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Pharm > Antiparasitics > Flashcards

Antiparasitics Flashcards

1
Q

Prevalence in U.S.A.:

A
  1. Helminth infections: >1 million per year
  2. Toxocara (from dogs, cats) roundworms: 14% of population
  3. Malaria: 2000 endemic cases per year
  4. Amebiasis: 3–5% of population
  5. Giardia: 2–10% of population
  6. Trichomonas vaginalis: ~3 million/year
  • Infection associated with poor economic
    conditions
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2
Q

Approaches To Antiparasitic Chemotherapy:

A
  1. Selective Chemotherapy
  2. “Cure” vs. “Control”
    • Can agent(s) be found to eradicate all stages of parasite in host
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3
Q

Nematodes (Roundworms) Infections (10):

A
  1. Ascaris lumbricoides (common roundworm)
  2. Strongyloides stercoralis (threadworm)
  3. Enterobius vermicularis (pinworm)
  4. Necator americanus (hookworm)
  5. Dracunculus medinensis (guinea worm)
  6. Trichuris trichiura (whipworm)
  7. Trichinella spiralis (trichinosis)
  8. Toxocara canis (canine ascarid)
  9. Ancylostoma braziliense (dog hookworm)
  10. Wuchereria bancrofti, Loa loa, Onchocerca volvulus (filariasis)
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4
Q

Chemotherapy for Nematode (Roundworm) Infections (4):

A
  1. Mebendazole (Vermox®)
  2. Albendazole (Albenza®)
  3. Thiabendazole (Mintezol®)
  4. Pyrantel pamoate (Antiminth®, Pin-X®)
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5
Q

Mebendazole:

  • Mechanism:
  • Use:
  • Absorption/Excretion:
A
  • Mechanism:
    • ​selective damage to cytoplasmic microtubules
    • immobilizes and kills parasite
  • Use:
    • ​effective for many intestinal roundworms
    • kills some ova
  • Absorption/Excretion:
    • ​low systemic bioavailability = low systemic toxicity
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6
Q

Albendazole:

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • ​same as mebendazole
    • except liver quickly converts it to albendazole sulfoxide which is an active metabolite with good systemic distribution
  • Use:
    • ​Echinococcus
      • 1st choice
      • hydatid cyst disease, actually a cestode
    • neurocysticercosis due to Taenia solium
    • cutaneous larval migrans
    • active against many intestinal roundworms but not a labeled indication
  • Side Effects:
    • ​elevated hepatic enzymes
    • abdominal pain, nausea, vomiting, headache
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7
Q

Thiabendazole:

  • Mechanism:
  • Use:
  • Administration:
  • ​Side Effects:
A
  • Mechanism:
    • ​Hookworms: probably affects energy metabolism via inhibition of mitochondrial
      fumarate reductase
    • Strongyloides: inhibits assembly of parasitic microtubules
  • Use:
    • strongyloidiasis
    • cutaneous larva migrans
    • alternate agent for other roundworm infections
  • Administration:
    • ​oral or topical (if cutaneous larval migrans limited)
  • Side Effects:
    • ​anorexia, nausea, vomiting, dizziness
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8
Q

Pyrantel pamoate:

  • Mechanism
  • Use
  • Side Effects
A
  • Mechanism:
    • ​depolarizing neuromuscular blocker
    • causing spastic paralysis of worm
  • Use:
    • ​hookworm, pinworm, and roundworm
  • Side Effects:
    • ​not effective against Trichuris (whipworm)
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9
Q

Trematode (Fluke) Infections:

A
  1. Intestinal:
    • Fasciolopsis buski
  2. Blood:
    • Schistosoma haematobium
    • S. japonicum
    • S. mansoni
  3. Lung:
    • Paragonimus westermani
  4. Liver:
    • Clonorchis sinensis
    • Fasciola hepatica
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10
Q

Chemotherapy of Trematode (Fluke) Infections:

A

Praziquantel (Biltricide®)

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11
Q

Praziquantel:

  • Mechanism
  • Use
  • Side Effects
A
  • Mechanism:
    • ​increases cell membrane permeability to calcium
    • resulting in marked muscle contraction
  • Use:
    • ​drug of choice for all species of Schistosoma
    • some activity against other trematodes
      • e.g. Chlonorchis, Paragonimus, Opisthorchis
    • good activity against many cestodes
  • Side Effects:
    • ​abdominal discomfort, nausea
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12
Q

