Cost-Sharing and Initiation of Disease-Modifying Therapy for Multiple Sclerosis | Page 2

For patients using DMTs, total DMT spending averaged $16,742 (2009 dollars) per year over 2004-2009. Mean out-of-pocket expenditures on DMTs were $691 per year. For half of MS patients, cost-sharing was 1.6% or less of DMT costs (Table 2). On average, the cost-sharing rate was 4.3%. Ten percent of patients faced a rate of at least 12.0%, 5 percent faced a rate of 17.8% or more, and 1 percent faced an extreme rate of 39.5% or higher. In terms of out-of-pocket spending, half of DMT users spent less than $251 per year, while 5 percent of users spent more than $2625 (all in 2009 dollars).

Only 17% of incident MS cases (586 patients) initiated DMTs over the 8 quarters after the initial diagnosis. In the regression results, the coefficient estimate for the interaction between the cost-sharing rate and quarters since diagnosis was negative in sign and statistically significant (P = .019). Thus the negative effect of cost-sharing on the proportion of MS patients who initiated DMTs increased with time since diagnosis. Complete results are reported in the eAppendix (available at www.ajmc.com). The preferred specification excluded the cost-sharing rate on its own (that is, the level effect). In an alternative specification, the coefficient estimate for the cost-sharing rate on its own was positive, but was not statistically distinguishable from zero.

To interpret the regression results, the Figure shows cumulative initiation rates at various cost-sharing levels, by time since diagnosis. In the quarter of diagnosis, we predict that 4.2% of patients would have initiated if there were no cost-sharing. The predicted initiation rate decreases to 4.1% at the 75th percentile of cost-sharing (3.4%, as shown in Table 2), and to 3.9% at the 95th percentile (17.8%). The effect of cost-sharing increased in magnitude with time since diagnosis, and was largest at 2 years post-diagnosis: The cumulative initiation rate is 22.6% without cost-sharing, but 19.7% at the 95th percentile (P = .019 for the difference). This 2.9 percentage point reduction in the initiation rate is a 12.7% reduction in relative terms.

DISCUSSION

This study contributes to the literature regarding the impact of cost-sharing on drug utilization, focusing on initiation of DMTs among incident MS cases commercially insured by large companies over 2004-2009.

Cost-sharing rates for DMT therapy tended to be modest (4.3% on average). Mean out-of-pocket costs among DMT users were $691 per year (2009 dollars), due to the high cost of the treatments ($16,742 per year on average). Within the same commercially insured population, persons with type 2 diabetes who used antidiabetic drugs experienced a mean costsharing rate of 32.3%, and average out-of-pocket spending of $219. Considering the specialty cancer drugs studied in Goldman et al,21 mean cost-sharing rates for the oral therapies imatinib mesylate and erlotinib were comparable to the DMT rate (3.7% and 4.8%, respectively, vs 4.3% for DMTs). Mean outof-pocket spending was also similar ($857 and $449 per year, vs $691). For the injectable agents bevacizumab, rituximab, and trastuzumab, mean cost-sharing rates were much higher than for DMTs (24.1%, 16.8%, and 11.7%, vs 4.3%). Mean out-of-pocket spending by users of these agents was also higher than for DMT use in MS ($3542, $5610, and $5602, vs $691).

This study also found that high cost-sharing for DMTs was associated with a reduced likelihood of initiating therapy in the 2 years after an initial MS diagnosis, most commonly relapsing-remitting MS.²² A negative effect of cost-sharing has been found in numerous prior studies of drug utilization.³ For 8 therapeutic classes used by the chronically ill, a doubling of copayments was associated with anywhere from a 25% to a 45% reduction in utilization, with a smaller reduction for essential classes.¹⁸ In the present context, a doubling of the cost-sharing rate from its mean level (4.3%) is predictedto decrease initiation of DMTs by 4% within 2 years of initial MS diagnosis. Cost-sharing has a larger effect at the extremes. An increase in the DMT costsharing rate from zero to its 95th percentile (17.8%) is associated with a 13% reduction in initiation within 2 years.

Although cost-sharing may be a method for reducing health plan costs, it may have unintended consequences. This study showed that only 17% of patients initiated DMT treatment within 2 years of an initial diagnosis of MS. There is growing evidence that earlier initiation of DMTs may prevent relapses and disability progression.23,24 A recent study also demonstrated that treatment with DMTs prior to a confirmed MS diagnosis was associated with fewer hospitalizations and lower expenditures compared with DMT treatment after a confirmed diagnosis.25 In the present context, additional regression analysis showed no association between DMT cost-sharing rates and hospitalization with a primary diagnosis of MS (patients who never initiated DMTs within 2 years of diagnosis were less likely to have been hospitalized for MS, 6.1% vs 11.8%, P <.001). For patients with a confirmed diagnosis, the effect of DMT use on disease progression and healthcare utilization may manifest itself beyond the 2-year post-diagnosis window analyzed here.¹⁵ Altogether, this study and the related literature suggest that high cost-sharing for DMTs discourages initiation, which in turn may lead to negative clinical outcomes.

There are several limitations of our study that are reflective of administrative claims data studies. First, DMT initiation is based on filled prescription claims and therefore does not capture utilization based on samples provided by physicians. However, physicians are unlikely to provide 2 years of samples, the time frame after diagnosis over which we analyze initiation. In addition, the plan fixed effects in our analysis control only for confounders that do not change over time. They do not control for unobserved factors which vary over time. Given the high cost of DMTs, it is possible that enrollees with a strong preference for these drugs switched to plans with low cost-sharing when confronted with an increase in cost-sharing in their current plan. If so, our analysis may understate the degree to which high cost-sharing actually discourages utilization.