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(UNI) Chemotherapy & Selective Toxicity (3rd Year) > Anti-Malarials > Flashcards

Anti-Malarials Flashcards

1
Q

Which parasites cause malaria?

A

Plasmodium falciparum, vivax, malariae, ovale.

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2
Q

In 2015, how many deaths did malaria cause?

A

429,000.

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3
Q

Which continent carries a disproportionately high share of the global malaria burden?

A

Africa.

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4
Q

What agents are commonly used to treat or prevent malaria?

A

Chloroquine, mefloquine, primaquine, proguanil, pyrimethamine.

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5
Q

What is chloroquine used for?

A

The prophylaxis of malaria in areas of the world where the risk of chloroquine-resistant falciparum malaria is still low.

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6
Q

What is mefloquine used for?

A

Used for prophylaxis of malaria in areas of the world where there is a high risk of chloroquine-resistant falciparum malaria.

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7
Q

What is primaquine used for?

A

Used to eliminate the liver stages of P. vivax or P. ovale following chloroquine treatment.

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8
Q

What is proguanil used for?

A

Used (usually with chloroquine) for the prophylaxis of malaria.

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9
Q

What is pyrimethamine used for?

A

It is used with sulfoxadine and shouldn’t be used alone.

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10
Q

By what mechanisms do anti-malaria drugs work?

A

Interference with haem disposal mechanisms, inhibition of parasitic dihydrofolate reductase, free radical formation and alkylation, interfering with parasitic mitochondrial electron transport.

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11
Q

Why are multiple mechanisms targeted in the treatment of malaria?

A

This improves the chance of defeating the disease and overcoming resistance.

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12
Q

Which enantiomer of chloroquine is used in the prophylaxis/treatment of malaria?

A

Both, they both have pharmacological activity and neither are toxic.

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13
Q

What are the consequences of parasitic haemoglobin metabolism? How does the malaria parasite combat this?

A

Haemoglobin is metabolised into heam which is toxic to the parasite, to combat this haem is cinverted into insoluble crystals of haemozoin through bio-crystalisation.

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14
Q

Chloroquine is a basic drug; when it enters the parasitic digestive vacuole how does it change?

A

When chloroquine enters the parasitic digestive vacuole it becomes protonated so it can’t leave. Here it caps the growing crystal of haemozoin, preventing further crystallisation. This causes haem to build up to toxic levels, killing the parasite.

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15
Q

How does chloroquine work to kill the malaria parasite?

A

It caps the growing crystal of haemozoin, preventing further crystallisation. This causes haem to build up to toxic levels, killing the parasite. It also forms a complex with haem which is highly toxic to the parasite by disrupting membrane function. These two effects lead to cell lysis and ultimately parasitic cell autodigestion.

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16
Q

What other drugs work in the same way as chloroquine?

A

Mefloquine, primaquine, lumefantrine, quinine/

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17
Q

What beverage has weak anti-malarial properties and why?

A

Tonic water as it contains a small concentration of quinine.

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18
Q

Which anti-malarial drug’s use has been called into question based on serious negative side effects such as severe anxiety and paranoia?

A

Mefloquine (Lariam).

19
Q

What are the side effects of mefloquine (Lariam)?

A

Severe anxiety, paranoia, hallucinations, depression, feeling restless, unusual behaviour, feeling confused.

20
Q

What is the active metabolite of the anti-malarial drug proguanil?

A

Cycloguanil.

21
Q

How does the anti-malarial drug proguanil work?

A

Through inhibition of parasitic dihydrofolate reductase which prevents the formation of purines and pyrimidines, essential for the synthesis of DNA.

22
Q

What potential selectivity issue is there with proguanil? Is this of major concern?

A

The drug may potentially target mammalian DHFR however there is often enough difference between the enzymes for this to not be of concern.

23
Q

What is the major problem with proguanil?

A

Metabolism of proguanil to its active metabolite (cycloguanil) is carried out by CYP450 enzymes in the liver. Different races can have different levels of expression of these enzymes. African and Asian people usually have lower levels of the required enzymes, so do not produce enough of the active metabolite even after multiple doses. This is a problem as these peoples are often the most likely to be affected by malaria.

24
Q

How does pyrimethamine work in the treatment of malaria?

A

By inhibiting parasitic dihydrofolate reductase, preventing DNA synthesis.

25
Q

WHere did the anti-malarial drug artemisinin originate?

A

China.

26
Q

Why can’t artemisinin be synthetically produced?

A

It is a very complex molecule, it must be derived from the herb.

27
Q

Although it can’t be synthetically produced, can artemisinin be made into semi-synthetic forms? Name some.

A

Yes. Artesunate, artemether.

28
Q

What is the active metabolite of the anti-malarial drug artemether?

A

Dihydroartemisinin.

29
Q

How does artemether work to treat malaria?

A

It works against the erythrocytic stages of P. falciparum by inhibiting nucleic acid and protein synthesis. The full reaction isn’t known however it is believed to involve a reaction with haem to produce cytotoxic free radicals.

30
Q

How does artemether provide rapid symptomatic relief for those suffering from malaria?

A

It has a rapid onset of action and is rapidly cleared from the body, possibly rapidly reducing the number of malaria parasites in the body.

31
Q

Artemether and lumefantrine are used in combination therapy for malaria; why is lumefantrine used?

A

It has a much longer half-life than artemether and is thought to clear residual parasites.

32
Q

How does atovaquone act to treat malaria?

A

It acts by selectively inhibiting mitochondrial electron transport and parallel processes such as ATP and pyrimidine synthesis.

33
Q

Why is atovaquone useful for patients who have undergone a bone marrow transplant and need treatment for malaria?

A

It does not cause myelosupression/bone marrow supression.

34
Q

What is myelosuppression/bone marrow suppression?

A

The decrease in the production of cells responsible for immunity (leukocytes), oxygen transport (erythrocytes), and normal blood clotting (thrombocytes).

35
Q

Recently, where has artemisinin resistance been seen?

A

Cambodia, Laos, Myanmar, Thailand, Vietnam.

36
Q

What drug is P. falciparum resistant to in most parts of the world?

A

Chloroquine.

37
Q

What drug regimens are used to treat P. falciparum?

A

Quinine, mefloquine, proguanil with atovaquone. Or artemether with lumefantrine.

38
Q

What drug regimens are used to treat unknown or mixed malaria?

A

Quinine, mefloquine, proguanil with atovaquone. Or artemether with lumefantrine.

39
Q

In malaria infections caused by P. vivax or P. ovale, what radical treatment is required?

A

Primaquine to destroy the parasites in the liver, preventing relapse.

40
Q

What is the drug of choice for the treatment of benign malaria?

A

Chloroquine.

41
Q

What is the most effective strategy for the prevention of mosquito bites, to prevent malaria?

A

Mosquito nets impregnated with permethrin.

42
Q

What non-pharmacological interventions can be used to prevent mosquito bites leading to malaria?

A

Mosquito nets, vapourised insecticides (coils, sprays), DEET lotions, wearing long sleeves and trousers at dusk.

43
Q

How long should mefloquine be used for prophylaxis of malaria?

A

One week before travel to the exposed area continued for the length of the trip then 4 weeks after returning.

44
Q

How long should atovaquone/proguanil be used for the prophylaxis of malaria?

A

1-2 days before travel to the exposed area continued for the length of the trip and then continued for one week after returning.

(UNI) Chemotherapy & Selective Toxicity (3rd Year) (18 decks)

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