Non-adherence is a significant issue in the treatment of systemic lupus erythematosus (SLE), associated with the risks of disease flare, early damage and 5-year mortality as demonstrated for hydroxychloroquine (HCQ).1 It is important for clinicians to objectively assess adherence to treatments, especially in cases of resistance to standard of care treatment. For this purpose, serum, plasma or blood measurements of drugs with long elimination half-lives can help clinicians to identify patients with very low adherence to treatments, as previously shown for HCQ.2

Intravenous and subcutaneous belimumab (BLM) is an effective treatment for SLE3 4 progressively used as maintenance therapy. However, adherence to BLM poses a challenge when administered subcutaneously, as the physician does not know whether the treatment is truly administered. The aim of the study was (1) to assess adherence to BLM using questionnaires and measurements of its plasma levels; (2) to identify factors associated with non-adherence to BLM treatment and (3) to explore the links between the adherence to BLM and to HCQ. This single-centre study included consecutive patients treated with subcutaneous BLM from March 2023 to September 2023, regularly examined by physicians specialist in SLE. Adherence to BLM and HCQ was assessed using the Morisky Medication Adherence Scale 8 (MMAS-8) and the Medication Adherence Self-Report Inventory (MASRI) questionnaires for each of these drugs, at random times relative …