Capecitabine (Xeloda) is an oral prodrug of 5-fluorouracil that is designed to be selectively activated by tumor cells. Capecitabine undergoes a three-step conversion to 5-fluorouracil, the last step being phosphorylation by thymidine phosphorylase (TP). TP levels are reported to be higher in tumor cells than normal tissues; therefore, the systemic exposure of active drug is minimized and tumor concentrations of the active

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drugs are optimized. Once the drug is converted to 5-fluorouracil, it has the same mechanism of action. The current FDA-approved indication for capecitabine is for use in metastatic and adjuvant colorectal cancer when monotherapy is desired, though it is actively being investigated as a replacement for 5-fluorouracil in most combinations of colon and rectal cancer regimens. Capecitabine has been demonstrated to be at least equivalent to bolus IV 5-fluorouracil in the metastatic and adjuvant setting

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with improved patient tolerability. Hand-foot syndrome and diarrhea are common with capecitabine as its toxicities (and pharmacologic activity) appear to mimic those of continuous infusions of 5-fluorouracil. Both irinotecan and oxaliplatin have been combined with capecitabine. Capecitabine in combination with oxaliplatin appears to be as safe and effective as IV-based 5-fluorouracil in the treatment of colorectal cancer.41,44 Combinations with irinotecan have had mixed results and are not routinely recommended.39,41

The dose of capecitabine ranges from 1,000 to 1,250 mg/m twice a day when used by itself; lower doses are often used when it is given in combination with irinotecan or oxaliplatin or in patients with renal insufficiency. The dose should be taken on a full stomach with breakfast and dinner. Capecitabine administered with warfarin can result in significant increases in patients' International Normalized Ratio (INR) and requires close monitoring. The convenience of oral administration potentially requiring less clinic visits and an improvement in toxicity makes capecitabine a useful al ternative to IV 5-fluorouracil both by itself and incorporated into other regimens used in colorectal cancer.

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