OBJECTIVE: To probe into the interval value of area under the curve（ AUC） of ideal blood concentration-time of 5-fluorouracil（ 5-FU） when patients with advanced colorectal cancer（ CRC） were receiving5-FU based chemotherapy. METHODS: Totally 49 patients with advanced CRC receiving 5-FU based chemotherapy from Aug. 2017 to Jun. 2018 in Harbin Medical University Cancer Hospital were involved in this study

the dosage of5-FU was determined according to the patient’s body surface area（ BSA）. Using ultra-high performance liquid chromatography-tandem mass spectrum technology to determine the 5-FU steady-state blood concentration（ CSS） in CRC patients receiving 5-FU in continuous intravenous infusion for 18-30 h

the start time and end time of 5-FU infusion in patients were accurately recorded

the continuous infusion time（ TCI） was calculated

and the AUC value was calculated according to AUC = CSS× TCI. At the same time

the treatment effect and adverse drug reactions of patients were evaluated

in order to analyze the relationship between 5-FU AUC and efficacy and adverse drug reactions in CRC patients

and explore the ideal AUC range of 5-FU in the treatment of colorectal cancer. RESULTS: The CSS range of 5-FU was 180-880 ng/ml; the AUC of 5-FU presented an abnormal distribution

ranging from 8. 43 to41. 1 mg·h/L

with an average value of 19. 01 ± 7. 32 mg·h/L

and the AUC value had obvious inter-individual differences up to 5 times. Correlation analysis results revealed that there was a significant correlation between AUC of5-FU and clinical efficacy and adverse drug reactions. The ideal AUC range of 5-FU was 21. 75-28. 63 mg·h/L.CONCLUSIONS: There are obvious individual differences in AUC value in CRC patients receiving different dosages of5-FU based on BSA. The ideal AUC interval value of 5-FU is 21. 75-28. 63 mg·h/L.