Capecitabine Dosage Calculation for TNT Regimen in Rectal Cancer
For a patient with a BSA of 2.32 m², the appropriate capecitabine dosage is 1,914 mg twice daily (rounded to 1,900 mg twice daily) when using the recommended dose of 825 mg/m² for the TNT regimen in rectal cancer.
Dosage Calculation
The calculation is straightforward:
- Prescribed dose: 825 mg/m²
- Patient BSA: 2.32 m²
- Total dose = 825 mg/m² × 2.32 m² = 1,914 mg
Administration Details
- Capecitabine should be administered twice daily (morning and evening)
- Dose should be taken with water within 30 minutes after a meal
- Round to the nearest 100 mg for practical administration (1,900 mg)
Evidence-Based Rationale
The NCCN guidelines for rectal cancer specifically recommend capecitabine at a dose of 825 mg/m² twice daily when used concurrently with radiation therapy 1. This is the standard dosing for the TNT (Total Neoadjuvant Therapy) regimen which includes:
- Capecitabine 825 mg/m² twice daily on days of radiation
- Radiation therapy for 5 weeks (typically 45-50 Gy in 25-28 fractions)
Important Considerations
Dose Rounding
- For practical administration, the calculated dose of 1,914 mg should be rounded to 1,900 mg
- Capecitabine tablets are available in 150 mg and 500 mg strengths, so a combination of these can be used to achieve the target dose
Monitoring Requirements
- Monitor for hand-foot syndrome, which is a common dose-limiting toxicity
- Watch for gastrointestinal toxicities, particularly diarrhea
- Regular complete blood counts to assess for myelosuppression
Dose Modifications
- Dose reductions may be necessary for:
- Elderly patients (≥65 years)
- Patients with renal impairment (CrCl 30-50 mL/min: reduce to 75% of starting dose)
- Development of grade 2-4 toxicities
Common Pitfalls to Avoid
- Using incorrect dosing for the indication (rectal cancer with radiation requires 825 mg/m², not the higher 1000-1250 mg/m² used in other settings)
- Failing to round to practical tablet combinations
- Not considering renal function when determining dosage
- Overlooking the need for twice daily administration specifically on radiation days
The TNT regimen has shown promising efficacy in downstaging rectal tumors prior to surgery, with acceptable toxicity when the appropriate dose of capecitabine (825 mg/m²) is used 2, 3.