Purpose: To examine the efficacy and tolerability of adalimumab (ADA), a fully human, anti-TNF-αα monoclonal antibody, in the closure of perianal fistulae in patients with fistulizing Crohn's disease (CD) and history of intolerance (INT) or lost response (LR) to infliximab (INF). Methods: In the first 4 weeks of this ongoing, 52-week, open-label, multicenter study, ADA was administered sc 160 mg at BL, 80 mg at Week 2, and 40 mg at Week 4 to patients who had discontinued previous INF therapy. The subset of patients either had fistulae only with CDAI < 220, or moderately to severely active (CDAI>220) luminal (mucosal) and fistulizing CD. Patients were assessed for complete or partial (≥50% decrease in the number of draining fistulae compared to BL) fistula closure, Perianal Disease Activity Index (PDAI) score, and adverse events (AE). Results: Of 22 patients with fistulae, all had previously discontinued INF: 23% (n = 5) for LR, 77% (n = 17) for INT. Ten (45%) patients had luminal and fistulizing CD, 12 (55%) had fistulae only. The mean BL PDAI score overall (n = 22) was 10.5 ± 2.8; the mean number of fistulae at BL was 2.5 ± 1.2 in patients with fistulizing CD only and 3.8 ± 5.5 in patients with both luminal and fistulizing CD. Week 4 results are presented (table). Treatment-related AE were mild to moderate in severity and similar to those observed in studies of ADA in patients with rheumatoid arthritis (RA). The most common AE were erythema, nausea/dizziness, weakness, and myalgia. One patient with fistulizing CD dropped out due to non-pruritic erythema. No serious AE were reported.Table: PDAI Scores and Fistula Closure at Week 4 of Adalimumab Treatment.Conclusions: Adalimumab induced complete or partial fistula closure in these patients and was well-tolerated. No new safety concerns were identified compared with ADA-treated RA population.