Adherence to oral immunosuppressors using therapeutic drug monitoring: A retrospective study

BackgroundAfter hospital discharge, recipients of allogeneic hematopoietic stem cell transplantation (HSCT) must adhere to immunosuppressants to reduce the risk of complications such as graft-versus-host disease (GvHD). The use of therapeutic drug monitoring (TDM), a measure of medication adherence (MA), in the transplantation field has received limited research attention.ObjectivesWe used TDM to measure MA to the oral calcineurin inhibitors (CNIs) cyclosporine A (CSA) and tacrolimus (FK), from the patient's first follow-up visit after discharging up to 100 days after HSCT. The secondary aim was to identify risk factors for medication non-adherence (MNA) and the relationship between MNA and HSCT-related complications.Materials and MethodsA retrospective observational study was conducted at an academic hospital in northeast Italy. We included 269 adults undergoing allogeneic HSCT and a total of 1493 CNI serum assays.ResultsUsing an MA threshold of ≥ 80%, 37.2% of patients were adherent (57.9% to CSA and 17.9% to FK). There were no differences at the analyzed time points; however, MNA with TDM below the target range increased over time. There were no risk factors for MNA, nor differences in GvHD or hospital readmissions between adherent and non-adherent patients.ConclusionTDM can be used to assess MA to CNIs up to 100 days after HSCT, but due to the limitations of this measure, it would be useful to corroborate the results with other MA measurement systems. Prospective studies are required to identify risk factors, outcomes of MNA, and to validate which MA threshold could establish clinical relevance.