A LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY METHOD FOR THE SIMULTANEOUS DETERMINATION OF CAPECITABINE, 5′-DEOXY-5-FLUOROCYTIDINE, 5′-DEOXY-5-FLUOROURIDINE, 5-FLUOROURACIL, AND 5-FLUORODIHYDROURACIL IN HUMAN PLASMA

Abstract

The objective of the present study was to develop a selective and sensitive liquid chromatography-mass spectrometry (LC-MS) method for the simultaneous quantitation of capecitabine, 5′-deoxy-5-fluorocytidine (5′-DFCR), 5′-deoxy-5-fluorouridine (5′-DFUR), 5-fluorouracil (5-FU), and 5-fluorodihydrouracil (5-FUH₂) in human plasma. Chromatography was performed on an Atlantis dC18 column with a mobile phase consisting of 1% formic acid in acetonitrile and 1% formic acid in water gradient elution. 5-fluorocytosine (5-FC) was used as internal standard. LC-MS data were acquired in SIM mode at m/z 130 for 5-FC, m/z 131 for 5-FU, m/z 133 for 5-FUH₂, m/z 246 for 5′-DFCR, m/z 247 for 5′-DFUR, and m/z 360 for capecitabine. The drug/internal standard peak area ratios were linked via quadratic relationships to concentrations (100–10000 μg/L for 5-FU; 50–10000 μg/L for 5-FUH₂; and 25–10000 μg/L for 5′-DFCR, 5′-DFUR, and capecitabine). The analysis of blank matrices from different donors showed the absence of interfering endogenous components at the retention times of the analytes. No evidence of matrix effect was observed. The method was precise (precision, 0.2–8.3%) and accurate (recovery, 99–104%). Mean extraction efficiencies >89% for each analyte were obtained. The lower limits of quantitation were 25 μg/L for capecitabine, 5′-DFCR, and 5′-DFUR; 50 μg/L for 5-FUH_2; and 100 μg/L for 5-FU. This method was successfully used to investigate plasma concentrations of capecitabine and its metabolites in a pharmacokinetic study carried out in patients with metastatic solid tumors receiving oral administration of capecitabine (1600 to 3420 mg according to the patient) twice a day.

Keywords:

• 5′-deoxy-5-fluorocytidine
• 5′-deoxy-5-fluorouridine
• 5-fluorodihydrouracil
• 5-fluorouracil
• capecitabine
• LC-ESI-MS quantitation

Notes

^a Quadratic unweighted regression, formula: y = ax ²  + bx + c.

r²: determination coefficient; n: number of replicates; S.D., standard deviation.

5′-DFCR, 5′-deoxy-5-fluorocytidine; 5′-DFUR, 5′-deoxy-5-fluorouridine; 5-FU, 5-fluorouracil, 5-FUH₂, 5-fluorodihydrouracil.

n: number of replicates; 5′-DFCR, 5′-deoxy-5-fluorocytidine; 5′-DFUR, 5′-deoxy-5-fluorouridine; 5-FU, 5-fluorouracil, 5-FUH₂, 5-fluorodihydrouracil.

n: number of different matrices studied; S.D., standard deviation; 5′-DFCR, 5′-deoxy-5-fluorocytidine; 5′-DFUR, 5′-deoxy-5-fluorouridine; 5-FU, 5-fluorouracil, 5-FUH₂, 5-fluorodihydrouracil.

Each value is the mean from 3 replicates in each batch of matrix.

n: number of replicates; 5′-DFCR, 5′-deoxy-5-fluorocytidine; 5′-DFUR, 5′-deoxy-5-fluorouridine; 5-FU, 5-fluorouracil, 5-FUH₂, 5-fluorodihydrouracil.

S.D., standard deviation; 5′-DFCR, 5′-deoxy-5-fluorocytidine; 5′-DFUR, 5′-deoxy-5-fluorouridine, 5-FUH₂, 5-fluorodihydrouracil.

V, volume of distribution; CL/F total clearance uncorrected for bioavailability (F); t_1/2, terminal elimination half-life; AUC, area under curve normalized to a 2500 mg administered dose.