Uracil pharmacokinetics in a DPD-deficient patient with a novel DPYD mutation compared to volunteers with normal DPD activity.

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e13134 Background: Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the metabolism of 5-fluorouracil (5-FU). Patients with a partial or complete DPD deficiency are at risk to develop severe toxicity after 5-FU administration. Uracil (U) is degraded in dihydrouracil (DHU) in a similar way as 5-FU. An oral uracil test dose might be useful to determine the systemic DPD activity by measuring uracil and its metabolite dihydrouracil in plasma. DPD deficiency is hypothesized to result in higher uracil levels and a reduced turnover of uracil into dihydrouracil. Methods: Uracil (500 mg/m2) was administered to 11 healthy volunteers with normal DPD activity (≥ 6 nmol/mg/hour) and 1 patient with colorectal carcinoma with a novel DPYD mutation and decreased DPD activity (4.6 nmol/mg/hour). DPD activity was measured in PBMC, as determined as described earlier. Blood samples were taken at t= 15, 30, 45, 60, 80, 100, 120, 150, 180, and 220 or 240 min after oral uracil intake. U and DHU pla...