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FM3-2: Parasites, STDs, etc > Antiparasitic Drugs > Flashcards

Antiparasitic Drugs Flashcards

1
Q

Treating nematodes

A
  • Albendazole: Ascaris lumbricoides, hookworms, whipworms, pinworms, trichinosis
  • Strongyloides (filarial infection) best treated w/ ivermectin
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2
Q

Treating cestodes

A
  • Praziquantel is DOC except for echinococcosis. Praziquantel used for Taenia saginata, Taneia solium, Fish tapeworm
  • Use albendazole for Echinococcus and cysticercosis
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3
Q

Treating trematodes (flukes)

A

Praziquantel is DOC for schistosoma (blood flukes)

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4
Q

Are helminths or protozoans prone to drug resistance?

A

Protozoans

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5
Q

Treating enteric protozoans

A
  • Entamoeba histolytica and Giardia lamblia treated w/ metronidazole
  • Cyclospora is treated w/ TMP-sulfa
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6
Q

Treating Trichomonas vaginalis

A

Metronidazole

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7
Q

Benzimidazoles
Use of Albendazole
Mechanism of Mebendazole / Albendazole
Toxicity of Albdendazole

A
  • Use of Albendazole: used for roundworm, hookworm, pinworm, whipworm, echinococcus, and cysticercosis. Effective against both larval and adult stages of roundworms.
  • Mechanism of Mebendazole: inhibits polymerization of worm beta-tubulin. Binds to worm beta-tubulin much better than human.
  • Mechanism for Albendazole: albendazole sulfoxide is the active metabolite, which penetrates into tissues well, which is why it works well for echinococcosis and cysticercosis. Often only need 1 dose.
  • Toxicity of albendazole: do NOT use in pregnant women and hepatic cirrhosis
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8
Q

Ivermectin
Use
Mechanism
Toxicity

A
  • Use – Treats filarial worm infections. Kills larvae, not adult worms. Also treats stronyloides (threadworm) and other roundworms (Ascaris, whipworm, pinworm). Heartworm prophylaxis in dogs.
  • Mechanism – lactone ring potentiates the glutamate-gated Cl channels in nematodes → tonic paralysis of worm musculature, especially pharyngeal muscle. Works against larvae, but not adult filarial worms. Prevents egress of microfilariae from uterus of adult worm.
  • Toxicity: well tolerated overall. Side effects from dead / dying microfilariae. Don’t use in pxs w/ compromised BBB → CNS toxicity.
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9
Q

Praziquantel
Use
Mechanism
Toxicity

A
  • Use – strong activity against cestodes and trematodes but not nematodes. DOC for Schistosoma spp.
  • Mechanism – At low doses it induces muscular activity and spastic worm paralysis. At high doses it causes Ca-dependent blebbing of the tegument → susceptibility to host immune response.
  • Toxicity – NO pregnancy. Abdominal pain, headache, dizziness.
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10
Q

Diethylcarbamazine
Use
Mechanism

A
  • Use – treats and prevents filarial worm infections (W bancrofti and B malayi). 1st line for lymphatic filariasis.
  • Mechanism – kills microfilariae. Alters the arachidonic acid pathway. Involves decreased muscular activity → paralsysis or alteration in surface membrane → susceptibility to host immune attack
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11
Q 
Metronidazole
Use
Mechanism
Toxicity
Resistance
A
  • Use – DOC for T vaginalis and symptomatic amebiasis. Also for giardiasis.
  • Mechanism – prodrug metabolized in liver. Reduction of nitro group in anaerobic bacteria as a consequence of electron transfer from protozoal ferredoxin proteins to metronidazole → free radical damage on DNA.
  • Toxicity – overall well tolerated. Anorexia, diarrhea, cramping, some neurotoxicity. Disulfuram-like rxn to alcohol. Contraindicated in 1st trimester of pregnancy.
  • 10% of T vaginalis is resistant
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12
Q

General mechanism of malarial prophylaxis
DOC for prophylaxis if no resistance
If resistance to chloroquine
Prophylaxis against P vivax / P oval

A
  • General: Strong activity against schizont form to abort early stages of infection
  • Chloroquine is DOC if no resistance.
  • Mefloquine given in areas w/ chloroquine resistance.
  • Pxs in areas of P vivax or P ovale get primaquine, which is the only drug effective against hypnozoites.
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13
Q

Treating acute malaria

Chloroquine resistant areas

A
  • Chloroquine is DOC for P ovale, P malariae, and susceptible forms of P vivax / P falciparum
  • 1) Quinine + (doxycyline or tetracycline) or 2) atovaquone + chloroguanide used for chloroquine-resistant strains.
  • Primaquine added to chloroquine for pxs infected w/ P ovale and P vivax to prevent relapse.
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14
Q

Treating malaria during pregnancy

A

Chloroquine or quinine in 1st trimester; mefloquine used for prophylaxis in 2nd / 3rd trimesters. Drugs should be taken while breast feeding, but this does not protect the infant.

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15
Q

What do sporotocides do?

