Pharmacokinetic and Pharmacodynamic Analyses of 5-Fluorouracil in East-Asian Patients with Nasopharyngeal Carcinoma

5-Fluorouracil plus cisplatin is the most commonly used chemotherapy regimen for nasopharyngeal carcinoma (NPC). The objective of this study was to establish an individualized 5-fluorouracil treatment model based on pharmacokinetic and pharmacodynamic analyses of 5-fluorouracil in East-Asian NPC patients.A total of 122 NPC patients were administered 5-fluorouracil plus cisplatin treatment. Blood samples were collected to calculate the area under the concentration-time curve (AUC) for 5-fluorouracil, and expressions of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) at both protein and messenger RNA (mRNA) levels were analyzed in the tumor tissues from 73 patients in the same cohort.The results showed a wide (sevenfold) pharmacokinetic variability of 5-fluorouracil exposure (measured as AUC) based on body surface area (BSA) dosing. Pharmacokinetic analyses revealed that the 5-fluorouracil AUC range had a significant impact on the response of patients to 5-fluorouracil and related toxicities. Patients with 5-fluorouracil AUC 25 mg·h/L responded unsatisfactorily to 5-fluorouracil (overall response rate [ORR] 17.5 % lower than patients with AUC 25-35, p = 0.176; and 26.1 % lower than patients with AUC 35, p = 0.031). On the other hand, patients with 5-fluorouracil AUC35 mg·h/L experienced more 5-fluorouracil-related toxicities (a grade 3 or higher toxicity rate 57.1 % higher than patients with AUC 25-35, p 0.001; and 60.0 % higher than AUC35, p 0.001). The established 5-fluorouracil therapeutic window in head and neck cancer (HNC) [AUC 25-35 mg·h/L) was verified in our study. Pharmacodynamic analyses indicated a positive correlation between TS and DPD expression (p 0.001) and, despite the pharmacokinetic influences, low expression of TS mRNA in tumor tended to have a better ORR (81.0 vs. 54.3 %, p = 0.051). No significant association was found between DPD expression and ORR.The therapeutic window of 5-fluorouracil for East-Asian NPC patients was verified as 25-35 mg·h/L based on lower toxicity and higher efficacy. TS mRNA expression showed potentially predictive value in 5-fluorouracil treatment, and personalized treatment based on pharmacokinetics and pharmacodynamics proved to be clinically beneficial and is worthy of further clinical studies.