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BMSC2210 - Chemotherapy > L10 - Pyrimidine & Polyenes > Flashcards

L10 - Pyrimidine & Polyenes Flashcards

1
Q

What is only pyrimidine drug?

A

5-fluorocytosine

a.k.a. Flucytosine

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2
Q

How is flucytosine converted to 5-fluorouracil (5-FU)?

A

CYTOSINE deaminase (fungi/bacteria ONLY)

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3
Q

How is flucytosine specific?

A

5-FU not taken up into mammalian cells

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4
Q

What are the outcomes for the 2 pathways of 5-FU

A

disrupt translation

inhibits DNA synthesis

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5
Q

How does 5-FC disrupt translation?

A

5-FC > FUMP > FUTP > incorporated into RNA

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6
Q

How does 5-FC inhibit DNA synthesis?

A

F-FU > FdUMP > inhibit thymidylate synthetase

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7
Q

What is 5-FC active against?

A

C. neoformans

most Candida

some brown moulds

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8
Q

What is 5-FC inactive against?

A

C. Krusei

Aspergillus

Histoplasma capsulatum

MOST MOULDS

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9
Q

What is the formulation of 5-FC?

A

IV

Oral

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10
Q

What fungal species develop resistance to 5-FC?

A

candida

cryptococcus

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11
Q

What is used in combination therapy with 5-FC?

A

Amphotericin B

Fluconazole

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12
Q

What is 5-FC mainly used for?

A

Cryptococcal Meningitis (with Amphotericin B)

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13
Q

Facts about Pharmacokinetics of 5-FC?

A

water soluble

not metabolised by gut flora

half life 3-6h

repeat dose 3-4 times/day

excreted in urine

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14
Q

What happens if serum 5-FC level is high for 2 weeks?

A

Leucopenia

Thrombocytopenia

Aplastic anaemia

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15
Q

Other side effects of 5-FC?

A

rare allergies

liver toxicity

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16
Q

What are drug interactions with 5-FC?

A

Brivudine - inhibits DPD which usually degrades fluorouracil

Fluoruracil - higher phenytion (anti-epileptic) levels

17
Q

what are the 3 main places where mechanisms of resistance occur to 5-FC?

A

Cytosine permease

Cytosine deaminase

(MAINLY) - Uracil Phospho-ribosyl transferase

18
Q

What are the 2 types of polyene antifungals?

A

Nystatin

Amphotericin B

19
Q

What is the hydrophobicity of polyenes?

A

AMPHIPATHIC

20
Q

How do polyenes work?

A

increase cell permeability

bind ergosterol

macrolide rings - hydrophobic sides - distort membrane layers

OXIDATIVE DAMAGE

21
Q

What is the spectrum of activity of Amphotericin B?

A
  • broad
  • most yeast/ moulds sensitive
  • A. terreus, Scedosporium, Lomentospora = resistant
22
Q

What is the spectrum of activity of Nystatin?

A

most yeasts sensitive

23
Q

Formulations of Amphotericin B?

A

Amphotericin B deoxycholate (CONVENTIONAL)

Lipid formulations - AMBISOME, Abelcet

24
Q

Formulations of Nystatin?

A

topical
not absorbed orally
too toxic for IV

25
Q

What is Amphotericin B used to treat?

A

empirical treatment - fungal infections

used topically

26
Q

What is Nystatin used for?

A

oral/vaginal candidosis

27
Q

How can amphotericin B help antibiotics resistant fever?

A

fever may be due to infection being fungal NOT bacterial

28
Q

Is ambisome better than voriconazole?

A

slightly

29
Q

Is ambisome better than caspofungin?

A

same

30
Q

Is Amphotericin B better at treating Invasive aspergillosis than voriconazole?

A

NO

voriconazole is better

31
Q

The pharmacokinetics of ambisome?

A

IV

daily dose

good tissue distribution

24hr half life - longer later

32
Q

adverse effects of amphotericin B?

A 
fever*
chills*
nausea
vomit*
headaches
hypotension*

hypokalemia
^creatine in serum*

33
Q

Drug interactions with amphotericin B?

A

nephrotoxicity - ciclosporin, anti-neoplastic agents

hypokalemia - corticosteroids, diuretics

muscle relaxants

bone marrow suppression from ambisome induced nephrotoxicity - Flucytosine

34
Q

What fungi are resistant to Amphotericin B?

A

A. terreus (ALWAYS)

fusarium
Scedosporium
Lomentospora

35
Q

mechanisms of resistance to amphotericin B?

A

mutated EGR genes - ergosterol synthesis - less ergosterol = more resistant

increased catalase = reduce oxidative damage by drug

36
Q

What is candida auris?

A

biofilms on skin

30% resistant to AmpB

BMSC2210 - Chemotherapy (17 decks)

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