Generic substitution does not seem to affect adherence negatively in elderly polypharmacy patients

PURPOSE: To investigate the association between generic substitutions and medication adherence in elderly patients with prescribed polypharmacy. METHODS: Our study included 672 patients aged 65+ years, living at home in the municipality of Aarhus (Denmark), who at the time of enrolment took at least five prescription drugs daily including both short-term and long-term treatment independently of kind of administration route but without assistance. In this paper, only oral drugs for long-term treatment are included in the analysis resulting in median of three drugs per patient. Adherence was assessed by pill counts. Patients with a mean adherence rate <80% across all oral drugs consumed for long-term treatment were categorised as non-adherent. The number of generic substitutions during 1 year was retrieved from the National Health Insurance prescription database. Each change in either a drug's or a manufacturer's name was regarded as a substitution. The association between generic substitution and the mean adherence rate to all drugs was analysed by contingency table analyses and a trend test. RESULTS: During 1 year, at least one substitution was experienced by 83.6% of patients (n = 562). Patients non-adherent to long-term oral treatment (n = 46) amounted to 8% of all patients who experienced substitutions. Amongst 110 elderly patients (16.4%) who did not experience substitutions, 16% were non-adherent (odds ratio 0.46; 95% confidence interval 0.25-0.82). CONCLUSION: As generic substitution in elderly patients undergoing polypharmacy appears not to affect adherence to long-term drug treatment negatively, there seems to be no obvious reason for avoiding generic substitution in such patients.