Determination of N ‐methyl‐4‐isoleucine‐cyclosporin (NIM811) in human whole blood by high performance liquid chromatography‐tandem mass spectrometry

A liquid chromatographic method with tandem mass spectrometric detection (LC‐MS/MS) for the determination of N ‐methyl‐4‐isoleucine‐cyclosporin (NIM811) was developed and validated over the concentration range 1–2500 ng/mL in human whole blood using a 0.05 mL sample volume. NIM811 and the internal standard, d 12 ‐cyclosporin A (d 12 ‐CsA), were extracted from blood using MTBE via liquid–liquid extraction. After evaporation of the organic solvent and reconstitution, a 10 µL aliquot of the resulting extract was injected onto the LC‐MS/MS system. Chromatographic separation of NIM811 and internal standard was performed using a Waters Symmetry RP‐8 (50 × 4.6 mm, 3 µm particle size) column. The mobile phase consists of 10 m m ammonium acetate in water (A) and acetonitrile (B), with 45% B from 0 to 0.2 min, 45 to 85% B from 0.2 to 0.8 min and 85% B from 0.8 to 2.2 min. The total run time was 3.5 min with a flow rate of 0.8 mL/min. The method was validated for sensitivity, linearity, reproducibility, stability, dilution integrity and recovery. The precision and accuracy of quality control samples at low (2.00 ng/mL), medium (20.0 and 400 ng/mL) and high (2000 ng/mL) concentrations were in the range 1.1–4.3% relative standard deviation (RSD) and −2.5–10.0% (bias), respectively, from three validation runs. The method has been used to measure the exposure of NIM811 in human subjects. Copyright © 2007 John Wiley & Sons, Ltd.