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Yr 2 Gastrointestinal > Wk 1 - Pharmacology: Anti-Malarial Drugs > Flashcards

Wk 1 - Pharmacology: Anti-Malarial Drugs Flashcards

1
Q

What is malaria?

A

Febrile illness in which circulating red cells are haemolysed by repeated attacks of protozoan parasites (Plasmodium spp.)

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2
Q

What organism causes most malaria cases and almost all malaria-related deaths?

A

Protozan parasite ‘plasmodium falciparum’

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3
Q

List the different Plasmodium species that cause malaria.

A
  1. Falciparum
    • Most malignant tertian malaria
    • ‘Blackwater fever’
    • 50% of cases, 95% of deaths
  2. Vivax/ovale
    • Moderate, ‘benign’ tertian
    • Dormant liver infections
  3. Malariae
    • Mild, quartan
    • Long-term dormant liver parasite
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4
Q

Briefly describe the life cycle of the malaria parasite.

A
  1. Malaria infection begins when an infected female Anopheles mosquito bites a person, injecting Plasmodium parasites, in the form of sporozoites, into the bloodstream.
  2. The sporozoites pass quickly into the human liver (do not hang in circulation so cannot be attacked by immune system).
  3. The sporozoites multiply (x10-40K) in the liver cells over the next 5-12 days, causing no symptoms.
  4. In the bloodstream, the merozoites invade red blood cells (erythrocytes) and multiply again (x10-20 fold) until the cells burst.
  5. Then they invade more erythrocytes. This cycle is repeated, causing fever each time parasites break free and invade blood cells.
  6. Small leftover from the RBCs block vessels + other RBCs become gametocytes, which are taken up by other mosquitos then spread further to other humans.
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5
Q

What’s the difference between tertian and quartan malarias?

A
  • Tertian: fever is on FIRST and THIRD days (every TWO days)
  • Quartan: fever is on FIRST and FOURTH days (every THREE days)
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6
Q

List the 4 stages of malaria (p.vivax).

A
  1. Premonitory: lassitude (ie tiredness and fatigue)
  2. Cold stage: shivering, 15-60 mins
  3. Hot stage: fever, 2-6 hours
  4. Sweating: exhausted sleep, 2-10 hours

P.falciparum -

  • Fever, 16-36 hours
  • Renal failure
  • Cerebral malaria -> coma
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7
Q

What are the ABCDs of malaria prevention?

A
  • Awareness: know the risks
  • Bites by mosquitoes: prevent or avoid
  • Comply with Chemoprophylaxis
  • Diagnose breakthrough malaria swiftly
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8
Q

How do you prevent malaria? (nb this is related to places like the UK - mainly people TRAVELLING not people living in countries with high levels of malaria).

A

Preventative measures: No adverse effects, but low efficacy!

  • Lifestyle:
    • Air-conditioned hotel or camping?
    • Dusk & dawn exposure, stagnant water
  • Barriers:
    • Clothing
    • Mosquito netting (beds, windows/doors)
    • Skin repellent (DEET)
  • Insecticides:
    • Knock-down sprays
    • Room repellents / insecticides (permethrin)
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9
Q

What are the different ‘types’ of chemoprophylaxis?

A
  • Causal (True) prophylaxis:
    • prevent liver infection (not possible to do this practically)
  • Clinical prophylaxis:
    • suppress blood parasites until risk of re-infection from liver is low (what we actually do)
  • Radical cure:
    • eliminate existing liver infection
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10
Q

When are clinical prophylaxis usually given?

A
  • 2-3 weeks before travel
  • During malaria exposure
  • 4 weeks after return (most typical approach)
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11
Q

What are schizonticides?

A

Group of drugs used in prophylaxis ‘treatment’ of malaria

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12
Q

List the different prophylaxis drug groups used in malaria.

A
  1. Rapid-acting blood schizonticides e.g. quinine, chloroquine and mefloquine
  2. Slow-acting blood schizonticides e.g. folate inhibitors, proguanil and pyrimethamine
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13
Q

What are quinine, chloroquine and mefloquine?

A

Rapid-acting blood schizonticides

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14
Q

What is the mechanism of action of rapid-acting blood schizonticides?

A

Mechanism of action: not entirely clear!

  • Bind to haemin (Hb breakdown product)
  • Concentrated 100-fold in infected RBCs
    • Intercalation in plasmodial DNA?
    • Increase in lysosomal pH of malarial parasite so stop them from digesting RBC?
  • These drugs do NOT kill liver parasite
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15
Q

What is Chloroquine used for?

A
  1. Acute malarial infection: high doses clear parasitaemia in 3-4 days
  2. Clinical prophylaxis: weekly dose

Nb chloroquine-resistant falciparum is common

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16
Q

List some of the adverse effects of Chloroquine when prescribed as prophylaxis.

A
  1. NVD
  2. Retinopathy
  3. Hypersensitivity (skin reactions)
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17
Q

When is the use of Chloroquine contra-indicated?

