Enzyme-linked immunosorbent assay for the quantitative determination of free Infliximab (Remsima®) in serum and plasma. Remsima® is the worlds first biosimilar mAb (approved in 2013 by EMA). The Committee for Medicinal Products for Human Use (CHMP) decided that in accordance with EU requirements, Remsima® has been shown to have a comparable quality, safety and efficacy profile to Remicade®. The Assay Genie Infliximab (Remsima®) ELISA has been specially developed for the quantitative analysis of free infliximab in serum and plasma samples.

Solid phase enzyme-linked immunosorbent assay (ELISA) based on the sandwich principle. Standards and samples (serum or plasma) are incubated in the microtitre plate coated with the reactant for infliximab biosimilar (Remsima®). After incubation, the wells are washed. A horse radish peroxidase (HRP) conjugated probe is added and binds to infliximab captured by the reactant on the surface of the wells. Following incubation wells are washed and the bound enzymatic activity is detected by addition of chromogen substrate. The colour developed is proportional to the amount of infliximab in the sample or standard. Results of samples can be determined directly using the standard curve.

Infliximab reduces the amount of active human tumour necrosis factor alpha (hTNF alpha) in the body by binding to it and preventing it from signalling the receptors for TNF alpha on the surface of various cell types. TNF alpha is one of the key cytokines that triggers and sustains the inflammatory reactions.

Remsima is a tumour necrosis factor alpha (TNF alpha) antagonist used to treat rheumatoid arthritis, ankylosing spondylitis, ulcerative colitis, adult Crohn's disease, plaque psoriasis, and psoriatic arthritis. Single intravenous (IV) infusions of 3 mg/kg to 20 mg/kg showed a linear relationship between the dose administered and the maximum serum concentration. The volume of distribution at steady state was independent of dose and indicated that infliximab was distributed primarily within the vascular compartment.

Median pharmacokinetic results for doses of 3 mg/kg to 10 mg/kg in rheumatoid arthritis and 5 mg/kg in Crohn's disease indicate that the terminal half-life of infliximab is 8.0 to 9.5 days. In controlled trials, clinical response rates of 20-40% have been achieved with above- mentioned regimens in Crohn's disease and rheumatoid arthritis.

However, the therapeutic benefits must be balanced against the risk of a variety of severe adverse events (e.g. severe infections including tuberculosis, hepatotoxicity, infusion reactions, serum sickness-like disease and lymphoma). The volume of distribution of infliximab is low (3-6 L) and represents the intravascular space.

Elimination of infliximab is most probably accomplished through degradation by unspecific proteases. It seemed that methotrexate delayed the decline in the serum concentrations of infliximab. When relating serum concentrations to the clinical response in patients, it can be assumed that through concentrations above 1mg/mL could be used as a kind of therapeutic target. The rate of clinical remission was higher for patients with a detectable trough serum infliximab compared with patients in whom serum infliximab was undetectable, including those without antibodies. A detectable trough serum infliximab was also associated with a lower C-reactive protein and a higher rate of endoscopic improvement.

For Crohn's disease patients treated with scheduled maintenance infusions of infliximab, the serum concentration of infliximab seemed to predict clinical outcome. It was also proposed that, the surveillance of circulating infliximab concentration during maintenance therapy represents an indirect but reliable method to monitor anti-infliximab immunization. In this context, identification of biomarkers for (non-)response and risk factors for adverse drug reactions relating to serum concentrations and therapeutic drug monitoring of infliximab would be very helpful.

REMSIMA is a trademark of CELLTRION, INC.