Cestodes (Tapeworms) Infections (5):

A
  1. Taenia saginata (beef)
  2. Diphyllobothrium latum (fish)
  3. Taenia solium (pork)
  4. Hymenolepsis nana (dwarf tapeworm)
  5. Echinococcus granulosus, E. multilocularis (hydatid cysts)
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13
Q

Chemotherapy of Cestodes (Tapeworms) Infections (3):

  • Use:
A
  1. Praziquantel (Biltricide®):
    • Use:
      • for Taenia solium (pork tapeworm)
      • will prevent neurocysticercosis
      • good activity against many cestodes
  2. Albendazole
    • Use:
      • treat neurocysticercosis
  3. Paromomycin Sulfate (Humatin®)
    • Use:
      • good activity against many cestodes
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14
Q

Malaria Life Cycle:

A
  1. Sporozoites in mosquito salivary gland are injected into human blood
  2. Exoerythrocytic stage—
    • sporozoites multiply in liver ⇒ tissue schizonts
  3. Escape from liver into bloodstream as merozoites
    • ​​begins the erythrocytic stage
    • merozoites invade red blood cells
    • multiply in them to form blood schizonts
  4. Infected erythrocytes eventually rupture
    • releasing a new crop of merozoites
    • this erythrocytic cycle may be repeated several times
  5. During the erythrocytic stage:
    • gametocytes (sexual stage) form
    • are released into the blood stream
    • where they may be taken up by a mosquito
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15
Q

Classification of antimalarials based on life cycle stage (4):

A
  1. tissue schizonticides:
    • eliminate latent liver hypnozoites
    • e.g. primaquine
  2. blood schizonticides (suppressive agents):
    • act on blood schizonts
    • e.g. chloroquine, mefloquine, quinine
  3. gametocides:
    • kill gametocytes in blood
    • e.g. primaquine for P. falciparum, chloroquine for P. vivax, malariae, ovale
  4. sporonticidal agents:
    • render gametocytes noninfective in mosquito
    • e.g. pyrimethamine
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16
Q

Antimalarial Drugs (6):

A
  1. Chloroquine (Aralen®)
  2. Mefloquine (Lariam®)
  3. Atovaquone + Proguanil (Malarone™)(2000)
  4. Quinine
  5. Doxycycline (Atridox™, Doryx®, Doxy®, others)
  6. Primaquine
17
Q
  • *Chloroquine** (Aralen®):
  • *Mechanism**
A
  • blood schizonticide
  • selectively toxic to parasite because parasitized erythrocytes concentrate the drug (>25-fold)
  • only intraerythrocytic trophozoites that are actively degrading hemoglobin are chloroquine-susceptible
    • polymerize potentially toxic free heme into unreactive hemozoin
  • chloroquine inhibits this heme polymerization
    • ​heme accumulates to toxic levels
18
Q

Chloroquine:

  • **Use: **
  • Side Effects:
A
  • Use:
    • prevent attacks of all 4 species of malaria
    • eradicate P. malariae and chloroquine-sensitive P. falciparum
    • will not effect a complete cure of P. vivax or ovale
      • must give primaquine
  • Side Effects:
    • visual impairment
19
Q

Mefloquine:

  • Mechanism:
  • Use:
A
  • Mechanism:
    • not proven, but probably similar to chloroquine
    • blood schizonticide for P. falciparum and P. vivax
    • resistance can develop rapidly
  • Use:
    • treatment of chloroquine-resistant and multidrug-resistant P. falciparum and P. vivax
    • used as prophylaxis in areas where organisms are resistant to chloroquine
20
Q

Atovaquone + Proguanil (Malarone™):

Mechanism

A
  1. Atovaquone
    • ​​selectively inhibits malarial mitochondrial electron transport (cytochrome bc1 complex)
    • ultimate effect is disruption of protozoal
      pyrimidine synthesis
  2. Proguanil
    • ​​prodrug
    • inhibits malarial dihydrofolate reductase and ultimately pyrimidine synthesis
21
Q

Atovaquone + Proguanil:

  • Use:
  • Side Effects:​​
A
  • Use:
    • ​prevention and treatment of chloroquine- resistant P. falciparum
  • Side Effects:
    • ​nausea, diarrhea, vomiting, rash
22
Q

