Objective: This study aimed to examine the degree of clinical and functional improvement after paliperidone long-acting injectable (LAI) administration according to the duration of illness. Methods: Patients with schizophrenia diagnosed by ICD-10 criteria who were planned to start once-monthly paliperidone LAI were recruited from 2010 to 2017. Clinical and functional changes were measured every 4 weeks using the Clinical Global Impressions-Severity of Illness scale (CGI-S) and Personal and Social Performance scale (PSP), respectively, for 6 months after paliperidone LAI initiation. Improvements after starting paliperidone LAI were compared among patients with duration of illness < 3 years, ≥ 3 and < 10 years, and ≥ 10 years. Results: A total of 1,166 participants (duration of illness < 3 years, n = 240; 3 ≤ duration of illness < 10 years, n = 442; duration of illness ≥ 10 years, n = 484) were enrolled. The total olanzapine-equivalent doses of antipsychotics and the LAI monotherapy proportion at the final visit were significantly different among the 3 duration of illness groups (dose: F2,1163 = 18.41, P < .001; monotherapy: χ22 = 11.73, P = .003). The changes in CGI-S score were significantly different according to the duration of illness, and those with duration of illness < 3 years showed the best improvement (group × week: χ212 = 25.33, P = .013). All 3 groups showed significantly improved PSP scores (week: χ26 = 294.2, P < .001). Conclusions: Starting paliperidone LAI significantly improved clinical and functional outcomes in patients with schizophrenia, especially those with shorter duration of illness. These findings suggest that LAI antipsychotic administration may be considered in early-stage schizophrenia for improved outcomes.
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