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BIOM 4090 > pharmacology of anti-parasite drugs > Flashcards

pharmacology of anti-parasite drugs Flashcards

1
Q

what are the two classes of parasites of people?

A
  1. Macroscopic parasites:
    - Taenia species (tapeworms) - Enterobius (pinworm)
    - Pediculus (head louse)
  2. Microscopic parasites:
    - Entamoeba (amebiasis)
    - Giardia (beaver fever)
    - Trichomonas (trichomoniasis)
    - Plasmodium (malaria) Prevention:
    To what extent can control be achieved without drugs ?
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2
Q

what is Taenia saginata and Taenia solium

A

Taenia saginata: beef tapeworm - by eating raw beef

Taenia solium: pork tapeworm - by eating raw pork

  • flat and segmented
  • live in river - will go with the flow until anchored to GI tract
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3
Q

what is the life cycle of Taenia saginata/Taenia solium?

A
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4
Q

info slide

A
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5
Q

what are the structures at the anterior end of tapeworm for attachment to wall of small intestine

A
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6
Q
A
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7
Q

what are cestocidal drugs?

A

cestodes = tapeworms

  1. praziquantel
  2. niclosamide
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8
Q

praziquantel pharmacokinetics and moa

A

Chemistry & pharmacokinetics:
- synthetic isoquinoline derivative
- systemic bioavailability ~80% after oral dosing within small intestine
Action: (exact mechanism unknown)
- binds to parasite integument → focal vacuolization
- influx of Ca2+ causes muscle contraction (in seconds)
- impaired function of hooks and suckers at anterior end:
→ paralysis, dislodgement, death

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9
Q

praziquantel clinical uses and adverse reactions

A

Clinical uses:
- effective against most cestode infections (drug of choice)
- safe and effective as single oral dose
- swallow without chewing (bitter taste → retching/vomiting)
Adverse reactions:
- mild, transient reactions = common (e.g. nausea, headache, abdominal discomfort)

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10
Q

niclosamide pharmacokinetics and moa

A

Chemistry & pharmacokinetics:
- salicylanilide derivative
- minimally absorbed from gastrointestinal (GI) tract
Action:
- rapidly kills scolex + segments of adult tapeworms
- mechanism of action:
* inhibition of mitochondrial anaerobic phosphorylation of ADP results in ↓ ATP production

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11
Q

niclosamide clinical uses and adverse reactions

A

Clinical uses:
- second-line choice for treatment of Taenia saginata and Taenia solium
- single oral dose effective
- cheap and readily available in many parts of world
Adverse reactions:
- minor GI complaints rarely encountered - nausea, vomiting, diarrhea

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12
Q

prevention of reinfection of Taenia saginata and Taenia solium

A
  • start cooking your beef
  • start cooking your pork
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13
Q

Life cycle of Enterobius vermicularis (pinworm)

A
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14
Q

what is Enterobius vermicularis transmission and clinical presentation?

A
  • most common nematode infection in temperate countries
    Transmission:
  • female parasite on perianal skin → pruritus
  • eggs → hands → ingestion
  • eggs sticky + can survive long periods in environment
  • contamination of nightclothes / bedding
  • eggs → wide dispersal in bedrooms / house
    Clinical presentation:
  • most frequent in school age children
  • most infections asymptomatic, high risk of reinfection
  • itching → irritability, incontinence, weight loss
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15
Q

how to minimize risk of infection of enterobius vermicularis and drug of choice for treatment?

A

Minimise risk of infection:
- personal hygiene – handwashing, fingernail cleaning, regular bathing
- keep bedrooms scrupulously clean + dust free
- bed linen / nightclothes – change and launder frequently
Treatment:
- Drugs of choice: mebendazole, pyrantel

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16
Q

mebendazole chemistry and pharmacokinetics and moa

A

Chemistry & pharmacokinetics:
- benzimidazole (broad spectrum activity against endoparasites)
- administered orally - less than 10% absorbed (want it in the gut)
- tablets should be chewed (maximized dispersion in GIT)
MOA:
- binds to β-tubulin (parasite specific):
* inhibits polymerisation to microtubules:
→ inhibits parasite motility, glucose uptake, cell division
- slow kill → expelled in feces (within day or two)
- efficacy varies with gastro-intestinal (GI) transit time (diarrhea decreases efficacy, transit time is quicker)

