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Pharmacology > Pharm of Protozoans and Helminths > Flashcards

Pharm of Protozoans and Helminths Flashcards

1
Q

what drugs are available for nematode infections?

A

benzimidazoles

Diethylcarbamazine

Ivermectin

Pyrantel pamoate

Doxycycline

anti-helminth

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2
Q

What are the types of Benzimidazoles?

A

Albendazole

Mebendazole

Thiabendazole

anti-helminth

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3
Q

MOA of Benzimidazoles

A

Binds beta-tubulin and inhibits polymerization of parasitic tubulin dimers into microtubules

other effects on the nematodes include - inhibition of mito fumerate reductase, decreased glucose transport causing depleted glycogen stores of larvae, uncoupling of ox-phos -> decreased energy production leads to parasite immobilization and death

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4
Q

Albendazole - PK and Adverse Effects

A

Benzimidazoles. poor absorption, distributes to CSF and hydatid cysts

hep metabolism w/ active metabolite, fecal excretion, half life 12 h

Adverse Effects - ab discomfort, diarrhea, rash, alopecia, dizziness

In high doses for Echinococcus Rx can cause hepatitis or myelosuppression

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5
Q

Albendazole - Therapeutic Uses

A

Broad Spectrum -
Intestinal nematodes,
Hydatid disease (echinococcus - cestode),
Neurocysticercosis
Lymphatic filariasis (combination with diethylcarbamezine or ivermectin)

high cure rates – Ascariasis (hookworm), Trichuras trichuria (whipworm), Necator, Ancylostoma, Enterobius vermicularis (pinworm), Trichinella spiralis (undercooked meat)

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6
Q

Mebendazole

A

Benzimidazoles, anti-helminthic, poor oral absorption, widely distributed with hepatic metabolism

fecal excretion, half life is 3 hours - does the job in the intestines as long as it’s in the intestines

Active against Intestinal nematodes only

Adverse effects are abdominal pain, distention, diarrhea in cases of massive infection&raquo_space; expulsion of GI worms

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7
Q

Thiabendazole

A

Benzimidazoles, anti-helminthic, rapidly absorbed

extensive hepatic metabolism with renal excretion of glucuronide and sulfate metabolites

short half life

Broad Spectrum - therapy is limited by toxicities

Used for cutaneous larva migrans - eruption of nematodal larvae

used for strongyloidiasis in the past but Ivermectin is now first line

Adverse effects in 50% + pts - diarrhea, headache, tinnitus, hypotension, bradycardia, allergic manifestations, crystallurai and abnormalities in liver function.

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8
Q

Diethylcarbamazine (DEC) - PK and MOA

A

Anti-helminthic, nematodal

oral with wide distribution, hepatic metabolism and renal excretion.

MOA in adult unknown, action against microfilaraie - inhibition of arachidonic acid metabolism on the surface of microfilariae, this causes the nematode to be immobile and more susceptible to the host immune response

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9
Q

Therapeutic Uses of Diethylcarbamazine (DEC)

A

Lymphatic filariasis: caused by Wuchereria bancrofti, Brugia malayi/timori

One dose mass treatment with ivermectin/albendazole

Loa loa - microfilariae and adult filariae

Mansonella streptocirca (adult and micro-filariae)

contraindication in onchocerciasis

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10
Q

Adverse Effects of Diethylcarbamazine (DEC)

A

anti-helminthic,

Anorexia, nausea, headache, vomiting (high dose)

Bancroftian, brugian filiariasis - lymphangitis, swelling and lymphoid abscess

Loiasis - skin wheals, heavy infections with severe side effects (retinal hemorrhages and severe encephalopathy)

Mazzotti reaction when rx Onchocerciasis – from killing of microfilariae – intense itching, papular rash, enlarged tender lymph nodes, tachycardia, arthralgia and headache. Ocular lesions.

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11
Q

Ivermectin

A

Anti-helminthic, nematodal

Oral, doesnt cross BBB, hepatic meta, fecal excretion, half life 18hr

MOA - induces tonic paralysis of parasite musculature by binding to glutamate-gated Cl- ion channels in invertebrate muscle and nerve cells ↑ permeability of the cell membrane causing hyperpolarization leads to the paralysis and death of the nematode

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12
Q

Ivermectin - Activity and Uses

A

Activity: anti-helminthic,

  • Microfilaria (not adults) of W. bancrofit, B. malayi, L. loa, Mansella ozzardi
  • A. lumbricoides, S. stercoralis, cutaneous larva migrans

Drug of choice for -

Onchocerciasis: aborts microfilariae from gravid female, decreases transmission

Strongyloidiasis: as effective as thiabendazole and better tolerated. More effective than albendazole

Contraindicated in meningitix

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13
Q

Adverse Effects of Ivermectin

A

Generally well tolerated

Mazzotti-like reaction due to killing of microfilariae but usually limited to mild itching and tender, swollen lymph nodes

seldom exacerbates oculra lesions

Loa encephalopathy with high loa microfilariae burden

not known to be safe in pregnancy or breast feeding

interacts with GABA drugs - benzos, barbituates and valproic acid

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14
Q

Doxycycline

A

Antibacterial that fights Wolbachia species (similar to Rickettsia) within filarial nematodes — Wuchereria and Oncocerca

