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125. Adherence to Antipsychotic Medications among Patients with Schizophrenia: Comparing Atypical and Conventional Antipsychotics

Valenstein, M, HSR&D COE, Ann Arbor; McCarthy J, SMITREC, HSR&D, Ann Arbor; Blow, FC, SMITREC, HSR&D, Ann Arbor; Zeber, J, SMITREC, HSR&D, Ann Arbor; Gillon, L, SMITREC, HSR&D, Ann Arbor; Liebfried, T, SMITREC, HSR&D, Ann Arbor

Objectives: Anti-psychotic medications are an essential component of the treatment of patients with schizophrenia, but many patients are non-adherent with these medications. Non-adherence with antipsychotics increases the risk of relapse and is more likely if patients experience side effects from their medication.

The newer atypical antipsychotics are reported to have fewer side effects than conventional antipsychotics and prescribing these agents is frequently proposed as a strategy for improving compliance. However, the newer antipsychotics are more costly than conventional antipsychotics and few data exist that support higher rates of adherence among patients receiving these agents.

We used national VA outpatient pharmacy data to examine whether adherence was greater among veterans with schizophrenia receiving newer antipsychotics than among veterans receiving conventional agents.

Methods: Patients with a diagnosis of schizophrenia during fiscal year 99 were identified through the Patient Treatment File (PTF) or Outpatient Care Files (OPC). Pharmacy data were obtained from the Pharmacy Benefits Management Group. The medication possession ratio (MPR) was calculated for all patients receiving one type of antipsychotic medication (N=55,507). The MPR is the "number of days supply" of medication that a patient has received divided by the "number of days supply" that they should have received had they been taking medication as prescribed. The MPR was calculated for the time period between the patient's first antipsychotic prescription during FY 99 and the end of the fiscal year or death. Calculations took into account days spent in hospital (when patients did not require an outpatient medication supply) and excluded patients who had a medication fill only on the day of discharge or who received outpatient fills during nursing home stays.

Results: 55, 000 veterans with schizophrenia received one type of antipsychotic during FY99. Approximately 41% of these had MPRs below 0.8, indicating difficulties with adherence.

The percentage of patients with low MPRs did not differ between patients receiving atypical antipsychotics (41.3%) and those receiving conventional antipsychotics (40.2%). (c2=2.68; df=1; p=0.10). Clozapine, which has stringent visit and monitoring requirements, had the lowest percentage of patients with poor adherence; only 6.4% of these patients had MPRs < 0.8. When patients on clozapine were excluded, the percentage of patients with low MPRs was actually higher among patients receiving atypical agents (43.0%) than among patients receiving conventional agents (c2=34.83; df=1; p<0.0001).

Conclusions: In keeping with the literature, approximately 40% of veterans with schizophrenia have poor adherence with antipsychotic medications. Although the more costly atypical agents have fewer side effects, patients on aytpical antipsychotics appear to be no more adherent than patients on conventional agents.

Impact: Non-adherence to antipsychotic medication is common among veterans with schizophrenia, placing patients at risk for relapse. Data from this large sample of veterans indicate that adherence is not likely to be dramatically improved by simply prescribing atypical antipsychotic agents.