Medication Adherence and Healthcare Costs among Fibromyalgia Patients Treated with Duloxetine

OBJECTIVE: The study aims to examine predictors associated with duloxetine adherence and its association with healthcare costs among fibromyalgia patients. METHODS: Administrative claims from both commercially and Medicare supplemental-insured fibromyalgia patents aged 18+ who initiated duloxetine in 2006 were analyzed. Initiation was defined as a 90-day clean period without duloxetine. The dispense date of the first duloxetine prescription was denoted as the index date. Two cohorts were constructed based on duloxetine adherence over the 12-month postindex period (high adherence as medication possession ratio ≥0.8). Predictors of high adherence were examined via logistic regression. Generalized linear regressions were performed to estimate the association between duloxetine adherence and healthcare costs. RESULTS: A total of 4,869 commercially and 566 Medicare supplemental-insured fibromyalgia patients were identified. Two-thirds of patients had low adherence. Higher duloxetine average daily dose (ADD) was associated with increased adherence (reference group=30mg; Commercial: Odds ratio [OR]=3.03, 2.40, and 3.73 for 31 to 59mg, 60mg, and >60mg, respectively, all P<0.05; Medicare supplemental: OR=3.11, 2.33, and 4.76 for 31 to 59mg, 60mg, and >60mg, respectively, all P<0.05). Commercially insured patients with high adherence had significantly lower total healthcare costs than low-adherence patients (-$1,164, P<0.05), primarily because of lower inpatient (-$2,222, P<0.05) and outpatient (-$1,075, P<0.05) costs. Medicare supplemental-insured patients with high adherence had similar overall and inpatient costs, but significantly lower outpatient costs (-$2,025, P<0.05). CONCLUSION: Fibromyalgia patients with higher duloxetine ADD were more likely to adhere to the therapy. High duloxetine adherence was associated with lower (Commercial) or similar (Medicare supplemental) healthcare costs.