The Relationship Between Average Daily Dose, Medication Adherence, and Health-Care Costs among Diabetic Peripheral Neuropathic Pain Patients Initiated on Duloxetine Therapy

Abstract

To examine the relationship between average daily dose (ADD) of duloxetine, adherence to therapy, and health-care costs among patients with diabetic peripheral neuropathic pain (DPNP). A retrospective analysis of commercially insured DPNP patients was conducted among those aged 18 to 64 years who initiated duloxetine therapy between Ocotober 1, 2004 and December 31, 2006. The dispense date of the first duloxetine prescription was defined as the index date. All duloxetine prescriptions over the 12-month post-index period were used to assess ADD and adherence. Four study cohorts were constructed based on ADD: 30 mg, 31 to 59 mg, 60 mg; and >60 mg. High adherence was defined as having a medication possession ratio for duloxetine of ≥0.8. Health-care costs over 12-month post-index period were estimated. Multiple regression models were used to examine the association between ADD, adherence, and health-care costs. The study sample included 1,351 DPNP patients (mean age: 55 years; male: 41%). Twelve percent of patients had a duloxetine ADD of 30 mg, 17% of 31 to 59 mg, 56% of 60 mg, and 15% of >60 mg. Patients with ADD of 30 mg (>60 mg) were significantly less (more) likely to adhere to duloxetine therapy compared with those in the 60 mg cohort. Controlling for cross-cohort demographic and clinical differences, patients with ADD of 30 mg, 31 to 59 mg, or >60 mg had significantly higher total health-care costs than those with ADD of 60 mg (adjusted differences: $6,090, $6,320, $6,466 for 30 mg, 31 to 59 mg, >60 mg, respectively, all P < 0.05). The findings suggest that having an ADD of 60 mg for duloxetine among commercially insured DPNP patients is associated with improved medication adherence and lower health-care costs.