Primaquine is lethal for intracellular but not extracellular Trypanosoma cruzi

Primaquine has been used to treat Chagas' disease in humans and has been reported to be active against extracellular Trypanosoma cruzi. Experiments were designed to evaluate the relative activity of primaquine against extra- and intracellular T. cruzi and to determine if primaquine might be combined advantageously with ketoconazole. Primaquine at 0.5 micrograms/ml significantly inhibited T. cruzi replication in infected mouse peritoneal macrophages and also effectively treated infected L929 cells. To examine the effect of primaquine on extracellular organisms, tissue culture T. cruzi were incubated with primaquine for different periods of time and then used to infect macrophages. Incubation with 10 micrograms/ml for 14 hr but not 8 hr significantly inhibited but did not eradicate replication. Incubation of spleen amastigotes or blood trypomastigotes for 2 hr with 10 micrograms/ml did not inhibit replication. Incubation of extracellular tissue culture T. cruzi with primaquine for 2 hr did not potentiate the activity of ketoconazole against intracellular organisms. The combination of primaquine and ketoconazole administered to acutely infected mice significantly decreased parasitemias in comparison to treatment with primaquine or ketoconazole alone. Thus primaquine acts primarily on intracellular rather than extracellular T. cruzi. Primaquine and ketoconazole appear to have additive activity in vivo.