Chloroquine

Mode of action of Anti-malarial drug.

Contributed by – Ashika G

Malaria

Malaria can occur if a mosquito infected with the Plasmodium parasite bites you.
Life cycle of parasite involves cyclic infection of humans and the female Anopheles mosquitoes. In humans, the parasites grow and multiply first in the liver cells and then in the RBC (red blood cells). In the blood, successive multiplication of parasite takes place and grow inside the red blood cells and destroy them, releasing daughter parasites (“merozoites”) that continue the cycle by invading other red blood cells.

Chloroquine :

Chloroquine belongs to 4 amino quinoline with molar mass of 319.872 g/mol and chemical formula C18H26ClN3
It is a neutral drug primarily used for treating Malaria as it stops RBC from rupturing by entering inside the RBCs and attacking the merozoite.

Mechanism of action :

Plasmodium parasite use haemoglobin (is a protein found in the red blood cells) as their food. The “Heme” group in hemoglobin is toxic to the parasite so it is converted into hemozoin (non toxic) by the parasite and the “Globin” (protein) group is converted into peptide which is utilised by the parasite. When chloroquine (Ch) is taken, it enters RBCs and then into the vacuole of parasite which is residing inside the RBCs of host.
Since pH of parasite’s vacuole is highly acidic, protonation of Ch takes place and is converted into Ch+2. Ch+2 is polar in nature and cannot move outside the vacuole hence it’s concentration increases inside the vacuole.
Now it has more affinity towards the heme group and binds to heme forming “Ch-heme complex” which cannot be converted to hemozoin by the parasite anymore. Then, Heme itself or its complex with Chloroquine damages the plasmodium membrane. Clumping of pigment which is present inside the parasite and changes in parasite membranes takes place thereby destroying the parasite.