Our study was a nationwide retrospective observational cohort study featuring within-subject comparisons. Claim databases are widely used in medical research including pharmacoepidemiological studies . An advantage of claim databases is that they allow researchers to evaluate associations between specific drugs and events  that may be confounded by time-invariant variables, including genetic factors, chronic medical conditions, and patient lifestyle. However, it is difficult to adjust for time-invariant variables because medical databases often lack such information. In within-subject designs, each patient serves as their own control, thereby minimizing the confounding effects of time-invariant risk factors. Thus, the use of a within-subject analysis to investigate the real-world effectiveness of LAIs is the strength of our study.
LAIs offer an alternative to oral antipsychotics. Several second-generation LAI agents, including risperidone microspheres, paliperidone palmitate, aripiprazole monohydrate, and olanzapine pamoate monohydrate, are currently available. These agents were developed to improve treatment adherence and simplify the medication process . Despite having several advantages, many clinicians have not routinely used LAIs due to fear of, or concern about, the injection, as well as concern over side effects, lack of insight, and high cost .
Although LAIs were developed to reduce the relapse rate in patients with schizophrenia, the findings of recent RCTs have called into question the benefit of LAIs over oral antipsychotics . RCTs may not represent real-world settings, particularly in relation to schizophrenia. The patients who consent to participate in LAI clinical trials may not be representative of those who are prescribed LAIs in real-world settings. And clinical trial participants may be more adherent to a treatment, have less severe illness and better cognitive abilities to understand complex issues, and be more frequently monitored during clinical trials. All of which may attenuate the potential advantages of LAIs . A meta-analysis of 21 RCTs found that LAIs and oral antipsychotics were similarly effective in preventing relapse at the longest time point (relative risk = 0.93, 95% CI 0.71–1.07, P = 0.31). Previous studies showing that fluphenazine-LAI was more effective than oral antipsychotics were all conducted prior to 1992 .
Our findings on the association between antipsychotics and readmission are consistent with those of a previous large observational study, which found that the risk of readmission was 20–30% lower in patients treated with LAIs compared with those receiving oral medication . We found that LAIs lowered the readmission rate by 29% compared with oral antipsychotic medication, and by 43% in patients who had not received medication. Our large population sample contributed to the increased precision of our results, as indicated by the narrower CIs compared with a previous observational study .
Recurrence, characterized by acute psychotic exacerbation, is common in patients with schizophrenia. Repeated psychotic episodes may worsen psychopathology and social functioning . The neurotoxicity hypothesis of psychosis suggests that active psychosis has a toxic effect on the brain and that acute psychotic exacerbations promote disease progression and impair the treatment response [14, 15]. A 7-year follow-up study found that 80% of patients with schizophrenia deteriorated over time and that the degree of deterioration was significantly correlated with the number of recurrence . Our study design controlled for time-invariant confounders, but not for changes in the severity of the schizophrenia. Therefore, we analyzed the data according to each re-hospitalization to examine the effectiveness of LAIs on multiple episodes. With each hospitalization, the risk of readmission increased significantly under all of the medication conditions; however, the risk was highest during the no medication period.
Given that, the patients prescribed LAIs were more likely to have been non-adherent, and to have had a more severe disease status than those receiving oral medications, so LAIs significantly lowered the readmission rate compared with oral medication in real-world settings.
We found that the risk of readmission increased with repeated admissions, and that the benefit of LAIs was greater than that of oral antipsychotics in patients with multiple admissions. However, it is not clear whether the effect is due to heterogeneity of schizophrenia, reflected as a diverse spectrum of severity, or to blunting of the medication response by repeated exacerbations.
Our findings support those of a recent observational study suggesting that LAIs decrease the readmission rate . Furthermore, we found that LAIs significantly reduced the risk of readmission, particularly in patients who experienced admissions in real-world settings. These findings warrant further research of each specific second-generation LAIs on the risk of readmission, to provide more detailed information of treatment options for targeting patients with multiple relapses.
Our study had several limitations. First, we assumed that refill compliance was an indicator of medication adherence, introducing a potential definition bias. Claims data provide information on drug prescriptions, but not patient adherence, which may have led to misclassification of the exposure periods. It is likely that some patients were not taking their prescribed medication during the periods we classified as medication-exposed, leading to a potential overestimation of adherence, particularly for oral medications. Therefore, our estimations of the medication and non-medication periods may have been inaccurate. Quantifying adherence is difficult because it is rarely an all or none phenomenon, and clinicians have a limited ability to identify patients who are not compliant . However, despite limitations in evaluating medication adherence, drug prescriptions are widely used in large-scale population studies. Second, as with all claim-based studies, the data were collected for administrative purposes and may be subject to coding errors. Therefore, it is possible that the inclusion of false-positive patients who presented with schizophrenic symptoms led to an underestimation of the readmission rate during the non-medication period, although the most severe cases, i.e., patients who were readmitted 30 days after discharge, were excluded from the study. We included typical cases of schizophrenia characterized as a primary diagnosis of F20 Schizophrenia or F25 Schizoaffective disorder at index admission, undergoing treatment with SGAs and hospitalized between 7 and 120 days. Third, our analysis grouped the medications into oral and LAI agents rather than assessing the effectiveness of the individual drugs, which may have helped clinicians identify appropriate drugs for specific patients. Different drug agents have effects of varying magnitudes. Moreover, differences among second-generation LAIs have been observed in relation to the onset of clinical efficacy and the relationships between symptoms and functioning scores . However, in general, the association between treatment and outcome is consistent among specific antipsychotics . Finally, we enrolled patients with coexisting conditions and those who were taking concomitant medications. Nevertheless, these data are representative of a variety of real-world clinical settings in which patients with schizophrenia are treated.
LAIs lowered the readmission rate by 29% compared with oral antipsychotic medication in a real-world setting. The higher the readmission rate, the greater the benefit of LAIs in reducing the risk of re-hospitalization compared to oral antipsychotics. Our real-world findings strongly support the benefit of using LAIs over oral antipsychotics in schizophrenia patients with multiple recurrences by reducing 58% of readmissions.
Our result shows that clinicians may not hesitate to prescribe LAIs especially those with recurrent schizophrenia patients. Considering various expenses needed to those of individual patients and their families for hospital admissions, LAIs could relieve much financial burden. Lower readmission rate is one of the main health outcomes in mental health. This would allow decrease psychiatry inpatient beds and improve the quality of life for patients. There should be no limitation of usage or reimbursement of LAIs in case low compliance or high readmission probability is expected.