Pafuramidine or DB289, [2,5-bis-(4-amidinophenyl)furan bis-O-methylamidoxime] is a pro-drug of DB75, [2,5-bis(4-amidinophenyl)furan] also known as furamidine. The biotransformation process of DB289 to DB75 in the human liver consists of three O-demethylation reactions catalyzed by the Cyp4F enzyme subfamily and three N-dehydroxylation reactions catalyzed by cytrochrome b5 and NADH-cytochrome b5 reductase. DB289 was studied for therapeutic treatment against human African trypanosomiasis, Pneumocystis pneumonia and malaria. In November 2006, Immtech Pharmaceuticals, Inc. announced that the U.S. Food and Drug Administration (FDA) had granted orphan drug designation for pafuramidine (DB289) to treat Pneumocystis jiroveci pneumonia (PCP), a common life-threatening opportunistic infection in HIV/AIDS and other immunosuppressed patients. Despite the high efficacy of DB289 in patients, the mechanism of action of DB75 is unknown. The mechanism of antimicrobial activity of diamidine compounds is incompletely understood. They undergo active uptake by purine transporter systems in trypanosomes and their mechanism of action may involve interference with DNA-associated enzymes inhibition of heme crystallization11 or/and collapse of the transmitochondrial membrane potential.