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Pharmacology > Antiparasitics > Flashcards

Antiparasitics Flashcards

1
Q

Antiparasitic Drugs - General

A

No vaccines
Commercial incentives limited for many parasitic infections
Parasites often have unique systems that can provide selective targets
Resistance is always a problem

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2
Q

Neglected Parasitic Infections in the US

A 
Trypanosoma cruzi (Chagas Disease)
Taenia solium (cysticercosis and neurocysticercosis)
Toxocara (Dog and cat roundworms)
Toxoplasma gondii (TOrches)
Trichomonas (STD)
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3
Q

Parasitic infections associated with HIV

A

In US: Pneumocystis jirovecii, Toxoplasma gondii, Cryptosporidium

Globally: Malaria, Leishmania, Trypanosoma cruzi

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4
Q

What are the 5 human malaria parasites?

A 
P. falciparum - constant - all RBCs
P. vivax - 48 hr - hypnozoites in liver
P. ovale - 48 hr - relapsing
P. malariae
P. knowlesi - 24 hr - zoonotic infections
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5
Q

Malaria parasite life cycle

A

sporozoites injected by mosquito –> go to liver –> merozoites formed (hypnozoites in vivax and ovale) –> merozoites invade and divide and rupture RBCs –> sexual stages produce gametocytes –> gametocytes taken up by mosquito

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6
Q

True or False: No drug kills malarial sporozoites.

A

True

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7
Q

Malarial drugs that attack LIVER stages (exoerythrocytic schizonticides)

A

Primaquine - merozoties and hypnozoites

Atovaquone and Artemisinins - merozoites

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8
Q

Malarial drugs that attack BLOOD stages (erythrocytic schizonticides)

A 
Chloroquine
Mefloquine
Artemisinins 
Quinine
Doxycycline & tetracycline
Clindamycin
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9
Q

Malarial chemoprophylaxis

A

Prevention: insect repellant, insecticides, bed nets

Awareness

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10
Q

Drugs for PREVENTION of Clinical Disease

A 
Chloroquine [Aralen] 
Hydroxychloroquine sulfate [Plaquenil]
Atovaquone + Proguanil [Malarone]
Mefloquine [Lariam]
Primaquine 
Doxycycline
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11
Q

Chloroquine [Aralen]

A

start 1-2 wk prior

continue 4 wk after

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12
Q

Hydroxychloroquine sulfate [Plaquenil]

A

start 1-2wk prior

contine 4wk after

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13
Q

Atovaquone + Proguanil [Malarone]

A

used in all areas
start 1-2d prior
continue 7 days after

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14
Q

Mefloquine [Lariam]

A

start >2wk early
continue 4wk
TOXIC SIDE EFFECTS

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15
Q

Primaquine

A

mainly for P. vivax
start 1-2d prior
continue 7 d after

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16
Q

Doxycycline

A

used in all areas
start 1-2d prior
continue 4 wk

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17
Q

Tx for uncomplicated malaria or unidentified species

A

Chloroquine sensitive: Chloroquine, Hydroxychloroquine sulfate

Chloroquine resistant:
Atovaquone + Proguanil [Malarone]
Artemether + lumefantrine [Coartem] (NOT READILY AVAILABLE)
Quinine sulfate + Doxycycline or Tetracycline or Clindamycin
Mefloquine [Lariam]

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18
Q

Tx for uncomplicated malaria: P. vivax or P. ovale

A

CQ sensitive:
Chloroquine
Hydroxychloroquine sulfate + primaquine

CQ resistant (2 drug minimum):
Quinine sulfate + doxycycline
Tetracycline + primaquine 
Atovaquone + Proguanil + primaquine
Mefloquine + primaquine
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19
Q

Tx for uncomplicated malaria: P. malariae or P. knowlesi

A

Chloroquine

Hydroxychloroquine sulfate

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20
Q

Sx for complicated malaria

A

Sx: impaired consciousness/coma, severe normocytic anemia, renal failure, pulmonary edema, etc.

