Antiparasitics Flashcards
1
Q
Prevalence in U.S.A.:
A
- Helminth infections: >1 million per year
- Toxocara (from dogs, cats) roundworms: 14% of population
- Malaria: 2000 endemic cases per year
- Amebiasis: 3–5% of population
- Giardia: 2–10% of population
- Trichomonas vaginalis: ~3 million/year
- Infection associated with poor economic
conditions
2
Q
Approaches To Antiparasitic Chemotherapy:
A
- Selective Chemotherapy
- “Cure” vs. “Control”
- Can agent(s) be found to eradicate all stages of parasite in host
3
Q
Nematodes (Roundworms) Infections (10):
A
- Ascaris lumbricoides (common roundworm)
- Strongyloides stercoralis (threadworm)
- Enterobius vermicularis (pinworm)
- Necator americanus (hookworm)
- Dracunculus medinensis (guinea worm)
- Trichuris trichiura (whipworm)
- Trichinella spiralis (trichinosis)
- Toxocara canis (canine ascarid)
- Ancylostoma braziliense (dog hookworm)
- Wuchereria bancrofti, Loa loa, Onchocerca volvulus (filariasis)
4
Q
Chemotherapy for Nematode (Roundworm) Infections (4):
A
- Mebendazole (Vermox®)
- Albendazole (Albenza®)
- Thiabendazole (Mintezol®)
- Pyrantel pamoate (Antiminth®, Pin-X®)
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
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
-
Echinococcus
-
Side Effects:
- elevated hepatic enzymes
- abdominal pain, nausea, vomiting, headache
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
-
Hookworms: probably affects energy metabolism via inhibition of mitochondrial
-
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
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)
9
Q
Trematode (Fluke) Infections:
A
-
Intestinal:
- Fasciolopsis buski
-
Blood:
- Schistosoma haematobium
- S. japonicum
- S. mansoni
-
Lung:
- Paragonimus westermani
-
Liver:
- Clonorchis sinensis
- Fasciola hepatica
10
Q
Chemotherapy of Trematode (Fluke) Infections:
A
Praziquantel (Biltricide®)
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
12
Q
Cestodes (Tapeworms) Infections (5):
A
- Taenia saginata (beef)
- Diphyllobothrium latum (fish)
- Taenia solium (pork)
- Hymenolepsis nana (dwarf tapeworm)
- Echinococcus granulosus, E. multilocularis (hydatid cysts)
13
Q
Chemotherapy of Cestodes (Tapeworms) Infections (3):
- Use:
A
-
Praziquantel (Biltricide®):
-
Use:
- for Taenia solium (pork tapeworm)
- will prevent neurocysticercosis
- good activity against many cestodes
-
Use:
-
Albendazole
-
Use:
- treat neurocysticercosis
-
Use:
-
Paromomycin Sulfate (Humatin®)
-
Use:
- good activity against many cestodes
-
Use:
14
Q
Malaria Life Cycle:
A
- Sporozoites in mosquito salivary gland are injected into human blood
-
Exoerythrocytic stage—
- sporozoites multiply in liver ⇒ tissue schizonts
-
Escape from liver into bloodstream as merozoites
- begins the erythrocytic stage
- merozoites invade red blood cells
- multiply in them to form blood schizonts
-
Infected erythrocytes eventually rupture
- releasing a new crop of merozoites
- this erythrocytic cycle may be repeated several times
- During the erythrocytic stage:
- gametocytes (sexual stage) form
- are released into the blood stream
- where they may be taken up by a mosquito
15
Q
Classification of antimalarials based on life cycle stage (4):
A
-
tissue schizonticides:
- eliminate latent liver hypnozoites
- e.g. primaquine
-
blood schizonticides (suppressive agents):
- act on blood schizonts
- e.g. chloroquine, mefloquine, quinine
-
gametocides:
- kill gametocytes in blood
- e.g. primaquine for P. falciparum, chloroquine for P. vivax, malariae, ovale
-
sporonticidal agents:
- render gametocytes noninfective in mosquito
- e.g. pyrimethamine
16
Q
Antimalarial Drugs (6):
A
- Chloroquine (Aralen®)
- Mefloquine (Lariam®)
- Atovaquone + Proguanil (Malarone™)(2000)
- Quinine
- Doxycycline (Atridox™, Doryx®, Doxy®, others)
- 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
-
Atovaquone
- selectively inhibits malarial mitochondrial electron transport (cytochrome bc1 complex)
- ultimate effect is disruption of protozoal
pyrimidine synthesis
-
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
What Causes Amebic Dysentery?
Entamoeba histolytica
26
**Drugs that Treat Ambesias (3):**
1. **Metronidazole**
2. **Iodoquinol**
3. **Paromomycin**
27
How are Amebic Drugs Classified?
**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
**Metronidazole:**
**Use**
**tissue amebicide** for mild to severe **symptomatic infections** of **E. histolytica**
29
**Paromomycin Sulfate** (Aminosidine; Humatin®)**:**
* **Mechanism:**
* **Use:**
* **Side Effects:**
* **Mechanism:**
* aminoglycoside-like, **inhibiting protein synthesis**
* **Use:**
* **luminal amebicide**
* **Side Effects:**
* ****diarrhea, nausea, vomiting, epigastric pain
30
**Iodoquinol** (diiodohydroxyquin)(Yodoxin®; Diquinol, Yodoquinol)**:**
* **Mechanism:**
* **Use:**
* **Side Effects:**
* **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
**Chemotherapy for Other Protozoal Diseases (4):**
1. Metronidazole (Flagyl®)
2. Atovaquone (Mepron®)
3. Paromomycin Sulfate
4. Nitazoxanide
32
What other protozoa can **metronidazole** be used for?
**Drug of choice for:**
1. Giardia lamblia
* most common intestinal protozoal infection in U.S.
2. Trichomonas vaginalis
33
**Atovaquone** (Mepron®)**:**
* **Mechanism:**
* **Use:**
* **Side Effects:**
* **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
**Nitazoxanide** (Alinia®)**:**
* **Mechanism:**
* **Use:**
* **Side Effects:**
* **Mechanism:**
* **inhibits pyruvate:ferredoxin oxidoreductase** which is required for **anaerobic energy
metabolism**
* **Use:**
* Giardia lamblia
* Cryptosporidium parvum
* **Side Effects:**
* abdominal pain, diarrhea, nausea
35
What are the drugs used to treat **Pneumocystis jorveci (carnii)** in AIDS patients (4)?
1. **Trimethoprim + sulfamethoxazole (TMP-SMX)**
2. **Clindamycin + primaquine**
3. **Atovaquone**
4. **Dapsone**