HOLLYWOOD, FLA. — In a military-based health care system with no out-of-pocket medication expenses, 35% of nearly 8,000 adults did not refill their prescription for an overactive bladder treatment, according to a retrospective, observational study.
However, among the 65% who did refill their antimuscarinic prescription at least once, most compliance measures were superior to those in previously published studies, suggesting copayment or out-of-pocket expenses might be a deterrent, Dr. Christine L. Sears said. Antimuscarinic medications are often prescribed as first-line treatment for symptoms of overactive bladder, a common condition. Other investigators have estimated the prevalence at 12%-16% among adult women (Eur. Urol. 2006;50:1306–14; Eur. Urol. 2009;55:783–91).
Because previous reports in the United States regarding compliance with these medications assessed patients with pharmacy copayments, Dr. Sears and her colleagues assessed compliance in a health care system where patients do not pay for medication.
They identified 7,858 adult patients in the national capital region, including Washington, D.C., Maryland, and Virginia, from pharmacy dispensing records from January 2003 to December 2006.
The median duration of medication adherence for all patients was 273 days. But when the 2,760 patients (35%) who never refilled their prescription were excluded, the median duration was 582 days.
“Our [35%] nonpersistence rate is really lower than in previous published studies,” Dr. Sears said at the annual meeting of the American Urogynecologic Society. For example, researchers in one study reported a 45% nonpersistence rate in 1,117 patients (J. Manag. Care Pharm. 2008;14:291–301). The current study included 5,501 women (70% of the total) and 2,357 men. Compliance was better among women, said Dr. Sears of the department of urology at the National Naval Medical Center, Bethesda, Md. For example, among patients who refilled the prescription at least once, women remained on their medication a median of 606 days, compared with 547 days among men.
Dr. Sears and her colleagues also assessed the medication possession ratio (MPR). An MPR of 1.0 reflects 100% compliance, calculated as the sum of the supply of medication divided by the number of days it is prescribed. An MPR greater than 1.0 would result from early medication refilling, and a ratio less than 1.0 would indicate a lapse in refilling. The overall median MPR in the study was 0.82. Men had a significantly higher median MPR (0.86) than women (0.81), Dr. Sears added.
The medication switch rate was almost 26%. This means that of the 5,098 patients who refilled their prescriptions, 1,305 changed medications or dosage at least once. Dr. Sears said the overall switch rate was similar to that reported in other antimuscarinic agent studies.
The most commonly used antimuscarinic agent was tolterodine extended release (Detrol LA) with 4,716 prescriptions. Dr. Sears and her associates reported no relevant financial disclosures.
Not surprisingly, overall compliance was better with the extended-release medications than with the immediate-release formulations, Dr. Sears said. For example, patients prescribed tolterodine extended release had a significantly higher MPR, 0.89, compared with those prescribed oxybutynin immediate release, 0.68.
The small sample size of patients prescribed oxybutynin extended release is a limitation of the study, Dr. Sears said. In addition, although they had access to the medical records, the investigators did not assess patient demographic or health care data because this information was not included in the study's institutional review board application.