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21
Q

Tx for complicated malaria

A

IV Quinidine gluconate + doxycycline or tetracycline or clindamycin
[consult cardiologist and experienced physician
monitor: BP, cardiac function, glucose levels (hypotension, widening QRS and/or lengthening QTc interval, hypoglycemia)]

IV Artesunate followed by Malarone, Doxycycline, Mefloquine (if Quinidine gluconate doesn’t work)

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22
Q

Artemisinin

A

Derived from Chinese wormwood (Artemesia)
Endoperoxide active group
RAPIDLY acting blood schizonticide
No effect on liver stages
active against all species
short half-life
high recrudescence rate after short course
commonly paired with other drugs (ex. mefloquine or lumefantrine)

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23
Q

Artemisinin combination therapy

A

Artemisinin provides rapid knockdown
Longer half-life component eliminates remaining parasites

Combinations:
Artemether + lumefantrin (Coartem)
Artesunate + mefloquine
Dihydroartemesinin + piperaquine

24
Q

Artemisinin antimalarial effect is associated with _____

A

Cmax

concentration dependent killing

25
Q

Artemisinin derivatives

A

Artemisinin (insoluble - oral)
Artesunate (water-soluble - oral, IV, IM, rectal)
Dihydroartemisinin (soluble - oral)
Artemether (lipid-soluble - oral, IM, rectal)

26
Q

Artemisinin adverse effects

A

well tolerated
nausea, vomiting, diarrhea, and dizziness
EMBRYOTOXIC

27
Q

Examples of 4-aminoquinilones

A

quinine, chloroquine, mefloquine, aminoquinoline

Block the polymerization of heme

28
Q

Hemoglobin metabolism

A

Malaria parasites ingest hemoglobin from host cell –> hemoglobin is degraded into amino acids and free heme(toxic) –> parasite polymerize heme into hemozoin(nontoxic)

29
Q

How does chloroquine effect parasite hemoglobin metabolism

A

chloroquine accumulates in food vacuole and inhibits heme polymerization (heme(toxic) –> hemozoin(nontoxic))

30
Q

Chloroquine (CQ)

A

drug of choice for Tx and prophylaxis
oral use, well absorbed, large Vd
half life 3-5d (terminal half-life 1-2mo)

31
Q

CQ antimalarial effect is associated with _____

A

T > MIC

opposite of Artemisinin

32
Q

How did CQ resistance occur

A

developed in at least 2 foci in P. falciparum

  1. mutations in PfCRT1 (caused reduced accumulation of CQ)
  2. over-expression of PfMDR1 (drug transporter)

P.vivax developed resistance later under a different mechanism

33
Q

Adverse effects of CQ

A

Usually “very well tolerated”
Pruritus is common (esp in Africans)
Not recommended in IV
CONTRADICTED in psoriasis, porphyria, retinal abnormalities, and myopathy

Antidiarrheal agents KAOLIN AND CALCIUM interfere with CQ absorption

34
Q

What are some other CQ related compounds

A 
Mefloquine
Lumefantrine
Piperaquine
Amodiaquine
Halofantrine
Tafenoquine
35
Q

What substance contains quinine

A

tonic water

36
Q

Quinine and Quinidine

A

rapidly acting blood schizonticide
active against all Plasmodium and Babesiosis
Mode of Action similar to CQ
IV for severe falciparum malaria
oral for uncomplicated “ “
Metabolized by CYP3A4 (can raise levels of warfarin and digoxin; also interact with HIV drugs)

37
Q

Adverse effects of Quinine

A 
Cinchonism: tinnitus, headache, nausea, dizziness, flushing, and visual disturbances
Cardiotoxicity
Stimulates uterine contractions
Hemolysis 
Severe hypotension with rapid infusion
38
Q

Mefloquine [Lariam] Usage

A

Resistance increasing
Both prophylaxis and Tx
Erythrocytic forms - falciparum & vivax

