BACKGROUND: Ustekinumab (UST) is commonly used to treat Crohn's disease and ulcerative colitis. However, some patients may experience diminishing response or require increased dosage. Intravenous (IV) UST maintenance is explored as a solution. OBJECTIVES: We sought to evaluate IV UST maintenance effectiveness and safety in inflammatory bowel disease patients with partial or lost subcutaneous UST response. METHODS: This was a multicenter retrospective study of inflammatory bowel disease patients on IV UST maintenance. Clinical response and remission at weeks 12 and 52, defined as Harvey-Bradshaw Index </=4 for Crohn's disease or partial Mayo score </=2 for ulcerative colitis. Objective markers reduction (fecal calprotectin, C-reactive protein), UST trough levels pre- and post-IV maintenance, and adverse events were assessed. RESULTS: A total of 59 patients were included. Clinical remission at weeks 12 and 52 achieved by 47.5% and 64.3% respectively. 96.6% continued IV UST at follow-up. UST serum levels quadrupled. No adverse events reported. CONCLUSIONS: IV UST maintenance effectively sustained remission in most patients at 52 weeks.