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17
Q

mebendazole clinical uses and adverse reactions

A

Clinical uses:
- approved for pinworms (+ roundworms, whipworms, hookworms)
- for pinworms – treat twice at 2-week interval
Adverse reactions:
- short-term therapy – nearly free of adverse effects (abdominal pain, nausea, diarrhea = infrequent)
- embryotoxic + teratogenic in animals – contraindicated in pregnancy

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18
Q

pyrantel chemistry and pharmacokinetics and moa

A

Chemistry & pharmacokinetics:
- tetrahydropyrimidine
- poorly absorbed from GI tract  activity within GI tract
Action:
- “nicotinic anthelmintic”
- acts selectively at neuromuscular junction of parasite on
nicotinic acetylcholine receptors:
→ release of acetylcholine + inhibition of acetylcholinesterase
→paralysis (very rapid paralysis of parasite)→ expulsion

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19
Q

pyrantel clinical uses and adverse effects

A

Clinical uses:
- approved for pinworms (+ roundworms, hookworms)
* narrower spectrum of activity than mebendazole
- for adult pinworms only – treat twice at 2-week interval
Adverse reactions:
- adverse effects = mild (rare for this particular drugs), transient: nausea, vomiting, diarrhea

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20
Q

what is pediculus capitis?

A

head louse - lays eggs on hair called nymph - needs blood from scalp

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21
Q

Life cycle of Pediculus capitis

A
  • entire life cycle on head
  • nymphs and adult lice feed on human blood
  • egg to 1st nymph = 8-9 days (for eggs to hatch)
  • egg to adult = 18-21 days (right in time for 2nd treatment)
  • survive <2 days away from scalp at room temperature
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22
Q

Pediculus capitis clinical presentation, transmission and epidemiology

A

Clinical presentation:
- itchy head – Note: many children = asymptomatic
- adult lice + eggs (nits) on hair
– most easily seen behind ears / back of neck
Transmission:
- mainly by direct head-to-head contact
- uncommon via combs, hairbrushes, hats etc
Epidemiology:
- most common in children in childcare and elementary schools
- not a sign of poor hygiene (affects everyone)
- all socioeconomic groups affected

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23
Q

how do you treat Pediculus capitis?

A
  1. Permethrin
  2. Malathion
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24
Q

Treatment of Pediculus capitis: what is permethrin moa and pharmacokinetics?

A
  1. Permethrin:
    - drug class = synthetic pyrethroid:
    – synthetic derivative of the insecticide pyrethrin (applied topically)
    – obtained from Chrysanthemum plant Action and pharmacokinetics:
    - causes voltage-gated sodium channels to remain open → membrane depolarisation → rapid paralysis
    - absorption through skin = minimal
    - rapidly degraded to inactive metabolites in liver (typically pretty safe)
    - resistance to permethrin in ~50% head lice in USA
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25
Q

what are some suggestions when treating Pediculus capitis?

A
  • neither drug is significantly ovicidal (i.e. do not kill eggs)
  • more than one application is typically required – retreat at
    10-11 day interval
  • treat bed mates at the same time
  • examine and treat infested household / close contacts at the same time
  • manual removal of nits after successful treatment is helpful, e.g. with fine-toothed nit comb
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26
Q

Treatment of Pediculus capitis If living lice on scalp 24+ hours after treatment?

A

– incorrect use of drug
– hatching of lice eggs after treatment
– reinfestation
– drug resistance
Adverse reaction:
- itching/mild burning sensation of scalp → inflammation of skin in response to agents – can persist for many days after lice are killed

27
Q

what are cestocidal drugs?

A

drugs used to treat tapeworms

28
Q

what are microscopic parasites?

A
  • Entamoeba (amebiasis) - causes potential lethal disease (intestinal disease)
  • Giardia (beaver fever) - intestinal disease very closely related to Entamoeba just not lethal
  • Trichomonas (trichomoniasis)
    treatment for all three is similar, trichomoniasis means they have infection and disease
29
Q

what are antiprotozoal drugs?

A
  • Protozoa = eukaryotes:
  • metabolic processes more similar to those of human host than prokaryotic bacterial pathogens
  • less easily treated than bacterial infections
  • May cause significant toxicity in host – especially cells with high metabolic activity
30
Q

what is amebiasis?

