Observed time between prescription refills for newer ocular hypotensive agents: the effect of bottle size

To describe prescription refill patterns of ocular hypotensive therapies and to measure differences among refill rates across bottle sizes.

Retrospective, population-based, cohort study.

This study included patients dispensed bimatoprost, brimonidine, dorzolamide/timolol, latanoprost, timolol gel (XE) 0.5%, or travoprost between January 1, 1996, and March 30, 2002. The initial fill date was identified for the cohort-defining ocular hypotensive, and the number of days between each subsequent refill was calculated. The analysis was repeated in patients with at least four refills to evaluate potential bias. Descriptive and survival analyses evaluated differences in refill rates across bottle sizes.

In the 27,387 patients contributing up to four evaluable refill sequences, the amount of drug contained in bottles did not predict the number of days between fills. Patients dispensed larger bottles typically refilled sooner than drop-count studies would predict; results for patients with at least four refills (n = 12,976) confirmed these findings. Survival analysis demonstrated that the bottle size trend held across classes of therapy. Compared with 5.0-ml bottles, patients dispensed 10.0-ml and 15.0-ml bottles returned for refills at approximately 1.5 times the expected rate. When average wholesale prices were applied to refill intervals for selected agents, a 45% excess cost per month was found for the larger bottle sizes (10.0 ml vs 5.0 ml or 5.0 ml vs 2.5 ml).

Expected refill patterns predicted by bottle size and mean number of drops do not reflect observed refill patterns. Patients dispensed larger bottle sizes return for refills much sooner than expected, regardless of the class of therapy.