Currently Viewing:
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
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
The Impact of Urinary Incontinence on Quality of Life of the Elderly
Yu Ko, MS; Swu-Jane Lin, PhD; J. Warren Salmon, PhD; and Morgan S. Bron, PharmD, MS
Safety and Tolerability of Tolterodine for the Treatment of Overactive Bladder in Adults
Richard G. Roberts, MD, JD; Alan D. Garely, MD; and Tamara Bavendam, MD
Currently Reading
Medical Costs After Initiation of Drug Treatment for Overactive Bladder: Effects of Selection Bias on Cost Estimates
Nicole M. Nitz, PhD; Zhanna Jumadilova, MD, MBA; Theodore Darkow,   PharmD; Jennifer R. Frytak, PhD; and Tamara Bavendam, MD
Urinary Incontinence in the Nursing Home: Resident Characteristics and Prevalence of Drug Treatment
Zhanna Jumadilova, MD, MBA; Teresa Zyczynski, PharmD, MBA, MPH; Barbara Paul, MD; and Siva Narayanan, MS, MHS
Treatment of Overactive Bladder: A Model Comparing Extended-release Formulations of Tolterodine and Oxybutynin
Eleanor M. Perfetto, PhD; Prasun Subedi, MS; and Zhanna Jumadilova, MD, MBA
PARTICIPATING FACULTY

Medical Costs After Initiation of Drug Treatment for Overactive Bladder: Effects of Selection Bias on Cost Estimates

Nicole M. Nitz, PhD; Zhanna Jumadilova, MD, MBA; Theodore Darkow,   PharmD; Jennifer R. Frytak, PhD; and Tamara Bavendam, MD

Objectives: To compare posttreatment medical costs for patients with overactive bladder (OAB) initiating treatment with oxybutynin chloride immediate release (oxybutynin IR), oxybutynin chloride extended release (oxybutynin ER), or tolterodine extended-release tartrate capsules (tolterodine ER).

Methods: Data were drawn from administrative claims of enrollees aged 18 years and older of a large US health plan. OAB patients were identified if at least 1 claim with an International Statistical Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code for OAB appeared in medical claims from January 1, 2001, to December 31, 2002. The index prescription was assigned as the first filled prescription of oxybutynin IR (n = 3052), oxybutynin ER (n = 4503), or tolterodine ER (n = 7027) during the subject identification period. Medical costs over the year after initiation were calculated as a function of the health plan and member liability. Independent variables were treatment cohort, sex, age group, geographic region, baseline costs, specific OAB diagnosis codes, and comorbid illnesses. To compare medical costs across treatment cohorts, multivariate regressions correcting for potential selection bias were used.

Results: Multivariate analysis results revealed that costs for patients taking oxybutynin IR were 48% higher than costs for patients taking tolterodine ER (P = .026), and costs for patients taking oxybutynin ER were 191% higher than costs for patients taking tolterodine ER (P <.0001). Adjusted medical costs were $7486 for patients taking oxybutynin IR and $14 766 for patients taking oxybutynin ER compared with $5074 for patients taking tolterodine ER.

Conclusion: Differences in medical costs that remained after adjusting for patient characteristics suggest that treatment with tolterodine ER may be associated with lower medical care utilization after initiation of therapy for OAB.

(Am J Manag Care. 2005;11:S130-S139)


Despite recognition of the prevalence of overactive bladder (OAB) and its costly consequences in terms of patient outcomes, there is a dearth of evidence on the cost effectiveness of the most common pharmacological therapies for this condition. The overall prevalence of OAB in the United States has been estimated at 16.9% for women (9.3% with frequency, urgency, and urgency incontinence) and 16% for men (2.6% with frequency, urgency, and urgency incontinence).1 These figures translate to approximately 33.3 million adults in the United States with OAB and 12.2 million adults with urgency incontinence.

