Ketoconazole is a clinically safe antifungal agent that also inhibits the growth of Leishmania
spp. A study was undertaken to determine whether Leishmania
parasites are prone to becoming resistant to ketoconazole by upregulating C14-demethylase after stepwise pharmacological pressure. Leishmania amazonensis
promastigotes [inhibitory concentration (IC)50
= 2 μM] were subjected to stepwise selection with ketoconazole and two resistant lines were obtained, La8 (IC50
= 8 μM) and La10 (IC50
= 10 μM). As a result, we found that the resistance level was directly proportional to the C14-demethylase mRNA expression level; we also observed that expression levels were six and 12 times higher in La8 and La10, respectively. This is the first demonstration that L. amazonensis
can up-regulate C14-demethylase in response to drug pressure and this report contributes to the understanding of the mechanisms of parasite resistance.