OBJECTIVES: To compare dosing patterns between duloxetine and pregabalin among patients with fibromyalgia. METHODS: Using a large US administrative claims database, we examined commercially insured individuals aged 18-64 with fibromyalgia who initiated duloxetine or pregabalin in 2006. Initiation was defined as 90-day medication gap, with the dispense date of the first initiation as the index date. All patients included had 12-month continuous enrollment in the pre- and post-index period, and at least 30 days supply of duloxetine or pregabalin in the 12 months post-index period. Patients with diabetic peripheral neuropathic pain or depression in the 12 months pre-index period were excluded. Duloxetine or pregabalin cohorts were constructed based on the index agent. Average daily doses of all duloxetine or pregabalin prescriptions per person, average daily dose in each of the first 12 prescriptions, and percent of daily dose change from previous prescription were compared between duloxetine and pregabalin cohorts. RESULTS: Both the duloxetine (n = 3773) and pregabalin (n=4189) cohorts had the mean age of 50 years. The duloxetine cohort had an average initial daily dose of 55.7mg, while 161.5mg for the pregabalin cohort. The average daily dose per patient was 55.5mg for duloxetine and 195.7mg for pregabalin. The average daily doses for the first through twelfth duloxetine scripts varied from 55.68mg (95% Confidence Interval (CI): 54.96, 56.40) to 60.34mg (95% CI: 54.71, 65.97), while the numbers were 161.50mg (95% CI: 159.02, 163.98) and 282.41mg (95% CI: 266.89, 297.93) for pregabalin. The percentages of changes in daily dose from previous prescriptions were -4.2~1.6% for duloxetine and 1.3~14.3% for pregabalin, respectively. CONCLUSIONS: Among patients with fibromyalgia, duloxetine and pregabalin initiators had very different dosing patterns. The average daily dose for duloxetine was relatively stable over time, while pregabalin patients had significant dose escalation over the 12-month follow-up period.