A

Infected with this parasite but they also got the disease (intestinal disease)
Entamoeba histolytica - most common to kill you
- 500 million people infected globally (W.H.O.)
- asymptomatic (can affect other people) ↔ diarrhea ↔ bloody diarrhea
- 110,000 deaths per year globally
- more common in poor socioeconomic communities

31
Q

Life cycle of Entamoeba histolytica and the clinical manifestations of infection in people

A
32
Q

Entamoeba histolytica
Clinical presentations

A

Clinical presentations:
- asymptomatic intestinal infection
- mild to moderate colitis (present with diarrhea)
- severe intestinal infection (dysentery - fresh blood in feces)
- ameboma (pseudotumoral lesion)
- liver abscess / other extra-intestinal infection

33
Q

Chemotherapy for E. histolytica - Amebicidal drugs

A

a) Luminal amebicides (only against cysts and throphs in the lumen):
→ parasites in bowel lumen
b) Systemic amebicides (don’t get rid of intestinal infection):
→ parasites in intestinal wall & liver - can go elsewhere in the body
c) Mixed (luminal and systemic) amebicides:
→ parasites in bowel lumen, intestinal wall & liver

34
Q

Mixed amebicide - metronidazole is the choice for what?

A

Mixed amebicide of choice for Entamoeba histolytica - kills trophozoites, not cysts
Also extensive use in treatment of:
- Giardia lamblia
- Trichomonas vaginalis
- anaerobic cocci
- anaerobic gram-negative bacilli
- pseudomembranous colitis ↔ Clostridium difficile

35
Q

metronidazole chemistry and pharmacokinetics

A
  • nitroimidazole
  • administered orally – readily absorbed:
  • extensive tissue distribution ↔ simple diffusion
  • therapeutic levels in vaginal and seminal fluids, saliva,
    cerebrospinal fluid
  • metabolism ↔ hepatic oxidation by mixed-function oxidase, then glucuronylation
  • metronidazole + metabolites excreted in urine
  • rate of plasma clearance ↓ if impaired liver function
  • simultaneous treatment with inducers of hepatic mixed- function oxidase (e.g. phenobarbital) → enhanced metabolism
  • drugs that inhibit hepatic mixed-function oxidase (e.g. cimetidine) → prolonged excretion
36
Q

metronidazole moa and adverse effects

A

Mechanism of action:
- some anaerobic protozoal parasites – lack mitochondrial activities for generating ATP + disposing of electrons
- instead:
* ferredoxin-like, low redox potential, electron-transport
proteins:
→ can transfer electrons to nitro groups of metronidazole → cytotoxic reduced products (bind to DNA + proteins)
Adverse effects (high dose most likely to see side effects):
- nausea, vomiting, headache, abdominal cramps, metallic taste in mouth – all occur commonly (take with food)
- nausea & vomiting if alcohol ingested simultaneously
- mutagenic in bacteria:
* best avoided in pregnant or nursing women

37
Q

metronidazole clinical uses

A

Amebiasis (E. histolytica):
- drug of choice for treatment of diarrhea/dysentery
- not reliably effective for luminal parasites
* must be used with luminal amebicide:
→ iodoquinol (unknown mechanism of action)
→ paromomycin (not as commonly used) – aminoglycoside

38
Q

what are luminal amebicides used for and what is the drug of choice for its infection?

A

Used:
(i) after treatment of invasive intestinal or extra-intestinal amebic disease
(ii) for treatment of asymptomatic infections (for travel)
Iodoquinol:
- drug of choice for asymptomatic luminal infections
- active against luminal stages (trophozoites + cysts)
- side effects = rash, diarrhea, dose-related peripheral neuropathy (including rare optic neuritis)
- long-term use should be avoided

39
Q

what are metastatic infections

A

(usually hepatic abscesses)
- need to kill parasites within liver abscess + intestinal wall + intestinal lumen
- high dosage of metronidazole used to eliminate trophozoites in liver abscess & intestinal wall (not gut lumen)
- followed by iodoquinol:
* to treat intestinal infection + prevent further
amebic liver abscesses

40
Q

Life cycle of Giardia lamblia

A
  • most common intestinal parasitic infection of people
  • no tissue development
41
Q

what is Giardia lamblia (“beaver fever”) and the drug of choice for its infection?

