Evaluation of 5-Fluorouracil Pharmacokinetics in Cancer Patients with a C.1905+1G>A Mutation in DPYD by Means of a Bayesian Limited Sampling Strategy

Background and Objective Dihydropyrimidine dehydrogenase (DPD) is the initial enzyme in the catabolism of 5-fluorouracil (5FU) and DPD deficiency is an important pharmacogenetic syndrome. So far, only very limited information is available regarding the pharmacokinetics of 5FU in patients with a (partial) DPD deficiency and no limited sampling models have been developed taking into account the non-linear pharmacokinetic behaviour of 5FU. The aim of this study was to evaluate the pharmacokinetics of 5FU and to develop a limited sampling strategy to detect decreased 5FU elimination in patients with a c.1905+1G>A-related DPD deficiency. Methods Thirty patients, heterozygous for the C.1905+1G>A mutation in DPYD , and 18 control patients received a dose of 5FU 300 mg/m 2 and/or 5FU 450 mg/m 2 , followed by pharmacokinetic analysis of the 5FU plasma levels. A population pharmacokinetic analysis was performed in order to develop a compartmental pharmacokinetic model suitable for a limited sampling strategy. Clinical aspects of treating DPD-deficient patients with 5FU-based chemotherapy were assessed from the retrospectively collected clinical data. Results In a two-compartment model with Michaelis-Menten elimination, the mean maximum enzymatic conversion capacity (V max ) value was 40% lower in DPD-deficient patients compared with controls (p < 0.001). Using a limited sampling strategy, with V max values calculated from 5FU concentrations at 30 or 60 minutes, significant differences were observed between DPD-deficient patients and controls at both dose levels (p < 0.001). The positive predictive value and negative predictive value for V max , calculated from 5FU levels at 60 minutes, were 96% and 88%, respectively, in patients treated with a single dose of 5FU 300 mg/m 2 . All seven DPD-deficient patients (two males and five females) who had been genotyped prior to initiation of standard 5FU-containing chemotherapy developed grade 3–4 toxicity, with one case of lethal toxicity in a female patient. No grade 4 toxicity or lethal outcome was observed in 13 DPD-deficient patients treated with reduced doses of 5FU. The average dose of 5FU in DPD-deficient patients with mild toxicity (grade ≤2) was 61 ± 16% of the normal 5FU dose (n= 10). Conclusions Profound differences in the elimination of 5FU could be detected between DPD-deficient patients and control patients. Pharmacokinetic 5FU profiling, using a single 5FU concentration at 60 minutes, may be useful for identifi