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The American Journal of Managed Care May 2018
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Impact of Formulary Restrictions on Medication Intensification in Diabetes Treatment
Bruce C. Stuart, PhD; Julia F. Slejko, PhD; Juan-David Rueda, MD; Catherine E. Cooke, PharmD; Xian Shen, PhD; Pamela Roberto, PhD; Michael Ciarametaro, MBA; and Robert Dubois, MD
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Impact of Formulary Restrictions on Medication Intensification in Diabetes Treatment

Bruce C. Stuart, PhD; Julia F. Slejko, PhD; Juan-David Rueda, MD; Catherine E. Cooke, PharmD; Xian Shen, PhD; Pamela Roberto, PhD; Michael Ciarametaro, MBA; and Robert Dubois, MD
Formulary restrictions on brand name noninsulin antihyperglycemic drugs have little impact on treatment intensification patterns among low-income patients with diabetes in Medicare Part D.

Objectives: To explore formulary restrictions on noninsulin antihyperglycemic drugs (NIADs) in Medicare Part D plans and to estimate the impact of formulary restrictions on use of NIADs among low-income subsidy (LIS) recipient enrollees with type 2 diabetes (T2D) undergoing treatment intensification.

Study Design: Retrospective cohort study.

Methods: A cohort of 2919 LIS enrollees with T2D receiving metformin monotherapy during the first quarter of 2012 who intensified treatment later in the year was tracked to assess selection of and days’ supply with sulfonylureas, dipeptidyl peptidase-4 (DPP-4) inhibitors, and other NIADs. We tested whether being enrolled in a Part D plan with significant formulary restrictions on sole-source brand name NIADs reduced the likelihood of receiving such agents and, if so, what the impact was on days of therapy with the second agent. A 2-part regression model was estimated with explanatory variables for plan-level restrictions and individual covariates.

Results: We found that 63% of study subjects initiated a sulfonylurea, 25% a DPP-4 inhibitor, and 12% another NIAD. Greater restrictions on DPP-4 inhibitors as a class were associated with small reductions in initiation of DPP-4 inhibitors and a concomitant increase in use of sulfonylureas, but neither effect was statistically significant. For individual DPP-4 inhibitors, step therapy requirements on sitagliptin and formulary exclusion of saxagliptin resulted in significant reductions in uptake of the specific drugs but had no significant impact on total days’ supply of antihyperglycemic therapy.

Conclusions: Part D formulary restrictions on sole-source brand name NIADs had little impact on patterns of treatment intensification for T2D among LIS recipients enrolled in Medicare Part D plans in 2012.

Am J Manag Care. 2018;24(5):239-246
Takeaway Points

The objectives of this study were: (1) to examine formulary restrictions (exclusion, prior authorization, step therapy) imposed on noninsulin antihyperglycemic drugs by Medicare Part D plans in 2012 and (2) to test whether the presence and type of formulary restriction influenced choice of second-line agent among low-income beneficiaries with type 2 diabetes undergoing treatment intensification from metformin monotherapy. To avoid confounding of cost sharing and formulary restrictions, we restricted the study to low-income subsidy recipients who faced the same nominal co-pays regardless of Part D plan. Our main findings include:
  • For glucagon-like peptide-1 (GLP-1) receptor agonists, 78% of all formularies analyzed excluded at least 1 of the 2 drugs available in 2012; 69% required prior authorization and 29% required step therapy.
  • For dipeptidyl peptidase-4 (DPP-4) inhibitors, 22% of formularies placed no restriction on any of the 3 drugs on market in 2012, whereas 20% either excluded or required step therapy for all 3 drugs in the class.
  • Generic sulfonylureas were the most commonly prescribed second-line agent (63% of subjects). Formulary restrictions had no statistically significant impact on selection of and days’ supply with GLP-1 receptor agonists and DPP-4 inhibitors.
Type 2 diabetes (T2D) is a progressive disease in which most patients who begin therapy with an antihyperglycemic agent will eventually require treatment intensification to maintain glycemic control. The American Diabetes Association recommends metformin as the drug of choice for initial treatment,1 but it does not make specific recommendations about which of many medications should be used in follow-up therapy. The most commonly used second-line agents are sulfonylureas that, like metformin, are available as inexpensive generics. However, sulfonylureas increase the risk of hypoglycemia2,3 and have been associated with higher rates of cardiovascular disease and death.4-8 In recent years, there has been a trend toward prescribing newer brand name–only antihyperglycemic agents, including dipeptidyl peptidase-4 (DPP-4) inhibitors and glucagon-like peptide-1 and -2 (GLP-1 and GLP-2) receptor agonists, resulting in sharply higher diabetes-related pharmacotherapy costs.9,10

