NAC-REPAIR for Post-surgical Pain

Intervention: Oral N-acetylcysteine capsules, 600 mg twice daily. Timing/Duration: Begin the evening before surgery (≤24 h pre-op) and continue through Post-op Day 14 (total 15 days; bottle overfilled to cover missed doses). Administration: Self-administered at home; counseling at baseline dispense; pill diary + pill counts. Concomitant care: All peri-operative care per standard of care (SoC), including multimodal analgesia; no high-dose antioxidant supplements; nitrates excluded. Objective: Test whether peri-operative NAC improves early pain, function, and recovery via redox-immune modulation.

Intervention: Matched inert capsules (e.g., microcrystalline cellulose), identical in size/appearance/labeling to NAC. Timing/Duration: 600 mg-equivalent capsule count, twice daily, evening before surgery through Post-op Day 14. Administration: Same counseling, diary, and adherence checks as NAC arm. Concomitant care: Identical SoC allowances/restrictions as NAC arm. Randomization/Blinding: 1:1, stratified by surgery type (upper- vs lower-extremity); double-blind (participants, investigators, assessors). Primary comparisons: Early postoperative pain and function (e.g., PROMIS-PI/PF, QuickDASH or LEFS), opioid consumption; safety/tolerability.