The cost of OAB in the United States is estimated to be greater than $12 billion annually, a burden that is comparable with other chronic conditions, such as osteoporosis ($13.8 billion).2,3 In contrast to many long-term diseases, a large portion of the cost of OAB ($3.9 billion) is related to indirect costs beyond the costs of the condition itself.2,4 This is caused, in part, by the higher risk faced by patients with OAB for experiencing related comorbidities.4-6 A recent analysis of the prevalence of falls and fractures, urinary tract infections, skin infections, vulvovaginitis, and depression among 23 112 OAB patients and matched controls, found that patients with OAB were significantly more likely than controls to have each of the studied comorbidities.7 Compared with the general population, patients with OAB may also incur greater costs in managing these conditions.7

Although management of OAB may involve nonpharmacologic methods, antimuscarinic agents are the primary treatment for OAB.8-12 These agents appear to improve both clinical outcomes and patients' quality of life,13-21 and there is some indication that use of pharmacotherapy as initial treatment is associated with decreased utilization of healthcare resources.22 Further, better treatment of OAB is expected to decrease the incidence of healthcare resource utilization associated with OAB-related comorbidities. Unfortunately, treatment rates are low because of a number of factors, including a reluctance to discuss OAB symptoms with a physician23; possible physician undertreatment of OAB23; and low rates of adherence and persistence with OAB therapy.24-27 The extent to which increasing treatment rates may reduce healthcare costs for patients with OAB depends on the impact of the specific therapies used on costs.

Few studies have directly examined the impact of specific pharmaceutical treatments for OAB on expenditures for medical care in a "real-world" population. Specifically, with the introduction of extendedrelease formulations of both oxybutynin and tolterodine, there are little data quantifying the extent to which these newer formulations may reduce medical costs for patients with OAB, or comparing the relative effects of the extended-release formulations on costs. Hall and colleagues found that although average per-patient-per-month total healthcare costs increased after the first indication of OAB, patients filling prescriptions for tolterodine immediate release (tolterodine IR) or oxybutynin immediate release (oxybutynin IR) did not have a statistically significant difference compared with untreated patients in the percentage change in total healthcare costs.25 However, a lengthier follow-up time than was available in that study may be necessary to fully evaluate the impact of OAB therapies on costs.

This study assessed medical cost outcomes for patients with OAB who initiated treatment with tolterodine tartrate capsules extended release (tolterodine ER) compared with patients initiating treatment with oxybutynin chloride extended release (oxybutynin ER) or oxybutynin IR.

Methods

Study Design, Data Source, and Study Population. This retrospective study used eligibility, medical, and pharmacy claims of a large national US health plan affiliated with Ingenix. The research database includes discounted, fee-for-service, independent, practice- associated model plans covering all regions of the United States. During the study period, approximately 5.7 million patients older than the age of 18 years had claims in the database.

Patients were included in the study if they had commercial or Medicare insurance with a prescription drug benefit. For each subject, an index date was identified as the first filled prescription for tolterodine ER, oxybutynin ER, or oxybutynin IR during January 1, 2001, to December 31, 2002. The study period consisted of a 6-month baseline period before and a 12-month follow-up period after the index prescription. Subjects who filled prescriptions for these drugs during the 6-month baseline period were excluded, as were subjects who filled prescriptions for more than 1 of the 3 drugs on their index date. In addition, subjects with International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis codes for Alzheimer's disease, spinal cord injuries, or spina bifida were excluded (see Appendix). Subjects were required to be continuously covered by the health plan for 6 months before and 12 months after their index date. Claims with OAB-related diagnosis codes were identified during the subject identification period (Table 1).

Figure

Statistical Analyses. Drug cohorts were compared on medical costs over 12 months of follow-up. Medical costs were calculated as a function of health plan and member liability for nonpharmacy costs, including hospital, emergency room, physician, outpatient, laboratory, and other nonpharmacy costs. Differences between cohorts in proportions were tested using chi-square tests. Kruskall-Wallis chi-squares were used to test for differences in distribution of costs, and Bonferonni-adjusted t-tests were used to compare pairs of drug cohorts. Multivariate analyses assessed medical costs adjusted for drug cohort and covariates. Other covariates included in multivariate models were sex, age group, geographic region, logged total healthcare costs in the 6-month baseline period, OAB-related diagnosis code, and diagnoses of comorbid conditions. Comorbid illnesses were identified during the baseline period using the Washington method of clustering illnesses.28 Specific interactions were tested to examine whether the effect of treatment cohorts on medical costs differed by sex, age group, baseline total healthcare costs, or specific OAB-related diagnosis code.