Health insurers and their pharmacy benefit managers (PBMs) have reacted to growing drug spending by excluding selected high-cost brand name drugs from their formularies and by subjecting covered medications to utilization management (UM) restrictions, including prior authorization (PA), step therapy (ST), and quantity limits (QLs). Nowhere is this trend more evident than in Medicare Part D plans. In 2007, Part D plans covered, on average, 87% of all drugs on their formularies, with 18% requiring some form of UM.11 By 2016, the share of covered drugs had dropped to 77%, with 42% requiring UM.12

Virtually all Part D formularies routinely exclude brand name drugs for multisource antihyperglycemic drugs, including metformin, sulfonylureas, α-glucosidase inhibitors, and thiazolidinediones (TZDs).13 Plans also commonly restrict access to various sole-source noninsulin antihyperglycemic drugs (NIADs), including DPP-4 inhibitors, GLP-1 receptor agonists, and GLP-2 receptor agonists for which there are no direct generic equivalents. Although restricting access to brand name drugs with identical generic equivalents is noncontroversial, placing constraints on sole-source brand name drugs may lead to suboptimal therapeutic substitution in some patients. The extent to which this occurs in conventional diabetes treatment is unknown.

There is a substantial literature on the impact of formulary restrictions on medication use in health plans, including several general systematic reviews,14-17 as well as focused reviews on formulary exclusion policies,18 ST,19 and PA.20 The general consensus is that formulary restrictions reduce utilization of the targeted drugs, but there is much less agreement on the impact of restrictions on costs and health outcomes. The literature is also limited in that few studies have analyzed formulary restrictions imposed on diabetes medications,21-24 and none of these have a Medicare focus. Our study was designed to fill these gaps in the literature.

We had 2 objectives. The first was to characterize formulary coverage for NIADs in the Medicare Part D market in 2012, and the second was to test whether the presence and type of formulary restrictions influenced the choice of add-on NIADs among Medicare beneficiaries with prevalent diabetes who intensified antihyperglycemic therapy in that same year. We focused on beneficiaries prescribed metformin monotherapy early in the year who then initiated an additional NIAD later in the year. Our expectation was that formulary restrictions on sole-source brand name drugs would reduce uptake of these medications while increasing the use of generic alternatives. We also expected to find that restrictions would reduce days’ supply of the restricted drug among patients who eventually did initiate the medication due to possible formulary-related delays in treatment initiation.


Data Source and Sample Selection

Data for the study were obtained from a random 5% sample of the Medicare population in 2012 from the Chronic Condition Data Warehouse (CCW) maintained by CMS. The inclusion criteria for the sample were: (1) a T2D diagnosis code in Medicare claims prior to 2012; (2) continuous LIS enrollment with coverage under Medicare Part A, Part B, and Part D throughout 2012 or up to date of death; (3) enrolled in a single stand-alone Part D prescription drug plan (PDP); (4) treated with metformin monotherapy during the first quarter of the year; (5) filled at least 1 prescription for a DPP-4 inhibitor, sulfonylurea, or other NIAD during the final 9 months of the year; and (6) refilled at least 1 prescription for metformin following the first date the second-line agent was filled. All study subjects were linked by encrypted beneficiary identification numbers to Part D plans. We restricted the sample to PDP enrollees because beneficiaries enrolled in Medicare Advantage Part D plans did not generate Part A and B claims data necessary to characterize subjects’ disease severity and comorbidities. We focused exclusively on LIS recipients because they paid the same nominal co-pays regardless of Part D plan, thereby avoiding bias associated with any correlation between formulary design and posted co-pays levied for those not receiving an LIS. The requirement that a metformin fill follow the first fill of a second NIAD ensured that the new medication represented treatment intensification rather than drug substitution.

Dependent Variables

The dependent variables of interest were utilization and days’ supply of NIAD drugs prescribed for treatment intensification in the 9 months following metformin monotherapy during the first quarter of 2012. Days’ supply for prescriptions extending into 2013 were truncated at December 31, 2012. The categories of NIAD drugs considered were: (1) sulfonylureas, (2) DPP-4 inhibitors, and (3) other NIADs (GLP-1 receptor agonists, TZDs, α-glucosidase inhibitors, amylinomimetics, and meglitinides). The sample sizes for specific drugs included in the third category (other NIADs) were too small to warrant separate analysis.

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