Personalized dosing via pharmacokinetic monitoring of 5-fluorouracil might reduce toxicity in early- or late-stage colorectal cancer patients treated with infusional 5-fluorouracil-based chemotherapy regimens

INTRODUCTION

Therapeutic plasma 5-fluorouracil (5-FU) levels are achieved in only 20% to 30% of patients with the current practice of administering 5-FU doses based on body surface area (BSA). Alternatively, 5-FU doses can be adjusted based on 5-FU pharmacokinetic (PK) monitoring. Although benefits of PK monitoring of 5-FU in metastatic colorectal cancer (CRC) have been reported, its utility among patients with early stage disease has not been reported.

PATIENTS AND METHODS

We retrospectively examined the effect of 5-FU PK monitoring in 84 CRC patients (49 stage IV and 35 stage II/III) receiving mFOLFOX6 (modifiedFOLFOX6; modified 5-fluorouracil, leucovorin, oxaliplatin protocol) or mFOLFIRI (modified 5-fluorouracil, leucovorin, irinotecan protocol). Forty-six of the 84 patients received 5-FU doses based on BSA and 38 received doses that were adjusted with PK monitoring. 5-FU plasma levels were measured using a nanoparticle immunoassay method.

RESULTS

5-fluorouracil PK monitoring significantly improved disease-free survival in stage II/III patients (P = .0429). There was also a trend towards improved progression-free survival among stage IV patients who had their 5-FU levels PK-monitored (P = .16). Moreover, 5-FU PK monitoring significantly reduced (P = .0437) and delayed (P = .0144) adverse effects in stage II/III patients. Toxicity occurred after the second 5-FU dose in the BSA group and after the sixth to seventh dose in the PK monitoring group. In stage IV patients, the onset of toxicities was also delayed with PK monitoring (P = .0605).

CONCLUSION

We provide evidence that PK monitoring of 5-FU is potentially beneficial for late stage and early stage CRC. These results contribute to the growing body of evidence regarding patient benefit when treatment decisions are based on the individual patient characteristics, in this case, a patients' 5-FU levels.

Abstract 1176: Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens

The mainstay of colorectal cancer chemotherapy has been 5-fluorouracil (5-FU) alone or in combination with other agents. Unfortunately, therapeutic plasma 5-FU levels are achieved in only 20-30% of patients, in response to administration of 5-FU doses calculated from the patient's body surface area. Pharmacokinetic (PK) monitoring of 5-FU has been found to be beneficial for metastatic colorectal cancer patients. However, its utility among Stage II and III patients has not been reported. Purpose: We examined the impact of pharmacokinetic monitoring of 5-FU in colorectal patients with Stage II- Stage IV disease, receiving different 5-FU-based chemotherapy regimens, in terms of therapeutic response and safety. Methods: The study involved 73 colorectal cancer patients. The patients received different 5-FU based regimens; namely, FOLFOX6, mFOLFOX, FOLFIRI, and capecitabine. Thirty-five patients received 5-FU doses based on the traditional body surface area (BSA) method, which takes into account the patient's height and weight. On the other hand, in 38 patients, their 5-FU dose was adjusted based on their plasma 5-FU levels from their previous cycle. 5-FU plasma levels were measured using the commercially available OnDose test (Myriad Genetic Laboratories Inc., Salt Lake City, UT). The 5-FU levels were monitored per cycle and administered doses were adjusted accordingly until a target plasma AUC level of 20-24 mg.h/L was achieved. Results: Pharmacokinetic monitoring among Stage IV patients (n=17) had a trend toward improved survival. Out of the 8 patients that needed at least one dose adjustment, 7 of them involved increasing the 5-FU dose. 5-FU doses were not increased in the patients that did not have their 5-FU levels monitored. The ability to maximize the 5-FU dose administered without risking toxicity with PK monitoring may explain at least in part the trend towards prolonged survival in patients that underwent pharmacokinetic dose adjustment. Among Stage II and III patients, toxicities were markedly reduced by pharmacokinetic dose adjustment of 5-FU. In patients that had their doses adjusted by the BSA method, 38% experienced (7 out of 18 patients) dose-limiting toxicities, that included Grade III diarrhea, fatigue, nausea and vomiting, and cardiotoxicity. In contrast, none of the patients (n=19) that underwent pharmacokinetic monitoring experienced dose-limiting toxicity (Fisher's exact test, p=0.0031). The toxicities observed in the BSA group were not among the patients that received capecitabine. Conclusions: 5-FU dose adjustment in response to pharmacokinetic monitoring results in a trend towards improved survival of Stage IV patients. Moreover, dose-limiting toxicities are reduced in Stage II and III patients. The results presented point to the benefits of pharmacokinetic dose adjustment of 5-FU in clinical practice.

Citation Format: Christina Leah B. Kline, Angelique Schiccitano, Jay Zhu, Cheryl Beachler, Hassan Sheikh, Harold Harvey, Heath Mackley, Walter Koltun, Kevin McKenna, Lisa Poritz, Evangelos Messaris, David Stewart, Jeffrey Sivik, Wafik El-Deiry. Pharmacokinetic monitoring of 5-FU appears beneficial in stage II-IV colorectal cancer patients treated with different 5-FU-based chemotherapeutic regimens. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1176. doi:10.1158/1538-7445.AM2013-1176