39
Q

Adverse effects of Mefloquine

A

Neuropsychiatric toxicity: seizures, toxic psychosis, and sleep disturbance

40
Q

What is an example of an 8-aminoquinoline

A

Primaquine

41
Q

Primaquine effects

A 
MOA unknown - probably involves ROS
Drug of choice for liver stages of vivax and oval (with CQ)
gametocidal against all types
well absorbed orally 
some resistance
42
Q

Adverse effects of Primaquine

A

too toxic for long term Tx
Contradicted in G6PD deficiency and pregnancy (predisposes to HEMOLYTIC ANEMIA)
Avoid in patients with:
granulocytopenia, methemoglobinemia, receiving myelosuppressive drugs (ex quinidine), or disorders that commonly include myelosuppression

43
Q

What are 2 types of antifolates

A

Pyrimethamine and Proguanil

44
Q

Fansidar [Pyrimethamine-Sulfadoxine]

A

Folate synthesis inhibitor
slow acting erythrocytic schizonticides

Sulfadoxine inhibits DHPS in malaria (can’t make dihydrofolic acid)
Pyrimethamine and Proguanil inhibit DHFR (can’t make THF)
overall decreases the formation of purines for DNA/RNA

45
Q

Other uses of antifolates

A

Toxoplasmosis (Pyrimethamine + sulfadiazine (clindamycin can replace sulfadiazine))

Pneumocystis (SxT aka Bactrim; Atavaquone is alternative)

46
Q

Use of Antifolates

A

Use of single antifolates is not recommended (resistance develops easily)
Synergistic effect
combination chosen b/c of matching pharmacokinetics (both have long half-lives)
Resistance is spreading rapidly (no longer recommended)

47
Q

Malarone

A

combination of proguanil and atavaquone
Atavaquone MOA: disrupts mitochondrial electron transport
Tx and prophylaxis usage
Generally well tolerated (TAKE WITH FOOD)
Atavaquone is alternative therapy for P. jiroveci

48
Q

Antibiotics used as antimalarial drugs include

A

Tetracycline, doxycycline, and clindamycin are blood schizonticides
They target components of the apicoplast
Doxycycline commonly paired with quinine or quinidine for Tx for falciparum
Doxycycline is used for chemoprophylaxis in mefloquine resistant areas

49
Q

Drugs for Anaerobic Parasites

A

Metronidazole used for: E. histolytic, Giardiasis, trichomoniasis
Kills trophozoites but not cysts
usually followed by luminal drug to eliminate asymptomatic infection
may target parasite DNA??

Tinidazole is a similar drug with less toxicity

50
Q

Metronidazole and alcohol

A

Metronidazole inhibits acetaldehyde dehyrdrogenase –> acetaldehyde –> hypotension. nausea, vomitting, discomfort

51
Q

What is Iodoquinol

A 
luminal amebicide 
low bioavailabilty 
sole agent in "asymptomatic" carriers
combine with metronidazole for amebic dysentery
kills trophozoites
52
Q

What is Pentamidine

A

parental administration
mechanism unknown
highly toxic
First line agent for West African trypanosomiasis (alternative for visceral leishmania and pneumocystosis)

53
Q

What is Nifurtimox

A 
Most commonly used for T. cruzi
MOA unknown (generate ROS??)
reduces severity of acute phase (unlikely to completely eliminate parasite)
orally available 
3-4mo course of Tx
Toxicity common
54
Q

Miltefosine

A 
phospholipid analog 
approved for use against visceral leishmaniasis 
28 daily doses - almost 100% cure rate
MOA unknown 
side effects tolerable
TERATOGENIC - avoid during pregnancy
55
Q

What is used to treat Giardia and Cryptosporidium

A

Nitazoxanide

56
Q

What is used to treat T. cruzi

A

Nifurtimox or Benznidazole

57
Q

What is used to treat T. brusei

A

West African - Early: Pentamidine; Late: Eflornithine

East African - Early: Suramin; Late: Melarsoprol(not good)

Pharmacology (11 decks)

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