Pentamidine (formulated as a salt, pentamidine diisethionate or dimesilate) is an antimicrobial medication given for prevention and treatment of pneumocystis pneumonia (PCP) caused by Pneumocystis jirovecii (formerly known as Pneumocystis carinii), a severe interstitial type of pneumonia often seen in patients with HIV infection. The drug is also the mainstay of treatment for stage I infection with Trypanosoma bruceigambiense (West African trypanosomiasis). Pentamidine is also used as a prophylactic against PCP in patients receiving chemotherapy and in some patients who have undergone organ transplantation, as they also have a depressed immune system as a direct side-effect of the drugs used. The mortality of untreated PCP is very high. Additionally, pentamidine has good clinical activity in treating leishmaniasis, and yeast infections caused by the organism Candida albicans. Pentamidine is also used as a prophylactic antibiotic for children undergoing treatment for leukemia. Studies suggest that the pentamidine isethionate interferes with microbial nuclear metabolism by inhibition of DNA, RNA, phospholipid and protein synthesis. However, the mode of action is not fully understood.