TNF and inflammatory bowel disease: A 2016 systematic review demonstrated robust evidence in thiopurines inducing remission in IBD when used as combination therapy with an anti-TNF, as well as in maintaining remission in CD and preventing post-op CD recurrence when used as monotherapy.43 The levels of active thiopurine metabolites required to prevent anti-TNF antibodies have not been well defined, but are likely lower than levels required to achieve disease remission when used as monotherapy.44,45