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Pharm S2015 > Antiparasites > Flashcards

Antiparasites Flashcards

1
Q

Antamebics

A
  • Luminal: Act on parasite in bowel lumen
  • Systemic: Active both in intestinal wall and liver
  • Mixed: Active against both luminal & systemic disease
    • metro & tinidazole
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2
Q

Metronidazole

A
  • Amebicide of choice for treating invasive amebiasis
  • Patients should receive a luminal amebicide in addition after treatment with metronidazole

Other Clinical Applications

  • Giardia lamblia
  • Trichomonas vaginalis
  • Anaerobic cocci
  • Anaerobic Gram-negative bacilli
  • Combination regimens for H.pylori eradication

MOA

  • Once absorbed, metronidazole is non-enzymatically reduced by reacting with reduced ferredoxin
  • This reduction causes the production of cytotoxic compounds
  • The cytotoxic compounds bind to proteins & DNA, resulting in unstable molecules and cell death

PK

  • Oral
  • Well distributed (inc. vaginal & seminal fluids, saliva, breast milk & CSF)
  • Undergoes hepatic oxidation & glucuronidation (CYP P450’s)
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3
Q

Metro - Adverse

A
  • GI distress
  • Disulfiram-like reaction (avoid alcohol intake) • Unpleasant metallic taste
  • Oral moniliasis
  • Dark coloration of urine
  • Leukopenia, dizziness, ataxia.
  • Safety in pregnancy NOT established
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4
Q

Tinidazole

A
  • 2nd generation nitroimidazole
  • Similar to metronidazole but better tolerated and has shorter treatment course

Clinical Applications

  • Amebiasis
  • Amebic liver abscess
  • Giardiasis
  • Trichomoniasis
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5
Q

Tinidazole - Adverse

A

Same as metronidazole but reports indicate shorter duration of effects with tinidazole

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6
Q

Luminal antiamebics

A
  • Diloxanide furoate
  • Iodoquinol
  • Paromomycin
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7
Q

Diloaxanide furoate

A
  • Used as sole agent for treatment of asymptomatic amebiasis
  • Converted in gut to diloxanide freebase active form
  • Adverse Effects: Mild (GI distress)
  • Not currently available in US – however remains luminal amebicide of choice
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8
Q

Iodoquinol

A
  • Orally active against luminal trophozoite and cyst forms of E.histolytica
  • Used as an alternative to diloxanide furoate for mild- severe infections
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9
Q

Iodoquinol - Adverse

A
  • Rash, diarrhea, dose-related peripheral neuropathy
  • Long term use should be avoided (due to risk of optic neuritis)
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10
Q

Paromomycin including Adverse

A
  • Aminoglycoside antibiotic
  • Effective only against luminal forms of E.histolytica and tapeworm
  • Sometimes used with tetracyclines for mild intestinal disease
  • Alternative agent for cryptosporidiosis in AIDS patient
  • Amebicidal (causes cell membranes to leak)
  • Interferes with bacterial protein synthesis (binds to 30S ribosomal subunits)
  • Reduces intestinal flora population

Adverse Effects

  • GI distress & diarrhea
  • Systemic absorption may lead to headaches, dizziness, rashes and arthralgia
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11
Q

Systemic antiamebics

A
  • Chloroquine
  • Emetine
  • Dehydroemetine
  • Useful for treating liver abscesses or intestinal wall infections
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12
Q

Chloroquine

A
  • Used in combination with metronidazole & diloxanide furoate
  • **Indication: **severe intestinal infection w E. Histolytica
  • MOA: Eliminates trophozoites in liver abscesses
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13
Q

Emetine and Dihydroemetine

A
  • Backup drugs for treatment of severe intestinal or hepatic amebiasis
  • Used in combination with a luminal agent
  • MOA: Inhibit protein synthesis by blocking ribosomal movement along messenger RNA

PK

  • IM or SC
  • Concentrate in liver (persists for 1 month)
  • Slowly metabolized & eliminated
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14
Q

Emetine and Dihydroemetine - Adverse

A
  • Pain at site of injection
  • Transient nausea
  • Cardiotoxicity
  • Neuromuscular weakness
  • Dizziness
  • Rash
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15
Q

Amebiasis Rx

A
  • Asymptomatic, intestinal infection: Diloxanide furoate
  • Mild-moderate intestinal infection: Metronidazole + diloxanide furoate
  • Severe intestinal infection: metro or tinidazole + diloxanide furoate
  • Hepatic abscess & other extraintestinal disease: Metronidazole or tinidazole + diloxanide furoate
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16
Q

Antihelminthics durgs

A
  • Nematode
  • Trematode
  • Cestode
  • In most cases broad spectrum agents cure or control most human worm infections
  • Some systemic infections only respond partially to antihelminthic drugs (cysticercosis, echinococcosis, filariasis, trichinosis)
  • Antihelminthic drugs can act either:
  • locally (to expel worms from GI tract) or,
  • systemically (to eradicate adult helminths or developmental forms)
17
Q

Benzimidazoles

A
  • Albendazole
  • Mebendazole
  • Thiabendazole
18
Q

Albendazole

A

Used in the treatment of cestodal infestations, such as cysticercosis (Taenia solium larvae) and hydatid disease (Echinococcus granulosis)

MOA

  • Inhibits microtubule synthesis & glucose uptake
  • ATP production is decreased resulting in worm immobilization and death

PK

  • Oral (erratically absorbed, enhanced by high-fat meal)
  • Extensive first-pass metabolism, including rapid sulfoxidation to active metabolite
19
Q

