| Summary: | <p>Abstract</p> <p>Background</p> <p>The spread of drug resistance in malaria parasites and the limited number of effective drugs for treatment indicates the need for new anti-malarial compounds. Current assays evaluating drugs against <it>Plasmodium falciparum</it> require expensive materials and equipment, thus limiting the search for new drugs, particularly in developing countries. This study describes an inexpensive procedure that is based on the advantage of a positive correlation between the haemozoin level of infected erythrocytes and parasite load.</p> <p>Methods</p> <p>The relationship between parasitaemia and the haemozoin level of infected erythrocytes was investigated after converting haemozoin into monomeric haem. The 50% inhibitory concentration (IC<sub>50</sub>) values of chloroquine, quinine, artemisinin, quinidine and clotrimazole against <it>P. falciparum</it> K1 and 9A strains were determined using the novel assay method.</p> <p>Results</p> <p>The haemozoin of parasites was extracted and converted into monomeric haem, allowing the use of a colorimeter to efficiently and rapidly measure the growth of the parasites. There was a strong and direct linear relationship between the absorbance of haem converted from haemozoin and the percentage of the parasite (R<sup>2</sup> = 0.9929). Furthermore, the IC<sub>50</sub> values of drugs were within the range of the values previously reported.</p> <p>Conclusion</p> <p>The haemozoin-based colorimetric assay can be considered as an alternative, simple, robust, inexpensive and convenient method, making it applicable in developing countries.</p>
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