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Drug Mechanisms > Antifungals > Flashcards

Antifungals Flashcards

1
Q

What are the five classes of antifungals?

A

1) Polyenes
2) Flucytosine
3) Azoles
4) Echinocandins
5) Allylamine

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2
Q

What are the two Polyenes?

A

Amphotericin B and Nystatin

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3
Q

What are the two drug categories for Azoles?

A

Imidazoles and Triazoles

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4
Q

What drugs are Imidazoles?

A

1) Ketonconazole
2) Miconazole
3) Clotrimazole

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5
Q

What drugs are Triazoles?

A

1) Itraconazole
2) Fluconazole
3) Voriconazole
4) Posaconazole
5) Isavuconazole

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6
Q

What differentiates Triazoles from Imidazoles?

A

Triazoles have two nitrogens in their azole ring while imidazoles only have one nitrogen in their azole ring

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7
Q

What drug is an allylamine?

A

Terbinafine

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8
Q

What is the activity of the Polyenes?

A

Broad, fungicidal, and they are active in yeast infections

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9
Q

What is the activity of Flucytosine?

A

Narrow and fungistatic

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10
Q

What is the activity of the Azoles?

A

Broad and fungistatic

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11
Q

What is the activity of the Echinocandins?

A

Broad, fungicidal, and active against fungal and yeast infections

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12
Q

What is the activity of the drug Griseofulvin?

A

Narrow and fungistatic

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13
Q

What is the activity of the Allylamines?

A

Fungicidal against dermatophytes and fungistatic against yeast infections

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14
Q

How do Amphotericin B and Nystatin work against infections?

A

They bind to ergosterol in the fungal cell membrane forming pores, known as death rings, which disrupts cell membrane permeability and kills the cell

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15
Q

Why is resistance to the Polyenes rare?

A

Ergosterol is essential to certain functions in the fungal cell; therefore, if the cell modifies ergosterol, it could hurt its ability to function and launch infections

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16
Q

If a fungal infection were to try and become resistant to the polyenes, how would it do so?

A

It decreases the concentration of ergosterol or changes its structure to decrease affinity (target modification)

17
Q

What is the most prominent toxicity associated with Amphotericin B?

A

Dose-dependent nephrotoxicity

18
Q

What are the routes of administration for Nystatin?

A

Oral and topically because it is too toxic for parenteral use

19
Q

Why is Amphotericin B less toxic than Nystatin?

A

Because Amphotericin B has a higher affinity for ergosterol rather than cholesterol and it is more selective

20
Q

Mechanism of action for 5-FC (Flucytosine)

A

5-FC is converted to 5-FU by cytosine deaminase. 5-FU is then converted to F-dUMP and F-UTP. F-dUMP inhibits DNA synthesis and F-UTP inhibits RNA synthesis.

21
Q

Mechanism of resistance to 5-FC

A

Altered metabolism of 5-FC which happens faster in monotherapy

22
Q

Toxicity to 5-FC

A

Occurs when 5-FC is converted to toxic 5-FU by intestinal microflora. Can cause Thrombocytopenia, Leukopenia, Anemia, and Bone marrow toxicity

23
Q

In regards to Polyenes, which one is stronger with less toxicity and why?

A

Amphotericin B because it has more double bonds than Nystatin

24
Q

What happens when Polyenes interact with UV light?

A

Their double bonds become locked in the cis position and they are inactivated

25
Q

What is 5-FC combined with to create a synergistic reaction?

A

Azoles and Amphotericin B because they compromise the cell membrane and increase intracellular concentrations of 5-FC

26
Q

Mechanism of action for Azoles

A

They inhibit the biosynthesis of ergosterol by inhibiting the p450 14alpha-demethylase enzyme

27
Q

Mechanism of resistance to Azoles

A

Altered p450 14alpha-demethylase enzyme and active efflux

28
Q

Toxicity associated with Azoles

A

GI upset, liver enzyme abnormalities, rarely but sometimes hepatitis, and they all inhibit cytochrome p450 (especially CYP3A4)

29
Q

Which types of Azoles are more effective and less toxic?

A

Triazoles because they are more selective

30
Q

Which imidazole is a more potent inhibitor of human cyt. p450 meaning it is less selective and causes more adverse effects?

A

Ketoconazole

31
Q

What has the widest therapeutic index of all the Azoles?

A

Fluconazole

32
Q

What three drugs are Echinocandins?

A

Caspofungin, Micafungin, and Anidulafungin

33
Q

Mechanism of action for Echinocandins

A

They inhibit the biosynthesis of the fungal cell wall by inhibiting Beta(1, 3)-glucan synthase

34
Q

Mechanism of action for Griseofulvin

A

Not clearly understood but it binds to and protects newly formed keratin from fungal infection

35
Q

Toxicity of Griseofulvin

A

Inducer of cytochrome p450

36
Q

What is the route of administration for Griseofulvin?

A

Oral to treat systemic infections caused by dermatophytes

37
Q

Mechanism of action for Terbinafine

A

Inhibits the biosynthesis of ergosterol by inhibiting the squalene epoxidase enzyme. This also leads to an accumulation of sterol squalene which is toxic to fungal cells

38
Q

Toxicity for Terbinafine

A

Gi upset and headache. Inhibitor of cytochrome p450 2D6 enzyme

Drug Mechanisms (9 decks)

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