This is a Phase 1, randomized, double-blind, dose escalation, safety and pharmacokinetic study. The study will be conducted in approximately 10 sites in the United States. Up to 48 patients at high risk for AKI (CCF score ≥ 5 OR an estimated GFR (eGFR) <60 mL/min/1.73 m2) who have undergone major cardiovascular surgery will participate. Patients will receive a single IV injection of I5NP or placebo following cardiovascular surgery. I5NP will be administered 4 hours (+/- 30 minutes) following removal of the cardiopulmonary bypass machine (CBM).