Indigo naturalis is effective even in treatment-refractory patients with ulcerative colitis: a post hoc analysis from the INDIGO study

Background We recently reported the efficacy of indigo naturalis (IN) in patients with active ulcerative colitis (UC) in a randomized controlled trial (INDIGO study). However, few studies have been conducted to investigate whether IN is effective even in treatment-refractory cases, such as in those with steroid dependency and anti-TNF refractoriness. Methods In the INDIGO study, 86 patients with active UC were randomly assigned to an IN group (0.5-2.0 g daily) or placebo group. The rate of clinical response (CR), mucosal healing (MH), and change in fecal calprotectin (FCP) levels was compared between refractory [patients with steroid-dependent disease, previous use of anti-TNF-alpha, and concomitant use of immunomodulators (IM)] and non-refractory patients. We also analyzed factors predicting CR and MH at week 8. Results The rates of CR of IN group were significantly higher than placebo group, even in patients with steroid-dependent disease (p < 0.001), previous use of anti-TNF-alpha (p = 0.002), and concomitant use of IM (p = 0.013). The rates of MH in IN group were significantly higher than in placebo group in patients with steroid-dependent disease (p = 0.009). In the IN group, median FCP levels, at week 8, were significantly lower than baseline in patients with steroid-dependent disease and patients with the previous use of anti-TNF-alpha (p < 0.001, respectively). Multivariate analysis indicated that the previous use of anti-TNF-alpha was not a predictive factor for CR and MH at week 8. Conclusions In a sub-analysis of data from a randomized placebo-controlled trial, we found that IN may be useful even in patients with steroid-dependent disease and patients with the previous use of anti-TNF-alpha.