indication

For the treatment of patients with metastatic breast cancer resistant to both paclitaxel and an anthracycline-containing chemotherapy regimen. May also be used in combination with docetaxel for the treatment of metastatic breast cancer in patients who have failed to respond to, or recurred or relasped during or following anthracycline-containing chemotherapy. Capecitabine is used alone as an adjuvant therapy following the complete resection of primary tumor in patients with stage III colon cancer when monotherapy with fluroprymidine is preferred. The use or capecitabine in combination regimens for advanced gastric cancer is currently being investigated.

pharmacology

Capecitabine is a fluoropyrimidine carbamate with antineoplastic activity indicated for the treatment of metastatic breast cancer and colon cancer. It is an orally administered systemic prodrug that has little pharmacologic activity until it is converted to fluorouracil by enzymes that are expressed in higher concentrations in many tumors. Fluorouracil it then metabolized both normal and tumor cells to 5-fluoro-2′-deoxyuridine 5′-monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP).

mechanism of action

Capecitabine is a prodrug that is selectively tumour-activated to its cytotoxic moiety, fluorouracil, by thymidine phosphorylase, an enzyme found in higher concentrations in many tumors compared to normal tissues or plasma. Fluorouracil is further metabolized to two active metabolites, 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP) and 5-fluorouridine triphosphate (FUTP), within normal and tumour cells. These metabolites cause cell injury by two different mechanisms. First, FdUMP and the folate cofactor, N5-10-methylenetetrahydrofolate, bind to thymidylate synthase (TS) to form a covalently bound ternary complex. This binding inhibits the formation of thymidylate from 2'-deaxyuridylate. Thymidylate is the necessary precursor of thymidine triphosphate, which is essential for the synthesis of DNA, therefore a deficiency of this compound can inhibit cell division. Secondly, nuclear transcriptional enzymes can mistakenly incorporate FUTP in place of uridine triphosphate (UTP) during the synthesis of RNA. This metabolic error can interfere with RNA processing and protein synthesis through the production of fraudulent RNA.

biotransformation

Metabolized by thymidine phosphorylase to fluoruracil.

absorption

Readily absorbed through the GI tract (~70%)

half life

45-60 minutes for capecitabine and its metabolites.

route of elimination

Capecitabine and its metabolites are predominantly excreted in urine; 95.5% of administered capecitabine dose is recovered in urine. Fecal excretion is minimal (2.6%). The major metabolite excreted in urine is FBAL which represents 57% of the administered dose.About 3% of the administered dose is excreted in urine as unchanged drug.

drug interactions

Acenocoumarol: Capecitabine may increase the anticoagulant effect of acenocoumarol by increasing its serum concentration.

Anisindione: Capecitabine may increase the anticoagulant effect of anisindione by increasing its serum concentration.

Dicumarol: Capecitabine may increase the anticoagulant effect of dicumarol by increasing its serum concentration.

Ethotoin: Capecitabine increases the effect of hydantoin

Fosphenytoin: Capecitabine increases the effect of hydantoin

Mephenytoin: Capecitabine increases the effect of hydantoin

Phenytoin: Capecitabine increases the effect of hydantoin

Tamoxifen: Capecitabine may reduce clearance rate of Tamoxifen. Monitor for changes in therapeutic/adverse effects of Tamoxifen if Capecitabine is initiated, discontinued or dose changed.

Tolbutamide: Capecitabine, a strong CYP2C9 inhibitor, may decrease the metabolism and clearance of Tolbutamide, a CYP2C9 substrate. Consider alternate therapy or monitor for changes in Tolbutamide therapeutic and adverse effects if Capecitabine is initiated, discontinued or dose changed.

Torasemide: Capecitabine, a strong CYP2C9 inhibitor, may increase the serum concentration of Torasemide, a CYP2C9 substrate, by decreasing Torasemide metabolism and clearance. Consider alternate therapy or monitor for changes in the therapeutic and adverse effects of Torasemide if Capecitabine is initiated, discontinued or dose changed.

Trastuzumab: Trastuzumab may increase the risk of neutropenia and anemia. Monitor closely for signs and symptoms of adverse events.

Trimethoprim: The strong CYP2C9 inhibitor, Capecitabine, may decrease the metabolism and clearance of Trimethoprim, a CYP2C9 substrate. Consider alternate therapy or monitor for changes in therapeutic and adverse effects of Trimethoprim if Capecitabine is initiated, discontinued or dose changed.

Voriconazole: Capecitabine, a strong CYP2C9 inhibitor, may increase the serum concentration of voriconazole by decreasing its metabolism. Monitor for changes in the therapeutic and adverse effects of voriconazole if capecitabine is initiated, discontinued or dose changed.

Warfarin: Capecitabine may increase the serum concentration of warfarin by decreasing its metabolism. Monitor for changes in prothrombin time and therapeutic effects of warfarin if capecitabine is initiated or discontinued. Subsequent cycles of capecitabine may increase this effect.

Zafirlukast: Capecitabine, a strong CYP2C9 inhibitor, may decrease the metabolism and clearance of zafirlukast. Consider alternate therapy or monitor for changes in zafirlukast therapeutic and adverse effects if capecitabine is initiated, discontinued or dose changed.