Dihydropyrimidine dehydrogenase (DPD) deficiency can lead to severe toxicity following 5-fluorouracil (5FU) or capecitabine (CAP) treatment. Uracil (U) can be used as a probe to determine systemic DPD activity. The present study was performed to assess the sensitivity and specificity of a U loading dose for detecting DPD deficiency.METHODS
Cancer patients with Common Toxicity Score (CTC) grade III or IV toxicity after the first or second cycle of 5-FU or CAP treatment were asked to participate. Based on DPD activity in PBMCs, patients were divided into two groups: DPD activity in peripheral blood mononuclear cells (PBMCs) <5 nmol mg−1*h−1 (deficient group) and ≥ 5 nmol mg−1*h−1. U 500 mg m–2 was administered orally and plasma concentrations of U and dihydrouracil (DHU) were determined. In the deficient group, polymerase chain reaction amplification of all 23 coding exons and flanking intronic regions of DPYD was performed. A U pharmacokinetic model was developed and used to determine the maximum enzymatic conversion capacity (Vmax) of the DPD enzyme for each patient. The sensitivity and specificity of Vmax, U concentration and the U/DHU concentration ratio were determined.RESULTS
A total of 47 patients were included (19 DPD deficient, 28 DPD normal). Of the pharmacokinetic parameters investigated, a sensitivity and specificity of 80% and 98%, respectively, was obtained for the U/DHU ratio at t = 120 min.CONCLUSIONS
The high sensitivity of the U/DHU ratio at t = 120 min for detecting DPD deficiency, as defined by DPD activity in PBMCs, showed that the oral U loading dose can effectively identify patients with reduced DPD activity.