A simple colorimetric method to screen drug cytotoxicity against Leishmania using the dye Alamar Blue

A quantitative colorimetric assay using the oxidation–reduction indicator Alamar Blue® was developed to measure cytotoxicity of compounds against the protozoan parasite Leishmania. Absorbance increased linearly with the plating density of promastigotes of L. major MRHO/IR/76 vaccine strain up to at least 2.5×10 6 cells/ml when parasites were incubated for 72 h in the presence of 10% Alamar Blue®. The 50% effective dose values of common drugs (amphotericin B, pentostam and paromomycin) obtained by this assay were in the same range as previously determined by other methods. The Alamar Blue® assay permits a simple, reproducible and reliable method for screening antileishmanial drugs.