High-performance liquid chromatographic method for measurement of pentamidine in plasma and its application in an immunosuppressed patient with renal dysfunction.

A rapid method for the quantitation of pentamidine in plasma by high-performance liquid chromatography is described. Pentamidine was extracted from plasma using a mixed solvent of 40% acetonitrile in chloroform. Reversed-phase chromatography was then performed on a mu Bondapak C-18 column, using a mobile phase of acetonitrile containing 0.1% H3PO4 and 0.1% NaCl (20:80) and the eluting peaks detected by their UV absorbance at 262 nm. The assay had a within-day coefficient of variation of less than 3.8%, an absolute recovery of 92%, and a limit of detection of 15 nmol/L. The method was applied during pentamidine mesylate treatment (4 mg/kg/day) for Pneumocystis carinii pneumonia in an immunosuppressed patient with impaired renal function. Plasma levels rose slowly to a plateau (range 530-880 nmol/L) after 7 days of treatment, suggesting a half-life of around 1.5-2 days.