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Wrap up Block > Anti-parasite pharm => Ch 52 > Flashcards

Anti-parasite pharm => Ch 52 Flashcards

1
Q

What are the enzymes not found in host’s cells?

A

Dihydropteroate synthase;
Pyruvate-ferredoxin oxidoreductase
Nucleoside phosphotransferases
Trypanothione reductase

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2
Q

What parasites use dihydropteroate synthase? Why do they use it?

A

Sporozoans => Plasmodium, Toxoplasma, Eimeria

lack ability to use exogenous folate

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3
Q

What Drug class works against DHPS? How?

A

Sulfonamides => antimetabolites of PABA to inhibit dihydrofolate reductase

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4
Q

What is Fansidar? Use?

A

Combo of sulfadoxine & pyrimethamine for chloroquine resistant Plasmodium falciparum malaria

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5
Q

What parasites use PFO? Why do they use it?

A

some anaerobic protozoans (trichomonad, entamoeba) due to lack of mitochondria but need to produce acetyl CoA & H+ via electron transport

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6
Q

Other than PFO making acetyl CoA, what else is it responsible for?

A

Transferring electrons from pyruvate to nitro groups of nitroimidazoles

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7
Q

What is primary nitroimidazole and how does it work?

A

Metronidazole

forms cytotoxic products to inn growth by binding to parasite’s proteins & DNA

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8
Q

What provides metronidazole with its safety & effectiveness against amebiasis & trichomoniasis?

A

selective toxicity => exploits biochem & physio differences bw parasite & host

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9
Q

What Rx is used to take advantage of Giardia lamblia & Cryptosporidium parvum?

A

Nitazoxanide inhibits PFO pathway

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10
Q

What is the purine salvage pathway in protozoan parasites? Why is it critical?

A

organisms unable to synthesize purine nucleotides de novo

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11
Q

What disease and what mechanism do allopurinol riboside, formycin B, & thiopurinol riboside share?

A

Leishmania
purine nucleoside phosphotransferase (transfers phosphate to 5’ of purine nucleosides) but also phosphorylates purine nucleoside analog

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12
Q

Triphosphate derivates of what Rx may be incorporated into nucleic acids or may inhibit enzymes in purine metabolism?

A

allopurinol riboside
formycin B
thiopurinol riboside

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13
Q

Toxicity of allopurinol riboside, formycin B, & thiopurinol riboside?

A

low bc mammalian cells lack salvage enzyme

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14
Q

What role does trypanothione reductase play in life of kinetoplastidans?

A

central role in maintaining reduced state of intracellular thiols & essential for survival of parasites

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15
Q

What molecule does Trypanothione relate to in mammals?

A

glutathione

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16
Q

What Rx inhibits Trypanothione reductase? What disease is it used in?

A

Nifurtimox for Chagas’ disease

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17
Q

What are the 3 mechanisms involving enzymes indispensable to parasites?

A 
Purine phosphoribosyl transferases (PPPR)
Ornithine decarboxylase (OD)
Glycolytic enzymes (Gly-en)
18
Q

What is key enzyme in Leishmania, Schistosoma, & Trypanosoma?

A

HGPRTase

19
Q

What is a good substrate for PPPR?

A

Allopurinol for certain parasites but not for mammalian enzyme

20
Q

MOA of allopurinol?

A

metabolized to ribotide, which is incorporated after phosphorylation into RNA forms that interfere w/ normal growth

21
Q

Purine salvage in Giardia depends critically on what?

A

adenine phosphoribosyl-transferase & guanine phosphoribosylttransferase

22
Q

What is the function of ornithine decarboxylase?

A

controls formation of polyamine, putrescine and appears more critical for growth of certain parasites.

23
Q

What is the action of the substrate against Trypanosoma, Plasmodium & giardia species?

A

Eflornithine is suicide substrate of ornithine decarboxylase w/ anti parasitic activity

24
Q

How does Eflornithine work against T. gambiense in African trypansomiasis?

A

irreversible inhibitory action of eflornithine transforms organism into non dividing form that can be eliminated by host immune system

25
Q

What enzyme can be inhibited by what Rx in the bloodstream form of African trypanosome T. brucei?

A

G-3-P oxidase can be inhibited by salicylhydroxamic acid leading parasite into anaerobic state

26
Q

Biogenesis of glycosides may be target for anti parasitic Rx. What Rx would do this and its MOA?

A

Suramin (large polar molecule) binds to glycolytic enzyme & prevent incorporation of enzymes into glycosome

27
Q

What are the 6 mechanisms involving biochem functions common to host & parasite? (more susceptible in parasite)

A 
Dihydrofolate reductase
Thiamin transporter
Mitochondrial electron transporter 
Microtubules
NeuroTx & muscle contractino
Lanosterol demethylase
28
Q

What enzyme is a target of ABx & CTX and the parasites - Plasmodium, Toxoplasma, Eimeria? What Rx is associated?

A

DHFR is inhibited by Pyrimethamine

29
Q

Which parasite species has some resistant strains to pyrimethamine? How?

A

P. falciparum uses point mutations in gene coding for DHFR to make it less susceptible

30
Q

What biochem function is the primary energy sours of coccidia? How can this be utilized for Rx? What Rx?

A

Carb metabolism thus needs thiamin transport for energy so can be inhibited.
Amprolium leads to thiamin deficiency in coccidia & low toxicity in hosts

31
Q

What mechanism is utilized for anticoccidial effects to interact w/ respiratory chain specific for Eimeria species? Is it just this species?

A

Mitochondrial electron transporter via
4-Hydroxyquinolone Rx

Only disrupts mitochondrial respiration in Eimeria (no others)

32
Q

What is a Rx of hydroxyquinoline that Tx Pneumocystis carinii infections? its MOA?

A

Atovaquone primarily binds to cytochrome bc1 complex where a drug binding site is present in cytochrome b

33
Q

What accounts for the selective toxicity of benzimadazole drugs? What is an Rx?

A

structural features of alpha-tubulins in helminths so they bind to microtubules to block transport processes

Mebendazole

34
Q

What are the Rx and how do anti parasitic effects stem from nicotinic agonist drugs?

A

levamisole, pyrantel pamoate acts in nematodes to lead to neuromuscular transmission leading to muscle contraction

35
Q

What is the MOA of piperazine?

A

GABA receptor agonist in nematodes leading to flaccid paralysis

36
Q

MOA of milbemycins & avermectins?

A

promote release of neuroTx & increase binding to post junctional receptors by actions of GABA

37
Q

Do milbemycins & avermectins cross BBB? toxicity

A

NO and relatively nontoxic

38
Q

MOA of praziquantel

A

antischistosomal & anti tapeworm agent that stimulates Ca+ entry into muscles of these parasites & causes unphysiologic contraction

39
Q

What parasites contain ergosterol as principal sterol in plasma membranes? What Rx class takes advantage of this and its MOA?

A

T. cruzi & Leishmania
Azoles inhibit CYP450 dependent C-14-alpha demethylation of lanosterol in the ergosterol biosynthetic pathway to inhibit growth of T cruzi & Leishamnia

40
Q

What is best Tx for cutaneous leishmaniasis?

A

Fluconazole

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