Albendazole - Adverse

A
  • Short course therapy (1-3 days) = mild & transient (headache, nausea)
  • Hydatid treatment (3 months) = risk of hepatotoxicity, agranulocytosis or pancytopenia
  • Treatment is associated with inflammatory responses to dying parasites in CNS (headache, vomiting, hyperthermia, convulsions, mental changes)
  • Contraindicated in pregnancy & children < 2y (FDA Category C)
20
Q

Mebendazole

A

Drug of choice in the treatment of infections by (will treat most infections):

  • Whipworm (Trichuris trichiura)
  • Pin worm (Enterobius vermicularis)
  • Hookworms (Necator americanus & Ancylostoma duodenale)
  • Roundworm (Ascariasis lumbricoides)

MOA

  • Inhibits formation of helminth microtubules
  • Irreversibly blocks glucose uptake
  • Affected parasites are expelled with feces

Pharmacokinetics

  • Oral (chewable) – nearly insoluble in aqueous solution, take with high-fat meal
  • Undergoes first-pass metabolism to inactive compounds
21
Q

Mebendazole - Adverse

A
  • Abdominal pain, diarrhea, headache, dizziness
  • Contraindicated in pregnancy (FDA Category C)
  • Use with caution in children < 2
  • Use with caution in patients with cirrhosis
22
Q

Thiabendazole

A

Effective in treatment of strongyloidiasis caused by Strongyloides stercoralis (threadworm), cutaneous larva migrans, and early stages of trichinosis

MOA: Affects microtubular aggregation

Pharmacokinetics

  • Oral
  • Nearly insoluble in H20
23
Q

Thiabendazole - Adverse

A
  • More toxic than other benzimidazoles
  • Dizziness, anorexia, nausea, vomiting
  • CNS disturbances (dizziness -> seizures)
  • Cases of erythema multiforme & Stevens-Johnson reported
  • Contraindicated in pregnancy (FDA Category C)
  • Should not be used in presence of liver or kidney disease
24
Q

Ivermectin

A

Drug of choice for the treatment of onchocerciasis (Onchocerca volvulus), cutaneous larva migrans & strongyloides

MOA

  • GABA agonist
  • Cl- influx increases leading to hyperpolarization of nerve /muscle cell. Death occurs due to paralysis of parasite

Pharmacokinetics: Oral (does not cross BBB)

25
Q

Ivermectin - Adverse

A
  • Mazotti-like reactions with onchoceriasis (fever, dizziness, somnolence, hypotension)
  • Contraindicated in pregnancy (FDA Category C)
  • Contraindicated in meningitis (may cross BBB)
  • Best to avoid concomitant use of ivermectin & other drugs that enhance GABAergic activity (eg, barbiturates, benzodiazepines)
26
Q

Piperazine

A

Alternative drug for treatment of pinworm & roundworm infections

MOA

  • GABA agonist
  • Expulsion of worm occurs by peristalsis

Contraindications: Patients with seizure disorders

27
Q

Pyrantel Pamoate including Adverse

A

Effective in treatment of infections by roundworms, pinworms and hookworms

MOA: Acts as a depolarizing, neuromuscular-blocker (causes persistent activation of parasite’s nicotinic receptors by release of acetylcholine & inhibition of cholinesterase)

PK: Poorly absorbed orally (exerts effects in intestinal tract)

**Adverse: **Mild (nausea, vomiting, diarrhea)

28
Q

Diethylcarbamazine

A

DOC for treatment of lymphatic filariasis, loiasis & tropical eosinophilia.

MOA: Immobilizes microfilariae & renders them susceptible to host defense mechanisms

**PK: **Oral (rapidly absorbed with meals)

29
Q

Diethylcarbamazine - Adverse

A
  • Most AE thought to be due to host responses following damage/death of parasite
  • Fever, malaise, rash, myalgias, arthralgias, headache
  • Leukocytosis (common)
  • Antihistamines or steroids can be coadministered
30
Q

Doxycycline - MOA

A
  • Tetracycline antibiotic.
  • Macrofilaricidal activity against Wuchereria bancrofti.
  • Also active against onchocerciasis
  • MOA: Acts indirectly by killing Wolbachia (intracellular bacterial symbiont of filarial parasites)
31
Q

Praziquantal

A

DOC for all forms of schistosomiasis & most trematode & cestode infections

Cysticercosis – albendazole is drug of choice (praziquantel has similar efficacy)

MOA: Increases permeability of cell membrane to calcium, causing contracture & paralysis of worm musculature, resulting in detachment of suckers from blood vessel walls.

**PK: **

  • Oral
  • Extensive first-pass metabolism (CYPs)
  • Inactive metabolites excreted via urine & bile
32
Q

Praziquantal - Adverse

A
  • Drowsiness, dizziness, malaise, anorexia & GI upsets
  • Drug interactions (CYP P450)
  • Contraindicated in pregnancy & nursing mothers (FDA Category B)
  • Contraindicated for treatment of ocular cysticercosis (destruction of organism may damage eye)
33
Q

Bithionol

A
  • Drug of choice for fasciolosis (sheep liver fluke)
  • Alternative drug for pulmonary paragonimiasis
  • MOA: Inhibition of helminth’s electron transport chain (probably)
34
Q

Niclosamide

A
  • 2nd line drug for treatment of most cestode infections
  • Use is uncommon due to excellent efficacy of praziquantel
  • No longer available in US

MOA

  • Inhibition of the parasite’s mitochondrial phosphorylation of ADP. Anaerobic metabolism may also be inhibited
  • Drug is lethal for cestode’s scolex & segments of cestodes but not for the ova

PK

  • Laxative is admin. prior to niclosamide (oral) to purge bowel of all dead segments in order to preclude digestions & liberation of ova (may lead to cysticercosis)
  • Alcohol should be avoided within 1 day of dose
  • Safety has not been established in pregnancy or children <2

Pharm S2015 (47 decks)

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