SAN DIEGO – It takes more than the usual 5 mg/kg of infliximab to heal perianal fistulas in some Crohn’s disease patients, according to a multicenter review of 117 cases.
The investigators aimed for trough levels of at least 10-20 mcg/mL, higher than the usual target of perhaps 7 mcg/mL or less. Doing so generally required 10 mg/kg every 8 weeks, but a few patients needed 10 mg/kg or even 15 mg/kg every 4 weeks. Fistulas healed in 63 (54%) patients and closed in 36 (31%).
Troughs of at least 10 mcg/mL and a history of dose escalation were both independent predictors of fistula healing, defined as the absence of drainage. Patients with fistula healing had significantly higher infliximab levels compared to those with active fistulas (18.5 vs. 6.5 mcg/mL; P less than .0001), and there was an incremental gain in healing with higher infliximab levels up to 50 mcg/mL. The association between infliximab levels and fistula healing had an area under the curve of 0.82 (P less than .0001) and the association with fistula closure was 0.69 (P = .014).
“Infliximab levels needed to achieve fistula healing were higher than what [has] been described for mucosal healing. Achieving higher infliximab levels in patients with Crohn’s disease and perianal fistulas may improve outcomes and should be considered in a treat-to-target strategy. At least 10-20 mcg/mL may be needed to achieve fistula healing in some patients,” concluded investigator Dr. Andres J. Yarur, a gastroenterologist at the Medical College of Wisconsin, Milwaukee.
“Obviously, in somebody with active perianal fistulas” at a trough of 30 mcg/mL, “it’s time to try something else, but I don’t give up on infliximab at a level of 7 mcg/mL, like a lot of people do. I’m kind of aggressive with these patients.” There wasn’t a formal assessment of adverse events, but “we have not really seen any side effects,” he said at the annual Digestive Disease Week meeting. One audience member remarked that the findings will likely change how he treats Crohn’s fistulas.
Dr. Yarur said he wasn’t surprised by the findings, “but I have more reassurance now” that aggressive dosing is the way to go for aggressive Crohn’s.
The patients were an average of 39 years old, with a mean disease duration of 12 years; about half were women. They were on infliximab for a median of 19 months. Infliximab antibodies dropped the likelihood of healing (odds ratio, 0.04; 95% confidence interval, 0.005-0.3; P less than .001) and closure (OR 0.038; 95% CI, 0.005-0.3; P less than .0001). About two-thirds of the patients were on concomitant immunomodulators, but they did not increase the odds of healing (OR 1.7; 95% CI, 0.8-3.7; P = .157).
“We usually start at a standard dose of 5 mg/kg, and then start checking troughs at week 14, before the first maintenance dose, and adjust” upward to hit the trough target. However, dosing also depends on “how much I think the patient needs. I don’t think we should standardize trough levels,” Dr. Yarur said. The team checks levels with the homogeneous mobility-shift assay from Prometheus Laboratories. “The type of assay you use is very important,” because interpretation of the results varies from one to the next.
De-escalation is on a case-by-case basis. “I would be very careful de-escalating somebody [who] has very aggressive disease. Many times patients don’t want to go down. They say ‘I feel good doc. I have no side effects. Leave me on my dose,’ ” he said.
There was a lack of cross-sectional imaging in the study; the investigators couldn’t distinguish simple fistulas from complex ones in their review.
Dr. Yarur had no disclosures. There was no industry funding for the work.