Adherence to and Utilization of Antimuscarinic Agents for OAB

San Diego—Compared with other chronic conditions, national trends indicate that adherence to medications to treat overactive bladder (OAB) is relatively poor. Antimuscarinic medications, including oxybutynin, are commonly prescribed for OAB. The updated 2012 Beers List recommends against using oral antimuscarinics in patients ≥65 years of age due to the increased risks of symptoms such as constipation.

There are newer brand-name antimuscarinic drugs available to treat OAB, but the costs for those agents are higher than those for oxybutynin. Researchers recently conducted an analysis to review overall patterns of utilization in patients newly treated with an oral antimuscarinic drug. They presented results during a poster session at the AMCP meeting. The poster was titled Utilization Patterns for Medications Used for the Treatment of Overactive Bladder—Potential Interventions Targeting Adherence and Possible Inappropriate Use of Oxybutynin in Patients Aged 65 Years and Older by a Pharmacy Benefit Manager.

The retrospective analysis compared 1 year of pharmacy benefit manager (PBM) (Catamaran) claims data and medical and pharmacy claims data from IMS Health. The PBM data were pulled by the generic product identifier associated with the drug and the IMS Health data were pulled using the International Classification of Diseases, Ninth Revision code for OAB. Adherence was examined at the drug class level using proportion of days covered (PDC) methodology.

The PBM dataset included a greater percentage of patients ≥65 years of age compared with the IMS Health data (70% vs 24%, respectively). When comparing PBM and IMS Health adherence data, the percentage of patients receiving only 1 fill of OAB agents is lower in the PBM data than in the IMS Health data (19% vs 44%, respectively). In a comparison of use of antimuscarinic agents in the IMS Health data, oxybutynin had the higher percentage of patients receiving only 1 fill.

Adherence to OAB agents was lower for medications to treat chronic conditions in patients with OAB in both the PBM and IMS Health data. Mean PDC for lipids was 0.88 (PBM) and 0.66 (IMS); for antidepressants, 0.87 (PBM) and 0.56 (IMS); and for antidiabetic agents, 0.86 (PBM) and 0.66 (IMS).

Compared with the IMS Health dataset, a larger percentage of patients in the PBM dataset received prescriptions for oxybutynin (17% vs 69%) and oxybutynin had higher utilization (51%) in the PBM dataset compared with other antimuscarinic agents in the IMS Health data set (48%).

Adherence was higher among patients with higher copayments compared with those whose copayments were lower in the Medicaid (31.2% vs 21.5%), commercial (23.6% vs 13.8%), and Medicare (53.8% vs 47.9%) populations. Among the patients taking an antimuscarinic agent in the PBM dataset, 24% were also receiving a diuretic.

In summary, the researchers said, “Overall adherence rates to OAB medications were higher in the PBM data compared with the IMS Health data. There was higher oxybutynin utilization in patients ≥65 years of age in the PBM data compared with data from the IMS Health database. Compared to the IMS Health data, more patients in the PBM data continued treatment past the original fill.

"Possible interventions can be made to improve patient adherence and to inform prescribers about oxybutynin's high rate of constipation in the elderly population and the use of diuretics in patients taking concomitant OAB agents," they added.