Factors associated with adherence over time to antipsychotic drug treatment

BackgroundPrevious studies have used cross-sectional designs to assess factors associated with adherence to antipsychotics giving little information about patients' adherence over time.ObjectiveThe purpose of this study was to examine antipsychotic adherence over four 6-month periods at the aggregate and individual level in a large cohort of patients.MethodsWe identified 8595 patients who received an antipsychotic prescription between January 2000 and December 31st 2003 with a clearance period of three months. We used the medication possession ratio (MPR) to assess adherence. We examined whether patients had consistently good adherence (MPRs greater or equal to 0.8 in all 4-periods), consistently poor adherence (MPRs less than 0.8 in all periods), or inconsistent adherence. General estimating equations analysis (GEE) was used to assess factors associated with adherence over time.ResultsThe cross-sectional prevalence of good adherence was highest at six-month but decreased at twelve-month and remained relatively stable at 27% overall. The overall proportion of consistently good adherence was 12.6% (95% CI = 11.88–13.28). About 13.71% of women and 11.01% of men were consistently good adherent. Factors associated with adherence among men are not always the same among women.ConclusionAdherence to medication is a core component of recovery from illness. Clinicians and medication prescribers should identify factors on which it is important to focus to enhance adherence.