Doxycycline x6 weeks causes sterility of the adult female

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15
Q

Pyrantel pamoate

A

anti-helminthic,

Treatment of pinworms caused by Enterobius vermicularis - nematodes - anti-helminthic

Poor oral absorption; Safe and effective

mechanism - Depolarizing NM blocking agent, activation of cholinergic nicotinic R in somatic muscles of nematodes causes a depolarizing blockade and paralysis

no marked effect on neuromuscular function

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16
Q

Praziquantel - Activity

A

anti-helminthic,

used against cestodes and flukes
- flat, segmented bodies that attach to host intestinal walls with hooks/suckers

Trematodes, parasitic flatworms (flukes)

Intestinal Cestodes - Taenia saginata (beef), Taenia solium (pork), Diphyllobothrium latum (broad fish), Hymenolepis nana (dwarf tapeworm)

Intestinal Trematode - Fasciolopsis buski (giant)

trematode tissue infections - Paragonimus westermani, Schistosoma mansoni (blood fluke), Schistosoma japonicum, and Schistosoma haematobium

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17
Q

Praziquantel - PK and MOA

A

anti-helminthic,

Oral; good bioavailability; CSF concentrations ~14-20% of plasma

plasma protein binding; extensive hepatic first-pass metabolism with renal excretion, short half life (1 - 4 hours)

MOA - increase cell permeability to Ca2_ whih increase muscular activity and causes spastic paralysis, causes detachment from blood vessel walls.

Damage exposes tegumental antigen - immune system activate

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18
Q

Adverse Effects of Praziquantel

A

anti-helminthic,

Generally safe - Abdominal pain, nausea, diarrhea, headache, dizziness, drowsiness - transient

Parasite destruction occasionally causes: fever, pruritus, urticaria, rashes, arthralgia, myalgia

In neurocysticercosis: there can be inflammatory reactions - meningismus, seizures, mental changes and CSY pleocytosis, delayed onset and last 2-3 days. Rx - analgesics and anticonvulsants

Safe in pregnancy

interacts with CYP3A4 induces

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19
Q

Triclabendazole

A

anti-helminthic

Drug of choice for the treatment of chronic fascioliasis in adults and children

Efficacy:
• Single dose
• Absence of adverse effects
• High tolerability
• High cure rate
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20
Q

What drugs are used to treat amoebiasis, giardiasis, and other intestinal protozoan infections?

A

Metronidazole - Tinidazole - Secnidazole:

Paromomycin

Nitazoxanide

21
Q

Metronidazole - PK and MOA

A

Oral, 100% bioavailability
-can be given IV, intravaginally, topically

wide distribution including abscessess, hepatic metabolism (oxidation and glucuronidation) with renal excretion.

MOA - radical-mediated killing, electron donated from ferredoxin, the drug is also catalytically recycled

22
Q

Resistance Mechanisms of Metronidazole

A

Impaired oxygen scavenging capabilities

An increase in local oxygen causes decreased reduction of metronidozole

leading to decreased PFOR and ferrodoxin levels

23
Q

Activity and Therapeutic Uses of Metronidazole

A

Kills E. hystolytica trophozoites - but not cysts

extra-intestinal infections - well absorbed + requires a liminal amebicide for full infectious Rx

Useful against - 
Amoebiasis
Trichomoniasis
Giardiasis
Bacterial infections - anaerobic bacteria
24
Q

