Comparative pharmacokinetics of cyclophosphamide administration alone and combination with vitamin B6 in rats

A fast and sensitive high performance liquid chromatography coupled with mass spectrometry (LC-MS) method was developed and validated for the determination of cyclophosphamide in rat plasma with and without the combination of vitamin B6. After addition of digoxin used as the internal standard (IS), plasma samples were extracted by protein precipitation with acetonitrile (1:1, v/v), and the analytes were separated by a Kromasil C18 column (150 × 4.6 mm, 5 µm) with a mobile phase of acetonitrile-0.1% formic acid water (40:60, v/v). The detection of the analyte was monitored in positive electrospray ionization by selected ion monitoringmode. The linear range was 0.01-40 µg/mL for cyclophosphamide. The intra- and inter-day precision and accuracy were all <15%. The extraction recoveries and matrix effects of the analyte and IS were all within acceptable range. The selectivity of the method was satisfactory with no endogenous interference. The results for stabilities of cyclophosphamide and IS under various conditions were all within the acceptance criteria. The validated method was successfully applied to evaluate the drug-drug interaction of cyclophosphamide and vitamin B6 in rat plasma. The results showed no differences of pharmacokinetic behaviors between cyclophosphamide administration with and without vitamin B6.