A
  • two life-cycle stages (i) trophozoite (ii) cyst
  • infection ↔ ingestion of cysts: usually in water
  • people-specific and zoonotic genotypes (animal infections wont infect people)
  • many infections = asymptomatic, severe diarrhea can occur
    Drug of choice = metronidazole:
  • dosage much lower than for amebiasis – better tolerated
  • treatment typically not used for asymptomatic infections – self clearance
  • only treat giardia if your sick completely different from the other one because it is deadly
  • can induce resistance
  • very seasonal late summer early fall - when we are out and about, children under 10 are most at risk and 20-39 years of age - most likely to be travelling inc infection
42
Q

Risk factors for Giardia infection in humans:

A

– Ingesting contaminated drinking water* (ppl travelling often drink unfiltered water)
– Children in child care settings
– Close contact with infected persons
– Swallowing contaminated recreational water (e.g. pools) – Taking part in outdoor activities (e.g. camping)
– Contact with infected animals – Men who have sex with men

43
Q

what is Trichomonas vaginalis and life cycle

A

Parasites reside in:
- female lower genital tract
- male urethra + prostate
Does not have cyst form - does not have environmentally resistant form
- Trophozoite replicates by binary fission
- Does not survive in external environment

44
Q

how does Trichomoniasis affect men and women and how is it treated?

A
  • one of most common sexually transmitted diseases, in North America >8 million new cases/year
    women = asymptomatic ↔ highly symptomatic
  • vaginal discharge
  • vulvar itching
  • discomfort during urination, occasionally dysuria
    men = usually no signs or symptoms
  • urethral discharge, burning sensation post urination
    Treatment:
  • metronidazole = drug of choice:
  • single and multiple dose regimens
  • single dose typically more effective ↔ compliance
  • metronidazole-resistant infections → treatment failure - repeat treatment at higher doses
  • systemic treatment preferred to topical therapy ↔ multifocal nature of infection
  • simultaneous treatment of sexual partner = important
45
Q

Should people with asymptomatic Entamoeba histolytica infections be treated?

A

yes - they can become sick and this can kill unlike other parasites

46
Q

Should people with asymptomatic Giardia lamblia infections be treated?

A

no - usually self clearing, we dont wanna over use metronitozole bc it is broad spectrum and can cause resistance

47
Q

Should asymptomatic Trichomonas vaginalis infections be treated?

A

yes - unknowling pass it onto others and readily transmissable
and can inc susceptibility to other sti’s

48
Q

Blood smear - Plasmodium falciparum

A

causes malaria

49
Q

Global impact of malaria

A
  • Endemic (risk) in 106 countries
  • Approximately 0.5 billion people infected each year
  • > 1 million people die every year:
  • most under the age of 5 years
  • mostly within Africa
  • In Africa, one child dies every 30 seconds
  • In Zambia, ~20% of babies do not live to see their fifth birthday because of malaria
  • Disease of poverty (easily preventable though lack financial)
50
Q

what is malaria and ist life cycle?

A
  • Plasmodium falciparum (nastiest of them), Plasmodium vivax,
    Plasmodium malariae, (Plasmodium ovale)
  • P. falciparum → most serious disease + death
  • Drug resistance = major prophylactic and therapeutic problem

Life cycle:
Note: Only erythrocytic parasites (damage to rbc is what makes people sick not anything else) → clinical illness

51
Q

Falciparum malaria Clinical disease:

A
  • incubation period generally 9-14 days
  • headache, pain in back and limbs
  • anorexia, nausea
  • fever, chills
  • anemia(common in young children - they dont have as many rbc as we do)
  • cerebral malaria = severe disease
  • usually ill for 4-5 days with fever - can be dead in 5 days very quick
  • slowly lapse in to coma → +/- convulsions * mortality = ~15-20%
52
Q

Plasmodium life cycle

A
53
Q

malaria - drugs that eliminate:

A

drugs that eliminate:
a) liver stages = tissue schizonticides (drug kills parasite that is asexually dividing in liver)
b) Erythrocytic stages = blood schizonticides (drug kills parasite that is asexually dividing in rbc)
c) sexual stages = gametocytes

Effective chemoprophylactic agents (what you give ppl to stop from getting sick):
* kill erythrocytic parasites before grow in numbers → disease

54
Q

what is the treatment of people with clincial malaria?

A
  1. P. falciparum + P. malariae:
    - one cycle of multiplication in liver (then leaves liver to rbc):
    * liver infection ceases in less than 4 weeks
    - elimination of erythrocytic parasites cures infection
  2. P. vivax + P. ovale:
    - dormant hepatic stage (hypnozoite) - not killed by most drugs (some parasites get dormant in liver not good)
    - must eliminate both erythrocytic + hepatic parasites
55
Q

how do you prevent malaria?