A
  1. Ocular disease
  2. Hepatic disease
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18
Q

What is Mefloquine (Lariam) used for?

A
  1. Chloroquine-resistant falciparum
  2. Acute malaria: 3-4 day course
  3. Clinical prophylaxis
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19
Q

List the main adverse effects of Mefloquine.

A
  • NVD
  • Neuropsychiatric disorder (VERY RARE - serious, 0.01%, mild 0.1-1%)

Nb risk of mefloquine SE is LOWER than risk of falciparum malaria (so take the drug)

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20
Q

When is use of Mefloquine contraindicated?

A
  • Depression
  • Fits
  • Epilepsy

Nb remember risk of drug SE is much lower than risk of malaria so still think of giving the prophylaxis

21
Q

What are folate inhibitors, proguanil and pyrimethamine?

A

Slow-acting blood schizonticides

22
Q

What is the mechanism of action of folate inhibitors (i.e. slow-acting schizonticides)?

A

Specific inhibition of plasmodial DHF reductase (BUT NOT HUMAN DHF reductase)

23
Q

List the uses of slow-acting blood schizonticides.

A
  • Slow-acting, used mainly for prophylaxis, daily dosing
  • Suppress blood infection (clinical prophylaxis)
  • Partly prevent liver infection (causal proph.)
  • No effect on established liver infection
24
Q

What other group of drugs are often prescribed with slow-acting blood schizonticides?

A

Sulphonamides (antibacterials) bs both act on DHF pathway

25
Q

List the S/E of the Sulphonamide component in combined Pyrimethamine/Sulphonamide drugs.

A
  • Sever skin reactions (this is why this drug not used as much)
  • Fatal hepatitis (v rare)
26
Q

What is Proguanil?

A
  • Slow-acting blood schizonticide
  • Often used alone (safe during pregnancy) or with atovaquone (C/I in pregnancy)
  • Pro-drug – cycloguanil is the active metabolite
27
Q

Name the active metabolite in Proguanil.

A

Cycloguanil

28
Q

List some of the S/E of Proguanil.

A
  • Mild NVD
  • Mild mouth ulcers
29
Q

What is Malarone?

A

Combination drug of Proguanil and Atovaquone

30
Q

What is the mechanism of action of Atovaquone?

A

Inhibits Plasmodial mitochondria

31
Q

What is Malarone used for? (and at what dosing)?

A
  • Prophylaxis
  • 1 tablet a day
    • 1 day before
    • during
    • 1 week after
32
Q

Name the drug that is 95-100% effective against drug-resistant falciparum.

A

Malarone (Proguanil + Atovaquone) - over 10 to 12 weeks treatment

33
Q

List the S/E of Malarone.

A

NVD

34
Q

When is Malarone contraindicated?

A
  • Renal failure
  • Pregnancy
35
Q

When is Doxycycline (tetracycline antibiotic) given in malaria treatment?

A
  • Prophylaxis of mefloquine-resistant falciparum
  • Useful in Px intolerant to other drugs
36
Q

What are the S/E of Doxycycline (tetracycline antibiotic)?

A

Photosensitivity* (3%) but sometimes very severe

*An extreme sensitivity to ultraviolet (UV) rays from the sun and other light sources

37
Q

When is Doxycycline (tetracycline antibiotic) contraindicated?

A
  • Pregnancy
  • Lactation
  • Children under 12
38
Q

What are liver schizonticides?

A
  • Only agent for radical cure (of benign malaria)
  • Rapidly kills liver parasites (12 days)
  • Often combined with blood schizonticide
39
Q

Name a liver schizonticide drug.

A

Primaquine

40
Q

What is the mechanism of action of liver schizonticides?

A

Blocks oxidative metabolism in plasmodia (unclear?)

41
Q

List some S/E of Primaquine.

A
  • Safe for short-term use
  • NVD
  • RARELY cyanosis
42
Q

When is Primaquine contraindicated?

A

With people who have glucose-6-phosphate dehydrogenase deficiency!

43
Q

What do you need to test for BEFORE prescribing Primaquine?

A

G6PD

44
Q

Why is Primaquine C/I in G6PD?

A

Because it can cause:

  • Intravascular haemolysis
  • Severe anaemia
45
Q

What is emergency treatment for malaria? (Nb always subject to change, check with BNF)

A

Rapid-acting blood schizonticide to which local Plasmodium is sensitive

46
Q

What are some malaria emergency kits that can be found on in local pharmacies (ie in the UK)?

A

If >24 hrs away from medical facilities, carry:

  • Chloroquine* then Fansidar® (pyrimethamine/sulphadoxine)
  • Mefloquine* then Fansidar® (*if no resistance)
  • Quinine then Fansidar®
  • Malarone®
  • Artemisinin-based combination therapy (ACT) (Riamet®)
47
Q

What is ‘Fansidar’?

A

Combination drug of Pyrimethamine and Sulphadoxine

48
Q

What is Maloprim?

A

Combination drug of Pyrimethamine and Dapsone

Yr 2 Gastrointestinal (37 decks)

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