Medication adherence and associated outcomes in medicare health maintenance organization-enrolled older adults with Parkinson's disease.

Maintenance of symptom control in Parkinson's disease (PD) requires continuous titration of medication and addition of multiple therapies over the course of the disease. Adherence to medication is vital to symptom control and key to maximizing the efficacy of existing therapies. However, adherence is compromised by a variety of factors, including motor symptoms, complex dosing regimens, multiple medications, and lack of patient/physician awareness of the impact and prevalence of suboptimal adherence. This retrospective, longitudinal cohort study assessed the prevalence of suboptimal adherence [measured as the medication possession ratio (MPR)] to PD medications, and its impact on the worsening of PD symptoms (measured as increase in monotherapy dose, augmentation of therapy, PD-related emergency department visit, or hospitalization), in a Medicare Health Maintenance Organization population in the United States. Irrespective of the MPR threshold chosen, a high percentage of patients were categorized as suboptimally adherent to their PD medications, and patients with suboptimal adherence to their PD medications had higher risks of worsening of PD symptoms, compared with those who were adherent. Increased awareness of both the magnitude and impact of suboptimal adherence to PD medications, coupled with dosage simplification and a unified effort by healthcare professionals and patients, may improve adherence to PD medications and ultimately improve symptom control.