Adherence to paroxetine CR compared with paroxetine IR in a Medicare-eligible population with anxiety disorders

There are many challenges in the pharmacologic management of elderly patients with anxiety disorders, including an increased sensitivity to drug effects, reduced drug metabolism, and socioeconomic barriers leading to poor medication adherence. As such, the purpose of this study was to evaluate differential rates of adherence between paroxetine controlled release (CR) and paroxetine immediate release (IR) in the treatment of anxiety disorders in a Medicare-eligible population. Patients aged 65 years or older initiating therapy with paroxetine CR or paroxetine IR with a diagnosis of anxiety were identified from the Integrated Healthcare Information Services National Managed Care Benchmark database from July 2001 to February 2004. Logistic regression models were used to assess differences in 6-month adherence rates, controlling for differences in multiple background characteristics. Adherence was defined as having a minimum medication possession ratio of 80% over 180 days without evidence of a 15-day gap before 90 days of therapy. Of the 604 patients included in the study, 18% received paroxetine CR and 82% received paroxetine IR; comorbid anxiety and depression were present in 37.3% of patients. Overall, only 37.3% of patients adhered to therapy, with a greater percentage of patients adhering to paroxetine CR (45.0%) compared with paroxetine IR (35.6%). After controlling for background characteristics, patients receiving paroxetine IR were 38.7% less likely to adhere to therapy compared with patients receiving paroxetine CR (P = .0328). When stratified by those with comorbid anxiety and depression, patients receiving paroxetine IR were 55.1% less likely to adhere to therapy compared with patients receiving paroxetine CR (P = .0292). This study demonstrates that antidepressant nonadherence is common in patients older than 65 years of age, with overall rates of nonadherence at 62.7% and patients receiving paroxetine IR having the lowest levels of adherence. Future work should assess differences in all available selective serotonin reuptake inhibitors while also directly assessing the economic impact of nonadherence in the elderly population.