Determination of colistin in human plasma, urine and other biological samples using LC–MS/MS

A liquid chromatography–tandem mass spectrometric (LC–MS/MS) method was developed to quantify colistin in human plasma and urine, and perfusate and urine from the isolated perfused rat kidney (IPK). Solid phase extraction (SPE) preceded chromatography on a Synergi Fusion-RP column with a mobile phase of acetonitrile, water and acetic acid (80/19/1) at 0.2 mL/min. Ions were generated using electrospray ionization and detected in the positive-ion mode. Multiple reaction monitoring was performed using precursor-product ion combinations. Calibration curves were linear from 0.028 μg/mL (human plasma, IPK perfusate and urine)/0.056 μg/mL (human urine) to 1.78 μg/mL (all four media) for colistin A sulfate; corresponding values for colistin B sulfate were 0.016/0.032 to 1.01 μg/mL. Accuracy and precision were within 10%. The LLOQ for colistin A sulfate was 0.028 μg/mL in human plasma, IPK perfusate and urine and 0.056 μg/mL in human urine; corresponding values for colistin B sulfate were 0.016 and 0.032 μg/mL. The low sample volume, short analysis time and low LLOQ are ideal for pre-clinical and human pharmacokinetic studies of colistin.