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B. Anti-microbials > 6. Anti-fungal and Anti-protozoal Agents > Flashcards

6. Anti-fungal and Anti-protozoal Agents Flashcards

1
Q

Classification of anti-fungal drugs

A
  1. Drugs for subcutaneous and systemic mycotic infection

2. Drugs for cutaneous mycotic infections

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2
Q

Types of drugs for subcutaneous and systemic mycotic infection

A
  1. Amphotericin B
  2. Antimetabolite antifungals: Flucytosine
  3. Echinocandins: Caspofungin
  4. Azole antifungals: Triazoles
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3
Q

Types of drugs for cutaneous mycotic infection

A
  1. Nystatin
  2. Squalene epoxidase inhibitors: Terbinafine
  3. Azole antifungals: Imidazoles
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4
Q

MOA of amphotericin B

A

Binds to ergosterol in the plasma membrane of sensitive fungal cells → forms pores (channels) → disrupts membrane functions → allowing electrolytes (particularly potassium) and small molecules to leak from the cell → cell death

→ fungicidal or fungistatic depending on the organism and the conc. of the drug

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5
Q

Indications for amphotericin B

A
  1. Candida albicans (candidiasis)
  2. Histoplasmosis
  3. Crpytococcus neoformans
  4. Aspergillus (Aspergillosis)
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6
Q

Adverse effects of amphotericin B

A
  1. Fever and chills
  2. Nephrotoxicity
  3. Hypotension
  4. Thrombophlebitis
  5. Bone marrow suppression
  6. Ototoxicity
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7
Q

MOA of 5-Flucytosine

A

5-Flucytosine enters the fungal cells through cytosine specific permeases and is then converted, by cytosine deaminase, to its metabolically active form 5-Fluorouracil (5-FU)

  1. Conversion of 5-FU into 5-fluorouridine triphosphate (FUTP). FUTP is incorporated into fungal RNA in place of uridylic acid; and inhibits protein synthesis
  2. Metabolism of 5-FU into 5-fluorodeoxyuridine monophosphate (FdUMP), a potent inhibitor of thymidylate synthase, which is a key enzyme of DNA synthesis

→ fungistatic

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8
Q

Indications for 5-Flucytosine

A

effective in combination with amphotericin B for treating candidiasis and cryptococcosis (meningitis and pulmonary infections)

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9
Q

Resistance to 5-Flucytosine

A

Decreased levels of any of the enzymes in the conversion of 5-FC to its metabolites and/or development of an increased synthesis of cytosine during therapy → not used as a single antimycotic drug, used in combination with amphotericin B which allows more 5-FC to penetrate the cell thus leading to synergistic anti-fungal effects and minimises resistance

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10
Q

Adverse effects of 5-Flucytosine

A
  1. GI effects
  2. Bone marrow suppression
  3. Hepatotoxicity
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11
Q

Types of Echinocandins

A
  1. caspofungin
  2. micafungin
  3. anidulafungin
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12
Q

MOA of Echinocandins

A

Inhibit the activity of the glucan synthase complex → loss of structural integrity of the cell wall

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13
Q

Indications for Echinocandins

A
  1. First-line option for invasive candidiasis, including candidemia
  2. Second-line option for aspergillosis (for those who have failed or cannot tolerate amphotericin B or an azole)
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14
Q

Adverse effects of Echinocandins

A
  1. GIT related symptoms
  2. Fever
  3. Chills
  4. Rashes
  5. Skin flushing
  6. Thrombocytopenia
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15
Q

Types of triazoles

A
  1. Fluconazole
  2. Itraconazole
  3. Voriconazole
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16
Q

MOA of triazoles

A

Inhibit C-14 alpha-demethylase (CYP450 enzyme) → blocking the demethylation of lanosterol to ergosterol → inhibition of ergosterol biosynthesis disrupts membrane structure and function → inhibits fungal cell growth

→ fungistatic

17
Q

Indications for fluconazole

A
  1. Treatment of candidemia, and most forms of mucocutaneous candidiasis
  2. Cryptococcal meningitis
  3. Histoplasmosis
  4. Blastomycosis
  5. Single-dose oral treatment for vulvovaginal candidiasis
  6. Most types of fungal meningitis
18
Q

