Capecitabine Overview
Capecitabine is an oral fluoropyrimidine chemotherapy agent indicated for adjuvant colon cancer, metastatic colorectal cancer, and metastatic breast cancer, with standard dosing of 1250 mg/m² twice daily for 14 days followed by 7 days rest, requiring dose reduction to 75% in moderate renal impairment and contraindicated in severe renal impairment (CrCl <30 mL/min) and DPD deficiency. 1
FDA-Approved Indications
Capecitabine is approved for:
- Adjuvant treatment of Dukes' C colon cancer following complete resection 1
- First-line metastatic colorectal cancer when single-agent fluoropyrimidine therapy is preferred 1, 2
- Metastatic breast cancer as monotherapy in patients resistant to anthracyclines and taxanes, or when further anthracycline therapy is contraindicated 1, 2
- Combination with docetaxel for metastatic breast cancer after failure of anthracycline-based chemotherapy 1, 2
Standard Dosing Schedule
The FDA-approved dose is 1250 mg/m² orally twice daily (approximately 12 hours apart) for 14 days, followed by a 7-day rest period, given as 3-week cycles. 1 This intermittent schedule was selected based on optimal safety and efficacy profile compared to continuous dosing 1.
Key Dosing Considerations:
- Take within 30 minutes after a meal - food reduces absorption but this is the intended administration method 1
- Median relative dose intensity in clinical trials was 93% 1
- Most patients (77%) in real-world practice start below the recommended dose 3
Renal Dose Adjustments
Renal function critically impacts capecitabine dosing due to accumulation of toxic metabolites, particularly FBAL and 5'-DFUR: 1, 4
Specific Adjustments:
- Normal renal function (CrCl >80 mL/min): Full dose 1250 mg/m² twice daily 1
- Mild impairment (CrCl 51-80 mL/min): No initial adjustment required, but monitor closely 1
- Moderate impairment (CrCl 30-50 mL/min): Reduce starting dose to 75% (950 mg/m² twice daily) 1, 4
- Severe impairment (CrCl <30 mL/min): CONTRAINDICATED - do not use 1, 4
The rationale: Moderate renal impairment causes 85% higher FBAL exposure and 42% higher 5'-DFUR exposure. All patients with severe renal impairment in clinical studies experienced grade 3-4 adverse events. 4 Japanese data confirms significantly higher toxicity rates with reduced renal function (100% adverse events in CrCl <50 mL/min group vs 61% in normal function). 5
Contraindications
Absolute contraindications include: 1
- Known DPD (dihydropyrimidine dehydrogenase) deficiency
- Severe renal impairment (CrCl <30 mL/min)
- Known hypersensitivity to capecitabine or 5-fluorouracil
DPD Deficiency - Critical Safety Issue:
DPYD gene variants occur in 4.1% of patients and increase treatment-related death risk from 0.1% to 2.3%. 6 The NCCN guidelines emphasize that prospective DPYD genotyping with dose reductions reduces grade ≥3 toxicity from 73% to 28% and eliminates treatment-related deaths (0% vs 10% in historical controls). 6
For patients with DPYD variants:
- Heterozygous (intermediate metabolizers): Reduce starting dose by 25-50% depending on specific allele 6
- Homozygous (poor metabolizers): Avoid fluoropyrimidines entirely 6
Major Adverse Effects
Dose-Limiting Toxicities:
The three primary dose-limiting toxicities are: 1, 2, 7
Hand-foot syndrome (palmar-plantar erythrodysesthesia)
Diarrhea
Hyperbilirubinemia 2
Other Significant Adverse Effects:
- Hematologic: Neutropenia, anemia (particularly in renal impairment - 83% incidence with CrCl <50 mL/min) 5
- Gastrointestinal: Nausea/vomiting, stomatitis (less than IV 5-FU/LV), abdominal pain 2
- Cardiotoxicity: Rare but documented 3
- Fatigue and weakness 2
Compared to bolus 5-FU/LV, capecitabine causes more hand-foot syndrome but significantly less stomatitis, alopecia, neutropenia, and nausea. 2
Critical Drug Interactions
Warfarin - BLACK BOX WARNING:
Capecitabine increases warfarin AUC by 57% and INR by 2.8-fold, with maximum INR increased by 91%. 1 Frequent INR monitoring is mandatory when co-administering these agents.
Other Interactions:
- Phenytoin: Capecitabine increases serum phenytoin levels 2
- Antacids: Aluminum/magnesium-containing antacids increase capecitabine AUC by 16% and Cmax by 35% 1
- No significant interactions with cytochrome P450 substrates 1
Pharmacokinetic Considerations
Capecitabine is a rationally designed prodrug converted to 5-FU preferentially in tumor tissue by thymidine phosphorylase, which is present in higher concentrations in tumors than normal tissue. 2, 7 This tumor-selective activation was intended to improve tolerability compared to IV 5-FU.
- Bioavailability: ~100% 2
- Tmax: 1.5-2 hours 1
- Elimination: 95.5% renal (57% as FBAL metabolite, only 3% unchanged drug) 1
- Protein binding: <60%, primarily albumin 1
Common Pitfalls and Management Strategies
Failing to dose-adjust for renal function: Always calculate CrCl before initiating therapy. Use Cockcroft-Gault equation as this was used in clinical trials. 1, 4
Not considering DPYD testing: While not universally required, consider testing in patients with family history of severe fluoropyrimidine toxicity or in populations where testing is cost-effective. 6
Inadequate monitoring in elderly: Age increases FBAL exposure by 15% per 20-year increment, though this doesn't mandate dose reduction. 1 However, elderly patients often have reduced renal function requiring adjustment.
Ignoring early toxicity signals: In clinical trials, 57% of patients required treatment interruption, cycle delay, or dose reduction. 1 Early intervention prevents severe toxicity.
Incorrect administration timing: Must be taken within 30 minutes after meals - this is not optional as food affects absorption parameters. 1