We assessed the renoprotective effect of the highest dose of N-acetylcystein sanctioned for clinical use in a prospective , double-blind , placebo-controlled study including @ chronic kidney disease patients , stage @ or @ , who underwent coronary artery bypass graft surgery , on cardiopulmonary bypass ( CPB ) and off CPB , and were randomly allocated to receive either N-acetylcystein @ mg/kg followed by @ mg/kg for @ hours in @ % saline or only @ % saline .