Tinidazole and Secnidazole

A

Tinidazole - amoebiasis, giardiasis, trichomoniasis: better tolerated

Secnidazole - bacterial vaginosis

25
Side Effects of Metronidazole
generally well tolerated common are headache, nausea, dry mouth, and a metallic taste occasional - vomiting, diarrhea, and abdominal distress, thrush, dark urine dizziness, vetigo, rarely - encephalopathy, convulsions Paresthesias of extremities Disulfiram-like effect Avoid in pregnancy in first semester
26
Paromomycin - PK, MOA, AE's
Luminal Antiamoebic Agent PK: oral; poor absorption, 100% fecal excretion MOA - protein synthesis inhibitor Generally safe but can cause bowel lesions, ototoxicity and nephrotoxicity
27
Paromomycin - Uses
Use - Acute and chronic intestinal amoebiasis after metronidazole treatment, E. histolytica Adidtional uses against Dientamoeba fragilis, cryptosporidiosis, giardiasis, cutaneous leishmaniasis and resistant trichomoniasis
28
Treatment of African trypanosomiasis
Melarsoprol (trivalent arsenical) Eflornithine (fluorinated ornithine analog) Suramin (polyanionic compound) Pentamidine (aromatic diamidine)
29
East African sleeping sickness
Trypanosoma brucei rhodesiense Tanzania. Uganda, Malawi, Zambia Melarsoprol - Meningoencephalitic stage Suramin - Hemolymphatic stage
30
West African sleeping sickness
Trypanosoma brucei gambiense Central and West Africa, Democratic Republic of Congo, Angola, Sudan, Central African Republic, Chad and northern Uganda Eflornithine - Meningoencephalitic stage Pentamidine - Hemolymphatic stage
31
Melarsoprol
East African sleeping sickness - Meningoencephalitic stage Melarsen oxide reacts with sulfhydryl groups on biomolecules - inactivates Slow IV infusion, intensely irritating, half like 35 h Adverse Effects - reactive encephalopathy (5-10% pts, 50% fatal), cerebral edema, seizures, coma, death - Myocardial toxicity, renal, hepatic dysfunction, agranulocytosis, hypersensitivity reaction
32
Suramin
East African sleeping sickness - Hemolymphatic stage Reversibly complexes with various enzymes essential to parasite energy metabolism IV (not absorbed), no CNS, 5 doses in 21 days Adverse effects - Renal toxicity, Hypersensitivity reaction, hypotension, shock, (from the dying parasites)
33
Eflornithine
West African sleeping sickness - Meningoencephalitic stage Suicide inhibitor of ornithine decarboxylase, inhibits polyamine synthesis, cell growth and differentiation IV every 6h x 14d, half life 3h Adverse Effects - myelosupprion, ototoxicity, diarrhea, nausea, vomiting
34
Pentamidine
West African sleeping sickness - Hemolymphatic stage Interference with DNA, RNA, protein synthesis and metabolism IV and IM, not absorbed, No CNS. Half life 5-8 hours ``` Adverse Effects - Nephrotoxicity; hypoglycemia; severe hypotension; QT interval prolongation; anemia, neutropenia, thrombocytopenia; GI effects ```
35
Treatment of Chagas disease
AMERICAN trypanosomiasis Nifurtimox Benznidazole
36
Nifurtimox
Oral; hepatic CYP metabolism, renal excretion MOA - reduced by microbe enzyme to nitro anion radicals and superoxide radicals causes membrane injury, enzyme inactivation and DNA damage Better effiicacy in acute disease Adverse effects - nausea, vomiting, polyneuropathy, headache, dizziness, vertigo, insomnia
37
Benznidazole
Oral; hepatic metabolism, excreted in urine/feces, half life 12 h MOA - activated by trypanosomal nitroreductases making reactive superoxide radicals causing parasitic proteins and DNA Better effiicacy in acute disease Adverse Effects - generally well tolerated but pruritic rash and abdominal pain is sometimes experienced
38
treatment of leishmaniasis
Sodium Stibogluconate / Meglumine Antimoniate Amphotericin B Miltefosine
39
Leishmaniasis
spread by sand fly, obligate intra-macrophage protozoa visceral, cutaneous or mucocutaneous leishmaniasis general chemotherapy - first line: Sodium Stibogluconate [Pentosam]* and Meglumine antimoniate alternatives - Pentamidine, Amphotericin B, Miltefosine*, Paromomycin + gentamicin
40
Sodium Stibogluconate / Meglumine Antimonate
Used first like for leishmaniasis Pentavalent antimonial Sb5+ converted into Sb3+ species - kills amastigotes in macrophages, by inhibiting trypanothione reductase I.V. for treatment of cutaneous and visceral disease cardiac toxicity; hepatotoxicity; pancreatitis; renal toxicity; muscle aches
41
Amphotercin B
Leishmaniasis Rx (and probably more) Complexes with sterol precursors in Leishmania cell and forms pores I.V. for treatment of visceral leishmaniasis Adverse Effects - Infusion reactions, nephrotoxicity, anemia and anaphylaxis
42
Miltefosine
oral; visceral and cutaneous disease; vomiting, diarrhea, ↑ transaminases (reversible); MOA undefined not starred
43
Pentamidine:
I.M. for cutaneous leishmaniasis alternate for visceral disease hypotension; tachycardia; GI Sx; sterile abscesses; and pancreatic, liver, and kidney abnormalities
44
treatment of toxoplasmosis
Spiramycin Pyrimethamine + Atovaquone or Dapsone or Clindamycin Toxoplasma gondii: cats are natural hosts, Acute, self-limiting illness, immunocompromised people at risk (encephalitis), also congenital toxoplasmosis
45
Spiramycin
(<18 weeks gestation) acute acquired infection to prevent transmission to the fetus
46
Treatment of cerebral toxoplasmosis
AIDS patients Pyramethamine + sulfadiazine + folinic acid (leucovorin) Clindamycin or atovaquone may be substituted if sulfonamide Primary prophylaxis: trimethoprim-sulfamethoxazole
47
Babesiosis:
Tick-borne zoonosis: erythrocyte invasion protozoan Clindamycin + Quinine Atovaquone + Azithromycin (fewer AEs)
48
Balantidiasis:
− Fecal-oral transmission: intestinal parasite | − Tetracycline

Pharmacology (23 decks)

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