A total of 12 RCTs (n=1,312) were included in the review. Eight were published in full (n=885) while four were published only in abstract form.
Primary analysis (8 RCTs, n=885).
The risk of RCN was statistically significantly lower with NAC than with placebo (RR 0.41, 95% confidence interval, CI: 0.22, 0.79, P=0.007). The number-needed-to-treat was 8 (95% CI: 5, 23).
Sensitivity analyses.
The exclusion of an RCT that used computed tomography and administered contrast media intravenously left the result essentially unchanged (RR 0.46, 95% CI: 0.24, 0.88, P=0.02; 7 RCTs).
The exclusion of an RCT that used intravenous NAC left the result essentially unchanged (RR 0.44, 95% CI: 0.22, 0.88, P=0.02; 7 RCTs).
The inclusion of results from the 4 RCTs published only as abstracts resulted in the risk of RCN being statistically significantly lower with NAC than with placebo (RR 0.55, 95% CI: 0.34, 0.91, P=0.02; 12 RCTs). However, the magnitude of this decrease was less when the abstracts were included.
Subgroup analyses.
Baseline kidney function: the beneficial effect of NAC in reducing the risk of RCN was statistically significant in patients with a baseline creatinine level of 1.9 mg/dL or less (RR 0.47, 95% CI: 0.29, 0.76, P=0.002), but not in patients with a baseline creatinine level of 1.9 mg/dL or greater (i.e. more severe renal dysfunction).
Volume of contrast medium: the beneficial effects of NAC were statistically significant in those who received more than 140 mL (RR 0.38, 95% CI: 0.21, 0.68, P=0.001), but not in those receiving a lower volume (140 mL or less).