The aim of this study is to determine the efficacy of Theophylline, N-Acetylcysteine and, and Theophylline plus N-acetylcysteine in the prevention of contrast-induced nephropathy. Investigators assume that Theophylline plus N-acetylcysteine is more effective than Theophylline alone and N-acetylcysteine alone. Investigators include patients referring for elective coronary angiography or angioplasty and allocate them to each of the mentioned treatments from 24 hours before to 48 hours after administration of contrast material. Investigators then measure serum creatinine and see if it is raised by ≥ 0.5 mg/dL or ≥ 25% of the baseline value.

Inclusion Criteria:

• adult patients
• candidate of elective coronary angiography or angioplasty
• at least moderate risk for contrast induced nephropathy

Exclusion Criteria:

• unstable angina or myocardial infarction, cardiac arrhythmia, seizures, acute renal failure, end-stage renal disease
• unstable serum creatinine
• unstable hemodynamic
• intravascular administration of contrast material in the past month
• using theophylline or N-acetylcysteine in the past month,
• known hypersensitivity to theophylline or N-acetylcysteine