Capecitabine is an oral prodrug of the antimetabolite 5-fluorouracil (5-FU) that is widely used in the treatment of several solid tumors, particularly colorectal and breast cancers. Developed to improve the therapeutic index and convenience of intravenous 5-FU, capecitabine undergoes a multistep enzymatic activation process preferentially in tumor tissues, thereby increasing local drug concentration while reducing systemic toxicity. This report provides a concise overview of capecitabine, covering its pharmacology, clinical indications, adverse effects, and practical considerations.

Mechanism of Action and Metabolism

Capecitabine is a rationally designed prodrug that is converted to 5-FU through a three-step enzymatic cascade. Following oral administration, it is absorbed intact from the gastrointestinal tract. In the liver, carboxylesterase hydrolyzes capecitabine to 5’-deoxy-5-fluorocytidine (5’-DFCR). Then, cytidine deaminase, primarily in the liver and tumor tissues, converts 5’-DFCR to 5’-deoxy-5-fluorouridine (5’-DFUR). Finally, thymidine phosphorylase (TP) cleaves 5’-DFUR to release active 5-FU. TP is significantly upregulated in many tumors compared to normal tissues, providing a degree of tumor selectivity. Within the cell, 5-FU is further metabolized to cytotoxic nucleotides that inhibit thymidylate synthase (TS) and incorporate into RNA and DNA, leading to disrupted DNA synthesis and cell death. The preferential activation in tumors enhances local efficacy and reduces exposure of healthy tissues.

Pharmacokinetics

Capecitabine is rapidly and extensively absorbed after oral intake, with peak plasma concentrations achieved within 1.5 to 2 hours. Food reduces both the rate and extent of absorption, so it is typically administered within 30 minutes after a meal to minimize variability. The drug is extensively metabolized in the liver, and its metabolites are excreted mainly renally. The elimination half-life of capecitabine and its metabolites is short (0.5–1.5 hours), but the active 5-FU is rapidly cleared. The pharmacokinetics are nonlinear at higher doses. Because of renal clearance, dose adjustment is required in patients with moderate renal impairment (creatinine clearance 30–50 mL/min). A hematopoietic and gastrointestinal toxicity profile is dose-limiting, with hand-foot syndrome (palmar-plantar erythrodysesthesia) being a common and characteristic side effect.

Clinical Indications

Capecitabine is approved for use in:

• Colorectal cancer: As adjuvant therapy for stage III (Dukes C) colon cancer after complete resection, and as first-line treatment for metastatic colorectal cancer, often in combination with oxaliplatin (XELOX) or irinotecan (XELIRI) or as a single agent.


• Breast cancer: In combination with docetaxel for advanced or metastatic disease after failure of prior anthracycline therapy, or as monotherapy in taxane-resistant patients. It is also used in some settings for HER2-positive breast cancer with trastuzumab.


• Gastric and esophageal cancers: Often in combination with platinum agents (e.g., cisplatin) or as part of perioperative regimens.


• Pancreatic cancer: In combination with gemcitabine or as part of chemoradiation protocols.

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Dosing Regimens

The typical dose for intermittent monotherapy is 1250 mg/m² twice daily for 14 days followed by a 7-day rest (21-day cycle). In combination therapy, lower doses are used, e.g., 1000 mg/m² twice daily with docetaxel or 850–1000 mg/m² twice daily with oxaliplatin. Continuous dosing schedules exist but are less common. Dose modifications are based on toxicity grade, with guidelines provided for managing hand-foot syndrome, diarrhea, stomatitis, and myelosuppression.

Adverse Effects

The most common adverse effects of capecitabine include:

• Gastrointestinal: diarrhea, nausea, vomiting, stomatitis, abdominal pain. Diarrhea can be severe and requires prompt management with loperamide and hydration.


• Dermatological: hand-foot syndrome (palmar-plantar erythrodysesthesia) presents as symmetrical, painful erythema, swelling, and desquamation of palms and soles. Incidence correlates with cumulative dose and schedule; management includes dose reduction, treatment breaks, and symptomatic measures such as emollients, steroids, and avoidance of heat/friction.


• Hematologic: neutropenia, anemia, thrombocytopenia (less common than with IV 5-FU).


• Hepatic: transient elevation of transaminases and bilirubin.


• Metabolic: hypercalcemia, particularly in patients with bone metastases.


• Cardiac: rare but serious; symptoms mimicking angina or myocardial infarction can occur, likely due to coronary vasospasm. Patients with prior coronary artery disease are at increased risk.


• Ocular: lacrimation, conjunctivitis.

Less common effects include fatigue, anorexia, headache, and neuropathy.

Drug Interactions

Capecitabine interacts with warfarin and other coumarin anticoagulants, potentiating their effect; frequent INR monitoring is essential during and after treatment. It also increases the toxicity of phenytoin. The antacid aluminum hydroxide/magnesium hydroxide can reduce absorption; separation by at least 2 hours is recommended. Leucovorin (folinic acid) potentiates 5-FU activity and toxicity when given with capecitabine, and this combination must be used with caution. Inhibitors and inducers of CYP2C9 and dihydropyrimidine dehydrogenase (DPD) may affect metabolism, though clinically significant interactions are limited.

Contraindications and Precautions

Capecitabine is contraindicated in patients with known dihydropyrimidine dehydrogenase (DPD) deficiency, a genetic disorder that leads to severe and potentially fatal toxicity from 5-FU. Screening for DPD deficiency (via genotyping or phenotype testing) is recommended in some regions before starting treatment, though not universal. Other contraindications include severe renal impairment (creatinine clearance <30 mL/min), severe hepatic impairment, known hypersensitivity, and pregnancy (Category D). Precautions include caution in patients with prior unanticipated severe toxicity to 5-FU, history of coronary artery disease, and those receiving concurrent radiation to certain sites.

Monitoring and Supportive Care

Before each cycle, complete blood count, renal and liver function tests are recommended. Patients should be educated about early signs of hand-foot syndrome (e.g., tingling, burning) and diarrhea. Loperamide is prescribed for diarrhea, and topical corticosteroids and emollients for hand-foot syndrome. Dose adjustments follow standard algorithms based on toxicity grade. For patients who develop severe or recurrent toxicity, testing for DPD deficiency is warranted, and alternative therapies may be considered.

Conclusion

Capecitabine is an effective and convenient oral alternative to intravenous 5-FU, offering similar efficacy in many settings with a distinct toxicity profile that includes hand-foot syndrome and diarrhea. Its tumor-selective activation provides a therapeutic advantage, though careful patient selection, dose adjustment, and vigilant management of adverse events are essential. Ongoing research continues to explore combinations and scheduling to optimize outcomes. Overall, capecitabine remains a cornerstone of modern chemotherapy for gastrointestinal and breast cancers.