Methods for improved administration and dosing of DPD inhibitors in combination with 5-FU and/or 5-FU prodrugs are provided, comprising first administering to a patient in need thereof a DPD inhibitor that substantially eliminates activity of the enzyme and thereafter administering 5-FU or a 5-FU prodrug, wherein the level of 5-FU or 5-FU prodrug is in substantial excess of DPD inhibitor in the patient.