The Importance and Challenges of Longitudinal Studies Among Patients Diagnosed With Schizophrenia : Predicting Response to Antipsychotic Medication Using Strata

Background: Longitudinal studies are essential for understanding the trajectory and prognosis of patients diagnosed with schizophrenia, in particular those who are treatment resistant as this outcome is difficult to predict. However, follow-up is challenging within this patient population due to high relapse rates, difficulties recontacting participants due to regular change of address, and patients’ symptoms leading to their refusal to take part. Methods: We describe one of the work packages of STRATA (Schizophrenia: Treatment Resistance and Therapeutic Advances) as an example of the challenges facing follow-up studies in schizophrenia research. The main aim of STRATA is to identify differences between treatment-resistant and treatment-responsive patients with schizophrenia and create a method for early identification of treatment resistant patients; thereby allowing earlier transition to more suitable treatments such as clozapine. Cohorts of patients from pre-existing studies of first-episode psychosis are presently being recontacted. Three studies across the UK (“AESOP,” Nottingham and London samples; “RPGI” and “NIFEPS,” Belfast samples) were included in STRATA. In total, 484 participants were eligible for recontact; 157 participants from AESOP, 85 from the RPGI; and 242 from the NIFEPS study. Participants were contacted via their clinical team, letter, or phone. Participants were invited to take part in a 40-minute interview in which demographic, substance use, medication history, and symptomatology (PANSS) data was collected. Participants were also asked to provide a blood and urine sample. Ethical permission was obtained to contact participants using information collected at previous visits and to obtain up to date contact addresses. Results: Out of the 484 participants who were recontacted, 13 were deceased, 9 were excluded, 23 requested information after the first contact but then ceased to respond, 47 declined to participate, and addresses were not identif