Background and importance A limited number of studies have related serum biological levels to clinical response in psoriasis. Studies on the clinical relevance of therapeutic drug monitoring for etanercept biosimilar (ETAb) are scarce.

Aim and objectives To analyse ETAb concentrations in patients with moderate to severe plaque psoriasis.

Material and methods This was an observational retrospective study of all psoriatic patients treated with ETAb (Erelzi) and monitored in the pharmacy service from January 2018 to September 2019. The ethics committee approved this study. Informed consent was obtained for all subjects before entry into the study. Patients received ETAb 50 mg every week. ETAb serum levels were assessed immediately prior to administration of drug (Ctrough). Concentrations were quantified by capture ELISA immunoassay (Triturus analyser).

Data sources sex, age, weight, date of psoriasis diagnosis, previous treatment with biologic drugs, duration of ETAb treatment, dosage/weight (mg/kg), concomitant treatment (immunosuppressive drugs, oral corticosteroids, retinoids), psoriasis area and severity index scale (PASI) before the start of ETAb treatment (PASIb) and at blood extraction time (PASIe), ETAb concentration and adverse events.

Patients were classified into two groups in accordance with efficacy at the various blood assessment times: good responders (>PASI75) and non-responders (<PASI75).

Statistics descriptive analysis of variables (SPSS V.19.0), quantitative variables (median (range)) and qualitative variables (number (percentage)).

Results Ten patients (70.0% men, 28 blood samples) were aged 48.5 (26.0–68.0) years and weighed 73 (64–112) kg. Dosage/weight was 0.7 (0.5–0.8) mg/kg. Age at diagnosis was 25.5 (8.0–47.0) years and 100% were naive patients. Concomitant treatments were methotrexate (n=3) and ciclosporin (n=1). PASIb was 9.0 (3.0–17.3) and PASIe 1.2 (0.0–14.8), 14/28 PASIe=0.0 and%PASI variation with respect to basal value 92.3 (−82.7–100). Treatment time at blood extraction was 3.9 (0.9–14.0) months. ETAb concentration was 2.7 (0.6–4.8) µg/mL. Efficacy: 57.1% good responders and 42.9% non-responders. There were no significant differences in demographic data between the patient response groups. There were no significant differences with respect to ETAb levels: 2.7 µg/mL (range 1.8–4.4) versus 2.6 µg/mL (range 0.6–4.8), respectively (p>0.05). No adverse events were reported.

Conclusion and relevance Drug concentrations were detected in all patients. No relationship was found between ETAb concentration and clinical response (efficacy and toxicity). Further research is needed to determine the clinical significance between ETAb concentration and clinical response, and hence the usefulness of therapeutic drug monitoring in psoriatic patients.

References and/or acknowledgements No conflict of interest.