What was the key study finding?

The COMBINE study compared the treatment of pediatric Crohn’s disease with an anti-TNF biologic alone versus an anti-TNF biologic combined with low-dose oral methotrexate.  The study found that adding methotrexate reduced the risk of treatment failure for adalimumab, but not for infliximab. Methotrexate did lead to more side effects, but these were mostly mild and rarely led to the stopping of treatment.

Why was the study done?

Anti-TNF biologic medications like infliximab and adalimumab are commonly used to treat pediatric Crohn’s disease. However, they do not always work, and some patients stop responding to them. Some clinicians combine biologic medications with an immune-suppressing medication called methotrexate to try to boost response.  Other pediatric gastroenterologists are hesitant to add a second medicine because of concerns that two medications might lead to more side effects. The COMBINE trial was launched by the ImproveCareNow network to study the safety and effectiveness of using these biologics and methotrexate together in pediatric patients with Crohn’s disease.

How was the study designed?

The COMBINE trial enrolled patients less than 21 years old with Crohn's disease being started on either infliximab or adalimumab and randomized them to add low-dose oral methotrexate or a placebo for methotrexate. The primary study outcome was treatment failure defined as:

  • Failure to achieve, or maintain, steroid-free remission 26 weeks after starting the treatment, or
  • Failure to complete a steroid wean by 16 weeks of treatment, or
  • Active Crohn’s disease at two or more consecutive visits beyond week 26, defined by a short Pediatric Crohn's Disease Activity Index (sPCDAI) score of greater than 15,  or
  • Hospitalization or surgery for Crohn's disease beyond 26 weeks, or
  • Use of steroids for Crohn's disease for more than a total of ten weeks after week 16, or
  • Discontinuation of infliximab or adalimumab or study drug for lack of effectiveness or toxicity

What were the results?

In total, 297 patients were randomized to either combination therapy (infliximab or adalimumab + oral methotrexate) or monotherapy (infliximab or adalimumab + placebo). Of the 212 infliximab-treated patients, 110 received oral methotrexate, and 102 received a placebo. Of the 85 adalimumab-treated patients, 46 received oral methotrexate, and 39 received a placebo. The combination therapy and monotherapy groups were similar in age, disease characteristics, and other parameters.

Study-defined treatment failure was seen in 26% of the patients in the combination therapy group and 34% in the monotherapy group, a difference that was not statistically significant (meaning, it is possible that this finding may have been due to chance).

When looking just at the participants who were treated with infliximab, the rates of treatment failure did not differ between those receiving this biologic alone or in combination with methotrexate. 

In contrast, participants who received combination therapy with adalimumab and methotrexate, experienced a 2-fold reduction in the rate of treatment failure, and a 60% longer time to treatment failure compared to those receiving adalimumab alone. 

Treatment with a combination of adalimumab and methotrexate, a combination of infliximab and methotrexate, and infliximab alone all had similar rates of treatment failure. All of these treatments resulted in a lower rate of treatment failure with adalimumab alone. 

Were there differences in side effects between the study arms?

The study showed that those who received combination therapy had a higher frequency of adverse events related to study treatment, as reported by the site investigator, compared to those who were in the monotherapy group. This difference was not statistically significant meaning it could have occurred by chance. This trend was observed across all the participants in the study. Among patients on combination therapy, 43% had a treatment-related adverse event recorded compared to 32% of those in the monotherapy arm.  Side effects that were more common with combination therapy compared to monotherapy included nausea and/or vomiting (reported in 22% of those on combination therapy compared to 13% of those on monotherapy) and elevated liver enzymes in blood tests (13% with combination and 6% with monotherapy). Most adverse events were mild and only 5 participants in each study arm stopped therapy due to toxicity. 

What are the limitations of the study?

All studies have limitations that should be considered when interpreting their results, including the COMBINE trial. One of these is that there could have been differences in clinician monitoring of blood levels of infliximab and adalimumab that are used to adjust the dose to achieve target levels. During the study, the dose of infliximab tended to increase but stayed about the same for adalimumab.

Additionally, since the study was designed to reflect real-world conditions, the investigators did not closely monitor adherence to the anti-TNF or study medication. Since the majority of pediatric patients receive infliximab in an infusion center, the increased number of touch points with the healthcare system could have provided more opportunities to reinforce adherence for patients treated with infliximab than for patients treated with adalimumab.

What does this mean for the decisions patients, families and clinicians need to make?

The COMBINE trial is the largest double-blind, randomized trial ever to be done in pediatric Crohn’s disease. The main results showed that adding methotrexate to infliximab did not provide any additional benefit. However, the combination of low-dose oral methotrexate added to adalimumab produced a two-fold reduction in treatment failure compared to when adalimumab was used alone. 

These results give patients with pediatric Crohn's disease, their families, and their clinicians important information that they can use when deciding among available treatment options. Pediatric Crohn's disease patients initiating treatment with infliximab will probably not benefit from combination therapy with a second immune-suppressing medication like methotrexate In contrast, those initiating adalimumab alone may want to discuss with their clinician the potential benefits and risks of adding methotrexate to the treatment regimen.

Will the COMBINE trial findings impact future research?

As with every important research study, answering one question leads to additional questions. In this case, future research can explore whether the differences between infliximab and adalimumab that were seen in the trial can be explained by differences in the frequency of drug level monitoring and drug dosage adjustment, or differences in adherence to these biologics. Additionally, the COMBINE study addressed the issue of whether or not to start combination therapy with methotrexate. Future studies will need to evaluate how long patients who initiate combination therapy should remain on both medications. The study team and ImproveCareNow are looking forward to examining these and other new questions raised by this study.

Study authors

Kappelman MD, Wohl DA, Herfarth HH, Firestine AM, Adler J, Ammoury RF, Aronow JE, Bass DM, Bass JA, Benkov K, Tobi CB, Boccieri ME, Boyle BM, Brinkman WB, Cabera JM, Chun K, Colletti RB, Dodds CM, Dorsey JM, Ebach DR, Entrena E, Forrest CB, Galanko JA, Grunow JE, Gulati AS, Ivanova A, Jester TW, Kaplan JL, Kugathasan S, Kusek ME, Leibowitz IH, Linville TM, Lipstein EA, Margolis PA, Minar P, Rios ZM, Moses J, Olano KK, Osaba L, Palomo PJ, Pappa H, Park KT, Pashankar DS, Pitch L, Robinson M, Samson CM, Sandberg KC, Schuchard JR, Seid M, Shelly KA, Steiner SJ, Strople JA, Sullivan JS, Tung J, Wali P, Zikry M, Weinberger M, Saeed SA, Bousvaros A.

Study status

Published in March 2023. You can locate it:

  • In Gastroenterology - the leading journal in the field of gastrointestinal disease
  • Gastroenterology. 2023 Mar 31:S0016-5085(23)00538-3. doi: 10.1053/j.gastro.2023.03.224. Epub ahead of print. PMID: 37004887.

About ICN Research Explained

We believe that in order to truly outsmart IBD, the questions we ask and the answers we find must be generated by and be useful to the people whose lives they will impact – patients and their families. ImproveCareNow (ICN) research is prioritized based on what matters most to patients and parents, and we are committed to sharing our results so everyone can understand and take advantage of what’s been learned. The ICN Research Committee has teamed up with patients and parents/caregivers to create and share accessible summaries of completed research called ICN Research Explained

Prepared by: Shehzad Saeed, Michael D Kappelman (first author), David Wohl & Lisa Pitch (parent partners)

Editors Note: this ICN Research Explained was originally shared on 4/12/23 and then edited for clarity and reshared on 4/27/23. 


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