Abstract: A total of six RCTs (326 patients) evaluating therapeutic discontinuation in patients with quiescent CD were eligible for inclusion. In four RCTs azathioprine monotherapy was discontinued, and in two RCTs azathioprine was discontinued from a combination therapy regimen consisting of azathioprine with infliximab. No studies of biologic monotherapy withdrawal were eligible for inclusion. The majority of studies received unclear or low risk of bias ratings, with the exception of three open-label RCTs, which were rated as high risk of bias for blinding. Four RCTs (215 participants) compared discontinuation to continuation of azathioprine monotherapy, while two studies (125 participants) compared discontinuation of azathioprine from a combination regimen to continuation of combination therapy. Continuation of azathioprine monotherapy was shown to be superior to withdrawal for risk of clinical relapse. Thirty-two per cent (36/111) of azathioprine withdrawal participants relapsed compared to 14% (14/104) of participants who continued with azathioprine therapy (RR 0.42, 95% CI 0.24 to 0.72, GRADE low quality evidence). However, it is uncertain if there are any between-group differences in new CD-related complications (RR 0.34, 95% CI 0.06 to 2.08, GRADE low quality evidence), adverse events (RR 0.88, 95% CI 0.67 to 1.17, GRADE low quality evidence), serious adverse events (RR 3.29, 95% CI 0.35 to 30.80, GRADE low quality evidence) or withdrawal due to adverse events (RR 2.59, 95% CI 0.35 to 19.04, GRADE low quality evidence). Common adverse events included infections, mild leukopenia, abdominal symptoms, arthralgias, headache and elevated liver enzymes. No differences between azathioprine withdrawal from combination therapy versus continuation of combination therapy were observed for clinical relapse. Among patients who continued combination therapy with azathioprine and infliximab, 48% (27/56) had a clinical relapse compared to 49% (27/55) of patients discontinued azathioprine but remained on infliximab (RR 1.02, 95% CI 0.68 to 1.52, P = 0.32; GRADE low quality evidence). The effects on adverse events (RR 1.11, 95% CI 0.44 to 2.81, GRADE low quality of evidence) or serious adverse events are uncertain (RR 1.00, 95% CI 0.21 to 4.66; GRADE very low quality of evidence). Common adverse events in the combination therapy studies included infections, liver test elevations, arthralgias and infusion reactions. The effects of withdrawal of immunosuppressant therapy in people with quiescent Crohn's disease are uncertain. Low quality evidence suggests that continuing azathioprine monotherapy may be superior to withdrawal for avoiding clinical relapse, while very low quality evidence suggests that there may be no difference in clinical relapse rates between discontinuing azathioprine from a combination therapy regimen, compared to continuing combination therapy. It is unclear whether withdrawal of azathioprine, initially administered alone or in combination, impacts on the development of CD-related complications, adverse events, serious adverse events or withdrawal due to adverse events. Further high-quality research is needed in this area, particularly double-blind RCTs in which biologic therapy or an immunosuppressant other than azathioprine is withdrawn.

Plain-language summary: We performed a comprehensive literature review and identified six randomized controlled trials (an experiment in which participants are randomly assigned to receive two or more interventions and the results are compared) that involved a total of 326 participants. Four of the six studies assigned patients who had been receiving azathioprine alone to either continue or discontinue therapy (215 participants). Two of the six studies assigned patients who had been receiving azathioprine in addition to infliximab to continue therapy or discontinue azathioprine (111 participants). Clinical relapse occurred in 13% (14/104) of patients who continued azathioprine monotherapy compared to 32% (36/111) of patients who discontinued azathioprine monotherapy. No differences were observed for Crohn's disease-related complications, side effects, serious side effects and withdrawal due to side effects. Common side effects included infections, mild decrease in the number of white blood cells, abdominal symptoms, joint pain, headache and elevated liver enzymes. Among patients who continued combination therapy with azathioprine and infliximab, 48% (27/56) had a clinical relapse compared to 49% (27/55) of patients discontinued azathioprine but remained on infliximab. No differences in side effects, serious side effects or withdrawal due to side effects were observed. Common side effects reported in the combination therapy studies included infections, liver test elevations, joint pain and infusion reactions (a hypersensitivity reaction to the biologic medication). Overall, the quality of evidence for each outcome was low due to a high risk of study bias and small numbers of patients evaluated. The effects of withdrawal of immunosuppressant therapy in people with Crohn's disease in remission are uncertain. Low quality evidence suggests that continuing azathioprine monotherapy may be superior to withdrawal of azathioprine for avoiding clinical relapse in people with Crohn's disease in remission. Low quality evidence suggests that stopping the immunosuppressive after combination therapy does not seem to impact on the risk of relapsing. It is unclear whether the withdrawal of azathioprine, initially administered alone or in combination, impacts on the development of Crohn's disease-related complications, side effects, serious side effects, or withdrawal from the studies due to side effects. Additional research is needed in this area to better inform clinical practice, particularly high-quality randomized controlled trials examining outcomes when biologic therapy is withdrawn.