Cost-Sharing and Initiation of Disease-Modifying Therapy for Multiple Sclerosis

Healthcare costs in the United States have been growing faster than the overall rate of inflation.¹ As policy makers and insurers search for ways to control cost growth, they have frequently turned toward cost-sharing. In particular, increasing costsharing for prescription drugs is often proposed as a cost-containment mechanism.^2-4

The rationale for this approach is 2-fold: First, the health plan may offset a portion of its drug acquisition costs through copayment or coinsurance revenue collected from patients. Second, when patients are directly affected economically by their treatment choices, they will be more discriminating consumers.⁵

However, cost-sharing can negatively impact therapy utilization, particularly among those with chronic conditions. Reduced initiation of pharmaceutical treatments with proven health benefits could result in worse long-term health outcomes.^6-8

Multiple sclerosis (MS) is an autoimmune disorder characterized by inflammation of the central nervous system.^9,10 Its most common symptoms are fatigue, reduced mobility, bowel and bladder disturbances, diminished cognitive function, pain, sensory loss, and depression. Currently, there are approximately 400,000 people living with MS in the United States.¹¹

Disease-modifying therapies (DMTs) have become the standard for MS treatment. Randomized clinical trials and long-term follow-up studies have found that DMTs are effective in reducing relapse rates, slowing the progression of disability, and reducing MS disease activity.^12-15 The costs of DMTs make them attractive targets for high cost-sharing by health plans seeking to contain pharmacy costs.¹⁶ The existing evidence on the link between cost-sharing and MS DMT utilization is limited and does not control for the selection of individuals into benefit plans.¹⁷

The objective of this study was to evaluate the association between health plan cost-sharing for DMT drugs and initiation of these therapies among US commercial health plan beneficiaries with MS.

METHODS

This was a retrospective longitudinal cohort study, which used a data set of deidentified administrative, claims, and benefit information from 33 Fortune 500 employers. The data provided information on enrollment, medical, and pharmacy records for the years 2003 through 2009. The data included detail on age of beneficiaries, gender, diagnoses, and relationship of beneficiary to the primary beneficiary. The data included total and beneficiarylevel spending for all outpatient pharmaceutical purchases, as well as all inpatient and outpatient medical services. National drug code and dosage were reported in drug claims; each medical claim reported up to 9 diagnoses and 6 procedures.

Inclusion and Exclusion Criteria

The study sample consisted of beneficiaries 18 years or older with 2 or more inpatient or outpatient diagnoses of MS (International Classification of Diseases, Ninth Revision, Clinical Modification code of 340) within 1 year. The index date was the date of the first MS diagnosis during the patient identification period between January 1, 2004, and March 31, 2008. Patients had to have at least 2 years of continuous enrollment after (and inclusive of) the index quarter and at least 1 year of continuous enrollment prior to the index quarter, with no MS diagnosis or DMT use in the pre-index period.

Key Variables and Outcomes

For all analyses, DMTs were identified by National Drug Codes in pharmacy claims or Healthcare Common Procedure Coding System codes in medical claims. DMTs included interferon beta-1a (subcutaneous and intramuscular), interferon beta-1b, glatiramer acetate, natalizumab, and mitoxantrone.

In measuring cost-sharing, our goal was to quantify how DMT utilization responds to cost-sharing. Plans have disparate benefit designs, differing with respect to multi-tier formularies, out-of-pocket discounts for mail order or in-network retail pharmacies, and deductibles, maximums, and caps. A cost-sharing measure that characterizes plan design in a consistent, comprehensive, and economically meaningful way was needed. Hence, we took the ratio of total out-of-pocket payments for DMTs to total payments for DMTs, among all MS patients in a given plan by year. This approach has been used in other studies in the literature.¹⁸ Treatment initiation was defined as any fill of a DMT prescription during the 2-year follow-up period after diagnosis.

Statistical Analysis

Multivariate regression analyses estimated linear relationships between health plan cost-sharing and DMT initiation controlling for patient age, gender, and whether the patient was the primary beneficiary. To measure health status, the Charlson Comorbidity Index was computed from inpatient and outpatient claims in each calendar year, and included in the analysis.^19,20

Each incident MS patient was tracked for 8 calendar quarters (including the diagnosis quarter). The cost-sharing rate in each quarter was the rate for the plan in the corresponding calendar year. In order to measure the cumulative initiation rate, patients who initiated remained in the analysis sample in subsequent quarters. We included the number of quarters since diagnosis in the regressions to allow for increases in the cumulative initiation rate. The cost-sharing rate was interacted with quarter since diagnosis, so the effect of cost-sharing could vary with time since diagnosis.

To control for any overall trends in initiation (due to, for example, factors such as disease management), indicator variables for each year were used. In addition, indicator variables for each plan (plan “fixed effects”) were used to help control for unobserved determinants of initiation which did not vary over time (for example, a tendency for MS patients with a strong unobserved preference for DMTs to enroll in plans with low DMT cost-sharing). This empirical approach was facilitated by the use of linear regression models.

RESULTS

The data included 4.76 million unique beneficiaries over 2004-2008. A total of 9513 beneficiaries had 2 or more claims with an MS diagnosis in at least 1 of these calendar years, with 9351 having an initial diagnosis prior to March 31, 2008. Of these, 5244 were enrolled throughout the prior year, and did not have an MS diagnosis or DMT use in that year. A total of 3460 incident MS cases were continuously enrolled for 2 years after initial diagnosis. This sample of patients was analyzed. The average age of the patients was 42.2 years (SD +/- 22 years), and the majority were females (66.6%). These and other summary statistics are shown in Table 1.