A major concern in estimating the cost models was the potential for selection bias as a result of unobserved differences between the treatment cohorts (ie, whether an unobserved factor was correlated with both the selection of a specific treatment and with medical cost in the follow-up period). To examine this issue, we estimated the cost equation using several methods. Ordinary least squares (OLS) regression did not include an adjustment for any potential selection bias. Treatment effects regressions estimated a pair of equations, with one equation to predict the selection of treatment and another equation to estimate cost. This technique estimates the correlation between the equation predicting treatment and the equation predicting cost, giving an estimate of the direction and size of the bias produced by the OLS estimation. A positive correlation indicates OLS estimates are biased upwards and a negative correlation indicates OLS estimates are biased downward. Chow tests assessed whether the coefficients for other covariates included in the cost model differed between the treatment cohorts. Treatment regression models were estimated separately for the comparisons of oxybutynin IR with tolterodine ER, and of oxybutynin ER with tolterodine ER.

Log-transformed medical costs were used as the dependent variable in all multivariate estimations to account for the non-normal distribution of the cost data. To interpret the coefficients in dollar terms (instead of log dollars), coefficients and predicted means were obtained by retransformation. Kennedy's correction was used to generate retransformed coefficients that represent the magnitude of the effect of the independent variables on cost in real dollar values.29 After retransformation, the coefficients represent the percent change in costs associated with the treatment cohort compared with the reference treatment cohort. Robust estimates of standard errors (SEs) using White's correction were obtained for models violating the assumption of homoscedasticity in the error term.30,31

We estimated the dollar value of the impact of treatment drug on medical cost by multiplying the Kennedy-corrected exponentiated coefficients for the oxybutynin IR and oxybutynin ER cohorts by the mean cost for the tolterodine ER cohort (reference group). To calculate 95% confidence intervals (CIs) for the adjusted means, the upper and lower limits for Kennedy-corrected logscale coefficients were exponentiated.

Results

Descriptive Statistics. A total of 14 582 subjects met all inclusion criteria. Of those subjects, 3052 initiated oxybutynin IR, 4503 initiated oxybutynin ER, and 7027 initiated tolterodine ER. Cohorts differed in baseline characteristics. The tolterodine ER cohort had the lowest proportion of men compared with the oxybutynin IR and oxybutynin ER cohorts (17% vs 32% and 23% respectively; P <.0001). Cohorts also differed slightly in geographic distribution. Mean age for oxybutynin IR was 55 years (standard deviation [SD] = 16.02), similar to the oxybutynin ER cohort (55 years, SD = 14.69) and slightly older than the tolterodine ER (54 years, SD = 14.28) cohort (P <.05). Cohorts also differed on the proportion of patients with specific OAB-related ICD-9-CM codes. Mean total costs during the 6-month baseline period were highest for the oxybutynin IR cohort ($4956), followed by the oxybutynin ER cohort ($4146) and the tolterodine ER cohort ($3349) (Table 2).

Figure

Total unadjusted medical costs over the follow-up period differed between cohorts. The majority of subjects in each cohort incurred some level of medical costs over the 12 months after initiation of therapy. Among the oxybutynin IR cohort, 3% of subjects did not incur medical costs compared with 2% in the oxybutynin ER and tolterodine ER cohorts, a difference which was statistically significant. With a mean of $7083, subjects in the oxybutynin IR cohort had the highest unadjusted medical costs during follow-up, followed by $5980 for the oxybutynin ER cohort and $5074 for the tolterodine ER cohort. The $2010 difference in mean cost (rounded to the nearest dollar) between the oxybutynin IR and tolterodine ER cohorts was statistically significant (95% CI, $924-$3096). However, differences in unadjusted mean cost were not statistically significant for comparisons of the oxybutynin IR and oxybutynin ER cohorts ($1103; 95% CI, $-72-$2278) and the oxybutynin ER and tolterodine ER cohorts ($906; 95% CI, $-50-$1863) (Table 3).

 
Copyright AJMC 2006-2020 Clinical Care Targeted Communications Group, LLC. All Rights Reserved.
x
Welcome the the new and improved AJMC.com, the premier managed market network. Tell us about yourself so that we can serve you better.
Sign Up