Does adjunctive glaucoma therapy affect adherence to the initial primary therapy?

OBJECTIVE: To examine the effect of adding complexity to a glaucoma medical treatment regimen--specifically, what would occur to the refill rate (and, by inference, to adherence) when a second medication was added to a currently used once-daily drug.
DESIGN: Open-label retrospective review of patient records. PARTICIPANTS: Patients of a large national health care provider who had received a prescription for latanoprost between July 1, 2001 and June 30, 2002. There were 1784 patients who had a second medication added and 3146 patients who remained on monotherapy.
METHODS: For each patient, the mean number of days between refills was calculated for both the period before and that subsequent to the addition of the second medication, and an interperiod difference in refill interval between the 2 periods was calculated. Probability comparisons were performed using paired t tests (continuous) and Wilcoxon signed rank tests (categorical).
RESULTS: The mean age of the population using second-line therapy was 68.3+/-14.5 years (range, 4-97), and 56% were female. In this population of 1784 patients who used 2 different ocular-hypotensive medications, mean refill intervals for latanoprost were 40.6+/-21.8 days before the addition of a second drug and 47.4+/-24.4 days after the addition of a second drug, with a mean increase of 6.7+/-25.6 days. For 22.9% (409/1784) of patients, the interval was increased by >2 weeks (P<0.0001). The mean refill interval was longer than that for the 3146 patients who continued on latanoprost monotherapy, which was 41+/-24 days.
CONCLUSIONS: This statistically and clinically significant increase in refill intervals may affect intraocular pressure control. We suggest that, when adding a second drug, physicians need to consider the possible impact on the patient's adherence to the first drug.