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The objective of this study was to quantify the direct medical resources used and the corresponding burden of disease in the treatment of patients with schizophrenia. Because low-frequency administration (LFA) of risperidone guarantees adherence during treatment intervals and offers fewer opportunities to discontinue, adherence and persistence were assumed to improve, thereby reducing relapses of major symptoms. A decision tree model including Markov processes with monthly cycles and a five-year maximum timeframe was constructed. Costs were adapted from the literature and discounted at a 3% annual rate. The population is a demographically homogeneous cohort of patients with schizophrenia, differentiated by initial disease severity (mildly ill, moderately ill, and severely ill). Treatment parameters are estimated using published information for once-daily risperidone standard oral therapy (RIS-SOT) and once-monthly risperidone long-acting injection (RIS-LAI) with LFA therapy characteristics derived from observed study trends. One-year and five-year results are expressed as discounted direct medical costs and mean number of relapses per patient (inpatient, outpatient, total) and are estimated for LFA therapies given at three, six, and nine month intervals. The one-year results show that LFA therapy every 3 months (LFA-3) ($6,088) is less costly than either RIS-SOT ($10,721) or RIS-LAI ($9,450) with similar trends in the 5-year results. Moreover, the model predicts that LFA-3 vs. RIS-SOT vs. RIS LAI therapy will reduce costly inpatient relapses (0.16 vs. 0.51 vs. 0.41). Extending the interval to six (LFA-6) and nine (LFA-9) months resulted in further reductions in relapse and costs. Limitations include the fact that LFA therapeutic options are hypothetical and do not yet exist and limited applicability to compare one antipsychotic agent versus another as only risperidone therapy is evaluated. However, study results have quantified the potential health state improvements and potential direct medical cost savings achievable with the development and use of LFA medication delivery technologies. [ABSTRACT FROM AUTHOR]