Background Promonitor-ADL test is routinely used to monitor IBD patients treated with adalimumab (ADL). ABP 501 (adalimumab biosimilar; Amgen) was authorised throughout the European Union in March 2017 and has been recently launched in several countries. Therapeutic drug monitoring (TDM) is broadly used as an aid for patient management. However, all TDM tests available should be properly validated against each new approved biosimilar in order to ensure safe application for patient monitoring as these may guide dose adjustments.

Objectives Here we validate the suitability and performance of Promonitor-ADL CE-marked test for quantification of the adalimumab biosimilar ABP 501 in comparison to the reference adalimumab drug (Abbvie).

Methods The validation study was in accordance with the design requirements established in the Clinical & Laboratory Standards Institute (CLSI) guideline EP17-A2 (Lower Limit of Quantification, LLOQ) and EP10-A3 (imprecision and bias). CLSI guidelines set a standard for the diagnostic industry accepted by all regulatory agencies. LLOQ was determined with four independent human serum sample matrices per each of three low level ADL concentrations, replicated three times per two lots of Promonitor-ADL (Progenika, Spain) kits for each drug, the reference drug and the adalimumab biosimilar ABP 501, over three days by one operator. Imprecision was evaluated using three replicates of five human serum sample matrices representative of clinically relevant ADL concentrations and spanning the measurement range of Promonitor-ADL, run on one instrument with one kit lot by one operator over six non-consecutive operating days and one run per testing day, with an acceptance criteria of CV%≤20%.

Results The LLOQ of Promonitor-ADL for the adalimumab biosimilar ABP 501 and reference adalimumab were 0.34 mg/mL and 0.36 mg/mL, respectively. LLOQ values met accuracy goal proposed based on total error =25% and precision. The imprecision of Promonitor-ADL calculated by estimating the components of variance due to within-run and between-day factors meet the accuracy goals proposed at all concentration levels of ABP 501 vs the reference adalimumab (CV% between 5% and 10%). The bias study showed that Promonitor-ADL can equally measure the active moiety ADL either in the reference biologic ADL or in the biosimilar ABP 501. The test is able to quantify the adalimumab biosimilar ABP 501 in the measurement range of 0.9 to 10.9 mg/mL with a bias estimate of -0.089 to 0.306 mg/mL and an overall imprecision of 6% to 9%. The measurement range includes the recommended clinical decision points.

Conclusion Promonitor-ADL test can equivalently measure either the reference ADL or the approved adalimumab biosimilar ABP 501 with the same sensitivity, precision and accuracy.

Disclosure of Interests M. Begoña Ruiz-Argüello Employee of: Progenika Biopharma - Grifols employee, Ainara Maguregui Employee of: Progenika Biopharma - Grifols employee, Antonio Martínez Employee of: Progenika Biopharma - Grifols employee, Daniel Nagore Employee of: Progenika Biopharma - Grifols employee