Pentamidine isethionate, an aromatic diamidine, is known to have activity against Pneumocystis carinii.

The mode of action of pentamidine is not fully understood. In vitro studies with mammalian tissues and the protozoan Crithidia oncopelti indicate that the drug interferes with nuclear metabolism producing inhibition of the synthesis of DNA, RNA, phospholipids and proteins.

Little is known about the drug's pharmacokinetics. Preliminary studies have shown that in seven patients treated with daily I.M. doses of pentamidine at 4 mg/kg for 10 to 12 days, plasma concentrations were between 0.3 and 0.5 mcg/mL. The levels did not appreciably change with time after injection or from day to day. Higher plasma levels were encountered in patients with an elevated BUN. The patients continued to excrete decreasing amounts of pentamidine in urine up to six to eight weeks after cessation of the treatment.

Tissue distribution has been studied in mice given a single intraperitoneal injection of pentamidine at 10 mg/kg. The concentration in the kidneys was the highest followed by that in the liver. In mice, pentamidine was excreted unchanged, primarily via the kidneys with some elimination in the feces. The ratio of amounts excreted in the urine and feces (4: 1) was constant over the period of study.

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