Quinoline anti-malarial drugs inhibit spontaneous formation of beta-haematin (malaria pigment).

Polymerisation of haematin to beta-haematin (haemozoin or malaria pigment) in acidic acetate solutions was studied using infrared spectroscopy. The reaction was found to occur spontaneously between 6 and 65 degrees C, in 0.1-4.5 M acetate and pH 4.2-5.0. The anti-malarial drugs quinine, chloroquine and amodiaquin were found to block spontaneous beta-haematin formation, while the anti-malarially inactive 9-epiquinine and 8-hydroxyquinoline had no effect on the reaction, as did primaquine, a drug which is active only against exo-erythrocytic stages of infection. It is argued that the intra-erythrocytically active anti-malarial agents act by binding to haematin, blocking beta-haematin formation and leaving toxic haematin in the parasite food vacuoles.