Abstract: Nine studies (484 patients) met the pre-specified inclusion criteria (Kappa 1.00). Six studies were rated as low risk of bias. Three studies were rated as high risk of bias due to blinding (two open label and one single-blind). The total daily dose of rectal 5-ASA ranged from 0.5 g to 4 g, and dose frequency ranged from once to three times daily. 5-ASA was delivered as liquid enema in five studies or as a suppository in four studies. Follow-up ranged from 6 to 24 months. Rectal 5-ASA was significantly superior to placebo for maintenance of symptomatic remission over a period of 12 months.Sixty-two per cent of patients in the rectal 5-ASA group maintained symptomatic remission compared to 30% of patients in the placebo group (4 studies; 301 patients; RR 2.22, 95% CI 1.26 to 3.90; I2 = 67%; P < 0.01). A GRADE analysis indicated that the overall quality of the evidence for the primary outcome was low due to imprecision (i.e. sparse data 144 events) and inconsistency (i.e. unexplained heterogeneity). Rectal 5-ASA was significantly superior to placebo for maintenance of endoscopic remission over a 12 month period. Seventy-five per cent of patients in the rectal 5-ASA group maintained endoscopic remission compared to 15% of patients in the placebo group (1 study; 25 patients; RR 4.88, 95% CI 1.31 to 18.18; P < 0.05). There was no statistically significant difference in the proportion of patients who experienced at least one adverse event. Sixteen per cent of patients in the rectal 5-ASA group experienced at least one adverse compared to 12% of placebo patients (2 studies; 160 patients; RR 1.35, 95% CI 0.63 to 2.89; I2 = 0%; P = 0.44). The most commonly reported adverse events were anal irritation and abdominal pain. No statistically significant differences between rectal and oral 5-ASA were identified for either symptomatic or endoscopic remission over a period of six months. Eighty per cent of patients in the rectal 5-ASA group maintained symptomatic remission compared to 65% of patients in the oral 5-ASA group (2 studies; 69 patients; RR 1.24, 95% CI 0.92 to 1.66; I2 = 0%; P = 0.15). A GRADE analysis indicated that the overall quality of the evidence for the primary outcome was low due to imprecision (i.e. sparse data 50 events) and high risk of bias (i.e. both studies in the pooled analysis were open label). Eighty per cent of patients in the rectal 5-ASA group maintained endoscopic remission compared to 70% of patients in the oral 5-ASA group (2 studies; 91 patients; RR 1.14, 95% CI 0.90 to 1.45; I2 = 0%; P = 0.26). In two small trials, one comparing 2 g/day 5-ASA enemas to 4 g/day 5-ASA enemas and the other comparing 0.5 g/day 5-ASA suppositories to 1 g/day 5-ASA suppositories no dose response relationship was observed. The limited data available suggest that rectal 5-ASA is effective and safe for maintenance of remission of mild to moderately active distal UC. Well designed randomized trials are needed to establish the optimal dosing regimen for rectal 5-ASA, to compare rectal 5-ASA with rectal corticosteroids and to identify subgroups of patients who are more or less responsive to specific rectal 5-ASA regimens. The combination of oral and rectal 5-ASA appears to be more effective than either oral or rectal monotherapy for induction of remission. The efficacy of combination therapy for maintenance of remission has not been assessed and could be evaluated in future trials.

Plain-language summary: This review includes nine randomized trials with a total of 484 participants. The limited data available suggest that rectal 5-ASA is effective and safe for maintenance of remission in UC. Rectal 5-ASA was found to be superior to placebo (e.g. enema or suppository with no active medicine). There was no difference in the incidence of side effects between rectal 5-ASA and placebo groups. Side effects were generally mild in nature and common side effects included anal irritation and abdominal pain. Studies comparing rectal 5-ASA with oral 5-ASA (pills) found no differences in effectiveness for maintenance therapy. Well designed randomized trials are needed to investigate different doses of rectal 5-ASA for maintenance therapy, Future studies should assess the effectiveness of combination therapy of oral 5-ASA with rectal 5-ASA as this has been found to be effective in active UC and has not been investigated for maintenance therapy. Future studies should also compare rectal 5-ASA with rectal corticosteroids.