High-performance liquid chromatographic determination of pentamidine in plasma

This report describes the analysis of pentamidine by isocratic reversed-phase high-performance liquid chromatography (HPLC) using a commercially available compound (melphalan) as the external standard. Previously described assays use ion-pairing HPLC, an internal standard (hexamidine) that is not readily available, and require a relatively large sample size. In the present assay, pentamidine was extracted from plasma using solid-phase extraction and was analyzed using a C18 column and a mobile phase containing 18% acetonitrile, 2% methanol, 0.2 M ammonium acetate and 0.5% triethylamine. The identity of the eluting peaks was verified using a diode array detector. The extraction yield of pentamidine was 82%. The limit of detection was 8.6 ng/ml with a sample size of 100 microliters. The inter-day and intra-day coefficients of variation ranged between 0.3% and 10% with an average of 5%. This method was applied to study the pharmacokinetics of pentamidine in rodents.