A

Sporotocides prevent development of oocysts and sporozoites in infected mosquitoes.

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16
Q

Malaria vaccine
Mechanism
Efficacy

A

•Recent vaccine (RTS,S) strings together 21 epitopes from each of the diff stages of P falciparum life cycle, targeting the circumsporozoite protein. 60% efficacy in kids 5-17 months old. Only 30% efficacy in 6-12 week old babies.

17
Q 
Quinine
Structure / source
Use
Mechanism
Toxicity (5)
A
  • Quinoline ring-containing molecule found in the bark of SA cinchona tree.
  • Use – Blood schizonticide used against chloroquine-resistant malaria. No longer widely used due to lower efficacy and higher toxicity compared to other drugs.
  • Mechanism – weak base raises pH of Plasmodium food vacuoles to inhibit polymerization of heme into hemozoin, which is an important detox rxn essential for surival in RBCs (heme generates ROS). Quinine binds heme, then complex binds heme polymers, terminating further polymerization.
  • Toxicity
  • Cinchonism = cluster of dose related sxs including tinnitus, headaches, nausea, and blurred vision.
  • Hypersensitivity may cause flushing, itching, and hemoglobinuria.
  • Blackwater fever is a rare form of hypersensitivity that produces massive hemolysis, Hb-emia, Hb-uria, and renal failure.
  • Hypoglycemia b/c quinine releases insulin
  • Decreases excitability of motor end plate of skeletal muscle so responses to Ach are reduced.
18
Q 
Chloroquine
Use
Mechanism
Toxicity (4)
Resistance
A
  • Use – blood schizonticide used for prophylaxis and treatment
  • Mechanism – Same mechanism as quinine, but more effective and less toxic. However, resistance is common.
  • Toxicity – overall very safe, but high doses may cause CV effects such as hypotension and ECG abnormalities. Contraindicated in pxs w/ liver disease and G6PDH deficiency
  • Resistance – some P falciparum does not display characteristic vacuolar swelling. Effluxed from vacuole. Associated w/ a lysine → threonine substitution in PfCRT gene (P falciparum chloroquine-resistance transporter)
19
Q 
Mefloquine
Use
Mechanism
Toxicity
Resistance
A
  • Use – DOC for prophylaxis in regions w/ chloroquine resistance. Also used to treat chloroquine resistant infections.
  • Mechanism – concentrates in food vacuoles to raise pH and cause swelling, but does not inhibit heme polymerization. May form toxic heme-mefloquine complexes.
  • Toxicity – well tolerated at prophylaxis dose. Treatment dose may cause nausea, dizziness, nightmares, and fatigue. Seizures and acute psychosis are rare. Contraindicated in pxs w/ history of psychiatric disturbances and pregnant women.
  • Resistance is spreading rapidly.
20
Q 
Primaquine
Use
Mechanism
Toxicity
Resistance
A
  • Use – DOC for treatment of latent tissue schizonts that are characteristic of chronic P vivax and P ovale infections.
  • Mechanism – may be converted to electrophiles that generate ROS or interfere w/ electron transport. Marked gametocidal acitivity.
  • Toxicity – Methemoglobinemia. Contraindicated in pxs w/ G6PDH deficiency due to risk of hemolysis.
  • Some strains of P vivax are resistant
21
Q 
Chloroguanide
Use
Mechanism
MEtabolism
Toxicity
Resistance
A
  • Use – prophlyaxis, active against tissue schizonts, but also terminate clinical attacks. Must be used in combo w/ atovaquone.
  • Mechanism – prodrug converted to cycloguanil, which is a competitive inhibitor of Plasmodium bifunctional dihydrofolate reductase-thymidylate synthetase, thus inhibiting parasite DNA synthesis. Slow acting.
  • Metabolism – CYP2C activates, but 20% of Asians and Kenyans lack CYP2C so drug does not work.
  • Toxicity – none
  • Resistance caused by mutation in dihydrofolate reductase binding site that decreases drug affinity.
22
Q

Atovaquone
Use
Mechanism
Toxicity

A
  • Use – Prophylaxis and treatment of chloroquine-resistant malaria. Given in combo w/ chloroguanide to treat P falciparum. Does not work well alone.
  • Mechanism – Inhibitory analog of ubiquinone
  • Toxicity – vomiting / diarrhea can cause therapeutic failure due to inadequate absorption. Maculopapular rash in 20% of pxs.
23
Q 
Artemisinin
Source
Use
Mechanism
Semi-synthetics
A
  • Derived from Chinese wormwood plant. 10x more expensive than other drugs.
  • Use – DOC for malaria. Used in combo w/ other drugs that have a different mechanism to reduce resistance (artemisinin combo therapy, ACT)
  • Mechanism – endoperoxide bridge or “warhead” forms a complex w/ ferrous non-heme iron → toxic carbon-centered free radicals and alkylation of macromolecules.
  • Semi-synthetic derivatives include artemether and artesunate

FM3-2: Parasites, STDs, etc (11 decks)

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