Analytical and pharmacological studies of cyclophosphamide

Abstract

Pharmacokinetic and pharmacodynamic studies are an essential in order to achieve better treatment efficacy and less drug related toxicity. The kinetic studies depend on measuring the drug concentrations in body fluids. Analytical methods, sampling methods and sample preparation are important factors that affect the drug assay and hence the drug concentrations. This subsequently may alter the accuracy of pharmacokinetic and pharmacodynamic investigations. Cyclophosphamide (CPA) is an anticancer drug, which is widely used for the treatment of hematological malignancies as well as solid tumors. It is a prodrug that undergoes complicated process of metabolic activation and inactivation in the liver. Many bioanalytical assays for the quantification of CPA and its metabolites have been developed over the past decade. However, these methods have several limitations including long analysis time, sample preparation and large sample volume.

The aim of the present studies was to develop a new sensitive analytical method for cyclophosphamide and subsequently to use this method for evaluattion of new sampling’s technique in mice for kinetic studies of cyclophosphamide in mice.

In study I, a simple and rapid method for the determination of CPA utilizing on line sample preparation method, microextraction in packed syringe (MEPS), was developed. The quantification of CPA was carried out using liquid chromatography in combination with tandem mass spectrometry (LC-MS/MS). The method was validated for linearity, selectivity, accuracy, precision and limits of detection and quantification. One hundred and seventy plasma samples from patients treated with CPA were analyzed with the new method and compared with the results obtained after liquid-liquid extraction (LLE) and analyzed using liquid chromatography with UV detection (LC-UV). The limit of detection (LOD) was 0.005 μg/mL and the limit of quantification was 0.5 μg/mL for LC-MS/MS. The accuracy of the quality control (QC) samples ranged from 91 to 106%. The inter-day variation was within the range 5-9%, while the intra-day variation was between 1-5%. The calibration curve in plasma covered the range 0.5-150 μg/mL. The regression correlation coefficient (r) was > 0.99 for all runs. This method improved the detection limit by 100 times (0.005 μg/mL) comparing to LLE-LC-UV (0.5 μg/mL). This new method also reduced the sample handling and the analysis time by several folds compared to LC- UV detection.

In study II, we compared the pharmacokinetics of CPA using serial bleeding from the tail vein with that obtained from conventional retro-orbital sinus bleeding in mice. CPA was administered intraperitoneally to two groups of mice and blood samples were collected at different time points. For the first group (n=6), 20 μL blood samples were collected from the tail vein by serial bleeding. In the second group, 3 animals were killed at each time point and blood was collected from both tail vein and retro-orbital sinus. CPA was analyzed using LC-MS/MS. No significant differences in estimated pharmacokinetic parameters including AUC, Tmax, Cmax and half-life were observed when comparing serial- with retro-orbital bleeding. This indicates that serial sampling using tail vein in mice can offer better alternative to retro-orbital bleeding.

The present results show that LC-MS/MS in combination with serial sampling in mice can be a good alternative method to be used for early preclinical kinetic studies. However, more studies are needed to evaluate different drug categories.