N-acetylcysteine reduces urinary albumin excretion following contrast administration: evidence of biological effect.

BACKGROUND: There are conflicting results regarding the effectiveness of N-acetylcysteine (NAC) in attenuating contrast-induced nephropathy (CIN). NAC administration independently reduces serum creatinine, potentially confounding studies utilizing creatinine-based endpoints. Albuminuria is a marker of renal injury and spot urine albumin: creatinine ratios (ACR) reflect 24-h urine albumin excretion. We performed a pre-specified secondary analysis from our published negative randomized control trial of NAC for prevention of CIN, to determine if NAC administration reduces albuminuria after contrast exposure following cardiac catheterization. METHODS: We included study patients who had paired urine specimens obtained pre- and post-cardiac catheterization. Baseline characteristics were compared using the chi square test or Mann-Whitney U-test, as appropriate. Changes in ACR were evaluated using binomial exact test. The effect of NAC on post-cardiac catheterization changes in ACR ratio was evaluated by ordinal logistic regression. RESULTS: A total of 125 patients met inclusion criteria (pre- and post-catheterization urinalysis within 7 days). Baseline characteristics neither differ between NAC and placebo groups, nor were they different from those who were excluded. Among the patients receiving NAC, 10.7% improved their ACR ratio and 7.1% worsened; in contrast, in patients on placebo only 4.3% improved, while 21.7% worsened (P=0.015). Change in ACR ratio was not associated with change in kidney function as measured by calculated creatinine clearance or GFR. CONCLUSIONS: The results of this analysis suggest NAC may attenuate contrast-induced glomerular or tubular injury, as defined by albumin excretion, and appears to be independent of any effect on creatinine-derived measures of kidney function. Larger studies are required to confirm this observation.