Case Report: 72-h concentration–time profiles of plasma total platinum and 5-fluorouracil in a patient with rectal cancer undergoing maintenance hemodialysis

Prospective evidence to guide drug therapy in patients with colorectal cancer who have end-stage kidney disease (ESKD) and receive maintenance hemodialysis remains limited, and the concentration–time profiles of plasma total platinum and 5-fluorouracil (5-FU) after oxaliplatin administration, particularly in relation to the timing of hemodialysis, are still largely informed by individual case reports. We report a 45-year-old man with rectal cancer who had been receiving long-term maintenance hemodialysis. He underwent radical surgery for rectal cancer at the age of 42 years, with postoperative pathology showing moderately differentiated adenocarcinoma, and subsequently received individualized treatment with oxaliplatin, 5-FU, and leucovorin. During one treatment cycle, serial plasma drug concentrations were monitored from 0 to 72 h, and the timing of two hemodialysis sessions relative to drug administration was recorded. The plasma total platinum concentration was 0.87 μg/mL at the end of oxaliplatin infusion (2 h), subsequently decreased to approximately 0.55–0.62 μg/mL, and remained relatively stable thereafter, with no clear stepwise decline observed during either hemodialysis session. Following the two short-duration administrations of 5-FU, the higher measured concentrations were 0.75 and 0.67 μg/mL, respectively, followed by a rapid decline to low levels before the initiation of both hemodialysis sessions. During follow-up, pulmonary lesions were considered metastatic rectal cancer based on pathological findings and clinical information. Serial chest computed tomography showed heterogeneous changes among individual pulmonary nodules, with overall radiographic progression of pulmonary disease by April 2026. Under the drug administration and hemodialysis schedule used in this case, plasma total platinum and 5-FU showed different concentration–time patterns: measured platinum concentrations did not show an obvious rapid decline during hemodialysis, whereas 5-FU concentrations had already decreased markedly before hemodialysis was initiated. This case report is not intended to establish a standard oxaliplatin/5-FU dose or an optimal timing of hemodialysis. Rather, its main claims are that plasma total platinum and 5-FU can exhibit different concentration-time profiles in a patient receiving maintenance hemodialysis, and that TDM (Therapeutic Drug Monitoring) results in such patients should be interpreted according to the specific analyte measured and the timing of drug administration relative to hemodialysis. The broader clinical usefulness of this case lies in clarifying what can and cannot be inferred from drug concentration measurements and in providing practical case-level information on low-dose, fractionated FOLFOX administration in this population. These findings suggest that, in patients receiving maintenance hemodialysis who are treated with oxaliplatin- and 5-FU-containing regimens, drug concentration measurements should be interpreted according to the specific analyte assessed and the timing of drug administration relative to hemodialysis. Therapeutic drug monitoring, together with treatment tolerability and changes in disease status, may provide complementary information for individualized treatment.