Quinine:

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • ​similar to chloroquine
    • blood schizonticide against all four malarial parasites
  • **Use: **
    • ​agent of choice for severe acute attacks
    • treatment of chloroquine-resistant P. falciparum (alternate choice)
  • Side Effects:
    • cinchonism: headache, visual disturbance, dizziness, tinnitus
    • gastric irritation, nausea, vomiting
    • cardiac effects similar to quinidine
23
Q

Doxycycline (Atridox™, Doryx®, Doxy®, others):

  • Mechnaism:
  • Use:​​
A
  • Mechanism:
    • ​decrease malarial protein synthesisanddepress dihydroorotate dehydrogenaseactivity, therebyinterfering with pyrimidine synthesis
  • Use:
    • multidrug-resistant P. falciparum
24
Q

Primaquine:

  • Use:
  • Side Effects:
A
  • Use:
    • ​radical cure or terminal prophylaxis of P. vivax and P. ovale because it will kill dormant liver schizonts
    • should be used in conjunction with blood schizonticide
    • in combination with clindamycin to treat Pneumocystis jiroveci (carinii) pneumonia in AIDS patients
  • Side Effects:
    • ​hemolytic reactions in those with G6PD deficiency
25
Q

What Causes Amebic Dysentery?

A

Entamoeba histolytica

26
Q

Drugs that Treat Ambesias (3):

A
  1. Metronidazole
  2. Iodoquinol
  3. Paromomycin
27
Q

How are Amebic Drugs Classified?

A

Site of Action

  1. Tissue Amebicides
    • eliminate organisms primarily in bowel wall, liver, and other extraintestinal tissues
    • metronidazole
    • needed for symptomatic infections
  2. ​Luminal amebicides
    • ​​used alone for asymptomatic infections
    • given with tissue amebicide for symptomatic infections
    • iodoquinol, paromomycin sulfate
28
Q

Metronidazole:

Use

A

tissue amebicide for mild to severe symptomatic infections of E. histolytica

29
Q

Paromomycin Sulfate (Aminosidine; Humatin®):

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • ​aminoglycoside-like, inhibiting protein synthesis
  • Use:
    • ​luminal amebicide
  • Side Effects:
    • ​diarrhea, nausea, vomiting, epigastric pain
30
Q

Iodoquinol (diiodohydroxyquin)(Yodoxin®; Diquinol, Yodoquinol):

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • luminal amebicide
  • Use:
    • in combination with metronidazole for mild to severe infections of E. histolytica
  • Side Effects:
    • diarrhea and other gastrointestinal symptoms
    • contraindicated for those hypersensitive to iodine-containing preparations
31
Q

Chemotherapy for Other Protozoal Diseases (4):

A
  1. Metronidazole (Flagyl®)
  2. Atovaquone (Mepron®)
  3. Paromomycin Sulfate
  4. Nitazoxanide
32
Q

What other protozoa can metronidazole be used for?

A

Drug of choice for:

  1. Giardia lamblia
    • most common intestinal protozoal infection in U.S.
  2. Trichomonas vaginalis
33
Q

Atovaquone (Mepron®):

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • selective inhibitor of protozoal mitochondrial electron transport
    • ultimate effect is disruption of protozoal pyrimidine synthesis
  • Use:
    • alternate prophylaxis or treatment for mild/moderate Pneumocystis jiroveci (carinii) in AIDS patients intolerant of TMP/SMX
  • Side Effects:
    • nausea, diarrhea, vomiting; rash
34
Q

Nitazoxanide (Alinia®):

  • Mechanism:
  • Use:
  • Side Effects:
A
  • Mechanism:
    • ​inhibits pyruvate:ferredoxin oxidoreductase which is required for anaerobic energy
      metabolism
  • Use:
    • Giardia lamblia
    • Cryptosporidium parvum
  • Side Effects:
    • ​abdominal pain, diarrhea, nausea
35
Q

What are the drugs used to treat Pneumocystis jorveci (carnii) in AIDS patients (4)?

A
  1. Trimethoprim + sulfamethoxazole (TMP-SMX)
  2. Clindamycin + primaquine
  3. Atovaquone
  4. Dapsone

Pharm (16 decks)

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