OBJECTIVES: Glaucoma is an optic neuropathy associated with visual field loss. Currently, treatment for glaucoma is focused on controlling intraocular pressure. First-line treatment typically involves â-blockers or prostaglandin analogs (PAs). â-blockers and other intraocular pressure lowering agents (IOPLAs) may be used as adjunctive therapy to prostaglandins. We quantified the use of adjunctive therapy in association with prostaglandins. METHODS: We conducted a cohort study using pharmacy dispensing data from the Netherlands using the PHARMO database. We identified all patients with a first dispensing for bimatoprost, latanoprost or travoprost between January 2, 1998 and July 1, 2006, and determined the proportions of patients who received adjunctive therapy in the first 12 months of prostaglandin use. Use of adjunctive therapy was identified by at least one intermittent dispensing of any IOPLA other than PAs in the 12-month follow-up period from their first prostaglandin dispensing. Rates were compared across the three prostaglandin analogs using chi-square tests. Statistical and descriptive analyses were performed using SAS 9.1. RESULTS: In total, 9402 patients were included, aged 70 (±SD=12) years, 56% were female. The proportions of patients requiring adjunctive therapy were 31%, 42%, and 31% for bimatoprost, latanoprost and travoprost, respectively. A significantly higher proportion of adjunctive therapy was associated with latanoprost users (bimatoprost vs. latanoprost: Chi-square=26.59, p<0.001; travoprost vs. latanoprost: Chi-square=19.82, p<0.001). Bimatoprost and travoprost did not differ Chi-square=0.01, p=0.94). CONCLUSIONS: Approximately 40% of continuous prostaglandin users required adjunctive therapy in the first 12 months. The latanoprost cohort had the highest rate of adjunctive therapy. Higher rates of adjunctive therapy use may result in higher overall patient care costs.