BACKGROUND: Superior efficacy of subcutaneous infliximab (CT-P13 SC) over placebo for maintenance therapy in patients with Crohn's disease (CD) and ulcerative colitis (UC) was demonstrated in the randomized LIBERTY-CD and LIBERTY-UC studies. The current post hoc analysis compared outcomes with CT-P13 SC by baseline immunosuppressant use. METHODS: Patients with moderately to severely active CD or UC randomized to the CT-P13 SC maintenance arm of the 54-week LIBERTY trials at week 10 and who were treated in the open-label extension (weeks 56-102) were included. Pharmacokinetic, efficacy, biomarker, safety, and immunogenicity endpoints were evaluated by baseline immunosuppressant use (monotherapy vs combination therapy). RESULTS: A total of 192 patients with CD (monotherapy, n = 126; combination therapy, n = 66) and 237 patients with UC (monotherapy, n = 180; combination therapy, n = 57) were included. In both studies, efficacy outcomes were generally comparable between monotherapy and combination therapy at week 54 or week 102. Serum concentrations were generally higher, and antidrug antibody-positive conversion rates were lower, with combination therapy relative to monotherapy. In combined analyses of CD and UC, comparable safety profiles were observed between monotherapy and combination therapy. CONCLUSIONS: Despite some differences in pharmacokinetics and immunogenicity between CT-P13 SC received alone or in combination with immunosuppressants in patients with CD or UC, efficacy outcomes at week 54 or week 102 were generally comparable. The overall safety profile and incidence of systemic injection reactions were also comparable between monotherapy and combination therapy.