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Drug Action IV > Antiparasitic (MC) - Block 3 > Flashcards

Antiparasitic (MC) - Block 3 Flashcards

1
Q

How do helmiths differ from other parastic infections?

A
  1. Multiplies outside definitive host
  2. Unique ability to evade host immune defenses
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2
Q

Examples of flatworms (platyhelminths)?

A

Cestode (tapeworms)
Trematode (Flukes or schistosomes)

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3
Q

Examples of nematodes/aschelminths?

A

Roundworm, hookworm, pinworm, whipworm

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4
Q

Common benzimidazoles?

A
  1. Albendazole
  2. Mebendazole
  3. Thiabenazole
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5
Q

MOA of benzimidazoles?

A
  1. Inhibition of fumarate reductase (involved with the oxidation of NADH ro NAD) -> diminished ATP production and parasite immobilization and death
  2. Tubulin binding to prevent tubulin polymerization to microtubules
    * Impairs glucose uptake and depletes glycogen stores
    * Prevents formation of spindle fibers needed for cell division -> blocking egg productio
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6
Q

PK of benzimidazoles?

A
  1. Fattymeal will increase absorption
  2. Poor absorption may be beneficial because the drugs are used to treat intiestinal helminths
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7
Q

Indication for thiabendazole?

A

Drug of choice for cutaneuos larva migrans (creeping erruption)

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8
Q

MOA of diethylcarbamazine (DEC)?

A
  1. Involvement of blood platelets triggered by action of filarial excretory antigens
  2. Inhibition of microtubule polymerization and diruption of preformed microtubules
  3. Interference with arachidonic acid metabolism
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9
Q

Describe the activity of DEC?

A
  1. Parent drug is active component
  2. Drug is inactive in vitro -> activation of a cellular component is essential to activity
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10
Q

Indication of DEC?

A

Effective against microfalariae, however, not effective against adult worm

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11
Q

ADR of DEC?

A

Mazzotti reaction from host immune response to the presence of dead microfilariae

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12
Q

Inidication for ivermectin?

A

Effective against nematode infection

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13
Q

MOA of ivermectin?

A
  1. interference of microfilarial motility
  2. Degeneration of microfilariae in utero
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14
Q

How does IVM cause microfilarial motility interference?

A

IVM binds irreversibly to glutamate gated chloride channels and GABA agonist -> Chloride ion influx appears to be more plausible mechanism -> hyperpolarization and muscle paralysis

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15
Q
A
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16
Q

How does IVM cause degerenation of microfilariae in utero?

A

Presence of degenerated microfilariae in utero prevents further fertilization and production of microfilariae

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17
Q

Metabolism of IVM?

A
  1. Absorption is significanly affected by the presence of alcohol
  2. Administration as an alcoholic solution -> 100% increase in absorptio
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18
Q

Indication for IVM?

A

Treatment for onchocerciasis (African river blindness) caused by Onchocerca vovulus

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19
Q

Indication for moxidectin?

A

Onchocerca infection (River blindenss) -> milbemycin class

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20
Q

Activity of Praziquantel?

A
  1. Highly effective against cestodes and trematodes
  2. No acivity against nematodes
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21
Q

MOA of Praziquantel?

A
  1. Ca2+ redistribution either directly or indirectly
  2. Helmiths found in the host’s lumen can cause muscle contraction and paralysis leading to worm expulsion
  3. Worm paralysis by inhibiting phosphoinositide metabolism
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22
Q

Indication of PZQ?

A

Drug of choice for treatment of schistosomiasis and liver flukes (trematode and cestode)
* Not active against liver stages

23
Q

Activity of oxamniquine?

A

Against Schistosoma mansoni

24
Q

MOA of oxamniquine?

A

Activated via esterification to biological ester that spontaneously dissociates to an electrophile which alkylates the helminth DNA
* Irreversible inhibition of nucleic acid metabolism
* Resistant helminths don’t esterify oxamniquine

25
Q

What is the drug of choice for pinworms? Activity

A

Pyrantel Pamoate:
* Not very soluble, not readily absorbed
* Improves usefulness of drug for treatment of interstinal helminths

26
Q

MOA of pyrantel pamoate?

A

Structural analog of Ach that acts as a depolarizing neuromuscular blocking agent that activate nicotinic receptors and inhibits cholinesterase -> worm paralysis

27
Q

What is the active form of metronidazole?

A

N-OH

28
Q

MOA of metronidazole?