A

Counselling of people:
- ↑ resistance of parasites to drugs
- no chemoprophylactic regimen is 100% protective
- prevent mosquito bites:
* insect repellents
* insecticides
* appropriate clothing
* bed nets, ideally
impregnated with insecticide, e.g. permethrin

Chemoprophylaxis recommendations (C.D.C.):
- chloroquine – if only chloroquine-S parasites
- mefloquine – most malarious areas
- doxycycline – if high prevalence of multidrug-resistant falciparum malaria

56
Q

how is permethrin used to prevent malaria?

A
  • Synthetic version of natural insecticide (see head lice)
  • Used on nets as mosquito repellent + insecticide
  • Residual activity for 2 weeks to 6 months
  • In environment, binds to soil and biodegraded in 1-20 weeks
  • ~5.5 lives can be saved each year for every 1000 children protected with insecticide-treated bed nets
57
Q

what is the clinical uses and pharmacokinetics of chloroquine and what happens with a parasite in rbc

A

Clinical uses – Drug of choice for:
- chemoprophylaxis IF chloroquine-S parasites in area
* e.g. Caribbean, Central America west of Panama canal
* taken weekly per os
- treatment of – chloroquine-S Plasmodium falciparum

Pharmacokinetics:
- synthetic 4-aminoquinoline – for oral use
- rapidly absorbed and distributed to tissues * blood schizonticide
- no activity against liver parasites
- dealkylated by hepatic mixed-function oxidase system (highly metabolized by liver)
* parent drug + metabolites → urine
Parasite in red blood cell:
- digests host hemoglobin →
(i) essential amino acids
(ii) heme = toxic to parasite
- polymerizes heme → hemozoin
* sequestered in food vacuole

58
Q

chloroquine moa

A

unclear, but:
- drug concentrated in parasite’s acidic food vacuole
- prevents polymerization of heme (by binding to heme) into hemozoin
- oxidative damage → lysis of parasite + red blood cell

59
Q

chloroquine resistance and adverse effects

A

Resistance:
- very common in P. falciparum (e.g. Africa, Asia, South America)
- mutations in membrane transporter thought to be responsible
Adverse effects:
- minimal at low doses for chemoprophylaxis
- nausea, vomiting, blurred vision – higher doses
- dosing after meals ↓ adverse effects

60
Q

mefloquine clinical uses and resistance?

A

Clinical uses:
- recommended chemoprophylactic drug in areas with: - chloroquine-R Plasmodium falciparum
- taken weekly per os
- treatment of – chloroquine-R Plasmodium falciparum
Resistance:
- uncommon except in regions of Southeast Asia with high rates of multidrug resistance
- associated with resistance to quinine and halofantrine, not chloroquine

61
Q

mefloquine pharmacokinetics and moa

A

Pharmacokinetics:
- synthetic 4-quinoline methanol – chemically related to quinine
- given orally – well absorbed
- extensive distribution in tissues – eliminated slowly
Action:
- blood schizonticide – P. falciparum
- no activity against hepatic stages or gametocytes
- mechanism of action – concentrated in parasite by unknown mechanism
* may inhibit heme polymerization
* final result = membrane damage

62
Q

mefloquine adverse reactions and cautions

A

Adverse reactions (toxicity a concern):
Weekly dosing for chemoprophylaxis:
- neuropsychiatric toxicities – much publicity
- nausea, vomiting, dizziness
- sleep and behaviour disturbances
- frequency of serious adverse effects no higher than other anti-malarials ?
Cautions:
- contraindicated – history of epilepsy, psychiatric disorders
Note: risks of mefloquine use must be balanced with risk of contracting falciparum malaria

63
Q

doxycycline uses

A

Clinical uses:
- standard chemoprophylactic drug in areas of:
* Southeast Asia with multidrug-R parasites
(including mefloquine-R)
* administered daily per os
- for treatment – should not be used as a single agent as slow action:
* commonly used for treatment of P. falciparum in conjunction with quinidine or quinine:
- allows shorter + better tolerated course of these drugs

64
Q

doxycyline action and adverse effects

A

Action:
- inhibits protein synthesis – as in bacteria
- blood schizonticide
- not active against liver stages
Adverse effects:
- infrequent gastrointestinal symptoms
- photosensitivity

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