Early Serum Infliximab Levels in Severe Ulcerative Colitis

The American Gastroenterology Association (AGA) recommends infliximab, a chimeric monoclonal antibody to human tumor necrosis factor (anti-TNF), in the treatment of patients with ulcerative colitis (UC) who don't achieve adequate clinical response despite treatment with conventional therapy. Infliximab is an FDA approved therapy for ulcerative colitis based on two large randomized trials, ACT I and ACT II. For patients who respond to induction therapy, scheduled maintenance therapy has been demonstrated to be both durable and safe. However, these trials did not include hospitalized patients.

Severe flares, or fulminant ulcerative colitis, remain highly morbid and potentially fatal presentations of disease. Traditionally, hospitalized patients who failed high-dose intravenous corticosteroid therapy require life-saving colectomy. Although the advent of infliximab has presented an alternative rescue therapy, some patients with severe ulcerative colitis are non-responders to anti-TNF induction therapy and proceed to colectomy. In the ACT I and II trials, outpatients with moderate to severe ulcerative colitis were randomized to placebo, 5mg/kg infliximab therapy, or 10mg/kg infliximab therapy. At 54 week follow-up, patients receiving infliximab had a 41% reduced risk of colectomy compared to the placebo group. Although infliximab at 5mg/kg was associated with a reduced risk of colectomy, only the 10mg/kg infliximab dosing yielded a statistically significant risk reduction. There were no differences in safety between the 5mg/kg and 10mg/kg infliximab groups; similar rates of serious adverse events, infections, and infusion reactions were reported. Thus, at our institution (University of California at San Francisco), it is our standard of care to administer infliximab at 10mg/kg IV for patients hospitalized with severe ulcerative colitis.

Dose escalation from 5mg/kg to 10mg/kg is routinely prescribed to recapture clinical response in subsets of patients with inflammatory bowel disease who experience loss of response during maintenance therapy and is supported in the FDA label for Crohn's disease. Loss of response to infliximab maintenance therapy is a well-recognized phenomenon, and there is abundant literature suggesting that durable and efficacious infliximab therapy is dependent upon optimizing serum infliximab levels. Specifically, high serum infliximab trough levels predict clinical response, but low serum trough levels and presence of infliximab antibodies are associated with loss of response. However, serum infliximab levels are not dependent upon drug dose and pharmacokinetics alone. Concurrent immunomodulator use may reduce immunogenicity against monoclonal antibody therapies, and more recently, there has been increased recognition of the importance of patient factors as well. Specifically, variability in drug metabolism and clearance has been associated with body-mass index, sex, and severity of inflammation - as measured by C-reactive protein, serum albumin, and tumor necrosis factor alpha levels. It has been demonstrated that patients with higher serum albumin levels maintain higher infliximab concentrations, lower clearance, and longer drug half-lives than patients with lower serum albumin levels; and low serum albumin correlates with poorer clinical response. Severe colonic disease is associated with higher early fecal infliximab concentration, which is inversely associated with serum infliximab levels and response to therapy. Moreover, high serum tumor necrosis factor alpha levels prior to infliximab infusion predict poorer clinical outcomes and need for dose escalation in patients with Crohn's disease and rheumatoid arthritis.

Patients hospitalized with severe ulcerative colitis can least afford suboptimal infliximab therapy, but are at highest risk given their malnutrition and uncontrolled inflammation. There is a growing trend towards the use of high dose of infliximab as the first line therapy in these severe, hospitalized patients as they have just one infusion (dose) to demonstrate clinical response before they are referred for colectomy. However, there is currently no pharmacokinetic data to support this practice. There is only a small body of literature that serum infliximab trough levels may predict clinical outcomes in acute ulcerative colitis. To our knowledge, there are no studies regarding the use of early infliximab levels - within the first 72 hours - to predict clinical response in the vulnerable subset of patients hospitalized for severe ulcerative colitis.

We propose a pilot study investigating the treatment of severe ulcerative colitis with high-dose infliximab (10mg/kg infusions), which is the standard of care at UCSF for severe, hospitalized ulcerative colitis. This will be a prospective, multi-site study which will consecutively enroll hospitalized ulcerative colitis patients meeting inclusion criteria from anyone of four UCSF-affiliated hospitals. Per routine care, enrolled subjects will undergo infectious work-up, receive intravenous corticosteroids in addition to supportive care, and undergo evaluation by a Colorectal Surgeon. Subjects that are eligible for anti-TNF therapy after routine screening will begin infliximab induction therapy on hospital day 3 at 10mg/kg. We will perform standardized pre- and post-treatment assessments of disease activity (Ulcerative Colitis Disease Activity Index - UCDAI), including acquisition of biochemical and endoscopic data. We will measure serum levels of tumor necrosis factor alpha, infliximab, and infliximab antibody throughout the course of treatment. The primary outcome will be avoidance of colectomy. This study will be the first to our knowledge to examine the empiric use of high-dose infliximab combined with early therapeutic drug monitoring to guide the care of patients hospitalized with severe ulcerative colitis. Our ultimate goal is to develop a rational approach to maximizing infliximab therapy in the setting of severe ulcerative colitis to minimize and predict primary non-response to infliximab induction therapy.