Low copay of generic PGA may improve adherence

In patients taking prostaglandin analogues (PGAs) for glaucoma, adherence to therapy may increase with the prescription of generic latanoprost, which has a lower copay than brand-name PGAs, according to a new study published online in Ophthalmology.

The US researchers say their study is the first to examine the effect of a glaucoma medication copay reduction on patient adherence. The results are important; researchers suspect that cost may be one reason that more than 50% of patients with glaucoma do not take the highly effective PGAs as prescribed.

In March 2011, the first and only generic PGA, latanoprost, became available in the US. At the time, it was priced to save a typical patient approximately $1,300 a year (US) when compared with buying brand-name products. To determine how the generic drug’s availability may have affected therapy adherence, researchers from the University of Michigan Medical School and University of Michigan College of Pharmacy examined claims data from 8,427 glaucoma patients for the 18 months before and after the generic drop became available. All patients in studied were taking brand-name PGAs before latanoprost became available generically. After the generic drug was introduced, some patients shifted to taking it, but others continued taking brand-name PGAs.

The researchers found that medication adherence improved, on average, among all patients who switched to generic latanoprost. Those who had been taking name-brand PGAs other than branded latanoprost (Xalantan, Pfizer), however, exhibited a greater improvement in adherence. For instance, among those who had switched from branded bimatoprost (Lumigan, Allergan), medication adherence rose, on average, from 47% to 61%. And among those who had switched from branded travaprost (Travatan, Alcon), average adherence rose from 43% to 54%.

In a subset of patients in whom adherence was suboptimal before the generic formulation became available, the researchers identified factors associated with an adherence improvement of at least 25%: higher prescription copays before generic latanoprost was introduced or lower prescription copays after the generic latanoprost was introduced. The researchers speculate that the lower cost of generic latanoprost may be the main reason for the improvement in adherence.

“Some of my patients require three or four different classes of medications. Individuals’ out-of-pocket costs for glaucoma medications can exceed $100 per month, and the high drug cost may deter patients on a tight budget from consistently buying and taking their medications as prescribed,” said Dr Joshua D. Stein, lead author and associate professor of ophthalmology and visual sciences at the University of Michigan Kellogg Eye Center. “It’s reassuring to find that switching patients to more affordable, generic drugs could be an effective solution for a subgroup of patients who have difficulty with adherence.”