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Supplements New Perspectives on Overactive Bladder: Quality of Life Impact, Medication Persistency, and Treatmen
New Perspectives on Overactive Bladder: Quality of Life Impact, Medication Persistency, and Treatment Costs
C. Daniel Mullins, PhD; and Leslee L. Subak, MD
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Persistence With Overactive Bladder Pharmacotherapy in a Medicaid Population
Fadia T. Shaya, PhD, MPH; Steven Blume, MS; Anna Gu, MA; Teresa Zyczynski, PharmD, MBA, MPH; and Zhanna Jumadilova, MD, MBA
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Richard G. Roberts, MD, JD; Alan D. Garely, MD; and Tamara Bavendam, MD
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Sujata Varadharajan, MS; Zhanna Jumadilova, MD, MBA; Prafulla Girase, MS; and Daniel A. Ollendorf, MPH
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Persistence With Overactive Bladder Pharmacotherapy in a Medicaid Population

Fadia T. Shaya, PhD, MPH; Steven Blume, MS; Anna Gu, MA; Teresa Zyczynski, PharmD, MBA, MPH; and Zhanna Jumadilova, MD, MBA

Statement of Problem and Rationale: The management of chronic conditions, such as overactive bladder (OAB), is often limited by lack of patient adherence to medication. This article compares persistence rates among Medicaid patients who were prescribed 1 of 3 drugs for treatment of OAB: 2 long-acting agents with once-daily dosing, tolterodine tartrate extended-release capsules (tolterodine ER) and oxybutynin chloride extended release (oxybutynin ER), and oxybutynin immediate release (oxybutynin IR), requiring 3 tablets daily.

Methodology: The study population was comprised of continuously enrolled Medicaid managed care patients filling prescriptions for tolterodine ER, oxybutynin ER, or oxybutynin IR between January 1, 2000, and December 31, 2003. Patients taking any OAB drug in the first 6 months of their observed period of enrollment were excluded to capture new users only. Using survival analyses adjusted for age, sex, and race, the rates of persistence by drug were analyzed. Possession time, the degree to which patients keep medication available even though they may not be taking it daily as prescribed, was also measured.

Results: Of 1637 patients (75% women, 45% African American, 26% younger than 18 years of age), 182 were started on tolterodine ER, 215 on oxybutynin ER, and 1240 on oxybutynin IR. Only 32% of those taking oxybutynin IR and 44% of those taking either long-acting agent remained adherent past 30 days. Of those remaining after 30 days, the risk of nonadherence was higher for oxybutynin ER than for tolterodine ER (hazard ratio = 1.47; 95% confidence interval, 1.01-2.14).

Conclusion: Persistence rates are better for patients taking drugs with once-daily dosing, but there is a need for a better understanding of non-persistent patients.

(Am J Manag Care. 2005;11:S121-S129)


Overactive bladder (OAB) has been described as a "syndrome of symptoms," and defined by the International Continence Society as urgency, with or without urge incontinence, usually with frequency and nocturia.1 OAB affects nearly 33 million people in the United States,2 making it more prevalent than asthma (15 million), osteoporosis (10 million), diabetes mellitus (7 million), or Alzheimer's disease (4 million).3 The estimated total economic cost of OAB was $12.02 billion in 2000, with $9.17 billion and $2.85 billion incurred in the community and institutions, respectively.4 This estimate is relatively conservative, because it did not include the costs of care for dry institutional residents with OAB.4

Medications used to treat OAB have anticholinergic properties. These agents block muscarinic effects inhibiting involuntary bladder contractions. Extended-release formulations of antimuscarinic agents offer the convenience of once-a-day dosing. Studies comparing extended-and immediate-release formulations of oxybutynin and tolterodine have reported a better therapeutic window with extended-release formulations and better side effect profiles.5 With good compliance and adherence to these medications, patients' quality of life can be improved and health services utilization costs can be reduced.6

Because of the chronic nature of OAB, it is essential that medication be taken as prescribed. Persistence has been shown to be one of the critical predictors of outcomes in chronic conditions.7 Despite improvements in recent years in the tolerability and efficacy of OAB medications, many patients do not comply with the instructions.8-10 With long-term treatment, persistence is even more difficult for these patients.

Medication persistence rates in patients with OAB have been found to be low regardless of setting.8,9,11,12 For example, Yu and colleagues10 investigated 1-year persistence patterns for OAB/urinary incontinence (UI) medication treatment in the California Medicaid program. They enrolled adult patients diagnosed with OAB/UI who had received at least 1 OAB/UI medication from July 1999 to April 2001. Persistence patterns of patients were measured as time to discontinuation; adherence was measured as medication possession ratio (MPR), which compares the cumulative days of drug supply with the elapsed time since the date of the first prescription of the drug being measured. They found that of 6518 eligible patients, 5751 patients (88.2%) discontinue within the following year, and only 14.6% patients have an MPR ³ 0.80. Significant predictors of higher persistence include Caucasian, 75 years of age or older, past medication use, and initiating the extended-release form of the drug.10

OAB is of special significance to state Medicaid plans because of its higher severity in women,2 the high population of women in Medicaid, and higher per capita expenditures for adults with Medicaid.13 Poor compliance can be attributed to a variety of factors, including low level of education, cultural and social support factors, and side effects.14-16 These factors, such as low education level, may be more prevalent among underserved populations, such as Medicaid beneficiaries. It would be likely that a higher prevalence of OAB and lower persistence rates exist simultaneously in the Medicaid population.

