Symptom severity and attitudes toward medication: impacts on adherence in outpatients with schizophrenia

Objective: The primary aim of this study was to compare electronic monitoring with other measures of adherence to antipsychotic medication in outpatients with schizophrenia. The secondary aim of the study was to analyze the relationships between adherence and other clinical parameters.

Method: Fifty-one patients diagnosed with schizophrenia were monitored over an eight-week period. Medication adherence was assessed using the Medication Event Monitoring System (MEMS), which is a bottle cap with a microprocessor that records the occurrence and times of bottle opening, patient self-reports, a clinician rating scale, and pill counts. Agreements among adherence measures and the relationships between adherence and other clinical factors were assessed.

Results: The rate of non-adherence according to the MEMS was 41.2%, considerably higher than those of pill counting (7.8%), clinician rating scale (7.8%), or self-reporting (25.5%). Excitement, impulse control, and preoccupation symptoms on the Positive and Negative Syndrome Scale (PANSS) were higher in the non-adherent patients than in the adherent patients. The full Drug Attitude Inventory (DAI) score was higher in adherent versus non-adherent patients and the significant other subscale of the Multidimensional Scale of Perceived Social Support score was lower in the adherent patients. The Clinical Global Impression-Severity score was negatively correlated with adherence as measured by the MEMS (r=-0.426, p<0.05) and DAI scores were positively correlated with adherence according to the MEMS and the clinician rating scale (r=0.498, p<0.01 and r=0.387, p<0.05). Multivariate analysis showed that PANSS and DAI scores significantly contributed to MEMS adherence.

Conclusion: Adherence as measured by the MEMS showed a discrepancy with other measures of adherence in patients with schizophrenia. The severity of disease and attitudes toward medication were related to adherence. Further studies are needed to evaluate the impacts of medication adherence in schizophrenia.