Clinical response and plasma levels of 5-fluorouracil in patients with colonic cancer treated by drug infusion

Concentrations of 5-fluorouracil (FU) were measured in the plasma of patients receiving i.v. infusions of the drug for 5 days as treatment for adenocarcinoma of the gastrointestinal tract. Concentrations of FU varied widely in many patients. Concentration of drug X time of infusion (C X t values) were calculated. Patients showing a partial response or stabilization of disease had significantly higher C X t values than non-responders. Methyl CCNU did not affect the C X t values of FU. Determination of the plasma concentration of FU would allow the dose of the drug to be adjusted to maintain high concentrations of FU in the plasma. Our data suggest that such high concentrations would increase the response rate in this disease.