Randomized phase II study of adding tramadol for prevention of venous pain in colorectal cancer patients who are receiving oxaliplatin through peripheral vein

Interventions: oxaliplatin 130mg/m2 day1 oral 5FU 80-120mg/m2 day1-14 every 3weeks Tramadol is given orally at a dose of 25mg once a day starting on the day of oxaliplatin infusion. Primary outcome(s): VRS improvement rate Study Design: Single arm Non-randomized