To establish the efficacy, safety, effectiveness and efficiency of monitoring the levels of anti-TNFα drugs and the levels of antibodies generated against these drugs in the treatment of patients with moderate or severe IBD (CD/CU).

An analysis will be made of the economic impact on the Health System of monitoring treatment with anti-TNFα drugs in CD/CU.

As a result of this specific objective, a standardized procedure will be established for the evaluation of the response to treatment with anti-TNFα drugs for CD/CU that includes the new trials and the new devices developed.

• To evaluate whether a dose and plasma level optimization strategy based on the use of Promonitor-IFX, Promonitor-Anti-IFX, Promonitor-ADL, and Promonitor-Anti-ADL kits in CD/CU patients on IFX/ADL treatment is superior in terms of the percentage of patients in clinical remission at 12 months compared to standard practice.
• To evaluate whether a dose and plasma level optimization strategy based on the use of Promonitor-IFX, Promonitor-Anti-IFX, Promonitor-ADL, and Promonitor-Anti-ADL kits in CD/CU patients on IFX/ADL treatment is superior in terms of the percentage of patients in deep remission at 12 months compared to standard practice.
• To analyze the influence of the use of the IFX/ADL antibody detection test in moderate to severe CD/CU patients on the annual direct cost to the health system of these patients, compared to the non-use of the tests.
• To evaluate the effectiveness of IFX/ADL antibody testing in moderate to severe CD/CU patients on the increase in quality-adjusted life-years compared to non-use of the tests.
• To evaluate the effectiveness of testing for antibodies to IFX/ADL in moderate to severe CD/CU patients in reducing the number of flares, compared to not using the tests.

Exploratory objective - To conduct a cost-effectiveness (utility) analysis of a strategy for the management of stable moderate to severe CD/CU patients based on treatment monitoring.

Page 10 of 83 anti-TNFα with the introduction of screening tests for plasma levels/antibodies to IFX/ADL with respect to standard practice based on clinical signs/symptoms.

Main operational objective

- To assess whether the prevalence of 1-year remission in moderate to severe CD/CU patients whose anti-TNFα treatment has been managed using Promonitor IFX/ADL kits is at least 16% higher compared to the group of patients in whom this technique has not been employed.

Inclusion criteria:

• patients of both sexes
• over 18 years of age
• diagnosis of CD/CU confirmed by endoscopy
• stable clinical status (remission) for at least 12 weeks prior to inclusion in the study
• on treatment with IFX/ADL for at least 3 months with stabilized dosage and outside the induction period
• negative for tuberculosis at the start of treatment
• who sign the informed consent form

Exclusion criteria:

• severe concomitant pathology preventing adequate follow-up of patients.
• continued corticosteroid therapy at prednisone equivalent doses higher than 40 mg/day
• patients with positive antibody levels at baseline
• there is treatment with immunomodulators and/or corticoids, when it is at high doses and with variations in time
• Patients with intestinal resection and Crohn's disease in prophylactic treatment with anti-TNF, but without recurrence.
• who are participating in a clinical trial or interventional study. Participation in the study will be offered to all patients who meet the above criteria, and in a consecutive manner, without a prior selection process. The comparison group will consist of a cohort of patients belonging to the same Digestive Services and meeting the same selection criteria.

Patients with inflammatory bowel disease (Crohn's disease or ulcerative colitis) on treatment with Infliximab or Adalimumab and who have been clinically stable for 12 weeks.