Abstract
INTRODUCTION: A phase IV clinical trial confirmed the safety and efficacy of repository corticotropin injection (RCI, Acthar(®) Gel) in patients with refractory rheumatoid arthritis (RA) that was nonresponsive to standard-of-care therapies. The objective of this post hoc analysis was to identify baseline demographics and clinical characteristics that may be predictors of response to RCI. METHODS: The phase IV trial was a two-part, randomized, placebo-controlled withdrawal study. Post hoc analysis was conducted with the open-label portion of the trial data, in which all 258 subjects received RCI (80 U) twice weekly for 12 weeks. Responders were subjects who achieved low disease activity (LDA) by a Disease Activity Score with 28-joint count and erythrocyte sedimentation rate (DAS28-ESR) of < 3.2 at week 12. Responders were compared with nonresponders by assessing the proportion of subjects in each group for demographics and clinical characteristics, including weight, disease duration, medical history including osteoarthritis and unrelated joint conditions, hemoglobin A1c, C-reactive protein, ESR, DAS28-ESR, Clinical Disease Activity Index (CDAI), depression, anxiety, tender joint count (TJC), and swollen joint count (SJC). Bivariate analysis followed by multiple logistic regression analysis were conducted to identify significant baseline predictors for the outcome of achieving LDA by week 12. RESULTS: Bivariate analysis showed that RCI responders had significantly lower baseline TJC (p = 0.0310), SJC (p = 0.0018), ESR (p = 0.0487), and CDAI (p = 0.0112) and shorter RA disease duration (p = 0.0446). Subjects were less likely to achieve LDA if they had osteoarthritis (p < 0.0001), other joint-related conditions unrelated to RA (p < 0.0001), anemia (p = 0.0132), depression (p = 0.0006), or prior or concomitant use of targeted-synthetic or biologic disease-modifying antirheumatic drugs (p < 0.0001). Multiple logistic regression analysis revealed that, of the above, only ongoing osteoarthritis (p = 0.0272) or other joint-related conditions (p = 0.0193) were significant negative predictors of RCI response. CONCLUSIONS: These results identify specific patient characteristics that may be considered predictors of positive or negative clinical response to RCI.