Calcimimetic Prescriptions in Fee-for-Service Medicare Beneficiaries Undergoing Dialysis

Calcimimetics are a mainstay of treatment for secondary hyperparathyroidism (sHPT), a ubiquitous condition in end-stage kidney disease (ESKD) associated with fractures, cardiovascular events, and mortality. In 2018, Medicare implemented the Transitional Drug Add-On Payment Adjustment (TDAPA), which shifted calcimimetic coverage from Part D prescription drug plans to Part B. Prior to TDAPA, Medicare beneficiaries with ESKD faced varying out-of-pocket costs for calcimimetics at the point of pharmacy depending on presence and magnitude of low-income subsidies (LISs). TDAPA differentially alleviated barriers to filling these costly medications.

To assess whether calcimimetic prescriptions increased post-TDAPA among patients subject to high out-of-pocket costs prior to the policy change (patients with Part D coverage without LIS and those lacking Part D coverage).

In this longitudinal cohort study, a difference-in-differences analysis was performed at the patient-quarter level. The sample included adult Medicare fee-for-service beneficiaries undergoing maintenance dialysis between July 1, 2016, and December 31, 2020, at US outpatient dialysis facilities. The US Renal Data System, a national registry of patients with ESKD, was used to collect patient, facility, and claims data. The data analysis occurred between May 2023 and October 2024.

LIS extent for patients with Part D coverage (fully subsidized, partially subsidized, not subsidized); presence of Medicare Part D coverage; and whether the patient-quarter was before/after TDAPA implementation.

The main outcome was having 1 or more filled calcimimetic prescriptions per quarter of the study period. A linear regression model was estimated, adjusting for demographics, dialysis modality and access, comorbidities, and facility characteristics, with 2-way fixed effects at the patient and quarter level.

A total of 509 765 adult Medicare fee-for-service beneficiaries were included in the analysis. The cohort had a mean (SD) age of 64 (14) years, was 57% male, 4% Asian, 38% Black, 15% Hispanic, 41% non-Hispanic White, and 3% other race and ethnicity. In adjusted difference-in-differences models, TDAPA's estimated effect was an absolute increase of 9.8 percentage points (pp) (95% CI, 9.3-10.2 pp) in calcimimetic prescriptions for patients with Part D but no subsidy and a 2.2 pp (95% CI, 1.8-2.6 pp) increase for patients with partial LIS compared to patients with full LIS.

The results of this longitudinal cohort study showed that after transitioning calcimimetic coverage from Part D to Part B via TDAPA, calcimimetic prescriptions increased in a graded manner, with the largest increases experienced by patients previously subject to the highest out-of-pocket prescription drug costs. Medicare's TDAPA policy has the potential to expand access to medications for patients.