SOX Regimen Dosage
The standard SOX regimen consists of oxaliplatin 130 mg/m² IV on day 1 plus S-1 80-120 mg/m²/day orally (divided into two daily doses) for 14 days, repeated every 3 weeks. 1
Dosing Details
Oxaliplatin Component
- Dose: 130 mg/m² intravenous infusion over 2 hours
- Schedule: Day 1 of each cycle
- Cycle frequency: Every 3 weeks (21 days)
S-1 Component (Body Surface Area-Based)
The S-1 dose is determined by body surface area (BSA):
- BSA <1.25 m²: 80 mg/day
- BSA 1.25 to <1.5 m²: 100 mg/day
- BSA ≥1.5 m²: 120 mg/day
Administration: Divided into two doses daily (morning and evening) for 14 consecutive days, followed by 7 days of rest 2, 3
Clinical Context and Evidence Strength
The SOX regimen is primarily established for gastric cancer treatment in Asian populations, where it has demonstrated comparable or superior efficacy to FOLFOX regimens 4, 1. The 2025 CSCO guidelines and 2018 Pan-Asian ESMO guidelines both recognize SOX as an alternative to FOLFOX/CAPOX in appropriate settings 1.
Important Dosing Variations by Clinical Setting
For advanced/metastatic gastric cancer (first-line):
- Standard dosing as above 5
- Phase II data showed 59% response rate with oxaliplatin 100 mg/m² (lower dose) 5
For neoadjuvant/perioperative gastric cancer:
- Recommended dose: Oxaliplatin 130 mg/m² with S-1 80 mg/m²/day 3
- Typically 2-4 preoperative cycles, followed by surgery, then 2-4 postoperative cycles 4
For adjuvant gastric cancer:
- 8 cycles of SOX followed by maintenance S-1 monotherapy has shown survival benefit 2
Critical Safety Considerations
Dose Modifications
- Peripheral neuropathy: Most common dose-limiting toxicity with oxaliplatin; consider dose reduction or discontinuation if ≥grade 2 develops
- Neutropenia: Grade 3/4 occurs in ~22% of patients 5
- Renal impairment: S-1 requires dose adjustment for creatinine clearance <60 mL/min
- Geographic considerations: North American patients may require lower fluoropyrimidine doses due to increased toxicity compared to Asian populations 6
Common Pitfalls to Avoid
- Do not confuse with CAPOX/XELOX dosing: SOX uses S-1 (not capecitabine) with different pharmacokinetics
- BSA calculation is mandatory: S-1 dosing errors are common when BSA is not properly calculated
- 14-day on/7-day off schedule: Unlike some regimens with continuous dosing, the rest period is essential
- Not interchangeable with other fluoropyrimidines: S-1 contains CDHP and OXO components that modify 5-FU metabolism 7
Regional Applicability
SOX is primarily validated and recommended for Asian populations with gastric cancer. The regimen appears in Pan-Asian adapted guidelines 1, 8 but is not prominently featured in Western colorectal cancer guidelines 9, 6, where FOLFOX and CAPOX remain preferred standards.
For colorectal cancer specifically, while S-1-based regimens are mentioned in Asian guidelines 9, the evidence base is substantially stronger for FOLFOX/CAPOX regimens in Western populations.