To date, there is a paucity of literature on medication adherence patterns among Medicaid-eligible patients with OAB. The objective of this study was to compare persistence and adherence patterns among Medicaid managed care patients prescribed 1 of 3 drugs for treatment of OAB: tolterodine tartrate extended-release capsules (tolterodine ER), oxybutynin chloride extended release (oxybutynin ER), and oxybutynin immediate release (oxybutynin IR).

Methods

Sample. The total population consisted of more than 400 000 Medicaid recipients from a mid-Atlantic state who were not in institutions or eligible for Medicare. Recipients had to be enrolled in 1 of 8, prepaid, state-contracted managed care organizations (MCOs). Enrollees include both those who qualified because of low income or by having high medical expenses relative to their income. All prescription claims were retrieved for the Medicaid MCO enrollees receiving at least 1 prescription between January 2000 and December 2003 for tolterodine ER, oxybutynin ER, or oxybutynin IR. For each patient, the longest period of continuous enrollment was identified. Successive enrollment periods that were less than 45 days apart were combined into a single continuous enrollment period. The sample was limited to new users by excluding those who had used tolterodine ER or oxybutynin (ER or IR) in the first 6 months of the selected enrollment period, or had any use in a prior enrollment period. Statistical significance is determined at the a = .05 level.

Medication-taking Status. OAB medication-taking status was categorized into switching, discontinuation, or persistence. The index date of a study drug (index drug) was captured for each patient. If that patient filled a prescription for a different OAB drug within 15 days of when their preceding prescription was scheduled to run out, the patient was classified as a "switch." If a patient did not fill any OAB prescription within the same time period, this patient was classified as "discontinued." If a patient did not switch or discontinue after the first prescription, they were considered persistent, and each subsequent prescription for the same drug was confirmed until a switch or discontinuation was identified or until the patient had no claims in the enrollment period. As a sensitivity analysis, results were computed with refill windows varying from 15 days to 30 days. If a patient had switched drugs, the dispensing date of the new drug was recorded as the switch date; if a patient had discontinued, the original dispensing date plus the day's supply were used to calculate the discontinuation date.

Medication Possession Time. Although it is recommended that patients take their medication on a daily basis, many patients with OAB do not follow this practice. For example, they may take the drug only when they are going to leave their house. Thus, also tracked was the length of time patients maintained possession of the drug. That is, the time patients kept a certain minimum level of medication on hand through refills was measured, although they may not have been persistent with the prescribed regimen.

Possession time was measured as the time patients maintained an MPR of at least 30%. The MPR typically compares the cumulative days of drug supply with the elapsed time. Here, the possession time was defined to be the period during which the patient maintained a given possession ratio. The patient may have continued to refill the prescription, but not often enough to be compliant with therapy every day. The calculation used was:

Figure

Because the denominator did not include surplus days, the surplus days after the nth prescription were not counted in the numerator either. The MPRn was an estimation of medication persistence during the period between the date of first prescription and the date of nth prescription.

Analysis. Patient demographic characteristics were examined by drug group. Percent by age category, sex, and race were calculated. A product-limit life table analysis was used to construct survival curves of patient persistence and possession time by index drug. Patients still persistent at the end of their enrollment period were censored at that point. To determine whether differences in persistence and possession time by drug are statistically significant after adjusting for age, sex, and race, a time-dependent, Cox proportional hazard model was used. The time-dependent model allows different hazard ratios (HRs) in different time periods, and it can be used to account for differences in behavior between patients who drop after the first prescription and those who refill at least once. Persistence was computed using the 15-day refill buffer. A model was also tested in which the maximum follow-up allowed was 360 days, in case extreme observations had a disproportionate effect on results. Finally, models were also run in which a variable was added (individually) to indicate whether a patient had a qualified diagnosis for OAB or a contraindication in the 6 months before initiating medication. The codes used for these diagnoses and contraindications are listed in the Appendix.

Results

Sample. The search of prescription records of more than 400 000 enrollees in Medicaid MCOs for tolterodine ER, oxybutynin IR, or oxybutynin ER filled between January 1, 2000, and December 31, 2003, yielded 20 667 prescriptions of 3054 unique patients. After exclusions, the sample by index drug included 1240 oxybutynin IR patients, 215 oxybutynin ER patients, and 182 tolterodine ER patients (Table 1). Another 48 patients had started on nonstudy OAB drugs. Of these 1637 patients, 75% were women, 26% were younger than 18 years old, and 45% were African American. The most significant difference between the index drug cohorts was that 30% of the oxybutynin IR users were younger than 18 years of age; only 3% of the tolterodine ER users and 17% of the oxybutynin ER users were younger than 18 years of age. The efficacy of tolterodine ER has not been demonstrated in pediatric populations.

Figure

Persistence. The unadjusted survival curves of patient persistence by index drug are shown in Figure 1. Only 32% of those starting on oxybutynin IR and 44% of those starting on either tolterodine ER or oxybutynin ER remained persistent after 30 days (P <.001). That is, they did not refill their initial prescription. The 1-year persistence rates were 9%, 6%, and 5% for tolterodine ER, oxybutynin ER, and oxybutynin IR, respectively (P = .086). Results are only slightly better if the more generous refill buffer of 30 days is allowed. By this criterion, 30-day persistence rates are 49%, 48%, and 39% for tolterodine ER, oxybutynin ER, and oxybutynin IR, respectively (P = .004). The corresponding 1-year rates are 12%, 5%, and 8% (P = .038).

Figure

 
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