IDeaL Pilot Study - Infliximab Dose to Level: Pilot Study

Crohn's disease (CD) is a chronic inflammatory bowel disease characterized by inflammation that can affect any part of the gastrointestinal tract from mouth to anus. Other complications may occur outside the gastrointestinal tract and include: anemia, skin rashes, arthritis, inflammation of the eye, and tiredness. Symptoms often include: abdominal pain, diarrhea (which may be bloody if inflammation is severe), fever and weight loss. Crohn's disease is caused by a combination of environmental, immune and bacterial factors in genetically susceptible individuals. It results in a chronic inflammatory disorder, in which the body's immune system attacks the gastrointestinal tract possibly directed at microbial antigens. The estimated prevalence of CD in Canada is 234 per 100,000 persons, with an incidence rate of 13.4 per 100,000. There are no medications or surgical procedures that can cure Crohn's disease. Treatment options help with symptoms, maintain remission, and prevent relapse. The burden of disease is high with disease flares and complications leading to hospitalizations, surgeries, school and work absenteeism, and impaired quality of life.

Infliximab (IFX) is a murine chimeric lgGl anti-TNFa monoclonal antibody shown in landmark clinical trials to be well-tolerated and effective for induction, and maintenance, of remission in pediatric and adult CD and ulcerative colitis. In Canada, the safety and efficacy of IFX is not established in children under the age of 9, yet is often prescribed to younger children off label when other therapies do not resolve their disease symptoms. IFX can be influenced by multiple factors such as body mass index (BMI), serum albumin level, burden of inflammation and the concomitant use of immunosuppressive medications. Loss of response to IFX can either be a result of Antibodies to IFX (ATI) or insufficient serum IFX level.

ATI have been shown to develop in about 17% of those treated with IFX. The risk for development of ATI is even higher in those who receive IFX mono-therapy, compared to those receiving concomitant immunomodulator. It is now clear that those with persistent ATI have a three to fivefold increased risk of loss of response to IFX compared to those without ATI. ATI appears to interfere with the bioactivity of IFX and those patients who develop ATI are more likely to subsequently manifest infusion reactions, including anaphylaxis.

The standard infusion regimen for IFX is three loading dose of 5mg/kg (dose is often rounded up to the nearest 100mg) at 0, 2, 6 weeks then every 8 weeks thereafter. The trough level of IFX after the 3rd loading dose (week 14 - i.e. before the 4th infusion) is often found to be at greatest risk of being low; especially in children.

A recent study has shown that 29% of children have an undetectable IFX level at the 4th medication infusion. A trough level of 5 ug /ml at this time point is associated with higher remission rates. Conversely, a low trough level (< 2.2 ug/ml) at week 14 predicts IFX discontinuation. Up to 40% of patients receiving scheduled IFX have undetectable drug level prior to their next infusion. However, whether having undetectable IFX level at trough increases the risk of ATI formation is currently unclear. Moreover, it is unknown if dosing adjustments based on trough levels will change rates of antibody formation to IFX and the sustained efficacy of IFX nor how we can achieve desired serum levels at clinically relevant time-points, mainly because the pharmacokinetics of IFX in children has not been well studied.