Indications for itraconazole

A
  1. Broad antifungal spectrum compared to fluconazole
  2. Treatment of blastomycosis and aspergillosis in patients intolerant to amphotericin B
  3. Onychomycosis in non-immunocompromised patients
  4. Oral solution for esophageal and oropharyngeal candidiasis
19
Q

Indications for voriconazole

A
  1. Broad-spectrum antifungal
  2. Treatment of choice for invasive aspergillosis
  3. Candida infections
20
Q

Adverse effects of triazoles

A
  1. Nausea, vomiting, headache, and skin rashes
  2. Hepatotoxicity
  3. QT prolongation
  4. Cardiotoxicity → Itraconzaole
  5. Neurotoxicity → Voriconazole
21
Q

Resistance to triazoles

A
  1. Mutations in the C-14 alpha-demethylase gene → decreased azole binding
  2. Development of efflux pumps that pump the azole out of the cell
22
Q

Drug interactions with triazoles

A
  1. Inhibit CYP450 3A4 isoenzyme to varying degree
  2. Also interfere with CYP2C9 and CYP2C19
  3. Enhance activity of drugs metabolised by CYP450 including warfarin, cyclosporine, oral hypoglycemic agents
23
Q

Contraindications to triazoles

A

Teratogenic → avoid in pregnancy

24
Q

Types of cutaneous anti fungal

A

Imidazoles

  1. Clotrimazole
  2. Miconazole
25
Q

Indications for imidazoles

A
  1. Epidermophyton
  2. Microsporum
  3. Trichophyton
  4. Candida → oropharyngeal and vulvovaginal candidiasis
  5. Malassezia
26
Q

Adverse effects of imidazoles

A

Topical:

  1. Contact dermatitis
  2. Valvular irritation
  3. Edema

Oral:

  1. GI disturbances
  2. Elevated liver enzymes
27
Q

Indications for nystatin

A

Broad spectrum anti-fungal agent → used to treat oral or GI fungal infections and vulvovaginal candidiasis

Commonly used for the treatment of cutaneous and oral candida infections

28
Q

Adverse effects of nystatin

A

Rare after oral administration

Topical and vaginal forms may cause skin infections

29
Q

MOA of terbinafine

A
  1. Inhibiting squalene epoxidase → blocking its conversion to lanosterol and biosynthesis of ergosterol, an essential component of the fungal cell membrane
  2. Accumulation of toxic amounts of squalene → increased membrane permeability and death of the fungal cell
30
Q

Indications for terbinafine

A

Trichophyton → causes tinea
Oral → dermatophyte onychomycoses and tinea capitis
Topical → tinea pedis, tinea corporis, tinea cruris

31
Q

Adverse effects of terbinafine

A
  1. GI disturbances
  2. Headaches
  3. Rash
  4. Hepatic failure
  5. Exacerbation of autoimmune diseases (SLE)
32
Q

Drug interactions with terbinafine

A
  1. Increase serum concentration with CYP450 inhibitors (azoles)
  2. Inhibits CYP450 2D6 isoenzymes which is involved in the metabolism of beta-blockers, MAO inhibitors
33
Q

MOA of metronidazole

A
  1. Amoebas possess electron transport protein that participate in metabolic electron removal reactions
  2. Metronidazole → nitroimidazole
  3. Nitro group of metronidazole is able to serve as an electron acceptor → forming reduced cytotoxic free radicals that result in protein and DNA damage → resulting in death of E. histolytica trophozoites
34
Q

Indications for metronidazole

A
  1. Amebic infections → Protozoa including Entamoeba histolytica, Trichomonas vaginalis, Giardia lamblia
  2. Anaerobes → Bacteriodes spp. and Clostridium difficile
  3. H. Pylori
  4. Surgical prophylaxis
35
Q

Adverse effects of metronidazole

A
  1. GI: nausea, vomiting, epigastric distress, abdominal cramps
  2. Unpleasant, metallic taste
  3. Oral candidiasis
  4. CNS and PNS effects: convulsive seizures, optic and peripheral neuropathy (rare). Discontinuation of drug. Avoid alcohol
36
Q

Drug interactions with metronidazole

A

Potentiate the effects of warfarin

37
Q

Contraindications with metronidazole

A

First trimester pregnancy

B. Anti-microbials (7 decks)

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