Antiparasitic drugs

a) Anti-malarial drugs

These drugs target various stages of the malaria parasite life cycle.

  • Chloroquine

It raises the pH of parasite vacuoles inhibiting haem-polymerase

– This stops the parasite feeding in RBCs stopping the life cycle

– It is taken weekly and used in malaria prophylaxis and attacks

– It is also used an anti-inflammatory in autoimmune disorders

Side effects: Headache + Contraindicated in epilepsy

– Unfortunately, resistance to chloroquine is emerging in many species of P. Falciparum.

 

  • Mefloquine

This acts similarly to chloroquine and is used for prophylaxis and treatment of chloroquine-resistance strains

Side effects: Dizziness + Psychiatric signs (suicidal thoughts)

– Contraindicated in patients with epilepsy

 

  • Quinine

This interferes with the erythrocytic stage of the parasite by inhibiting its ability metabolise haem

– Quinine is used in the management of P. Falciparum that has become resistant to chloroquine.

 

Side effects: Produces curare-like effects on skeletal muscle + tinnitus + visual disturbances

– Blackwater fever –> a haemolytic crisis that occasionally complicates malaria infection.

– Large numbers of red blood cells undergo haemolysis releasing haemoglobin into the bloodstream

– This can cause an AKI.

 

  • ArtemisininsDihydroartemisin + Artensuante

These are semi-synthetic drugs which are used in combination therapy to treat P. Falciparum

– They are broken down to dihydroartemisinin which generates free radicals to kill the parasite

Side effects: GI upset, dizziness

 

  • Fansidar

This is Pyrimethamine (inhibits dihydrofolate reductase) + Sulfadoxine (inhibits dihydropteroate synthase)

– Acts to prevent folic acid synthesis prevent DNA synthesis –> used to treat P. Falciparum

Side effects: Megaloblastic anaemia and folate deficiency

 

  • Proguanil

This is a prodrug whose active metabolite inhibits dihydrofolate reductase to stop parasite DNA synthesis

– It is commonly used in combination with chloroquine or atovaquone (electron transport chain inhibitor)

 

b) Drugs against other parasites

  • Mebendazole

This drug is used to treat many parasitic worm infections including threadworms, hookworms and giardia

– It inhibits the synthesis of microtubules which stops uptake of glucose and nutrients killing the helminth

Side effects: GI upset + Hepatotoxicity

 

  • Praziquantel

This drug is most famous for treating schistosomiasis arguably by increasing cell permeability to Ca2+

Side effects – These occur due to release of parasitic contents when it dies causing host inflammation

GI upset + CNS disturbance (dizziness, headache)

 

  • Ivermectin

Used against parasites like head lice, scabies. It opens Cl channels causing cell hyperpolarization and death

Side effects: CNS depression and ataxia

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