A Cochrane review included 12 studies with a total of 2146 subjects comparing 5-ASA to placebo.
There was no statistically significant difference in relapse rates at 12 months. 53% (526/998) of 5-ASA patients (dose 1.6 g to 4 g/day) relapsed at 12 months compared to 54% (544/1016) of placebo patients (RR 0.98, 95% CI 0.91 to 1.07; 11 studies; 2014 patients). One study found no difference in relapse rates at 24 months. 54% (31/57) of 5-ASA patients (dose 2 g/day) relapsed at 24 months compared to 58% (36/62) of placebo patients (RR 0.94, 95% CI 0.68 to 1.29, 119 patients). One paediatric study found no statistically significant difference in relapse rates at 12 months. 62% (29/47) of paediatric 5-ASA patients (dose 50 mg/kg/day) relapsed at 12 months compared to 64% (35/55) of paediatric placebo patients (RR 0.97, 95% CI 0.72 to 1.31; 102 patients). There was no statistically significant difference in the proportion of patients who experienced an adverse event, withdrawal due to adverse events or serious adverse events. Common adverse events reported in the studies included diarrhoea, nausea and vomiting, abdominal pain, headache and skin rash.
In 6 studies where participants were followed up for 12 months the OR for remission was 1.00 (95%CI, 0.80 to 1.24). For the seventh study where follow up was for 24 months, the odds ratio for relapse was 0.98; 95% CI, 0.51 to 1.90. In further sensitivity analyses, we analysed only participants who completed the study and ignored the dropouts. The odds ratio (fixed effects model) for the 6 studies where follow up was for 12 months was 0.74 (95% CI, 0.57 to 0.96), but using the random effects model, the OR was 0.68 (95% CI 0.45 to 1.02). The OR for the seventh study where follow up was for 24 months was 0.86; 95% CI, 0.42 to 1.78. Comment: The authors conclude: "We found no evidence in this review to suggest that 5-ASA preparations are superior to placebo for the maintenance of medically-induced remission in patients with Crohn's disease. Therefore it appears that additional randomised trials of this regime are not justified." A systematic review on the effectiveness of 5-ASA in maintaining remission in Crohn´s disease