Evaluation of an oral uracil loading test to identify DPD-deficient patients using a limited sampling strategy

TLDR: The high sensitivity of the U/DHU ratio at t = 120 min for detecting DPD deficiency, as defined by D PD activity in PBMCs, showed that the oral U loading dose can effectively identify patients with reduced DPD activity.

Abstract: AIM 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