Background The introduction of biosimilar infliximab (IFX-B) has led to a decrease in the costs of patients with inflammatory bowel disease (IBD). The molecular complexity in the manufacture of biological drugs makes it difficult to verify the similarity between the different drugs. Infliximab (IFX) therapeutic drug monitoring allows for objective decision-making in patients with IBD.

Purpose To compare the percentage of patients in therapeutic IFX concentrations, between originator infliximab (IFX-O) versus IFX-B, as well as the prevalence of immunogenicity between both.

Material and methods We conducted a retrospective observational study (March 2017–September 2018). We included all patients with IBD who received maintenance therapy with IFX and underwent pharmacokinetic monitoring.

The variables studied were: sex, age, diagnosis, type of drug (IFX-O or IFX-B), number of serum samples collected, serum trough levels IFX and the presences of antibodies. Blood extraction was performed in trough levels and determined by sandwich ELISA (Promonitor). The IFX therapeutic range was defined as between 3–10 mcg/mL. We used the X² test to compare the association between categorical variables and the student t-test for quantitative variables. All tests were performed using SPSS v.23.0.

Results We included 70 patients (65.7% were males). The average age of the study population was 41.8 (DE: 14.8) years. 74.4% had Crohn’s disease.

Concerning treatment, 49.3% were treated with IFX-O and 50.7% with IFX-B. We analysed 174 serum samples (61.5% IFX-O), 2.9 (SD: 1.1) and 1.8 (SD: 1.0) samples per patient of IFX-O and IFX-B respectively. Mean serum trough levels of IFX-O were 7.2 (SD: 4.5) mcg/mL versus 8.3 (SD: 7.8) mcg/mL with IFX-B (p=0.790), of which 61.9% and 47.8% (p=0.137) were in the therapeutic range respectively. In terms of immunogenicity, 13.1% patients presented antibodies anti-IFX (11.6% IFX-O and 15.4% IFX-B, p=0.43).

Conclusion In our study there was no significant difference in the mean concentration of drugs between IFX-O and IFX-B, and neither in immunogenicity, with IFX-B as a cost-effective alternative to the originator product. Pharmacokinetic monitoring represents a fundamental mainstay in the optimisation of these treatments.

Reference and/or acknowledgements Mitchell RA, et al. The utility of infliximab therapeutic drug monitoring among patients with inflammatory bowel disease and concerns for loss of response: a retrospective analysis of a real-world experience. Can J Gastroent Hepatol 2016.

No conflict of interest.