Since acetylcysteine is a vasodilator as well as an antioxidant, it may work in two distinct ways, by preventing reduction in renal blood flow (RBF) or contrast-induced oxidative damage. Previous studies have used changes in serum creatinine. In addition to being an insensitive marker of altered renal function, if contrast causes renal vasoconstriction and acetylcysteine vasodilatation, changes in serum creatinine will not be the ideal marker of effect. Finally the optimum dose and route of acetylcysteine administration is unclear, as illustrated by studies using a variety of doses and routes.