A
  1. Anaerobic organisms reduce the nitro group in metronidazole to a hydroxylamine
  2. Reactive species are produced that cause destructive effects on cell components (DNA, proteins, and membranes)
29
Q

Metabolism of metronidazole?

A
  1. Hydroxylation of the 2-methyl group to 2-hydroxymethylmetronidazole (HM)
  2. Oxidation to metronidazole acetic acid
  3. Both compounds have biological activity
30
Q

What is the drug of choice for protozoal infections?

A

metronidazole:
* Amebiasis
* Giardiasis
* Trichomoniasis

31
Q

ADR of metronidazole?

A
  1. Ab distress
  2. Metallic taste
  3. Disulfirum-like effect if taken with alcohol
32
Q

MOA of tinidazole?

A
  1. Hydroxylation at the 2-methyl group catalyzed by CYP3A4
  2. Same MOA as metronidazole but effective against some metronidazole resistant protozoa
33
Q

MOA of nitazoxanide?

A
  1. Prodrug metabolized to tizoxanide (TIZ)
  2. TIZ undergoes 4-electron reduction of the 5-nitro group -> short lived intermediates including the hydroxylamine derivative
  3. Inhibits the enzyme pyruvate:ferredoxin oxidoreductase
34
Q

How does MOA of NTZ and TIZ differ from metronidazole and tinidazole?

A

Don’t cause DNA fragmentation and not considered mutagenic

35
Q

Indication for nitazoxanide?

A

Tx of diarrhea in children with Giardia or Cryptosporidium

36
Q

Indication for diloxanide furoate?

A

Tx for asymptomatic amebiasis

37
Q

MOA of lindane?

A

CNS stimulatory action that occurs by blocking GABA:
* Super lipophilic in nature
* Penetrates the chitinous exoskeleton of the parasite
* Readily absorbed through intact human skin or scalp
* Systmeic neurotoxicity in the host

38
Q

Tx for protozoal infection?

A
  1. Metronidazole
  2. Tinidazole
  3. Nitazoxanide
  4. DIloxanide Furoate
39
Q

Pyrethrum and Pyrethroids are derived from what natural product?

A

Chrysanthemum

40
Q

Describe the formulation of pyrethroids?

A

Synthetic derivatives
* Clinically used permethrin exists as a 60:40 mixture of trans:cis isomers

41
Q

MOA of Pyrethrins and pyrethroids?

A

Nerve membrane sodium channel toxins:
* Don’t affect potassium channels
* Bind to specific sodium channel proteins
* Slow the rate of inacitvation of the sodium current
* Prolong the open time of the sodium channel

42
Q

Indication for pyrethrins?

A

Combination of a 10:1 ratio of piperonyl butoxide to pyrethrins

43
Q

What is the function of adding piperonyl butoxide to pyrethrins?

A

Provides synergy:
* No insecticidal activity on its own
* Inhibits CYP450 enxome of the insect
* Prevents oxidative inacitivation of pyrethrins

44
Q

What is the tx for scabies? ADR?

A

Scabies
ADR: less neurotox but causes skin irritation

45
Q

How are quinolines similar?

A
  1. Effective on the same stage of the parasite
  2. Share mechanism of resistance
  3. Quinidine structure
46
Q

MOA of Quinolines?

A
  1. Quinolines concentrate in the food vacuole of the parasite, where human hemoglobin is digested, which releases heme
  2. Heme kills parasite through oxidative damage
  3. The toxic heme is sequestered as an unreactive malarial pigment termed hemozoin to prevent toxic side effects
  4. Quinolines sequester the heme so that it cannot be made unreactive, resulting in the death of the parasite
47
Q

Mechanisn of Quinolines resistnace?

A
  1. Spontaneous gene mutation
  2. P. falciparium chloroquine-resistance transporter (pfrcrt):
    * Transmembrane transporter protein found in the food vacuole
    * Reduced accumulation of chloroquine
48
Q

SAR of chloroquine?

A

8-chloro increases activity

49
Q

MOA of mefloquine

A

Synthesized with the intent of blocking the site of metabolsim in quinine with the chemically stable CF3 group

50
Q

Types of Quinolines?

A

Quinine
Chloroquine
Hydroxychloroquine
Mefloquine
Halofantrine

51
Q

Antifolate antimalarials?

A
  1. Pyrimethamine
  2. Sulfadoxine
52
Q

MOA of pyrimethamine?

A

DHFR inhibitor selective to Plasmodium
* Antimalarial form of Bactrim

53
Q

MOA of sulfadoxine?

A

LA folate synthesis inhibitor

Drug Action IV (28 decks)

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