothers as it accumulates in the breastmilk

PR3151 Antibiotics + Antifungals (5 decks)

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