This study describes longitudinal patterns that represent chronic maintenance antipsychotic treatment. The lower adherence to antipsychotic treatment associated with a greater frequency and longer duration of schizophrenia-related hospitalizations was consistent with prior research that examined adherence over shorter periods of time (Gilmer et al. 2004
; Valenstein et al. 2002
; Weiden et al. 2004
). Also, the significant association between the degree of adherence and the likelihood of psychiatric hospitalization corroborates previously reported research involving partial antipsychotic adherence. Partially adherent individuals (i.e., 50−79% consumption of medication per days eligible) have lower hospitalization rates than non-adherent persons (i.e., 0−49% consumption per days eligible) and slightly higher rates than those adherent (i.e., 80% or more consumed per days eligible) to antipsychotic medication (Gilmer et al. 2004
; Weiden et al. 2004
). Lastly, the significant difference between light and continuous antipsychotic use when length of hospitalization was less than 60 days suggests more acute relapse with light use.
Research on differences in continuity between first and second generation agents has been mixed. Evidence from the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) suggests that the 74% treatment discontinuation before 18 months was not significantly different between first generation perphenazine and the second generation agents examined (Lieberman et al. 2005
), with the exception of olanzapine, which showed a slight advantage in duration of successful treatment. Using the Health Search Database (HSD) containing data for more than 800,000 individuals followed by 550 general practitioners in Italy, from 1999 to 2002 discontinuation was greater for the second generation than for first generation agents (Trifiro et al. 2005
). Discontinuation of antipsychotic medication two years after discharge was similar for first and second generation agents (Fleck et al. 2002
). Ours and other studies of outpatient community utilization ( Gilmer et al. 2004
; Valenstein et al. 2004
) have shown no difference between first and second generation antipsychotics, including olanzapine. This may in part be due to differences between community-based studies and clinical trials. Also, methodological differences in defining continuous treatment could also be a factor. Additional factors, such as denial of an illness, may play a key role in treatment discontinuation (Olfson et al. 2006
). Nonetheless, the current study may be more representative of community utilization because it captures periodic fluctuation over time.
The current findings are supported by recommendations for continuous antipsychotic treatment (Lehman et al. 2004
). Antipsychotic discontinuation is a significant predictor of relapse (Robinson et al. 1999
). Our analysis shows that continuous use was associated with fewer and shorter schizophrenia-related hospitalizations compared to light or moderate use. McCombs and colleagues reported a non-significant trend towards lower hospitalization costs with continuous antipsychotic treatment (McCombs et al. 2000
). That individuals in this study who received antipsychotic treatment were more likely to have had a hospitalization for schizophrenia relative to those who did not is counter-intuitive. It may be driven by the initiation of antipsychotic treatment during hospitalization for an acute episode of the illness.
There are several limitations to consider. Treatment patterns may only apply to this one state's Medicaid population aged 62 years or younger at the start of the study. Outpatient antipsychotic treatment may not represent the presumably more severe, chronically institutionalized patients. Lack of a standardized diagnostic assessment may have compromised reliability. Because clinical information is not available in Medicaid data, it was not possible to know if discontinuity of antipsychotic use was related to intolerable side effects. Monthly use of other psychotropic medications was not available, and thus not adjusted for in the longitudinal analyses.
These findings may reflect the inadequacy of community-based service systems in effectively promoting and maintaining the continuity of antipsychotic treatment among individuals with schizophrenia. Awareness of long-term utilization patterns could inform clinical and policy decisions that would maximize adherence.