Validation and Application of a Simple UHPLC-MS-MS Method for the Enantiospecific Determination of Warfarin in Human Urine

Validation of R/S-Warfarin Analysis Method in Human Blood Plasma Using HPLC with Fluorescence Detection and its Application to Patient Samples

Context

Warfarin is extensively used for venous thromboembolism and other coagulopathies. In clinical settings, warfarin is administered as a mixture of S-warfarin and R-warfarin, and both enantiomers are metabolized by multiple cytochrome P450 enzymes into many hydroxylation metabolites. Validation of analysis method and estimation of warfarin plasma levels are important, especially in narrow-index drugs such as warfarin.

Aims

This study aimed to obtain a validated method for analyzing warfarin in patient plasma according to the European Medicines Agency (EMA) guidelines.

Materials and Methods

A total of 77 patients were enrolled in this study. Five millimeters of venous blood was collected using sodium ethylenediaminetetraacetic acid (EDTA) tubes for pharmacokinetic analysis. Samples were prepared by the protein precipitation technique using acetonitrile. The optimum conditions for the analysis of warfarin in human plasma were tested using fluorescence detector (FLD) high-performance liquid chromatography (HPLC) with Chiralcel OD-RH column (4.6 × 150 mm i.d., 5 μm), Chiralcel OD-RH guard column (4.0 × 10 mm, 5 μm), and a column temperature of 45°C. The mobile phase used was acetonitrile: phosphate buffer pH 2 (40:60), with an isocratic flow rate of 1 ml/min and an injection volume of 20 μl. Excitation and emission wavelengths were 310 and 350 nm (warfarin) and 300 and 400 nm (griseofulvin). The retention time of griseofulvin was 6-7.5 minutes; R-warfarin was 10-11.5 minutes; and S-warfarin was 14-16 minutes.

Results

The result of this validation obtained the optimum conditions. This method yielded the limit of detection (LOD) values of 0.0674 ppm (R-warfarin) and 0.0897 ppm (S-warfarin). The limit of quantification (LOQ) values were 0.225 ppm (R-warfarin) and 0.298 ppm (S-warfarin). Linearity existed at concentrations of 0.2-3 ppm with the line equation y = 0.0705x + 0.0704 with R² = 0.978 for R-warfarin and y = 0.0513x + 0.0297 with R² = 0.9924 for S-warfarin. At least 75% of the seven concentrations met the reverse concentration requirements, which were below ± 15%. This method met the requirements of accuracy and precision within and between runs, selectivity, and carryover where the %RSD and %diff values were below ± 15%. The mean plasma concentrations of R-warfarin and S-warfarin were found to be 0.76 ± 1.87 (SD) μg/ml and 0.59 ± 0.81 (SD) μg/ml, respectively. The mean standard dose group plasma concentration from the analysis of 77 samples was 0.68 ± 0.61 μg/mL for R-warfarin and 0.52 ± 0.42 μg/mL for S-warfarin.

Conclusions

Based on these results, this analytical method can be declared valid and can be used for sample measurement in warfarin pharmacokinetic studies.

A novel, rapid and simple UHPLC-MS/MS method for quantification of warfarin in dried blood spots

Warfarin is a common first line anticoagulant with a narrow therapeutic window. Because of the large blood volume needed, previous warfarin determination methods were not applicable to small animals, such as mice. To reduce the number of small animals used needed, we developed and validated a sensitive rapid assay for the simultaneous detection of warfarin enantiomers in mouse dried blood spot (DBS) samples. Analytes were extracted by tert-butyl methyl ether and then separated by a chiral Cellulose-1 column with a mobile phase of 75% acetonitrile (containing 0.1% formic acid). The total chromatographic run time was 3 min. Negative mode electrospray ionization was used for MS/MS detection, where the monitored ion transitions were m/z 307.1 → 161.0 and 341.1 → 284.0 for warfarin and coumachlor (internal standard) respectively. The calibration curves were linear with a correlation coefficient of ≥0.994 for both enantiomers over a concentration range of 10-1000 ng/mL. The satisfactory accuracy and adequate reproducibility of both warfarin enantiomers were validated in terms of intra- and interday precision with mouse DBS cards. The samples were stable at room temperature for at least 14 days. The validated method was applied to a pharmacokinetic study in mice.

Enzyme-linked immunosorbent assays for therapeutic drug monitoring coumarin oral anticoagulants in plasma

The development of high-throughput immunochemical assays to assist on precision medicine for patients treated with coumarin oral anticoagulants (OA) is reported. The assays are able to quantitate Warfarin (W) and/or Acenocoumarol (ACL) directly in plasma samples without any previous sample pretreatment. The detectabilities (W, 3.52 ± 2.25 nM and ACL, 1.56 ± 0.64 nM) and the working ranges achieved (W, 1.19 ± 0.73 to 12.05 ± 2.99 nM and ACL 0.63 ± 0.20 to 10.19 ± 6.69 nM) are within the therapeutic levels usually found in patients treated with these drugs. The assays are specific with only cross-recognition of 4'-NH₂-ACL on the ACL ELISA, which is one of the main metabolites of this drug. Moreover, accuracy studies performed with blind spiked samples show very good correlation between the spiked and the measured concentrations. Finally, a small clinical pilot study has been performed analyzing 96 plasma samples from treated and untreated patients, showing that the assay is able to quantitate ACL. The results obtained allow envisaging the possibility to use these assays for pharmacokinetic studies, dosage assessment or therapeutic drug monitoring.